Although bat bites may be the main transmission route coming to mind, pathogen transmission involving bat bites has been documented mostly for rabies virus (Rhabdoviridae). The common vampire bat (Desmodus rotundus) can, for instance, naturally transmit rabies to other species when biting to feed on blood, particularly to livestock and sometimes to humans. Mycoplasma has also been detected in common vampire bat blood and saliva and might be transmitted between bats, for instance, during aggressive behaviors. Obligate blood-feeding bats are, however, restricted to Central and South America and represent only a very small proportion of the bat species diversity (<0.005%; 3/1,200). Most bat species do not naturally bite humans unless intentional contacts occur (e.g., veterinarian and field biologists involved in bat capture and handling, people trying to remove bats from houses).

Contact with bat body fluids (saliva, urine, and feces) is increasingly recognized as an important mechanism of pathogen spillover to humans. Human encroachment into bat habitats as well as increasing urbanization, which facilitates bat roosting in artificial structures, are likely to increase contact with bat body fluids. For example, Nipah virus (Paramyxoviridae) human infection cases reported in Bangladesh were associated with the consumption of raw sap from date palm trees contaminated with fruit bat saliva and urine. In the case of Marburg virus (Filoviridae), experimental studies indicate that bat-to-bat transmission may occur via saliva and aerosols, suggesting that the virus may be transmitted to other hosts by a similar mechanism. This hypothesis is supported by investigations revealing that most humans infected with Marburg virus had entered bat (Rousettus aegyptiacus) caves before becoming sick and reported regular contacts with bats or their secretions.

Hunting, preparation, and consumption of bats as bushmeat have also been pointed out as a potential source of infection, especially for Ebola virus. For instance, the putative first human case of the 2007 Ebola outbreak in the Democratic Republic of Congo would have bought freshly killed bats for consumption. The fruit bat Eidolon helvum, which is the most frequently hunted and traded bat species in many African countries (e.g., more than 120,000 E. helvum are sold yearly in markets in Ghana), has been shown to be infected with Henipa-related viruses. This highlights the substantial exposure of local hunters and consumers to viruses of potential zoonotic importance.

Zoonotic diseases are those infections that can be transmitted between animals and humans with or without vectors. There are approximately 1500 pathogens, which are known to infect humans and 61% of these cause zoonotic diseases (1). The unique dynamic interaction between the humans, animals, and pathogens, sharing the same environment should be considered within the “One Health” approach, which dates back to ancient times of Hippocrates (2, 3).

Bacterial zoonotic diseases can be transferred from animals to humans in many ways (4): (i) The transfer may occur through animal bites and scratches (5); (ii) zoonotic bacteria originating from food animals can reach people through direct fecal oral route, contaminated animal food products, improper food handling, and inadequate cooking (6–8); (iii) farmers and animal health workers (i.e., veterinarians) are at increased risk of exposure to certain zoonotic pathogens and they may catch zoonotic bacteria; they could also become carriers of the zoonotic bacteria that can be spread to other humans in the community (9); (iv) vectors, frequently arthropods, such as mosquitoes, ticks, fleas, and lice can actively or passively transmit bacterial zoonotic diseases to humans. (10); (v) soil and water recourses, which are contaminated with manure contains a great variety of zoonotic bacteria, creating a great risk for zoonotic bugs and immense pool of resistance genes that are available for transfer of bacteria that cause human diseases (11, 12).

Bacterial zoonotic infections are one of the zoonotic diseases, which can, in particular, re-emerge after they are considered to be eradicated or under control. The development of antimicrobial resistance due to over-/misuse of antibiotics is also a globally increasing public health problem. These diseases have a negative impact on travel, commerce, and economies worldwide. In most industrialized countries, antibiotic resistant zoonotic bacterial diseases are of particular importance for at-risk groups such as young, old, pregnant, and immune-compromised individuals (13).

Almost 100 years ago, prior to application of hygiene rules and discovery of neither vaccines nor antibiotics, some bacterial zoonotic diseases such as bovine tuberculosis, bubonic plague, and glanders caused millions of human deaths. The spread and importance of some bacterial zoonoses are currently globally increasing. That is precisely why most of the developing countries are sparing more resources for a better screening of animal products and bacterial reservoirs or vectors for an optimal preventative public health service (14).

Improvements in surveillance and diagnostics have caused increased recognition of emerging zoonotic diseases. Herein, changes in our lifestyles and closer contacts with animals have escalated or caused the re-emergence of some bacterial infections. Some studies lately have revealed that people have never been exposed to bacterial zoonotic infection risks as high as this before (15). It is probably due to closer contact with adopted small animals, which are accepted and treated as a family member in houses. On the other hand, more intensified animal farms, which have a crucial role in the food supply, are still one of the greatest sources of food-borne bacterial zoonotic pathogens in today’s growing world (4, 8).

People who have closer contact with large numbers of animals such as farmers, abattoir workers, zoo/pet-shop workers, and veterinarians are at a higher risk of contracting a zoonotic disease. Members of the wider community are also at risk from those zoonoses that can be transmitted by family pets.

The immune-suppressed people are especially at high risk for infection with zoonotic bacterial diseases. People can be either temporarily immuno-suppressed owing to pregnancy, infant age, or long-term immuno-suppressed as a result of cancer treatment or organ transplant, diabetes, alcoholism or an infectious disease (i.e., AIDS).

This manuscript reviews the most common bacterial zoonoses and practical control measures against them.

Among emerging zoonotic wildlife diseases, vector-borne infections pose a major challenge to public health both in terms of vector and pathogen abundance and diversity and of human and animal morbidity and mortality. Furthermore, the continuous discovery of new pathogens and the emergence of new epidemiological cycles, due for example to the invasion of new habitat by vector species, claim the need for a constant and intensified surveillance.

In general, vector-borne pathogens account for more than 17% of all infectious diseases, causing more than 700 000 deaths annually (https://www.who.int/news-room/fact-sheets/detail/vector-borne-diseases, accessed May 27, 2019). The burden of these diseases is highest in tropical and subtropical areas where especially mosquito-borne diseases disproportionately affect the poorest populations. In such areas, major outbreaks of dengue, malaria, chikungunya, yellow fever and more recently Zika have been afflicting populations, claimed lives and overwhelmed health systems. Other diseases such as Chagas disease and leishmaniosis affect hundreds of millions of people worldwide (https://www.who.int/news-room/fact-sheets/detail/vector-borne-diseases, accessed May 27, 2019).

Within the temperate areas of the northern hemisphere wildlife zoonoses carried by ticks pose the greatest challenge when compared to mosquito-borne infection. In general, reported cases of vector-borne infections have increased during the last 30 years in the northern hemisphere (Semenza and Suk, 2018). In Europe, the most challenging infections include Ixodes ricinus transmitted diseases such as Lyme borreliosis (LB) and Tick-borne encephalitis (TBE) with an average number of 85.000 and 16.000 cases reported annually respectively. Other tick-borne diseases with rising public health concern include rickettsiosis and Crimean-Congo Hemorrhagic Fever. Mosquito borne diseases of concern include viral infection induced by WNV, Usutu virus (USUV) and Chikungunya virus (CHIKV), while others (i.e. dengue virus, Plasmodium spp.) still represent a potential threat with few sporadic autochthonous episodes of local circulation, especially within the countries of the Mediterranean basin.

A similar trend has been reported for the USA where cases of mosquito-borne and tick-borne diseases have more than tripled since 2004, characterized by steadily increasing incidence of tick-borne diseases and sporadic outbreaks of domestic and invasive mosquito-borne diseases (Petersen et al., 2019).

Transmission of vector-borne pathogens is particularly sensitive to anthropogenic changes as they imply the interaction of three principal players: the pathogen, the vector (represented in many cases by an invertebrate) and a vertebrate host which can acquire and transmit the infection, if competent. Changes in vector-host interaction and in the vectorial capacity can determine a rise in infection hazard and disease incidence.

Globally, there are a number of emerging and re‐emerging pathogens. Some of these cause endemic disease in regions of the globe, where they are maintained in zoonotic reservoirs and transmitted to man either by direct or indirect contact. For most of the emerging pathogens there are no licensed vaccines available for human use, although there is ongoing research and development. However, given the extensive and increasing list of emerging pathogens and the time and investment required to bring vaccines into clinical use, the task is huge. Overlaid on this task is the risk of anti‐microbial resistance (AMR) acquisition by micro‐organisms which can endow a relatively harmless organism with pathogenic potential. Furthermore, climate change also introduces a challenge by causing some of the insect vectors and environmental conditions prevalent in tropical regions to begin to spread out from these traditional areas, thus increasing the risk of migration of zoonotic disease.

Vaccination provides a defence against these emerging pathogens. However, to date, vaccines for pathogens which cause severe, but occasional, disease outbreaks in endemic pockets have suffered from a lack of commercial incentive for development to a clinical standard. While approval of vaccines for diseases caused by such pathogens would make a significant impact on disease outbreaks, taking niche vaccines into clinical development, including Phase III clinical trials for efficacy, requires a large investment in time and money.

An alternative is to develop such vaccines to request US Emergency Use Authorization (EUA), or an alternative status in the United States, Canada and European Union (EU) making use of a considerable number of alternative regulatory mechanisms that are available prior to licensing, so that the products are deployable at the first indications of a disease outbreak.

This review covers the status of vaccine development for some of the emerging pathogens, the hurdles that need to be overcome to achieve EUA or an equivalent regional or national status and how these considerations may impact vaccine development for the future, such that a more comprehensive stockpile of promising vaccines can be achieved.

Companion animals are increasingly treated as family members, and pets have many bacteria that may infect their owners. The human population of the European Union (EU) was approximately 500 million1 in 2012. The number of pet owning households was estimated at around 70 million in 20102.

The most commonly suffered zoonotic bacterial infections in humans are transmitted via animal bites and scratches. Various dog breeds have been characterized for their role in killing dog bite attacks, such as pit bull breeds, malamutes, chows, rottweiler, huskies, German shepherds, and wolf hybrids (16–18). In USA, pit bull breeds accounted for almost half of the dog bite-related zoonotic infections, three times more than German shepherds (17). The oral cavity of healthy dogs and cats contains hundreds of different pathogenic bacteria including Pasteurella sp. (19). Only 20% of dog bites get infected overall compared with 60% in cats. There are 10 times higher Pasteurella multocida infection risks after a cat bite than a dog bite (20, 21). P. multocida infected bite wounds appear usually within 8 h.

It is estimated that approximately 20% of animal bites or scratches get infected in humans (5). Bacterial culturing from pet bite infections in humans is found to be smilar to the oral microbiota of the pets. Infections in dog bite wounds are usually dominated by aerobic bugs: P. multocida (50%), alpha-hemolytic Streptococcus (46%), Staphylococcus (46%), Neisseria (32%), and Corynebacterium (12%). However, following anaerobic bacteria are also isolated from infected wounds: Fusobacterium nucleatum (16%), Prevotella heparinolytica (14%), Propionibacterium acnes (14%), Prevotella intermedia (8%), and Peptostreptococcus anaerobius (8%) (22).

Normal human skin bacteria or other environmental microorganisms are scarcely isolated from infected wounds in bitten person (22–24). Usually, infection occurs within 8–24 h after the animal attack, with variable pain on the site of the injury. The cellulitis might be followed by discharge that contains pus, which can sometimes be foul-smelling. Immuno-suppressed patients with diabetes or liver dysfunction are frequently predisposed to develop serious infections after animal bites. In those cases, they may develop bacteremia faster and pass away in a shorter period of time (5). A penetrating bite close to the joints and bones may cause septic arthritis and osteomyelitis. Knowing the microbial composition of dental plaque biofilm formation in pets’ mouth is a key factor in wound chronicity in humans (5, 25).

Cat-scratch disease is a clinical syndrome that has been reported in people for over 100 years. Yet, the etiological agent Bartonella henselae, which was transmitted by cat scratches and bites, was only identified in 1992 (26). However, contact with cat saliva on broken skin or sclera can also cause Bartonellosis. A person who has had a cat scratch may show papules and pustules at the site of injury (the first initial sign). The disease may progress with a chronic non-healing wound, fever (sometimes), weak regional lymph circulation, and abscession. Cat owners and veterinarians are most at risk (27). Systematic medical treatment is usually needed in people with suppressed immune systems. Otherwise, encephalopathy, osteomyelitis, and granulomatous conjunctivitis might develop.

Horses and humans have always shared a close relationship due to recreation, sporting, and occupational reasons, for over thousands of years. In Europe, the number of horses per capita remained relatively stable during the past decade. Germany and Great Britain have the largest horse populations in the EU, whereas Sweden has the highest number of horses per capita. The frequency of infected horse bite wounds is estimated to be 3–5% in Europe (28, 29). However, it has been roughly estimated that the horse bites account for as high as 20% of overall animal bites in Turkey, which comes after dog bites (70%) (30). More extensive muscle damage may develop in most of the horse attacks, which is different from small animal bites. A mixture of aerobic and anaerobic organisms has been isolated from horse bites in humans, which are frequently dominated by Actinobacillus lignieresii (31, 32). Escherichia coli and Bacteroides species have also been isolated from foul-smelling infections and pus drainage after horse bites in humans (33).

Infectious diarrhea in companion animals is caused by Salmonella sp., Escherichia coli, Shigella sp., and Campylobacter sp. can also be transmitted to people through fecal oral route. It is difficult to estimate the distribution of these ubiquitous microorganisms. But it is known that they can be isolated from many healthy animals, which can be shed in their feces for long periods of time. Campylobacteriosis were the most frequently reported zoonotic bacterial diseases in 2009 among the EU member countries in humans (34). Like many other enteropathogens, they can cause gastroenteritis (diarrhea, vomiting), headaches, and depression, sometimes even leading to death. It is obvious that raw food diets for pets dramatically increase the risk of human exposure to such zoonotic bacterial enteropathogens, which cause gastrointestinal diseases.

Although pet birds, also called songbirds (e.g., canaries, finches, sparrows) and psittaciformes (e.g., parrots, parakeets, budgerigars, love birds) are a small fraction of adopted pets, they are widely popular in Europe and they are potential carriers of zoonotic diseases (35). Some of them could have an important impact on human health, such as chlamydophilosis (36), campylobacteriosis (37), and salmonellosis (38). Parrot fever (chlamydophilosis), which is caused by intracellular bacteria, Chlamydia psittaci, lives within the respiratory system of birds. Inhalation of dust, dander, and nasal secretions of infected birds is the main way of transmission to humans (39, 40). The mild to severe flu-like illnesses may develop and infected people might be misdiagnosed as influenza.

There is unfortunately a lack of quantitative research into the antimicrobial susceptibility of bacterial zoonotic organisms isolated from bite/scratch wounds or companion animal associated gastroenteritis. Zambori et al. (5) revealed an increased prevalence of drug resistance in animal bite isolates from people. Furthermore, methicillin-resistant Staphylococcus aureus (MRSA) or extended-spectrum beta-lactamases (ESBL) producing Enterobacteriaceae, which are known as nosocomial infections have been frequently isolated in companion animals (41), including horses (42). It might be one of the main reasons for the rising prevalence of these potential zoonotic pathogens in human clinical samples.

Hepatozoon species are apicomplexan parasites with a hematophagous arthropod final host and a vertebrate intermediate host. They are transmitted by ingestion of the final host containing mature oocysts by the intermediate host. The gamont stage of the parasite is found in leukocytes or erythrocytes of the intermediate host and infects the final host during the blood meal. Additional transmission pathways have been described in some Hepatozoon spp. including intrauterine transmission and carnivorism of the intermediate host by an intermediate host of a different species. More than 340 species of Hepatozoon have been described to date in amphibians, reptiles, birds, marsupials and mammals. A Hepatozoon parasite was reported for the first time from the blood of a domestic cat in India by Patton in 1908 and named Leucocytozoon felis domestici[7]. The feline parasite was later transferred to the genus Hepatozoon and it was suggested that Hepatozoon parasites from the cat, jackal and hyena are indistinguishable from Hepatozoon canis, which infects dogs, due to the similarity in morphology of the gamont stage seen in the blood of these animals. The classification of the Hepatozoon parasites found in domestic cats has thereafter been uncertain and most studies have carefully referred to Heptozoon-like parasites or Hepatozoon sp. without committing to a certain species. With the advent of molecular techniques, PCR using genus-specific primers for Hepatozoon spp. was used to amplify 18S rRNA gene DNA from the blood of a collection of wild and domestic animals including 2 cats from Spain. Although no parasites were morphologically described in the cat’s blood, the sequences from these cats were designated as H. felis and deposited in GenBank.

Domestic cat hepatozoonosis has been reported from several countries worldwide including: India, South Africa, Nigeria, the USA, Brazil, Israel, Spain and France. Most studies have focused on reporting the detection of feline hepatozoonosis and almost no information has been published on its pathogenesis, transmission, life cycle and epidemiology. In that context, the aims of this study were to carry out a survey on domestic feline hepatozoonosis, characterize its causative agents genetically and morphologically in blood and tissues, and evaluate its possible transplacental transmission.

6.What are the most common clinical findings of FeL due to L. infantum?

Detailed case reports of FeL have been available in recent years mainly from European countries where pet cats typically have a higher standard of health care. In the New World, other Leishmania spp. are endemic and may co-infect cats and complicate the clinical picture. Therefore, we have only reviewed case reports or case series originally from European countries. A total of 46 clinical cases have been published between 1989 and 2014, where the diagnosis of FeL was confirmed by serological and/or parasitological methods [11–14, 21, 26, 36, 37, 50–67].

The most common clinical signs reported in FeL include skin or mucocutaneous lesions and lymph node enlargement, and they have been described in more than half of the cases (Table 4). Some cats showed only dermatological lesions alone [13, 52, 56, 58], while others with skin lesions showed a combination with systemic signs [12, 14, 21, 26, 36, 51, 60, 62–64, 68]. Conversely, other cats did not have any skin detectable lesions on clinical presentation [11, 36, 50, 54, 55, 57, 66, 69, 70].

The cutaneous and mucocutaneous lesions are described in Question 7. Lymphadenomegaly may be solitary or multicentric. Ocular lesions have been reported in approximately one third of the affected cats. Uveitis, either unilateral or bilateral (Fig. 1), is the most common ocular lesion described, with occasionally a pseudotumoral granulomatous pattern and eventually progress to panophthalmitis [50, 53, 55, 64, 69]. Blepharitis and conjunctivitis have also been described in a number of clinical cases [66, 68, 70]. Amastigotes have been found by cytology in conjunctival nodules, corneal infiltrates and aqueous humor, and by histopathology after enucleation of the eye or post mortem even in uveal tissue [50, 53, 55, 64, 69]. Chronic gingivostomatitis is also a common clinical finding and has been found in about one fourth of the cats so far studied with leishmaniosis (Fig. 2) [11, 26, 53, 55, 63, 66, 70]. Nodular lesions are unfrequently seen on the gingival mucosa or the tongue [60, 66, 69, 71], where infected macrophages may be visualized in lesion biopses [60, 69].

Non specific signs such as weight loss, reduced appetite, dehydration, and lethargy also have been reported. A list of other sporadic clinical manifestations described includes: pale mucous membranes, hepatomegaly, jaundice, cachexia, fever, vomiting, diarrhea, chronic nasal discharge, splenomegaly, polyuria/polydipsia, dyspnea, wheezing, abortion and hypothermia.

The implication of Leishmania as a cause of some of these clinical signs has been associated with the presence of the parasite in cytological or histopathological examinations of liver, spleen, lymph nodes, stomach, large bowel, kidney, oral mucosa, nasal exudate and eye tissues [13, 14, 36, 50, 57, 63, 66, 68, 72]. However, clinical disease is commonly associated with an impaired immunocompetence due to several causes including retroviral infections (FIV and FeLV), immunosuppressive treatment and concomitant debilitating diseases such as malignant neoplasia or diabetes mellitus.

As also found in dogs, FeL does not exclude the possibility of concurrent diseases or co-infections. This fact may influence the clinical presentation and prognosis. The cause-effect relationship between various etiological and pathogenic factors is not always easy to establish.7.What are the most common dermatological findings of FeL due to L. infantum and to other Leishmania species?

Cutaneous lesions predominate in the clinical picture of FeL due to L. infantum. Dermal abnormalities include nodules, ulcerations or more rarely exfoliative dermatitis. They are generalized or localized, symmetrical or asymmetric and may, though less frequently, appear all over the body in a focal, multifocal, regional or diffuse pattern [12–14, 26, 36, 37, 51, 52, 56, 58, 60, 62, 64, 68, 70]. Some cats may harbour different types of skin lesions at the same time or develop them subsequently; they may coexist with mucocutaneous lesions (Fig. 3). Cutaneous and mucocutaneous nodules, of variable size, are more often localized on the head, including eyelids, nose and lips, or on the distal parts of the limbs. Nodules have also been reported in the anal mucosa and they are usually small (less than 1 cm), non painful or pruritic and have a normal, ulcerated or alopecic surface [26, 50, 51, 56, 60, 62–64, 66, 68, 70].

Ulcerations which may be diffuse and superficial or focal and deep (Fig. 4) are localized on the same body sites as nodules, and may be complicated by bacterial infections that explain why they are covered by hemorrhagic crusts and/or purulent material [13, 14, 52, 53, 56, 58, 60–62, 64, 65, 68, 70]. However, ulcerative dermatitis is sometimes diffuse and can be observed on the body trunk or on bony prominences [14, 36, 58, 62, 63].

In contrast to CanL, exfoliative dermatitis (Fig. 5) is rare in the feline disease [36, 52, 68]. Other uncommon dermatologic presentations include hemorrhagic papules and nodules where Leishmania amastigotes can be found [37, 52]. Alopecia (Fig. 6), which is also uncommon in FeL [12, 36, 52, 62, 64], may be associated with other skin diseases concurring in L. infantum infected cats such as demodicosis. Mild to severe pruritus is rare in FeL [58, 64, 65] and in some cases with a pruritic syndrome other compatible causes co-existed such as flea allergy, pemphigus foliaceus (PF) or neoplasia (squamous cell carcinoma).

Clinical disease caused by natural infection with species other than L. infantum is typically reported as nodular or ulcerative dermatitis with no systemic clinical signs. Skin lesions are often single but they can metastatize (Table 5) [73–76].8.What are the most common dermatopathological features of FeL?

Skin histopathology of lesions associated with L. infantum has shown that the most commonly observed alteration is a granulomatous dermatitis [26, 51, 56, 59, 60, 68]. It often has a diffuse pattern and the epidermis may present hyperkeratosis, acanthosis and ulceration [56, 68]. A nodular to diffuse arrangement of the granulomatous dermatitis is also reported [26, 60]. However, in a retrospective case series from Spain, two cats presented different histological findings. The first one had granulomatous perifolliculitis with a high number of lymphocytes and plasma cells surrounding the cutaneous adnexa. It was associated with a marked hyperplasia of epidermis and sebaceous glands. The other cat was diagnosed with a lichenoid interface dermatitis typically represented by infiltration of lymphocytes, plasma cells and a few neutrophils and macrophages at the dermoepidermal junction. In this case, epidermal necrosis and epidermal microabscesses were also observed. A perivascular infiltration of superficial skin layers by macrophages, mast cells, neutrophils and eosinophils was also observed in another case.

Leishmania amastigotes have always been identified in the affected skin. A semiquantitative estimation of amastigotes was also performed with the aid of immunohistochemistry (IHC), in which the parasitic load of the skin ranged from high (>50 immunolabelled amastigotes/field at x400) to moderate (10–50 immunolabelled amastigotes/field) in cases of diffuse granulomatous dermatitis. Conversely, it was low (1–9 immunolabelled amastigotes/field) in cases of granulomatous perifolliculitis or lichenoid interface dermatitis .

In biopsy samples taken from cases with ulcerative dermatitis, eosinophilic granulomatous dermatitis with a severe dermo-epidermal necrosis were found without the presence of amastigotes, but with a positive quantitative Leishmania PCR.

In some FeL cases, other dermatological diseases such as eosinophilic granuloma and PF were also diagnosed [52, 56, 68].

Interestingly, amastigotes were also found associated with neoplastic tissue in the lesion of two cats with squamous cell carcinoma (SCC). In one other case, SCC was diagnosed in a cat presenting concurrent Leishmania skin lesions [14, 59].

In two cases of skin disease caused by L. braziliensis, a mononuclear and neutrophilic inflammatory infiltrate of the dermal tissue was seen in histological sections.9.What are the most common differential diagnoses in L. infantum endemic areas for dermatological features?

The commonly seen cutaneous nodular form in FeL cases should be distinguished from nodules caused in cats with cryptococcosis, sporotrichosis, histoplasmosis, sterile or eosinophilic granuloma, mycobacterioses, and a wide variety of cutaneous neoplasms (e.g. feline sarcoids, mast cell tumor, fibrosarcoma, basal cell carcinoma, bowenoid in situ carcinoma and lymphoma). The main differentials of the ulcerative lesions include squamous cell carcinoma with which however it may co-exist [13, 14, 59], idiopathic ulcerative dermatitis, indolent ulcer, mosquito-bite dermatitis, atypical mycobacteriosis and feline leprosy, cutaneous vasculitis, erythema multiforme and cold-agglutinin disease. Finally, skin diseases such as dermatophytosis, systemic or cutaneous lupus erythematosus, exfoliative dermatitis due to thymoma or due to immune-mediated pathomecanisms, PF, sebaceous adenitis/mural folliculitis complex and paraneoplastic alopecia could be included in the differential list of those leishmanial cats that are admitted with the rare exfoliative/crusting dermatitis which may also be alopecic and erythematous. It has been postulated that PF and FeL may share a common pathomechanism (molecular mimicry) when they co-exist in the same cat.10.What clinicopathological findings may alert the clinician to the possibility of FeL due to L. infantum?

Limited information is available about clinicopathological abnormalities in cats and it is only based on case reports. Mild to severe normocytic normochromic non-regenerative anemia is the most frequent haematological abnormality reported in clinical cases. Moderate to severe pancytopenia may be observed [37, 50, 57] in association with aplastic bone marrow, but some of the cats reported with pancytopenia were FIV positive [37, 50, 57]. Curiously, in one of these cases, amastigotes were found in 4 % of neutrophils in buffy coat smears.

Hyperproteinemia with hypergammaglobulinemia is a common finding in FeL as also found in dogs, and hypoalbuminemia is occasionally reported [37, 50].

Renal proteinuria and increased serum creatinine are also reported at diagnosis or during follow-up in some cases [37, 68].

Relative lymphocytosis and an increase in serum ALT activity were significantly associated with seroreactivity to L. infantum.

The type of inflammatory infiltrate found in tissue cytology (aspirates, impression smears) or histopathology in organs such as skin, eye, oral mucosa, liver, spleen and kidney is commonly pyogranulomatous to granulomatous [66, 68, 72]. There was also lymphoid reactive hyperplasia in lymphoid organs such as lymph nodes and spleen, with variable numbers of Leishmania amastigotes observed (Fig. 7).11.What are the most common differential diagnoses in endemic areas for systemic illness caused by L. infantum in cats?

As lymph node enlargement is the most common sign, apart from skin and mucocutaneous lesions, FeL should be included in the differential list when this finding is noted on physical examination as solitary or generalized lymphadenomegaly. This list mainly includes infections with other infectious agents (FIV, FeLV, FCoV, Bartonella, Mycobacteria, T. gondii, Cryptococcus or other systemic mycoses), lymphoma or metastatic involvement from other neoplasia.

FeL should also be considered in cats with ophthalmologic disease, mainly in cats with acute, recurring or chronic uveitis and differentiated from similar clinical conditions caused by FIV, FeLV, FCoV, Bartonella, T. gondii, fungal infections, neoplasia or paraneoplastic syndrome. Some feline uveitis cases are considered idiopatic and treated with corticosteroids. A diagnosis of idiopatic uveitis was initially made in some cases of ocular FeL and corticosteroids worsened the disease [50, 55, 69]. This fact warrants a careful investigation to exclude FeL before treating ocular disease with corticosteroids.

Proliferative and ulcerative chronic inflammation of the oral mucosa associated with FeL can be included in the list of possible causes of the feline chronic gingivostomatitis syndrome (FCGS). This painful and common immune-mediated disease is considered multifactorial in cats and treated by full mouth teeth extraction for eliminating oral plaque antigenic stimulation. Corticosteroids are frequently used to improve the clinical signs; however, when this was tried in some cats with oral disease associated with L. infantum infection it induced worsening of FeL [11, 66].

Hyperglobulinemia with increased gammaglobulin level reported in FeL is usually found in chronic infections caused by viruses, bacteria or systemic fungi, or inflammation associated with FCGS or inflammatory bowel disease, or in neoplasia such as lymphoma, or multiple myeloma.

Leishmania infantum (syn. Leishmania chagasi) infection is found both in the Old and New Worlds with dogs as the main reservoir. Canine leishmaniosis (CanL) is an important and complex zoonotic disease whose transmission, pathogenesis, clinical manifestations, diagnosis, therapy and prevention have been extensively studied [1, 2]. Conversely, in the last century, the cat was usually considered as a relatively resistant host species to Leishmania infection based on two experimental studies (see Question 5) and on limited numbers of clinical case reports and histopathological descriptions of the presence of Leishmania infection in necropsies.

Historically, some studies have used cats for investigating their potential role as reservoir for Leishmania. Pet cats living in the same houses where human cases of cutaneous or visceral leishmaniosis were diagnosed were examined for the presence of Leishmania amastigotes in skin lesions or by post mortem histopathological evaluation of the bone marrow and spleen [3, 4]. In Sicily (southern Italy), no case of infection was found by cytological and histological examination of spleen, liver and bone marrow of 120 necropsied cats living in an endemic area. The same negative results were obtained in Egypt when spleen cytology and culture were performed on 28 stray cats, and six of them displaying skin lesions were negative also from skin. Conversely, in Jordan, amastigotes were detected in liver and spleen smears from about 20 % of 78 stray cats.

The development of both feline medicine and more sensitive and specific diagnostic techniques such as serological and molecular methods has led in recent decades to an increasing number of documented case reports of feline leishmaniosis (FeL) and subclinical infections. However, there is still limited information on epidemiological and clinical aspects of Leishmania infection in cats which is all derived from descriptive studies, case reports, information from canine leishmaniosis cases and personal experience of respected experts. This means that the current quality of evidence supporting any recommendation on feline leishmaniosis is low (grade IV).

In this report the LeishVet group presents an overview on current knowledge on Leishmania infection in cats. Moreover, recommendations on the diagnosis, treatment and monitoring, prognosis and prevention of FeL are also described in order to standardize the management of this infection in cats. These were constructed by combining a comprehensive review of evidence-based studies and case reports, clinical experience and critical consensus discussions. The goal of this review is therefore to offer the veterinary practitioners an updated approach with recommendations on the management of leishmaniosis in cats.

Documentation of an infectious agent in blood smears by cytologic examination requires skilled personnel, is time consuming (an adequate blood film examination can take 20–30 minutes), and lacks sensitivity for most pathogens. False positives can also occur, such as when staining artifacts are confused with micro‐organisms. Therefore, cytologic examination of blood smears is not recommended as the sole means of screening blood donors for infection.

Insect-borne diseases are infectious diseases spread among animals and human through hemophagia by blood-feeding arthropods, such as mosquitoes, ticks and midges, which are widespread in the environment. These infections lead to significant human and animal morbidity and mortality worldwide, which cause a huge economic loss. In recent years, epidemic outbreaks of insect-borne infectious diseases in countries neighboring and trading with China have posed a threat to public health, especially in the border areas of China. Many insect-borne diseases in the border areas of China have drawn public attention, such as West Nile virus (WNV) infection in Xinjiang, Tahyna virus infection in the Qinghai-Tibet Plateau, and mosquito-borne arbovirus (e.g. Japanese encephalitis virus and Sindbis virus) infection in Yunnan. It is remains difficult to develop effective vaccines against such viruses. Furthermore, the clinical symptoms of many infections by mosquito-borne arboviruses do not indicate a specific pathogen, and some infections are even asymptomatic. Therefore, accurate and timely diagnosis of these infections is a great challenge of utmost importance.

To date, multiple molecular detection methods have been established to detect insect-borne pathogens, including reverse transcriptase-polymerase chain reaction (PCR), real-time PCR, a liquid bead array and a microwell membrane array. Recent studies have established modified PCR or array methods for the detection of insect-borne pathogens [11–13]. However, these methods are only able to detect one type or a few types of viruses, which greatly restricts their application. Luminex xMAP technology is a multiplexed high-throughput detection system that uses fluorescent carboxylated microspheres. The Luminex array offers up to 100 independent channels and use microspheres embedded with various ratios of two fluorescent dyes. A mixed suspension of microspheres is mixed with the sample to bind analytes, which are then labeled with a fluorescent reporter and analyzed using a specialized flow cytometer [14, 15].

In this study, we established a method that was able to simultaneously detect multiple insect-borne pathogens rapidly and effectively, including bluetongue virus (BTV), epizootic hemorrhagic disease virus of deer (EHDV), Q-fever pathogen Coxiella burnetii (CB), African swine fever virus (ASFV), West Nile fever virus (WNV), Borrelia burgdorferi (BB), vesicular stomatitis virus (VSV), Rift Valley fever virus (RVFV), Ebola virus (EBV) and Schmallenberg virus (SBV). This optimized liquid array detection system may contribute to the rapid and effective detection of multiple insect-borne diseases at border ports in China.

A pathogen is defined as an organism causing disease to its host, with the severity of the disease symptoms referred to as virulence. Pathogens are taxonomically widely diverse and comprise viruses and bacteria as well as unicellular and multicellular eukaryotes. Every living organism is affected by pathogens, including bacteria, which are targeted by specialized viruses called phages.

The number of viruses and bacteria on earth is staggering and they occupy essentially every environment. A liter of surface seawater typically contains in excess of ten billion bacteria and 100 billion viruses. The number of viruses on Earth is estimated to be around 1031, which corresponds to roughly ten billion times the number of stars in the universe. An average human is made up of about 30 trillion cells but carries a similar number of bacteria, mostly in the gut.

The vast majority of viruses and bacteria we are exposed to have no negative effect and some can even be beneficial, though a tiny fraction of these can severely affect our health. Specifically, about one in a billion microbial species is a human pathogen. Indeed, approximately 1400 human pathogens have been described, whereas it has been estimated that there are one trillion microbial species on Earth, the vast majority of which remain uncharacterized.

OHFV distribution is restricted to western Siberia (Figure 1). The main vector of OHFV is the meadow tick, Dermacentor reticulatus, which can also transmit the virus to humans. However, humans are mainly infected after contact with infected muskrats (Ondatra zibethicus) which are very sensitive to the infection and often succumb to the infection. Muskrats develop high viremia which can last for several weeks. Human infection occurs through contact with urine, feces, and blood. Secretion of OHFV in unpasteurized goat milk has been reported but no milk-borne outbreaks have been observed. The exact number of annual cases are uncertain because of misdiagnoses and unreported cases, but 165 cases were reported between 1988 and 1997. OHFV may cause a biphasic disease; the initial phase is characterized by high fever, bleeding from the nose, mouth, and uterus. Thirty to fifty percent of the cases experience a second phase characterized by high fever and reappearance of the symptoms from the initial phase. Case fatality rates range from 0.5 to 2.5%. No antiviral treatments are available against OHFV, instead treatment is focused on supportive care to minimize hemorrhage and other complications.

Rudolf Virchow (1821–1902), one of the foremost 19th century German leaders in medicine and pathology, noted a relationship between human diseases and animals and then introduced the term “zoonosis” (plural: zoonoses) in 1880. Later, the World Health Organization (WHO) in 1959 specified that “zoonoses are those diseases and infections which are naturally transmitted between vertebrate animals and man”. Venkatesan and co-authors reported that the term zoonosis is derived from the Greek word “zoon” = animal and “noso” = disease. Zoonotic pathogens causing different kinds of diseases are of major public health issues worldwide. These zoonotic diseases include various infections such as viral, bacterial, fungal, protozoan and parasitic diseases shared in nature by man and animals (domestic and wildlife). Of these, an epidemiological study confirmed that about 61% of the total number of microbial diseases affecting man is zoonotic. Moreover, another study suggested that animals are the major sources of human zoonotic infections, globally and that among all the emerging infectious diseases, almost 75% are considered to be caused by animals. Thus, almost every year since the last two decades, a new virus has been emerging. During the last three decades, rats have been increasingly implicated in several emerging and reemerging human outbreaks of zoonotic diseases and have accounted for ~75% of the new zoonotic diseases in nature according to several studies. This constitutes about 61% of all communicable diseases causing illnesses in man. Furthermore, a study suggested that some zoonotic diseases could affect the socioeconomic output globally. A report on the impact of foodborne zoonotic diseases estimated its costs at about $1.3 billion every year worldwide.

Since zoonotic diseases can easily be transmitted to man in several ways, they target persons who work closely with animals; this plays a big role in zoonotic transmission. Such persons working with animals include veterinarians, slaughterers/butchers, farmers, researchers, pet owners (e.g., through bites and/or scratches of owners of indoor pet-animals), and animal feeders in animal companies using animal products, via animals used for food (e.g., meat, dairy, eggs, birds, infected domestic poultry, and other birds). Furthermore, transmission can also occur through animal vectors (e.g., tick bite, and insects like mosquitoes or flea). In addition, in the transmission of bacteria in comparison with viruses, the role of contaminated food and water, the importance of international travels as well as changes in land use and agriculture, are important. According to recent WHO data, more than 75% of the different zoonotic diseases that may cause illnesses in humans are transmitted through animals and/or animal products. Nevertheless, several zoonotic pathogens may be transmitted from various animals to man via several direct and/or indirect pathways such as close contact with the infected animals that might be shedding the infectious pathogen, when humans use contaminated sources of food or water, and/or by outdoor or indoor animal scratches or bites. The prevention and control strategies against zoonotic pathogens are considered important issues and a global challenge requiring efforts of all veterinarian and medical staff.

Animals have been domesticated for a long time in the Arabian Peninsula; and in Saudi Arabia, humans are living in close contact with animals. The spread of any zoonotic disease in Saudi Arabia is considered to be of a high public health importance because it might put the Saudi Arabia peoples, as well as millions of Muslim pilgrims from the about 184 Islamic countries worldwide, at great risk. Moreover, thousands of animals of unknown origin are sacrificed daily during the annual pilgrimage for all pilgrims in Makkah. Furthermore, pilgrims slaughter over one million sheep, cows, and camels in Mina to mark the successful completion of the Hajj, aside the 42,000 beasts that are slaughtered in Makkah abattoirs. While some people are at slaughterhouses to offer their sacrifices personally, others from nearby cities of Makkah, Jeddah, and Taif come to collect sacrificial meat.

Recently in Saudi Arabia, a huge number of new pet clinics and/or pet stores opened, selling all kinds of pets. They breed, shower, and clean pets, which bring major feeling of psychological well-being to the modern urbanized lifestyle of their Saudi Arabian owners. However, all these pet markets may need to be targeted by the Ministry of Health (MOH) and/or the Ministry of Agriculture because all kinds of pets—including cats, dogs, rodents, and monkeys—which are sold, may transmit several zoonotic diseases. In this review, we identified the most important and prevalent emerging and reemerging viral zoonotic pathogens in Saudi Arabia, taking into account the current incidence and prevalence of zoonotic diseases, the health situations, the zoonotic sources of human infection, and the current available control strategies that could prevent such infectious zoonotic diseases. In addition, we identified the primary sources of information on zoonotic pathogens in Saudi Arabia. Data sharing and dissemination of significant findings could make a remarkable difference in the global control; it could provide useful information, particularly to Muslims on pilgrimage, when they travel to Saudi Arabia during Umrah seasons and/or the annual Hajj pilgrimage.

A zoonosis is an infectious disease that can be transmitted from animals to humans. Currently 61% of pathogens known to affect humans are zoonotic (10). Most emerging infectious diseases considered to be serious public health problems have zoonotic origins (11), and approximately three-quarters have originated from wild animals (12). Zoonotic pathogens can be transmitted by close contact with an animal, generally through inhalation, ingestion, or other routes that contaminate mucous membranes and damaged or, in some cases, intact skin (12, 13). Aerosol-mediated transmission is occasional, particularly in confined spaces. Fomites can transmit some agents, and the likelihood of this route correlates with the persistence of the organism in the environment. Transmission of some organisms occurs via ingestion of contaminated food or water, and such organisms may infect large number of people. Sources of zoonotic pathogens in foodborne diseases include undercooked meat or other animal tissues, seafood, and invertebrates, as well as unpasteurized milk and dairy products and contaminated vegetables (14). Insects serve as important biological or mechanical vectors in transmitting some organisms (15). In this review, we have summarized representative bacterial zoonotic infections (Figure 1).

In veterinary medicine, S. aureus is a gram-positive bacterium that commonly exists on the skin and mucous membranes of healthy humans and animals. However, it has also been recognized as a significant opportunistic pathogen in chickens and farmed rabbits and has been reported to cause mastitis in dairy-producing animals (16). It is most commonly isolated from staphylococcosis cases, but species such as S. hyicus have been reported as causative agents of osteomyelitis in turkeys and of exudative epidermitis in pigs (13, 15, 16). The symptoms of staphylococcosis vary depending on the site and route of inoculation and can involve the bones, joints, tendon sheaths, skin, sternal bursa, navel, and yolk sac. Immunocompromised birds are also more prone to staphylococcal infections (16). Staphylococcosis can be treated with antibiotics; however, methicillin-resistant S. aureus has recently emerged (17). In staphylococci, methicillin resistance is mediated by penicillin-binding proteins (i.e., mecA and mecC), which are suggested to be of animal origin and have demonstrated low affinity for beta-lactams (18–20). Common antibiotics used to treat Staphylococcus infections are penicillin, erythromycin, lincomycin, and spectinomycin (19). Proper management to prevent injury and immunocompromised conditions in poultry facilitate the prevention of staphylococcosis (21).

In the poultry industry, campylobacteriosis is also a common disease transmitted from other livestock, e.g., farmed cattle, swine, or poultry, with staphylococcosis (22). Campylobacter jejuni and C. coli are representative pathogens that are a major cause of human gastroenteritis (22). Their predominant ecological niche is the gastrointestinal tract of a wide range of domesticated and wild vertebrates, and zoonotic transmission from animals to people via meat, especially chicken, is a food safety issue (23). Campylobacter spp. are also commonly isolated from a wide variety of birds, including waterfowl, raptors, crows, and pigeons, that pollute the habitats of grazing animals. In addition, insects and rodents, such as flies, rats, and mice, have been reported to transmit C. jejuni (22). Other species, such as C. lari, C. helveticus, and C. upsaliensis, have also been isolated from patients with diarrheal disease but are reported less frequently. Campylobacteriosis is most commonly treated with azithromycin, levofloxacin, clindamycin, aminoglycodies, fluoroquinolones (e.g., nalidixic acid), and cephalosporins (e.g., cephalothin). However, the emergence of resistance to cephalosporins has rapidly increased over the last 10 years (23). Thus, it is necessary to find new drugs or supplements to reduce resistance to antibiotics.

According to the American Pet Products Association, the pet industry has expanded steadily at an average of 4% per year over the last two decades (24). As a result, interest and research into pet-related zoonotic diseases is increasing. Common cat scratch disease is primarily caused by Bartonella henselae (25). Although this Bartonella sp. can cause many types of animal infections, pets have been identified as notable reservoirs for human infection, implying a potentially high risk of humans (25). Generally, B. bacilliformis and B. quintana are considered human-specific pathogens, but several zoonotic Bartonellae spp. specific to diverse animal hosts can also infect humans as incidental hosts (25, 26). Pathogenic Bartonella spp. are endotheliotropic bacteria with a distinctive mechanism for invasion into host cells involving the injection of peptides and transport of bacterial DNA into the cells; these species can move by infecting macrophages (26). Recently, significant associations have been found between amino acid alleles of Toll-like receptors and susceptibility to infection with the blood pathogenic and clinically isolated Bartonella sp. Cat fleas, sand flies, human body lice, and many other flea species can transmit certain Bartonella spp. (14, 26). It has been reported that in addition to pets, other animals, including rodents, cattle, deer, and sheep, can spread Bartonella infection through flies or deer keds (Lipoptena cervi) (27). Most cases of cat scratch disease get cured without treatment; however, some immunocompromised patients can present complications from disseminated diseases (25). Bartonella spp. can cause acute or chronic infection with vascular proliferative or suppurative manifestations. Blood culture-negative endocarditis and bacteremia can also be induced by a spectrum of Bartonella spp. in canine and human patients (15). Numerous antibiotics, including azithromycin, penicillin, tetracyclines, cephalosporins, and aminoglycosides, are effective against Bartonella infection (25, 26). Doxycycline, amoxicillin, enrofloxacin, and rifampin given for a long duration (more than 4 weeks) may effectively reduce the level of bacteremia in an infected cat or dog, although there is a risk of side effects (25).

Leptospira is an endemic bacterium in many domestic and wild animals that spreads through urine (28) and causes leptospirosis in humans and animals through contact with urine-contaminated water or soil. Thus, leptospirosis occurs in both humans and animals, including livestock and marine mammals (28). It is one of the most common and severe human infections worldwide. In addition, it can cause a variety of symptoms in animals and humans, some of which can be mistaken for other diseases. Further, some infected animals and humans may act as a source of infection without symptoms (29). Leptospirosis is generally limited to developing countries and has been reported as an imported disease in industrialized countries (28). Leptospirosis can cause fever, meningitis, kidney damage, respiratory distress, liver failure, and even death if it causes severe complications (30). Coinfections with common endemic bacteria that cause acute febrile illnesses (e.g., salmonellosis), can be a diagnostic dilemma if symptoms overlap (31). For example, Salmonella1 can enter the bloodstream and infect the spine through gastric mucosal vasculitis, which may be caused by Leptospira (30).

Human salmonella infections are typically caused by direct or indirect exposure to contaminated food or various host species, including dogs, cats, livestock, domestic poultry, and rodents (23). There are over 2,300 subtypes of the Salmonella enterica, including serovars Enteritidis, Agbeni, and Typhimurium, that can cause asymptomatic, mild clinical, or fulminant bacteremia/septicemia, and endotoxemic infections (23). According to a report by the Centers for Disease Control and Prevention, Salmonella infection in humans results in a diarrheal illness that is responsible for 450 deaths in the United States annually (32). Salmonella is an opportunistic pathogen that causes a wide range of infectious symptoms, including food poisoning, typhoid fever, enteric fever, and gastroenteritis, depending on the immunity of the host, the infection dose, and the virulence of the strain (30, 31).

Although considerable research is being conducted on zoonotic bacteria, there is still a lack of scientific knowledge about the distribution and infection cycles of Chlamydia spp. compared with other zoonotic bacteria. The respiratory illness psittacosis caused by Chlamydia sp. in humans and animals was first reported approximately 100 years ago (33); however, only 218 reports on illness were found when searched using “Chlamydial, Zoonoses” in the NCBI database. With the recent occurrences of severe acute respiratory syndrome and avian influenza, studies on Chlamydia infections and zoonoses have increased rapidly, and 53 related papers have been published since 2015. Transmission of C. psittaci infection primarily occurs through inhalation of contaminated aerosols from infected birds (34). C. trachomatis infection causes reproductive complications, and C. pneumoniae causes respiratory infections and atypical pneumonia in both humans and animals. C. suis infection is associated with diarrhea and failure to gain weight in domestic swine (33, 34). In general, most people infected with Chlamydia do not show any symptoms (34). However, in female animals with weak immune systems, pathogens can be transferred to the womb, causing pelvic inflammatory disease, a major cause of ectopic pregnancy and female infertility (33, 34). Chlamydia infections is most commonly treated by antibiotics, such as azithromycin and doxycycline (33). However, with antibiotic resistance of pathogenic bacteria becoming a major problem worldwide, there is a need to develop safe drugs with few side effects to treat infection in both humans and animals. In addition, the overuse and misuse of antibiotics are associated with both human and animal immune systems. The collapse of gut microbial ecosystems due to antibiotics could cause undesired negative effects, such as altered physiology of the body or susceptibility to infectious diseases (35, 36).

Demographic and clinical data such as age, sex, household origin (urban or suburban), the presence of disease clinical signs, outdoor access and the presence of other cats in the household were collected in a questionnaire specifically designed for the purpose of the study. A clinical examination assessed the presence of fever, lymphadenopathy, a loss of body mass and pale mucous membranes.

Feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) are immunosuppressive retroviruses that can infect both domestic and wild animals,1–3 and are the most common and important viral causes of infectious disease in cats worldwide.4,5 Furthermore, cats are reservoirs of zoonotic and opportunistic microorganisms such as Toxoplasma gondii, Microsporum canis, Mycobacterium tuberculosis, Cryptococcus neoformans and Mycoplasma haemofelis, and infection with FIV and FeLV increases their risk of infection with those pathogens,3,5–8 which, in turn, can be transmitted to humans. These pathogens are the main causative agents of morbidity and mortality in people with AIDS.9,10

In cats, FIV infection usually arises from direct inoculation of the virus into the body via bites,2,5 while FeLV infection is also associated with fighting or is spread during coitus, birth, nursing, or sharing of dishes and body fluids such as milk, plasma and urine, and via blood transfusions.2,5,11 The risk factors for acquiring these viruses vary, according to the literature. Some studies found that male sex, adulthood and exposure to the outdoors were the main risk factors,2,5 while other studies also considered non-neutered conditions and feline population density as relevant factors.2,5

Reports of the prevalence of FIV and FeLV worldwide are numerous, but information is lacking for most parts of Latin America and Africa.3 A study performed in Addis Ababa to determine the prevalence of antibodies (Ab) to T gondii, Bartonella quintana, FIV and FeLV in cats did not find any cat infected with FIV or FeLV.12 Another study carried out in South Africa in 56 cats reported a seropositivity of 14% and 32% for FIV antibodies (FIV-Ab) and FeLV antigens (FeLV-Ag), respectively, while coinfection with both viruses occurred in 9% of animals.13 There are also a few studies from Botswana, Uganda and Tanzania, mainly in lions, where the prevalence of FIV was reported to be 71%, while no Ag were detected for FeLV.14–16 Importantly, no studies have been published regarding the prevalence of FIV or FeLV in Mozambique; although at Eduardo Mondlane University (UEM) Veterinary Faculty Clinic in Maputo, Mozambique, some cats show clinical signs consistent with a clinical diagnosis of infection with one or both viruses.

There are approximately 36.9 million people living globally with HIV, and, of those, 19.6 million (53.1%) live in Southeast Africa.17 FIV and FeLV, as for other human pandemics, including HIV, originated from zoonotic infections18 through contact between humans and other animals. Because of the possibility that immunocompromised cats could transfer infections to humans infected with HIV, we conducted the present study to determine the occurrence of FIV and FeLV in domestic cats from Maputo city and Maputo province, and to evaluate risk factors associated with seropositivity in cats. From these data, we hoped to develop recommendations for further studies aiming to define the prevalence of these viruses in cats, coinfection with some zoonotic pathogens and the possible role played by cats in the transmission of these zoonotic and opportunistic diseases to humans, especially in AIDS patients.

According to phylogenetic differences, TBEV has been divided into three different subtypes, European, Siberian, and Far Eastern. The European subtype is mainly transmitted by Ixodes ricinus, whereas the Siberian and Far Eastern subtypes are primarily transmitted by Ixodes persulcatus. TBEV is found in central, eastern, and northern Europe and Asia (Figure 1) and correlates with the presence of infected ticks. Ixodes ricinus is found throughout Europe, whereas Ixodes persulcatus is found in Eastern Europe in the west, and China and Japan in the east.

TBEV is considered one of the most important arboviruses in central and eastern European countries and in Russia, with about 13,000 estimated human cases annually. In fact, over the last decade there has been an approximately 300% increase in the number of TBE cases in Europe, and TBEV is currently spreading into new regions in France, Sweden, Norway, and Italy. This increase is thought to be due to growth in population and spread of ticks, which is promoted by factors including climate change, social and political change, and changes in the land use. The increased expansion in Europe also poses an increased risk for the population engaged in outdoor activities.

TBEV is a zoonotic disease and the natural cycle of TBEV is dependent and maintained in a complex cycle involving ticks as the vector and reservoir of the virus and small rodents as hosts for ticks. Humans are not part of the natural transmission cycle of TBEV and are the incidental host when infected by a bite from an infected tick. Transmission through consumption of unpasteurized milk has also been reported for TBEV, as well as transmission via solid organ transplant.

During the tick bite, the virus is inoculated into the skin of the vertebrate host. The initial replication is believed to occur locally in the dendritic cells. This is followed by infection of the draining lymph nodes, resulting in the primary viremia and subsequent infection of the peripheral tissues, where further replication maintains the viremia for several days. The disease course of TBEV is biphasic; the initial phase is characterized by flu-like symptoms and is followed by a second phase involving CNS infection, with meningitis, encephalitis, or meningoencephalitis. The mortality rate of TBEV varies from 1 to 20% depending on the subtype, in which the European TBEV subtype has shown lower mortality rates compared to the Siberian and Far Eastern. Among the patients that experience neuroinvasive TBEV infection, approximately 25–40% of the survivors suffer from long lasting neurological sequelae. No antivirals are available for treatment of TBEV infection but there is an effective vaccine.

LGTV, which is closely related to TBEV, is found in south east Asia and Russia. LGTV has not been associated with human disease under natural infections although it shares 84% sequence identity with TBEV. Because of its avirulence in humans and close similarity to TBEV, LGTV is often used as a model virus for TBEV under biosafety level-2 conditions.

The plague bacillus causes a rapidly progressing, serious illness that in its bubonic form is likely to be fatal (40%–70% mortality). Without prompt antibiotic treatment, pneumonic and septicaemic plague are virtually always fatal. For these reasons Y. pestis is considered one of the most pathogenic bacteria for humans.

Yersinia pestis is transmitted by fleas, while the other two species of Yersinia known to be pathogenic for humans (Y. enterocolitica and Y. pseudotuberculosis) are transmitted by the faecal–oral route and cause intestinal symptoms of moderate intensity. Yersinia pestis is believed to be a clone of Y. pseudotuberculosis that emerged within the last 1,500 to 20,000 years. This divergence was characterised by the acquisition of a few genetic elements; more particularly, two plasmids that play a key role in flea-borne transmission. The exceptional pathogenicity of Y. pestis compared to the enteropathogenic species may be explained by its new mode of transmission. Indeed, the only means for this bacterium to be transferred to new hosts is through septicaemia, which allows the bacteria present in the bloodstream to be efficiently taken up by the flea during its blood meal.

Soon after Yersin's identification of the plague bacillus, it became clear that urban outbreaks were linked to transmission among commensal rats and their fleas. In this classic urban-plague scenario, infected rats (transported, for example, by ships) arrive in a new city and transmit the infection to local house rats and their fleas, which then serve as sources of human infection. Occasionally, humans develop a pneumonic form of plague that is then directly transmitted from human to human through respiratory droplets.

The epidemiology of plague, however, is much more complicated than this urban-plague scenario suggests, involving several other—more likely—pathways of transmission (Box 3 and Figure 2). This complicated epidemiology necessitates a reconsideration of plague ecology.

Coronaviruses (CoV) were for a long time associated with several major veterinary diseases such as avian infectious coronavirus, calf diarrhea, winter dysentery, respiratory infections (BRD-BCoV) in cattle, SDCV, PEDV, SECD in swine and dog, intestinal disease or Feline Infectious Peritonitis (Saif, 2014), and the human mild and common cold. However, SARS emerged in 2002 in China and spread across 29 other countries with a 10% death rate. More recently, the MERS-CoV outbreak in Saudi Arabia in 2012 displayed a death rate of 38%. The emergence of these two events of highly pathogenic CoVs shed light on the threat posed by coronaviruses to humans. Bats are hosting many viruses (Calisher et al., 2006) and in particular coronaviruses, which represent 31% of their virome (Chen et al., 2014). Furthermore, bats display a remarkable resistance to viruses (Omatsu et al., 2007; Storm et al., 2018). The risk of emergence of a novel bat-CoV disease can therefore be envisioned.

Positive blood culture results indicate the presence of cultivable bacteria in the blood. Although transient bacteremia can occur in healthy animals after disruption of mucosal barriers, transfusion of blood from animals with transient bacteremia has not been documented to cause disease in a recipient. Therefore, routine blood culture generally is not indicated for screening potential blood donors, with rare exceptions (see Bartonella section). In transfusion medicine, routine blood culture is more appropriate for screening individual units of blood for bacteria if contamination is suspected.

Infection of wild animals such as apes, monkeys, and antelopes with bat-borne infectious agents may also play a role in the transmission chain to humans, such as for Ebola virus. In the case of the severe acute respiratory syndrome (SARS) coronavirus, civets (Paguma larvata) got infected with a virus circulating in horseshoe bats (Rhinolophus sp.) and would have then acted as an intermediate amplifying host. Natural bat predation by other animals (e.g., monkeys, domestic cats) and its consequences on infectious agents transmission are poorly documented but could also favor spillover opportunities to other hosts.

In addition to wild animals, the role of livestock as intermediate and amplifying hosts between wild animals and humans has been clearly demonstrated in several outbreaks, such as for Filovirus and Henipavirus. Indeed, in Malaysia, the growth of commercial pig farms with fruit trees on the farm has created an environment where bats could drop partially eaten fruits contaminated with Nipah virus into pig stalls.

In contrast to rapid and short-time spillover events, long-time and silent circulation of viruses in livestock before transmission to humans may also occur, as is strongly suspected for the ongoing outbreak of Middle East respiratory syndrome (MERS). Although bats are likely to be a source of MERS-like coronaviruses, dromedary camels (Camelus dromedaries) act as the natural reservoir host in which the MERS coronavirus could have circulated for more than 30 years before its first detection in humans. Other animals such as llamas (Lama glama) and wild boars (Sus scrofa) have shown susceptibility to MERS coronavirus infection, suggesting a large host species range. The endemic human coronavirus 229E may also constitute a descendant of camelid-associated viruses and further supports that livestock plays a key role in the long-time establishment of bat-borne viruses in humans.

Of all the pathogens, only two (4%) were fungal; Coccidioides and Histoplasma capsulatum. Data were collected from the United States (2) and Brazil (1), and publication dates ranged from 2011 to 2017. A serosurvey of dogs from private veterinary clinics and a research control center in northeastern Brazil was performed, in which histoplasma antibodies were detected in 1.78% of serum samples, three of which were also positive for Leishmania spp.. The remaining two studies both evaluated rates of coccidioidomycosis infection in American dogs to indicate risk for human infection. Results demonstrated that areas with a high rate of coccidioidomycosis in dogs in Texas overlapped with those formerly identified as potential risk areas based on human surveys, and that there was significant correlation between reported human rates of infection and the generated risk map of canine coccidioidomycosis in California, thus providing evidence that dogs may be utilized as sentinels to describe the risk of coccidioidomycosis in humans.

Almost 120 years have passed since Walter Reed, James Carroll, Aristides Agramonte, and Jesse Lazear established that yellow fever is caused by a filterable infectious agent which is transmitted by the bite of a mosquito, then known as Stegomyia fasciata (Aedes aegypti). Lazear, who like his colleagues, had been stationed by the US Army in Cuba to study the disease, died of yellow fever in September 1900 after being exposed experimentally to mosquitos that had fed on sick patients. At about the same time in South Africa, James Spreull and Sir Arnold Theiler demonstrated that bluetongue disease of sheep is caused by an “ultravisible” agent that could be transmitted by the injection of an infected serum. Epidemiological evidence suggested that the agent was vector-borne, and it was subsequently shown by R.M. du Toit that the disease occurred in sheep inoculated experimentally with suspensions of wild-caught biting midges (Culicoides imicola). These and other seminal discoveries precipitated a century of research into vector-borne and zoonotic viral diseases, resulting in the discovery and isolation of many hundreds of novel viruses from insects or vertebrate hosts. Some were identified as important human or veterinary pathogens. Many other viruses were archived in reference collections, with only basic characterization of their biological or molecular properties. In recent years, the advent of next generation sequencing (NGS) has transformed this situation. Complete genome sequences are now available for many of the archived isolates, allowing more accurate taxonomic assignments, analysis of their phylogenetic and evolutionary relationships with other viruses, and evaluation of the potential risks they may present to humans and wild or domestic animal populations. NGS has also opened the door to viral metagenomics, which has greatly increased the pace of new virus discovery from a wide range of hosts, usually with complete or near-complete viral coding sequences, but no virus isolate and minimal biological data. This has presented both opportunities and challenges for virologists and epidemiologists, as well as viral taxonomists, evolutionary biologists, and bioinfomaticians. Sadly, this technological revolution has been accompanied by a period of progressive disinvestment in training in classical virology. In this review, we recall the rich history of the discovery of arboviruses and other zoonotic viruses in various settings around the world and the many outstanding scientists who have contributed to the endeavour. We also consider the impacts of NGS and metagenomic analysis, and the implications of these new technologies for the future of this important field of research.

Translating the theoretical idea of sentinel surveillance into a feasible and practical surveillance system requires examination of several factors. Firstly, the objective of the surveillance must be clear; for example, whether the objective is to measure frequency of disease or to provide a warning of disease emergence or expansion will determine which regions and dog populations will be most useful. The region(s) should be selected based on known or estimated prevalence of disease, or presence or risk of vector emergence, and sentinel units (e.g., veterinary clinics, shelters, and laboratories) selected to maximize the included population. Dog populations utilized would depend on the specific pathogen of concern and might include live sampling of dogs or the use of samples already taken for other diagnostic tests. Sampling strategy would be formed based on the objective of the study as well. For example, if the objective is to detect a new wave of viral transmission, then repeatedly testing naive juvenile dogs would provide an ideal sample, whereas, if measuring prevalence of a rare disease, dogs at high risk for exposure should be selected. The selected dog populations should be based on their availability for sampling, increased susceptibility to the pathogen in question, relationship to the pathogen and human population they are to represent, and the number of dogs available to sample. It is also important to note that, when samples represent a subset of clinically ill dogs, measured prevalence cannot be used to estimate regional prevalence.

Constraints such as time, cost, risks to research staff, and logistical feasibility should be considered. The ethical aspects of utilizing dogs as sentinels must also be thought through when designing an active surveillance system or conducting any type of research or testing. While the nature of utilizing dogs as sentinels precludes replacement, it might be possible to reduce the sample size by selecting dogs with increased risk exposure and to refine procedures by minimizing the number of times a dog is sampled. Ideally, tests would be performed on samples that had already been taken for a different purpose, or added on to a sample that would be taken anyway. Utilizing samples from a veterinary laboratory or asking veterinary staff to add on a test to future samples would be a way of achieving this. Many dog shelters would routinely test newly admitted dogs for a range of parasitic diseases, which can provide an opportunity to add on other tests.

There are limitations to the use of dog-sentinel surveillance that need to be considered when designing surveillance schemes and analyzing data outputs. Many variables cannot always be accounted for, such as travel history, previous medications (including prophylactic treatment), animal movements and owner compliance. Travel of dogs across regions and borders in particular affects data interpretation; ideally, anomalous results would be traceable to the animal so that a history could be obtained. The nature of the diagnostic test used would also aid interpretation of a positive result, for example, whether the test suggests active infection rather than previous exposure. Furthermore, animal-sentinel surveillance is an indirect method of measuring risk to human disease, and it is difficult to translate data obtained from such surveillance into a measured risk to humans. Therefore, it would be prudent to focus on the trends, patterns, and emergence of pathogens rather than to try and quantify risk. While not a limitation of dogs as sentinels, there is also the issue of funding sources, as it is not immediately obvious whether a sentinel-surveillance study of companion animals would fall under the mandate of the CFIA, which is typically concerned with animal health and food safety, or the Public Health Agency of Canada (PHAC), which includes disease prevention and response to public-health threats in its activities. This might be decided on a provincial basis and thus could vary across Canada.

Despite a lack of empirical studies of the transmission of influenza in rLBMs, well-established ideas from epidemic theory enable us to make mechanistic predictions about prevalence patterns within them. Incubation periods for AIVs in poultry can be up to 2 days when birds are inoculated with doses less than or equal to 103, and around 1 day when doses are higher. Making the worst-case assumption that susceptible and infectious hosts are in constant contact, this means that the minimum time infectious individuals can create other infectious individuals is 1 day, and higher on average. Thus, if the average stay-time of birds in rLBMs is ≤ 2 days, there is not time for exponential growth of prevalence due to direct transmission within rLBMs (e.g., “outbreaks”). In addition, direct transmission alone may not cause significant amplification of prevalence within rLBMs because birds that entered the market uninfected have a high probability of being slaughtered before they begin shedding AIV. A similar principle has been identified in other animal-disease systems. For example, epizootics of plague in prairie dog populations have been shown not to occur by blocked-flea or pneumonic transmission alone, because both blocked vectors and hosts capable of direct transmission are removed from the population by death before they reliably create large chains of transmission required for outbreaks. Essentially, direct transmission in rLBMs should be limited by the interplay of stay-times and incubation periods.

Retail LBMs are also thought to foster persistence of AIVs in the environment, creating another source of transmission. The importance of an environmental factor in viral persistence has been shown in an experiment that monitored AIV isolation rates before and after days that the market was disinfected. However, whether this environmental persistence adds to transmission has not been determined empirically. Theoretically, indirect transmission via an environmental reservoir could contribute to the overall force of infection within rLBMs by providing a sustained source of AIV (i.e., by providing a transmission link between birds even if they do not occupy the market at the same time). Indirect transmission can occur through a variety of routes, including viruses in drinking water, in feces on the ground or on surfaces in cages. All of these routes rely on three main processes: shedding rates into/on a particular environmental feature, decay rates of the virus in it, and contact of susceptible birds with it. Intuitively, one would predict that indirect transmission would be most significant when shedding rates are high, decay rates are low and contact rates are high.