Version May 2024
INTRODUCTION — Pets serve valuable social roles in society [1,2]. Pets may lower blood pressure, reduce cholesterol and triglyceride levels, and improve feelings of loneliness, while increasing opportunities for exercise, outdoor activities, and socialization [1,3].
Despite these benefits, pets present zoonotic risks, especially for immunocompromised hosts [4-7]. One modeling study in Ontario, Canada found that household pets resulted in higher amounts of Campylobacter exposure than any other [8]. In addition to infection from pets, there have been multiple outbreaks of enteric disease associated with animal exposure in public settings, such as county fairs, farms, and petting zoos [9]. In a review of 55 such outbreaks, most were due to Escherichia coli O157 (58 percent) and Salmonella species (22 percent) [10]. (See "Shiga toxin-producing Escherichia coli: Microbiology, pathogenesis, epidemiology, and prevention", section on 'Animal contact'.)
The epidemiology of zoonoses from pets other than dogs and cats will be reviewed here. The epidemiology of dog- and cat-related zoonoses is presented separately and the clinical management of specific zoonotic diseases is discussed in the appropriate topic reviews. (See "Zoonoses: Dogs" and "Zoonoses: Cats".)
DEFINITION
A zoonosis is any disease or infection that is naturally transmissible from vertebrate animals to humans. Humans with a zoonotic infection are frequently but not always an accidental host who acquires disease through close contact with an infected animal that may or may not be symptomatic. The most common route of infection related to pet contact is through bites, especially in children [11]. (See "Animal bites (dogs, cats, and other mammals): Evaluation and management".)
RISK FACTORS — Clinicians should ask about exposure to pets, wild or domestic animals, hobbies and occupational activities and travel when taking a medical history and formulating a differential diagnosis. Approximately 68 percent of households in the United States have at least one pet (www.avma.org) [12]. In both the United States and Europe, the most common types of pets include dogs, cats, fish, birds, small mammals, and reptiles [13-15].
Many of the risks posed by pet ownership can be reduced by good hygiene after handling pets, careful pet selection, and proper pet care. New pets can pose more of a health risk. Adult pets are generally safer than younger animals, since they are less likely to be involved in playful activities that include scratching and biting. Children are at highest risk for infection because they are more likely to have close contact with pets.
TRANSMISSION — Transmission of an extensive array of bacterial, viral, and parasitic zoonotic pathogens, including drug-resistant organisms [16-18], can occur from pets. Many different routes of transmission can cause infections related to pets including:
●Infectious saliva that contaminates bite wounds, skin abrasions, or mucous membranes
●Hand-to-mouth transfer of microorganisms, cysts, or oocysts (eggs) from feces of an infected animal
●Insect bites when these vectors are carried into the home by pets or when bites transmit disease from a pet, acting as a disease reservoir, to humans
●Aerosol from body fluids (eg, respiratory secretions, placenta)
●Scratches
●Contamination of water or the environment with pathogen-containing animal urine
●Contamination of an object that is subsequently put into the mouth (eg, pacifier) [19]
HORSES
Fecal transmission — Common zoonotic pathogens causing equine gastroenteritis include Salmonella, Campylobacter, Cryptosporidium, and Giardia. Although horses are not the usual source for human gastrointestinal infection, these pathogens should be considered in a patient who presents with compatible symptoms who has had contact with a horse with diarrhea.
Salmonella — An outbreak of salmonellosis in a population of hospitalized horses resulted in the closure of a veterinary teaching hospital for a period of 10 weeks [20]. Fecal samples were collected from suspected cases and cultured for Salmonella. Thirty-three cases of infection by a multidrug-resistant strain of Salmonella typhimurium were detected. S. typhimurium might have been introduced into the hospital environment by a foal presenting with diarrhea.
Salmonella spp infections transmitted to humans usually result in a mild, self-limited gastroenteritis. However, severe invasive illness, such as septicemia or meningitis, can occur especially in infants and immunocompromised persons. (See "Nontyphoidal Salmonella: Gastrointestinal infection and asymptomatic carriage".)
Campylobacter — Campylobacter enteritis in humans presents after an incubation period of one to seven days as a syndrome most commonly characterized by prominent abdominal pain and profuse diarrhea that is often bloody. (See "Campylobacter infection: Clinical manifestations, diagnosis, and treatment".)
Cryptosporidium — Cryptosporidium is an intracellular protozoan parasite that is associated with gastrointestinal diseases in all classes of vertebrates including horses. Cryptosporidial oocyst shedding is primarily found in immunocompromised or immature horses and rarely from healthy mature horses [21].
An example of such transmission was described in an outbreak of a zoonotic subtype of Cryptosporidium parvum in two hospitalized foals that were linked to cryptosporidiosis in six veterinary students [22].
Cryptosporidium infection in immunocompetent individuals has a variable presentation, it can be asymptomatic, cause a self-limited gastroenteritis (usually resolving in 10 to 14 days without treatment), or can cause more severe diarrhea [23]. In immunocompromised hosts, the illness is more frequently protracted and severe, and can lead to significant malabsorption and weight loss. Cryptosporidium parvum and Cryptosporidium hominis are the usual pathogens in humans; immunocompromised hosts can also be infected by other Cryptosporidium spp [24]. (See "Cryptosporidiosis: Epidemiology, clinical manifestations, and diagnosis".)
Giardia lamblia — Giardia lamblia (also known as Giardia duodenalis or Giardia intestinalis) is a flagellated protozoan parasite and one of the most common gastrointestinal parasites in the United States. There is evidence supporting the zoonotic transmission of Giardia; horses may constitute a potential source for human infection of Giardia either directly or via contamination of watersheds [25].
The spectrum of clinical disease in humans includes asymptomatic infection, self-limited acute giardiasis, and chronic infection. (See "Giardiasis: Epidemiology, clinical manifestations, and diagnosis".)
Clostridioides difficile — C. difficile infection occurs in foals and horses following treatment with antibiotics [26]. Outbreaks may occur in veterinary hospitals [27]. However, no case of horse-to-human transmission has been reported.
Aerosol
Rhodococcus equi — R. equi is a gram-positive pleomorphic organism that appears coccoid on solid media but forms long rods or short filaments in liquid media. The organisms can be acid fast with the Ziehl-Neelsen stain. (See "Microbiology, epidemiology, and pathogenesis of Rhodococcus equi infections".)
R. equi is a soil organism carried in the gut of many herbivores and widespread in their environment. On horse farms, progressive environmental contamination with R. equi has been related to the length of time that animals were present [28]. The highest numbers of organisms have been found in the surface soil on horse farms with endemic disease. Exposure to soil contaminated with herbivore manure is likely the major route of acquisition for both animal and human infection.
Foals less than six months old are uniquely susceptible to the development of a chronic suppurative bronchopneumonia due to R. equi that can lead to lung and bronchial lymph node abscesses [29]. Ulcerative colitis and mesenteric adenitis may also occur, usually associated with pulmonary infection.
Most human infections have been associated with immune system dysfunction (eg, HIV, solid organ transplant recipients). Pulmonary infections are the most common form of human disease. (See "Clinical features, diagnosis, therapy, and prevention of Rhodococcus equi infections".)
Brucella — Brucella spp infection in horses has a worldwide distribution, but human infections transmitted by horses are uncommon. The Brucella spp that are frequently associated with horses are Brucella suis and Brucella abortus [30,31]. Humans may become infected when they are exposed to body fluids from a B. suis or B. abortus infected horse. Most cases of human transmission from horses are in developing countries.
Human brucellosis is a well-documented cause of fever of unknown origin with varied and nonspecific symptoms. (See "Brucellosis: Epidemiology, microbiology, clinical manifestations, and diagnosis".)
Coxiella burnetii — Coxiella burnetii, the etiologic agent of Q fever, is a worldwide zoonosis. The most common animal reservoirs are goats, cattle, sheep, cats, and occasionally dogs or horses [32,33]. Infected mammals shed C. burnetii in urine, feces, milk, and birth products.
In humans, exposure results from inhalation of contaminated aerosols from parturient fluids of infected mammals, which can be present in the environment, on the coats of newborn animals, or from the placenta. A serosurvey of horses in Uruguay found a positive rate of 5.5 percent in 1979 and 21.7 percent in 1985 [33]. Outbreaks in humans in Uruguay have occurred in workers at meat-processing plants; no Q fever cases are reported that implicated transmission from pet horses to human [33].
Clinical signs of Q fever are often extremely mild or absent. Patients may be asymptomatic or can present acutely with one of three clinical presentations:
●A self-limited flu-like illness
●Pneumonia
●Hepatitis
Chronic infection most commonly involves the heart as endocarditis.
Further information regarding Q fever can be found on the United States Centers for Disease Control and Prevention website [34,35].
Streptococcus equi subspecies zooepidemicus — S. zooepidemicus can be transmitted by direct contact with horses or from eating horse meat [36-39]. The organism is part of the commensal flora of the upper respiratory tract. A case report from Washington State described a mother and daughter who had contact with an ill horse; the 71-year-old mother succumbed to infection [40]. A review of 34 cases of S. zooepidemicus meningitis attributes most cases to direct contact with horses, although consumption of unpasteurized dairy products was also identified as a source of infection [36]. In this series, seven (21 percent) died from infection and many others developed neurologic sequelae. Most cases of S. equi meningitis were caused by subspecies zooepidemicus, and only two cases were caused by subspecies equi.
Mosquito-borne disease — Horses can be infected by Eastern, Western, or Venezuelan equine encephalitis virus or West Nile virus. However, although both human and horses may develop encephalitis from each of these agents, infection with Eastern and Western equine encephalitis (EEE and WEE) and West Nile virus results in low or undetectable levels of viremia, thus these hosts do not serve as reservoirs for further spread of the virus. The horse, however, acts as a reservoir of disease for Venezuelan equine encephalitis (VEE) virus.
Equine encephalitis — Large outbreaks of WEE in humans and horses occurred in the western United States in the 1930s and 1950s. However, a declining horse population, equine vaccination, and improved vector control reduced the incidence of the disease; during 2003 to 2018 in the United States, an annual average of eight EEEV disease cases were reported (range: 4 to 21 cases) [41]. In 2019, the Centers for Disease Control and Prevention (CDC) received reports of 38 cases of EEEV disease, 23 of which were in northeastern states [42]; the etiology of this surge in cases is unknown. Infection of avian species results in a viremia of sufficient magnitude and frequency to maintain a reservoir of infected mosquitoes. Infection of horses causes low level viremia and thus the horse is not a reservoir of WEE or EEE virus.
In contrast, horses serve as the primary amplification hosts for VEE virus without which there would be little human disease [43]. Effective prevention of both human and equine disease can be accomplished by immunizing equines. Mosquitoes are required as a vector for human transmission. VEE has a widespread geographic distribution from Florida to South America.
Human VEE disease occurs after an incubation period of one to six days, and is heralded by a brief febrile illness of sudden onset accompanied by malaise, nausea, vomiting, headache, and myalgia. Less than 0.5 percent of adults and less than 4 percent of children develop encephalitis characterized by nuchal rigidity, seizures, coma, and paralysis. Long-term sequelae and fatalities are uncommon. (See "Arthropod-borne encephalitides".)
Cutaneous/mucosal transmission
Burkholderia mallei — Glanders is an illness caused by Burkholderia mallei. Although primarily an illness affecting horses, the organism can affect humans after transmission via mucosal membranes or through cuts in the skin. Clinical manifestations in humans can include localized infection with ulceration, mucosal inflammation, and constitutional symptoms [44,45]. Pulmonary involvement and disseminated infection have also been described. Glanders is most frequently seen in horses in geographic areas such as South America, the Middle East, South Asia, and some countries in Africa [46,47]; in the United States, no animal has developed glanders since the 1940s [44].
Infected saliva — Saliva can transmit and contaminate bite wounds, skin abrasions, or mucous membranes.
Rabies — Although rare, horses can become infected with rabies and die [48,49]. In 2017, there were 13 reported cases of rabid horses and mules [50]. Human rabies is rare in the United States, with only 125 cases reported between 1960 and 2018 [51]. However, rabies should be considered in the differential diagnosis of patients presenting with acute progressive encephalitis regardless of a history of an animal bite. Because of the nonspecific early symptoms, other more common infectious and noninfectious disorders (eg, encephalitis caused by arboviruses or enterovirus and Guillain-Barré syndrome or vasculitis) should be ruled out. (See "Clinical manifestations and diagnosis of rabies".)
RABBITS — Infections related to domestic pet rabbits are rare [52]. Although they can contract and potentially transmit a variety of zoonotic pathogens, infection with any one of these pathogens is unusual. The following zoonotic pathogens have been reported in pet rabbits:
Gastrointestinal — Salmonella spp, Yersinia pseudotuberculosis, and Cryptosporidium infection may be transmitted to humans through contaminated rabbit feces [53]. Hepatitis E has also been found in a significant proportion of rabbits, and may be a source for human disease [54,55]. Almost half of workers in a rabbit slaughterhouse in China were found to be seropositive for hepatitis E compared with 1 percent in the community [56].
Respiratory — Pasteurella multocida can colonize and cause a respiratory disease (snuffles) or eye infections in rabbits [57]. Although P. multocida has been found in the oropharynx of animal breeders and antibodies to P. multocida have been detected in their sera, occupational disease has not been reported [58].
●Bordetella bronchiseptica was isolated four times over 2.5 years from a 79-year old bronchopneumonia patient who lived on a farm and had contact with rabbits [59]. Epidemiologic investigation found that the rabbits had clinical symptoms consistent with B. bronchiseptica respiratory infection and sacrifice of one symptomatic rabbit led to the isolation of the organism from the lower respiratory tract.
Neurologic — Rabies virus infection was confirmed in seven pet rabbits in New York State [60]. The animals had been caged outside and had probably contracted the disease from a wild animal.
Cutaneous — Dermatophytes such as Trichophyton (ringworm) are prevalent in rabbits on farms and the skin infection can be transmitted to humans through direct contact with the skin lesions of rabbits [61,62].
●Cheyletiellosis (caused by the rabbit fur mite) can cause a papular, pruritic eruption in humans, although the human infection is limited by the inability of the mite to reproduce on human skin [63].
Zoonoses from wild rabbits — Infections related to contact with wild rabbits include:
●Francisella tularensis, the etiologic agent of tularemia, is an important pathogen in rabbits. F. tularensis can be secondarily transmitted to humans, often by handling infected rabbits. During 2001 to 2003, an outbreak of human tularemia in Wyoming was temporally associated with an outbreak among rabbits [64]. (See "Tularemia: Clinical manifestations, diagnosis, treatment, and prevention".)
●Wild cottontail rabbits on Nantucket Island, Massachusetts, have been found to harbor a Babesia spp that was identical to that causing human babesiosis [65,66]. In addition, cottontail rabbits on Nantucket Island also harbor Anaplasma phagocytophilum (the agent of human granulocytic anaplasmosis [HGA]), although the impact of this reservoir on human disease is unknown [67]. (See "Babesiosis: Microbiology, epidemiology, and pathogenesis" and "Human ehrlichiosis and anaplasmosis".)
DEER, SHEEP, CATTLE, GOATS, AND CAMELS
●Parapoxviruses – Parapoxvirus infections can be transmitted from deer, sheep, cattle and goats to humans. People with parapoxvirus infections can present with an erythematous maculopapular lesion (ecthyma contagiosum, also called contagious pustular dermatosis) after an incubation period of three to seven days [68]. Lesions usually occur at the site of inoculation (often fingers or hands) and evolve slowly over the course of four to eight weeks from a papule to a vesicle and then to an ulcer with subsequent crusting [69]. Recurrent lesions can occur since infection does not confer immunity.
The specific type of parapoxvirus varies by host; for example, orf virus infection occurs in sheep and goats while bovine papular stomatitis virus occurs in cattle:
•In 2009, parapoxvirus infection was diagnosed in two deer hunters in the eastern United States after the hunters had field-dressed white-tailed deer [70]. DNA sequence analysis suggested that the virus infecting the hunters was a unique parapoxvirus strain. One patient recovered without medical intervention; the other patient was treated with antibiotics.
•In 2012, four cases of orf were reported in the United States in association with the slaughter of goats and lambs for religious observances [71]. All infected humans incurred puncture wounds resulting in cutaneous lesions.
On histology, these lesions are characterized by epidermal hyperplasia with occasional cytoplasmic inclusions, prominent vascular proliferation, and mixed inflammatory-cell infiltrates [72]. The diagnosis can be confirmed through polymerase chain reaction (PCR) testing, which is available through the Poxvirus Inquiry Line of the United States Centers for Disease Control and Prevention (404-639-4129).
●Middle Eastern Respiratory Syndrome Coronavirus (MERS-CoV) – MERS-CoV is the virus that causes Middle Eastern Respiratory Syndrome (MERS), a severe respiratory illness seen among residents of or travellers to the Arabian Peninsula [73]. Exposure to camels is a primary risk factor for MERS, and the virus has been isolated from camels. More information about MERS is found elsewhere. (See "Middle East respiratory syndrome coronavirus: Virology, pathogenesis, and epidemiology", section on 'Epidemiology'.)
RODENTS — Rodents, including hamsters, gerbils, guinea pigs, mice, rats (including Gambian rats), and prairie dogs, are becoming more common pets. Transmission of infectious diseases from rodent to man usually results from bites or exposure to potentially infectious bodily fluids [74]. (See "Animal bites (dogs, cats, and other mammals): Evaluation and management", section on 'Bites from mammals other than dogs and cats'.)
Transmission by feces
●Pet rodents are a potential source of salmonellosis. During 2004, the Minnesota Department of Health (MDH) Public Health Laboratory reported the isolation of multidrug-resistant Salmonella enterica serotype Typhimurium from patients and their ill hamsters purchased from a Minnesota pet distributor; this was the first documented human salmonellosis outbreak associated with pet rodents [75,76]. (See "Nontyphoidal Salmonella: Microbiology and epidemiology", section on 'Animal contact'.)
Transmission by infected saliva (bites)
●Bubonic plague, caused by Yersinia pestis, has been reported after the bite of a wild Gunnison's prairie dog during a relocation from an endemic area [77].
●A three-year-old boy was diagnosed with tularemia associated with a pet hamster bite in 2004 [78]. A pet prairie dog was also linked to transmission of tularemia [79]. (See "Tularemia: Clinical manifestations, diagnosis, treatment, and prevention".)
●Rat bite fever, a rare disease caused by Streptobacillus moniliformis or Spirillum minus, can be transmitted by rats, mice, and squirrels. A fatal case of rat bite fever in a pet shop employee occurred following a superficial finger wound on a contaminated rat cage [80]. A review highlighted the importance of obtaining a history of rodent exposure to make the correct diagnosis [81]. (See "Rat bite fever".)
●Rabies very rarely is reported from rodents; however, a report in 2005 confirmed rabies in a pet guinea pig in New York State [60]. The animal was housed outside and probably came in contact with wild animals. Rabies prophylaxis is rarely indicated following rodent bites. (See "Rabies immune globulin and vaccine".)
Direct contact or aerosol
●Wild house mice are the primary reservoir for lymphocytic choriomeningitis virus (LCMV) [82]; an estimated 5 percent carry LCMV [83]. Pet rodents, such as hamsters and guinea pigs, may become infected after contact with infected mice [84]. Human acquisition of LCMV occurs by direct contact with fomites contaminated with infectious virus or inhalation of aerosolized virus. A large outbreak of LCMV infection associated with pet hamsters sold by a single distributor was reported in 1974, when 181 human cases were identified in 12 states; no deaths occurred [85]. The outbreak was controlled by voluntary cessation of the sale of pet hamsters and subsequent destruction of the infected breeding stock.
Authors of one case report of LCMV infection in an organ transplant recipient linked this infection to an asymptomatic donor who had a pet hamster infected with LCMV [82]. Further investigation revealed that this asymptomatic organ donor was the source of organs for five recipients, four of whom died. Four subsequent clusters of donor-related transmission LCMV infection have been reported [86]. (See "Infection in the solid organ transplant recipient", section on 'Donor-derived infections'.)
●The risk for pet-associated leptospirosis may be highest among pet rat owners, since wild rats are the main reservoir for Leptospira icterohaemorrhagiae, the most pathogenic Leptospira serovar in humans [87,88].
●Rodents including rats and mice are the primary reservoirs for hantavirus virus infections. Transmission of hantavirus from rodents to humans mainly occurs to inhalation of infected aerosols derived from infected rodent excretions. A discussion of the transmission of hantaviruses from rodents is found elsewhere. (See "Epidemiology and diagnosis of hantavirus infections".)
●Ill pet prairie dogs imported from West Africa were responsible for an outbreak of mpox infection in the Midwestern United States in 2003 [89]. (See "Treatment and prevention of mpox (monkeypox)".)
●A case report describes transmission of cowpox to a young boy from a sick pet rat in the United Kingdom [90]. Human cowpox infection primarily occurs in Europe.
●Ringworm, a Trichophyton species, is the most common zoonotic disease transmitted from rodents to people [52,91]. Parasitic diseases transmitted by rodents occur mostly in children and include teniasis (Hymenolepis nana and Hymenolepis diminuta), which can cause nausea, vomiting, and diarrhea, as well as sarcoptic mange (Trixacarus caviae) from guinea pigs (usually asymptomatic), but causes pruritic skin lesions in humans [52].
Zoonoses by wild rodents — Numerous outbreaks and cases of hantavirus infections in individuals exposed to wild rodents have been reported around the world. More information about hantavirus from wild rodents can be found elsewhere. (See "Epidemiology and diagnosis of hantavirus infections".)
In addition, Leptospira spp have been detected in the blood or urine of almost half of squirrels being sold in wildlife markets in Laos, suggesting a risk of exposure from handling squirrels and consumption of wild squirrel meat [92].
The most common pet-related avian bacterial zoonosis is infection due to Chlamydia psittaci (psittacosis).
Birds may also carry Mycobacterium avium and Salmonella spp in their gastrointestinal tracts. Although there is no evidence that pet birds transmit M. avium or Salmonella to man [93], in 2006, there were three outbreaks of salmonellosis that resulted from contact with chicks and other baby poultry (ducklings, goslings, and baby turkeys) purchased at agricultural feed stores in the springtime [94]. From 2004 through 2011, there was a prolonged, multistate outbreak of more than 300 cases of salmonellosis due to Salmonella montevideo, where a mail-order hatchery for young poultry was identified as the source [95]. In 2021, hundreds of people were sickened by contact with poultry, with more than 1 in 3 being under 5 years old [96].
Transmission by bodily fluids
●Psittacosis, also known as parrot fever, chlamydophilosis, and ornithosis, is a bacterial infection caused by C. psittaci. C. psittaci is a gram-negative, obligate intracellular bacterium that can survive in the environment for months in its infectious form (ie, elementary bodies). Humans are infected via inhalation of C. psittaci-containing dust or aerosols, or by direct contact with infected birds or their excreta.
Virtually all pet birds can carry C. psittaci, but psittacine birds (ie, parrots, parakeets, lovebirds, and cockatoos) are the most likely to be infected. Infected birds shed the bacteria through feces and nasal discharge, and humans become infected from exposure to these materials. Birds may display clinical illness or may be persistent carriers. Clinically, the disease in humans ranges from subclinical to severe with pneumonia. (See "Psittacosis", section on 'Clinical features'.)
From 1988 through 2003, 935 human cases of psittacosis were reported to the Centers for Disease Control and Prevention (CDC); most resulted from exposure to infected pet birds, usually cockatiels, parakeets, parrots, and macaws [97]. A case report of psittacosis in both members of an elderly couple who ran a pet shop serves as a classic example of environmental exposure [98].
●Cryptococcus neoformans has been found in soil samples from around the world in areas frequented by birds, especially pigeons and chickens. It colonizes the bird's gastrointestinal tract and is found in their excreta [99]. Human cryptococcal disease (pneumonia or meningitis) associated with pet bird contact (eg, cockatoo, cockatiel) primarily is seen in immunocompromised hosts [100,101]. Routine screening of healthy birds for C. neoformans is not recommended [102,103]. (See "Clinical manifestations and diagnosis of Cryptococcus neoformans meningoencephalitis in patients without HIV" and "Cryptococcus neoformans infection outside the central nervous system".)
●Avian influenza can be transmitted by both pet and wild birds [104]. (See "Avian influenza: Epidemiology and transmission".)
Transmission by the avian environment — Histoplasma capsulatum is not transmitted from pet birds to man, as birds are not carriers of the fungus. H. capsulatum is found in areas such as bird roosts, as growth of the fungus is stimulated in bird droppings. (See "Pathogenesis and clinical features of pulmonary histoplasmosis", section on 'Reservoir'.)
Zoonoses from wild birds — Wild birds, but not pet birds, have been associated with West Nile virus infection. (See "Epidemiology and pathogenesis of West Nile virus infection", section on 'Transmission' and "Clinical manifestations and diagnosis of West Nile virus infection".)
FISH — Pet fish are very rarely associated with human infection [4]. Most cases of fish-related human illness stems from the consumption of fish, rather than pet ownership.
Mycobacterium marinum — M. marinum causes fish tuberculosis and contaminates the water of aquaria housing infected fish. Humans develop M. marinum infection, "fish tank granuloma," when they sustain a minor skin injury while cleaning a fish tank [105]. Other atypical Mycobacteria species, primarily Mycobacterium fortuitum and Mycobacterium chelonae, cause a similar disease both in fish and man [106].
Human M. marinum infection presents as a cutaneous infection characterized by chronic skin papules, pustules, and ulcers that develop weeks following the injury. (See "Soft tissue infections following water exposure".)
Burkholderia pseudomallei — B. pseudomallei is the causative agent of melioidosis, an infection that is historically endemic to Southeast Asia and northern Australia. In a report of an individual from the United States with pneumonia and bacteremia due to B. pseudomallei, the infection was traced to the patient’s fresh-water aquarium which had been recently stocked with tropical ornamental fish [107]. (See "Melioidosis: Epidemiology, clinical manifestations, and diagnosis" and "Melioidosis: Treatment and prevention".)
Occupational exposure — Additional fish zoonoses are usually associated with occupational exposure (eg, fishermen) through skin puncture or open wounds and include Aeromonas hydrophila, Edwardsiella tarda, and Erysipelothrix rhusiopathiae. (See "Soft tissue infections following water exposure".)
In a case report, a woman with diabetes mellitus developed a thigh infection that drained foul-smelling pus [108]. Necrotizing fasciitis was diagnosed surgically and histopathologically and Erysipelothrix rhusiopathiae was isolated from the drainage. A pet goldfish might have been the source. (See "Erysipelothrix infection".)
REPTILES AND AMPHIBIANS — An estimated 5 percent of households in the United States own at least one reptile (turtles, snakes, iguanas, or other lizards) [13].
Salmonella and other gastrointestinal pathogens — The most common zoonoses related to pet reptiles is salmonellosis [109]. Seventy-four to >90 percent of reptiles are colonized with Salmonella spp and shed the organism intermittently in their feces [110-113]. This is true for both wild and captive reptiles [114]. In one survey, for example, fecal sampling of reptiles (18 turtles, 71 lizards, and 23 snakes) from a pet shop in Japan isolated Salmonella spp in 83 of 112 samples (74 percent) [110]. The predominant serovars were S. Bardo, S. Newport, and S. Panama; all of these species are capable of causing human salmonellosis.
Contact with reptiles and amphibians accounts for an estimated 74,000 (6 percent) of the approximately 1.2 million sporadic human Salmonella infections that occur annually in the United States (ie, cases not associated with an outbreak) [115]. In a case-controlled study of sporadic salmonellosis in infants, infants with Salmonella infection were five times more likely to have had exposure to reptiles [116]. In the Netherlands, a study that reviewed 63,718 cases of sporadic/domestic human salmonellosis over a 30-year period found that 2 percent originated from reptiles [117]. In this study, reptile-associated salmonellosis increased over time (0.3 versus 9.3 percent in 1988 and 2013, respectively), with the proportion of cases increasing in middle-aged adults and decreasing in young children. A review of patients from Minnesota with confirmed Salmonella infections from 1996 to 2011 found that of 8389 sporadic nontyphoidal salmonellosis cases, 290 (3.5 percent) reported reptile exposures, including exposures from lizards (47 percent), snakes (20 percent), turtles (19 percent), and multiple reptile types (14 percent) [118].
Rodents used to feed the reptiles have also been reported as the source of Salmonella across multiple different outbreaks [119,120]. Both a high level of contamination of the rodent carcasses and subsequent reptile owner handling of the rodent carcasses could be important sources for the salmonellosis outbreaks.
Frogs, turtles, and snakes can all transmit Salmonella spp. As examples:
●In one report, 224 human infections with a unique strain of Salmonella typhimurium occurred in 42 states from 2009 to 2011; these cases were associated with contact with African dwarf frogs purchased from a single breeder [121].
●Small turtles are the source of both sporadic cases of Salmonellosis as well as large outbreaks [122-126]. As an example, two multistate outbreaks of human Salmonella infection were reported in the United States between January 22 and September 8, 2015 [126]. The outbreaks were linked to contact with small turtles or their environments (eg, water from a turtle habitat). Fifty-one people were infected with the outbreak strains and 15 were hospitalized; approximately 50 percent of those who became ill were children five years of age or younger.
●Transmission of Salmonella from a snake is illustrated by a case of salmonellosis in a three month old infant whose father was a biology teacher [109]. The infant presented with fever and bloody diarrhea, and stool culture grew Salmonella nima. The father handled a boa constrictor during biology class that he often draped over his shoulder. A stool culture from the snake grew the same Salmonella spp. Although the father was careful to wash his hands after handling the snake, he did not change his clothing when he came home from work before holding his child.
In addition to salmonellosis, contact with reptiles has been associated with human transmission of Yersinia, Campylobacter, Edwardsiella tarda, Plesiomonas, and Aeromonas [52,127-130].
Wild reptile zoonoses — Parasitic and fungal infections may be transmitted by wild reptiles, although there are no reported cases associated with pet-reptile transmission. Pentastomiasis (Armillifer species) is a parasitic disease caused by worm-like arthropods that inhabit the respiratory system of the snakes. Although usually asymptomatic in humans, the encapsulated larvae are sometimes found during laparotomies or are diagnosed by radiographic examination. Infection in North Americans is very rare with only eight cases reported in the literature [131]. Most cases occur in people from West Africa and Congo [132]. Hypersensitivity or toxin release can cause neurologic findings and very rarely death [132].
Fungal infection has not been described as a reptilian zoonosis. In a surveillance study of common garden lizards in Nigeria for pathogenic fungi, the most important pathogenic fungus isolated was Basidiobolus haptosporus, the agent of subcutaneous zygomycosis, which was found in the intestinal contents of 112 (56 percent) lizards [133]. Other fungi isolated from lizards included Aspergillus spp in 24 (12 percent), Candida spp, Penicillium spp, and Fusarium spp each in 12 (6 percent), and Mucor spp in eight (4 percent) [133]. Although transmission from reptiles has not been directly linked to human disease, these fungi could cause serious disease in immunocompromised hosts. In 1995, a new species of Trichinella (Trichinella zimbabwensis) was discovered in farmed Nile crocodiles (Crocodylus niloticus) in Zimbabwe; further spread into wild reptiles has been documented [134]. Contact with exotic animals may allow for zoonotic spread of previously unknown parasites.
EXOTIC PETS — Zoonotic risks from exotic pets and wildlife used as pets are probably underestimated, since they may be traded illegally (thus, escaping standard surveillance systems), be fed exotic diets that may contain unusual pathogens, and harbor underrecognized pathogens. Public education about the risks from exotic pet trades, bushmeat, and wildlife should be augmented [135].
Ferrets — Ferrets have been associated with Salmonella and Campylobacter, and less commonly with cryptosporidiosis [136], toxocariasis, tuberculosis, leptospirosis, and listeriosis [52,137,138].
●Influenza is the most common zoonotic disease in ferrets [139]. The ferret can develop influenza, but the course is usually benign. Human cases of influenza have occurred from contamination by aerosols from infected ferrets [140]. The ferret has been used as an animal model for influenza research [52].
●Giardia has recently been isolated from a ferret in a pet shop; the genotype suggested it could be a causative agent of human giardiasis [141].
●Mycobacterium microti, known as vole tuberculosis and more commonly found in wild rodents than in pets, was isolated from a man with an illness featuring anorexia, weight loss, and malaise [142]. M. microti was subsequently isolated from the man's pet ferret.
●Although rabies transmission from ferrets to humans has not been documented, rabies should be considered with any ferret that has acute onset of paralysis or behavioral changes and a condition that rapidly deteriorates despite veterinarian intervention; need for prophylaxis of contacts should be evaluated. Pet ferrets should be immunized for rabies.
Hedgehogs — Hedgehogs are small, nocturnal, spiny-coated insectivores that have become popular as exotic pets [143]. Hedgehogs pose a risk for a number of potential zoonotic diseases [144]. The most common zoonosis is salmonellosis; several reports document transmission of Salmonella from hedgehogs to humans, with most cases occurring in children less than three years of age [145,146]. A multistate outbreak of S. typhimurium infection linked to pet hedgehogs occurred from 2011 to 2013, with 26 cases in 12 states [147]. A subsequent outbreak was reported in 2018, with 11 cases in 8 states [148].
Several reports document transmission of dermatophytes from hedgehogs to humans. Trichophyton mentagrophytes causes a pruritic eruption, which resolves spontaneously within two to three weeks after onset [149-151]. In addition, human ringworm cases have been associated with persons handling hedgehogs, some for only one to two minutes in a pet store [150,151].
Other potential zoonoses associated with sick hedgehogs include, Yersinia pseudotuberculosis, Yersinia pestis, and M. marinum, although no human infection directly related to hedgehog exposure due to these pathogens has been documented [152-154].
Flying squirrels — Flying squirrels transmit Toxoplasma gondii, Staphylococci, and Rickettsia prowazekii (etiologic agent of epidemic typhus) [29]. There have been many reports of human typhus after contact with wild flying squirrels or their nests, but no reports of transmission from pet flying squirrels [155].
Chinchillas — Chinchillas can harbor agents of dermatophytoses, including Trichophyton and Microsporum [156], human pathogenic fungi, Aspergillus niger and Cladosporium species [23], as well as the bacterial pathogens, Klebsiella pneumonia [24] and Pseudomonas aeruginosa [157]. However, there are no reports of transmission of these potential zoonoses from pet chinchillas to man.
Monkeys — Monkeys may be infected or colonized with many pathogens that infect humans, and monkey-human cross-species transmission could theoretically occur quite easily given the genetic similarity between monkeys and man. Transmission can occur through contact with feces and secretions or through bites. A rare report documents transmission of both Shigella and Salmonella from asymptomatic pet spider monkeys to their owners [158].
B virus — The most worrisome monkey-related zoonosis is B virus (Cercopithecine herpesvirus 1) infection, which is transmitted directly from macaques through bites or scratches or from their tissues and fluids [159]. B virus infection is highly prevalent (80 to 90 percent) in adult macaques, with most animals showing no sign of disease [160]. Human disease, however, usually results in fatal encephalomyelitis or severe neurologic impairment. (See "B virus infection".)
PREVENTION
Simple precautions — Preventive measures against the acquisition of infection from animals includes good hand-washing practices [82]. In a study using systematic unannounced observations of behaviors at petting zoos, compliance with hand-washing ranged from 0 through 77 percent [19]. Predictors for increased hand hygiene compliance included simple measures, such as the availability of hand hygiene stations at the exit from the petting zoo area.
Risk of pet-to-human transmission can be reduced by simple precautions.
●Pets should be seen by a veterinarian on a regular basis, treated promptly for diarrhea and dermatoses and, where appropriate, should be vaccinated for rabies.
●Pets should be fed high-quality commercial food and should not eat raw meat or eggs. They should not be allowed to eat garbage, feces, or hunt [89]. They should not be allowed to drink nonpotable water (eg, surface water or toilet water).
●Young pets present a greater risk for disease than older pets, as they are more likely to engage in playful nipping and biting, behavior which may transmit zoonotic pathogens. Kittens are more likely to be bacteremic and transmit Bartonella henselae, the agent of cat scratch fever. (See "Microbiology, epidemiology, clinical manifestations, and diagnosis of cat scratch disease".)
●Owners should wash their hands with soap and water following contact with their pet, handling of feed, or cleaning of their cages.
Measures to prevent disease in public settings — The Centers for Disease Control and Prevention (CDC) recommends that organizers of public venues (eg, state fairs, pet stores, circuses, child care facilities) should [161]:
●Prohibit food in areas where animals are housed
●Provide a transition between areas with and without animals
●Share information about disease risk and prevention with attendees
Immunocompromised hosts and pets — Groups at high risk for serious infection from pets include persons with waning immunity (eg, older adults); children less than five years old; and people who are pregnant, immunocompromised (eg, persons with HIV/AIDS [162], without a functioning spleen, or on immunosuppressive therapy), or cognitively impaired. To avoid infections, people at higher risk should take particular precautions with any animal contact. In addition to thorough and frequent hand washing, these precautions might include avoiding contact with animals and their environment (eg, pens, bedding, and manure). For children, risk for exposure might be reduced if they are closely supervised by adults, carried by adults in animal areas, or have animal contact only over a barrier. These measures discourage animals from jumping on or nuzzling children and minimize contact with feces and soiled bedding. At the veterinarian office, immunocompromised patients should avoid contact with the aerosol from the kennel cough vaccine, B. bronchiseptica, which can cause disease in this population [163].
Numerous reports exist of the transmission of zoonoses to humans during and after solid organ and hematopoietic stem cell transplantation [164]. Donor-derived infections from West Nile virus infection, Chagas disease, toxoplasmosis, rabies, lymphocytic choriomeningitis virus infection, and infection due to Brucella species have all been reported. Most zoonoses present as a primary infection in the post-transplant period; immunocompromised patients are more likely to experience significant morbidity and mortality from these infections. Risks of zoonotic infection in transplant recipients could be reduced by patient education. The American Society of Transplantation Infectious Diseases Community of Practice has issued guidelines outlining strategies for safe living following solid organ transplantation, which includes precautions that pet owners should take [165].
Guidelines for persons with HIV also provide recommendations for those who desire pet contact [166,167]. These include:
●When obtaining a new pet, persons with HIV should avoid animals aged <6 months (or <1 year for cats, to lessen the risk of cat scratch fever from B. henselae) [168].
●Persons with HIV should be cautious when obtaining a pet from pet-breeding facilities, pet stores, and animal shelters, because of highly variable hygienic and sanitary conditions. Stray animals should be avoided.
●Persons with HIV should avoid contact with any animal that has diarrhea. Pet owners with HIV should seek veterinary care for animals with diarrheal illness, and a fecal sample from such animals should be examined for Cryptosporidium, Salmonella, and Campylobacter.
●Persons with HIV should wash their hands after handling pets, including before eating, and should avoid contact with pets' feces.
●Persons with HIV should avoid or limit contact with reptiles (eg, snakes, lizards, iguanas, and turtles) as well as chicks and ducklings because of the risk for salmonellosis.
●Gloves should be used during aquarium cleaning to reduce the risk for infection with M. marinum.
●Contact with all exotic pets (especially reptiles, chicks and ducks, and nonhuman primates) should be avoided in HIV infected persons.
The CDC has an updated web page, "Healthy Pets Healthy People," which provides patients with more information about pet and infection risks.
Vaccination — Tetanus immune globulin and tetanus toxoid should be administered to all bite patients who have had two or fewer primary immunizations. Tetanus toxoid alone can be given to those who have completed a primary immunization series but who have not received a booster for more than five years. (See "Tetanus-diphtheria toxoid vaccination in adults".)
Patients with bites from animals that can carry rabies require prompt evaluation for the need for rabies vaccination and rabies immunoglobulin. The need for prophylaxis depends on the specific animal species and type of exposure. (See "Indications for post-exposure rabies prophylaxis".)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Rabies".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topics (see "Patient education: Psittacosis (The Basics)")
●Beyond the Basics topics (see "Patient education: Animal and human bites (Beyond the Basics)")
SUMMARY AND RECOMMENDATIONS
●Definition – A zoonosis is any disease or infection that is naturally transmissible from vertebrate animals to humans. Humans who acquire a zoonotic infection are usually an accidental host that acquires disease through close contact with an infected animal, who may or may not be symptomatic. (See 'Definition' above.)
●Risk factors – Children are at highest risk for some zoonotic infection that are transmitted by house pets because they are more likely to have close contact with pets. (See 'Risk factors' above.)
●Transmission – Animals are responsible for transmission of an extensive array of bacterial, fungal, and parasitic zoonotic pathogens. The route of transmission can be through the saliva (eg, bites or contaminated scratches), feces, respiratory secretions, direct contact, or by the animal acting as a vehicle and source of tick or flea exposure. (See 'Transmission' above.)
●Prevention – Although pets have been implicated in transmission of zoonoses to their owners, risk of transmission from contact with pets is low and may be further reduced by simple precautions. (See 'Prevention' above.)
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