Zoonotic infections are defined as infections that are transmitted from nonhuman vertebrates
to humans. These are acquired from farm animals, pets, beasts of burden, fish, and
wild animals via a number of routes (Figure 74-1
Examples of routes by which zoonoses are acquired.
The approach to the patient with a potential zoonotic infection involves the generation
of a differential diagnosis that includes those infectious agents that are potentially
transmissible from the specific animal(s) to which the patient was exposed. Historical
points to consider are summarized in Table 74-1
Selected Historical Points in Patient Exposure History
Worth Adding to Differential Diagnosis
Contact with any vertebrate, especially reptiles
Exposure to urine, either directly or via contaminated water
Leptospirosis, as essentially all mammals can become infected with Leptospira interrogans
and shed infectious organisms in the urine
Bites from wild mammals, with the exception of those from rodents other than groundhogs
Evaluate risk of rabies and the potential need for rabies prophylaxis
Itching and a history of cutaneous contact with a mammal
Allergic reaction, dermatophyte infection or infestation with ectoparasites, such
as species-specific varieties of Sarcoptes scabiei
Consumption of undercooked wild mammals
Trichinellosis and toxoplasmosis
Consumption of fermented fish or marine mammals
Botulism, most commonly due to the type E toxin
Consumption of uncooked fish
Any of more than 50 parasitic infections, depending upon the species of fish eaten
and the geographic locale
Although the number of infectious agents potentially transmissible from a specific
animal to humans may be great, many of these infections are limited geographically
and need not be considered unless a bioterrorist event or the introduction of an infection
to a new area is a possibility. Examples include the lack of plague transmission outside
endemic areas, countries that are free of brucellosis, and the limitation of tularemia
to the northern hemisphere.
In some cases a good animal exposure history will be elicited but a review of the
medical literature will not be able to identify any relevant diseases from that specific
The lack of an effective veterinary or human public health infrastructure in a given
country may result in a lack of knowledge of those zoonotic infections transmitted
from even commonly encountered animals. For example, camels have been noted to have
serologic evidence of infection with Coxiella burnetii, but human cases of Q fever
as a result of contact with camels or ingestion of camel milk have often been poorly
When there are few data about a particular animal and its role as a reservoir of zoonotic
agents, it is worth considering biologically similar animals from which zoonoses have
been acquired; for example, Escherichia coli O157:H7 infections have been most commonly
transmitted to humans via the ingestion of undercooked ground beef. Deer, like cattle,
are large grazing herbivores. Humans have been infected after eating venison.
Other important clinical clues to consider include:
The environment of the animal. For example, shark bite wounds may be infected with
Vibrio spp., which are commonly found in salt water and as part of the normal oral
flora of sharks, whereas freshwater alligator bites are most commonly infected with
Aeromonas hydrophila, an organism that is found in fresh water and as part of the
normal alligator oral flora.
Consider the diet of the animal. Cattle that have been fed material that includes
nervous tissue are at increased risk of having bovine spongiform encephalopathy (BSE).
Consider other species with which the animal has had contact, including contact with
humans while in captivity. Tuberculosis, measles and shigellosis are not normally
infectious agents of nonhuman primates. Rather, they are acquired from human contact.
Similarly, the housing of camels indoors with cattle increases the risk that the camels
will acquire bovine tuberculosis.
An occupational history, obtained in some detail, can provide important information
on those zoonotic agents to which an individual may have been exposed.
As many zoonotic agents are uncommon in humans and, for a number, have been established
as causes of laboratory-acquired infections, good communication with the clinical
microbiology laboratory is essential. In some cases the diagnosis is established serologically,
whereas in others a particular pathogen, perhaps one that requires special culture
media or handling, may be isolated. In addition to increasing the probability of correctly
identifying the etiology of the patient's illness, good communication is essential
for safety, especially when infections due to Francisella tularensis, Brucella spp.,
Macacine herpesvirus-1 (cercopithecine herpesvirus type 1; herpesvirus simiae; B virus)
and other highly biohazardous agents are under consideration.
In those cases in which the pathogen is a potential agent of bioterrorism or is uncommon
in humans, even a well-equipped clinical microbiology laboratory may be unable to
perform the necessary testing on-site.
The following discussion is organized by type of animal, as this is helpful for the
clinician who is attempting to generate a reasonable differential diagnosis.
Domesticated Herbivores (Cattle, Sheep, Goats, Pigs, Camels, Horses and Related Animals)
See also Chapter 72 for a further discussion of occupational risks associated with
Brucella melitensis is most commonly acquired from goats and has been acquired from
sheep and dromedary camels. Brucella abortus is associated with cattle. Although horses
can occasionally become infected, transmission to humans from horses, if it occurs,
is very rare. Brucella suis has been transmitted to humans from both domesticated
and feral pigs. The specificity of the association between the species of Brucella
and the animal host is not absolute.
Anthrax is most commonly acquired from large domesticated herbivores. Cutaneous anthrax,
inhalation anthrax (woolsorter's disease) and gastrointestinal anthrax are associated
with the domestication of sheep, goats, and cattle. In parts of the world in which
water buffalo are domesticated they have served as the source of outbreaks of human
anthrax, as have oxen. Animal products can transmit this disease.
Epizootics of tularemia, associated with heavy infestation by the wood tick, Dermacentor
andersoni, occur in sheep. Human cases have included infections in sheep shearers,
owners, and herders. In a review published in 1955, 189 human cases of tularemia were
reported in association with the sheep industry.
Tuberculosis due to Mycobacterium bovis subsp. bovis was the impetus for pasteurization
of cow's milk. Infection with M. bovis subsp. bovis is also associated with occupational
exposure, as in slaughterhouse workers.
Infection with Listeria monocytogenes occurs via ingestion of contaminated food, usually
meat and dairy products, and rarely by direct cutaneous exposure during parturition.
Cutaneous listeriosis has been reported among veterinarians and other individuals
Infections transmitted by ingestion of milk products are listed in Table 74-2
Agents Transmitted Via Milk Products and Cheese
Clostridium botulinum toxin
Many animals' milk and cheese
Cow's milk, cheese from goats
Cow's milk, contaminated by birds
Central European tick-borne encephalitis
Goat's milk, cheese from goats and sheep
Escherichia coli O157:H7 and other strains
Cow's and goat's milk, cream, cheese
Cow's milk, cheese
Mycobacterium bovis subsp. bovis
Many animals' milk, cheese, ice cream
Cow's milk (single outbreak in 1926)
Cow's milk, cheese
Yersinia enterocolitica, normally found in the fecal flora of pigs, has been transmitted
from pigs to humans via contact and by ingestion of chitterlings (pig intestines).
Erysipelothrix rhusiopathiae has been acquired from many different animals and animal
products. It typically is an occupational illness, often acquired via a hand wound
while handling animal material. Alerting the clinical microbiology laboratory to its
possibility is of great help, as the organism's identification is not difficult if
it is suspected.
Streptococcus suis, especially type 2, a pathogen of pigs, is a common cause of bacteremia
and bacterial meningitis among individuals working with pigs in Asia.
Rhodococcus equi is commonly found in the feces of horses and in the soil. Exposure
to farm animals, including horses, has been reported in some cases of human infection.
The association of leptospirosis with swine is well known. It has been called swineherd's
disease. Cattle, goats, camels, dogs, and rats are all sources of human infection.
Exposure of pregnant women to the birth products of sheep and goats that are infected
with Chlamydophila abortus (Chlamydia psittaci, serotype 1) has been reported in both
Europe and the USA, and can be severe, resulting in abortion.
Salmonellosis has been transmitted to humans by each of these animals. Pigs have been
documented as a source of human cases of multidrug-resistant Salmonella enterica serotype
typhimurium definitive phage type 104 (DT104) infection.
Escherichia coli O157:H7 is often present in the gastrointestinal tract of cattle
and is most commonly acquired via ingestion of undercooked ground beef. Transmission
due to fecal contamination of food products can occur, such as from unpasteurized
apple cider prepared from apples that were on the ground in a cattle pasture and used
for cider production. Deer, like cattle, are large grazing herbivores and have been
reported to transmit this infection to humans who have consumed venison. Outbreaks
have been associated with visits to petting zoos. Shiga toxin-producing E. coli other
than E. coli O157:H7 cause approximately half of human Shiga toxin-producing E. coli
Pasteurella aerogenes is the most commonly isolated organism from human infections
following the bites of swine.
A number of other gram-negative organisms have also been isolated from these infections.
Camel bite injuries typically become infected and are particularly likely from male
camels during the rutting season. Members of the genus Actinobacillus have been recovered
from bites of horses and cattle. Pasteurella caballi has been isolated from wounds
following horse bites. Rabies has been reported in all of these animals as well as
Human cases of Q fever are acquired from birth products of sheep, goats, and cattle,
as well as from cats. Airborne infection can occur over significant distances. The
data on human acquisition via contaminated milk are less compelling.
Glanders, due to Burkholderia mallei, has been transmitted to humans via equids. The
disease is limited geographically so its isolation from a patient in North America
or Europe must be assumed to be due to bioterrorism until proven otherwise.
Localized cutaneous involvement can be due to infection with parapoxviruses that include
orf virus (which causes contagious ecthyma and is transmitted by sheep and goats either
directly or via fomites), bovine papular stomatitis virus and pseudocowpox virus;
and by the orthopoxviruses cowpox virus (which is more commonly transmitted to humans
via cats than cattle) and buffalopox virus. The host range of influenza A virus includes
many mammals, including marine mammals, swine and horses.
Variant Creutzfeldt–Jakob disease (variant CJD) has been reported from the UK, France,
Japan and other countries. It is associated with the consumption of meat from cattle
that were infected with BSE. Although cases of BSE have been identified in the USA,
no cases of variant CJD have been identified from consumption of US cattle. Prion
diseases of large herbivores in the USA, including chronic wasting disease of cervids,
have raised the possibility of the introduction of additional prion diseases into
the human food supply. A detailed discussion of the molecular aspects of prion-associated
disease and the clinical manifestations of the spongiform encephalopathies is found
in Chapter 23.
Many cases of the Middle East Respiratory Syndrome (MERS) have occurred in people
who had contact with dromedary camels. Viruses isolated from infected camels are indistinguishable
from those isolated from people. As of April 2015, 1123 cases and 463 deaths have
been reported due to MERS. Cases from the Middle East have been imported into a number
of countries. On the basis of DNA sequencing, there appear to be multiple independent
viruses causing MERS.
Rift Valley fever, which infects domestic ruminants, can be transmitted to humans
by mosquitoes and by contact with the tissues of slaughtered, infected animals such
Similarly, Crimean–Congo hemorrhagic fever infects a variety of animals, including
cattle and sheep, and is transmitted to humans via ticks (especially Hyalomma spp.),
via contact with blood of infected animals, and in the hospital setting.
Hendra virus, a paramyxovirus, caused infections of horses and a few individuals in
contact with these horses in Australia. The natural reservoir is a flying fox (bat).
Nipah virus was the cause of an epidemic of encephalitis that affected more than 250
people in Malaysia and Singapore, killing 105 people. More recent outbreaks have occurred
in India in West Bengal in 2001 when it killed three-quarters of the 66 infected people
and in Bangladesh in 2004 when it killed 18 of 30 infected people. While in early
outbreaks infected people had contact with pigs, which were culled to stop the epidemic,
more recent outbreaks in Bangladesh have been associated with the consumption of fresh
date palm sap that had been contaminated by bats. There has been concern about the
possibility that some cases were due to person-to-person transmission. The natural
reservoir of Nipah virus, a paramyxovirus that is related most closely to the Hendra
virus, has been identified as a bat. Menangle virus, also a paramyxovirus, caused
infections of pigs and in humans in contact with infected pigs in Australia. The natural
reservoir has been identified as a flying fox (bat).
There is concern of the possibility of certain endogenous porcine retrovirus infections
causing disease in humans following xenotransplantation of organ tissues from pigs.
Some of these retroviruses can propagate in human cell lines and they could potentially
induce immunodeficiency in experimental systems.
This poses a potential risk of activation of porcine retroviruses in the setting of
an unnatural host such as an immunosuppressed, solid organ human transplant recipient.
Porcine heterografts for heart valve replacement surgery are unlikely to be complicated
by inadvertent activation of porcine retroviruses. Glutaraldehyde fixation and sterilization
of porcine heart valves eliminates infectivity of endogenous retroviruses.
There have been outbreaks in Brazil among cattle and people who had contact with cattle
infected with strains of vaccinia virus. In some cases there have been significant
deletions of parts of the viral genome.
A 1993 epidemic of cryptosporidiosis occurred in Milwaukee, Wisconsin, in which the
public water supply was contaminated and infected more than 400 000 people. The epidemic
was traced to untreated water from Lake Michigan from which the causative organism
was incompletely removed by water filtration. Possible sources included cattle along
two rivers, slaughterhouses and human sewage.
Human cases of cryptosporidiosis also occur via direct contact with cattle and sheep
(the disease primarily occurs in lambs).
Echinococcal disease, although not transmitted to humans directly from sheep, occurs
in areas of the world in which sheep serve as an intermediate host and in which dogs
ingest sheep viscera, subsequently excreting infective eggs in their feces.
The pig ascarid Ascaris suum has caused human infection.
Taenia solium, the pork tapeworm, is acquired via the ingestion of undercooked infected
pork. Alternatively, infection may occur as a consequence of ingestion of infective
eggs, as when someone infected by T. solium prepares food and contaminates the food
with infective eggs that are present in his or her feces.
Trichinella spiralis is most commonly acquired from eating undercooked pork. Trichinellosis
has also been acquired following the ingestion of horsemeat.
Taenia saginata, the beef tapeworm, is acquired via the ingestion of undercooked beef.
Toxoplasmosis can be acquired via the ingestion of undercooked meat, especially lamb,
as well as from contaminated goat's milk.
Infection with zoophilic dermatophytes commonly occurs following contact with these
animals. This includes, for example, Trichophyton verrucosum spread from cattle to
humans, and T. equinum from horses.
There is great interest in viral infections of bats. Rabies virus is known to occur
in many species of bat. Transmission of rabies to humans follows bite, scratch and,
far less often, inhalation of aerosolized saliva. Bats also account for many cases
of rabies in livestock. Other Lyssaviruses that have been transmitted to humans from
bats include European bat Lyssavirus-1, European bat Lyssavirus-2 and Australian bat
Most recent reports of human rabies from bat exposure find no clear evidence of a
documented bat bite. Transmission apparently occurs from inadvertent bites or from
unrecognized contact with the bat saliva. This forms the rationale for the administration
of rabies immune globulin and rabies vaccine when a bat is found in the room upon
awaking from sleep, in the room of a small child, or in the room of an intoxicated
or mentally challenged person
(see Chapter 171). However, given the large number of people (approximately 2.7 million
with bedroom exposure and without a bite) who would have to be treated with rabies
immune globulin and the rabies vaccine in order to prevent a single case of human
rabies, this recommendation is controversial.
As noted above, bats have been found to be reservoirs of the zoonotic paramyxoviruses
Nipah virus, Hendra virus and Menangle virus.
In addition, after decades of active research, bats have been identified as the reservoirs
of both Ebola virus
and Marburg virus.
Outbreaks of histoplasmosis due to Histoplasma capsulatum have been associated with
exposure to bat guano in caves, after disturbing piles of bat guano in old buildings
and clearing debris from a bridge.
While bacteria that are established as pathogens of humans, including members of the
genera Salmonella, Shigella, Campylobacter, Yersinia, Leptospira, and Pasteurella,
have been isolated from bats, transmission from bats to humans of these organisms
has not been documented.
The pathogens found in nonhuman primates (NHPs) include many human pathogens that
have subsequently caused human illness when the infected primates transmit these infections
back to humans. These pathogens include bacterial (Shigella and Salmonella spp.),
mycobacterial (M. tuberculosis), viral (hepatitis A virus), parasitic (Entamoeba histolytica),
and fungal (dermatophyte) agents. In addition, there are infectious agents of human
origin that infect NHPs and that have not been reported to be transmitted back to
humans. These include measles virus and (human) herpes simplex virus type 1.
The host range of viral pathogens of NHPs may include humans. Some of these viruses
are particularly virulent in humans. Historically, it is worth noting that molecular
evidence suggests that HIV-1 was originally a pathogen of chimpanzees, Pan troglodytes
troglodytes, and that HIV-2 was originally a pathogen of sooty mangabeys. There are
numerous simian immunodeficiency virus (SIV) strains and it is possible that one or
more might be transmitted to humans via contact such as through butchering, ingestion
or by growing the pathogen and subsequently be efficiently spread from human to human.
Transmission of SIV occurred in a laboratory worker.
Infections due to simian foamy viruses, which are also retroviruses, have been well
documented following exposure to NHPs in zoos, primate centers, and in people who
hunt and butcher primates in Africa. Human infections by simian foamy viruses originating
in such diverse species as gorillas, chimpanzees, baboons and macaques (in Asia) have
all been documented, though no long-term health effects on humans from these infections
have been demonstrated.
The possibility of life-threatening infection with the neurotropic Macacine herpesvirus-1
(also known as B virus, as cercopithecine herpesvirus-1, and as herpesvirus simiae)
must be considered in bites, scratches and contact with tissue or saliva from the
rhesus monkey, Macaca mulatta.
There are distinct genotypes of the virus and the isolates from different primate
species vary in their pathogenicity for humans. The National B Virus Resource Center
at Georgia State University (website: http://www2.gsu.edu/~wwwvir/) is the reference
laboratory for the USA.
There has been transmission from NHPs of filovirus infections, including both Ebola
strains of African origin and the Reston strain of Ebola, which is less pathogenic
for humans than other strains of Ebola. Marburg virus, a filovirus causing hemorrhagic
fever with high mortality, was first transmitted from vervet (or green) monkeys to
Monkeypox, an orthopoxvirus, was initially identified in human cases of illness that
were clinically consistent with smallpox, though adenopathy occurs in these infections.
It is found in NHPs and in squirrels and other rodents in Africa and has been transmitted
from human to human. Tanapox (benign epidermal monkeypox) has been transmitted to
humans both via mosquitoes and by direct contact with monkeys in primate centers in
the USA, but has not been transmitted from human to human. Yabapox virus has, rarely,
caused subcutaneous growths at the site of inoculation.
Kyasanur forest disease virus, a member of the tick-borne encephalitis subgroup, is
found in Karnataka, a state in India, and has a number of NHP reservoirs. The presence
of dead monkeys in the endemic area, which is expanding, may precede an epidemic.
Rabies has been reported in NHPs. With the exception of a report in which the white-tufted-ear
marmoset (Callithrix jacchus) was the source of eight human cases of rabies in Brazil,
transmission of rabies from NHPs to humans is rare.
Mustelids (Ferrets, Skunks, Otters, Mink, Weasels, Badgers, Martens)
Influenza A virus was transmitted in a laboratory setting when a researcher was infected
by a ferret that had been infected with a strain of influenza A virus and which ‘sneezed
violently at close range’ while it was being examined.
Ferrets are susceptible to influenza A and B viruses. Mink that are in mink farms
have been found to be infected with influenza A viruses.
There is a report of M. bovis subsp. bovis infection of the right palm more than 20
years following a ferret bite.
M. bovis subsp. bovis is known to infect wild ferrets and badgers. There is a case
report of sporotrichosis complicating a badger bite. Rabies infection is known to
occur in skunks, otters, badgers, weasels, mink and ferrets (including pet ferrets).
Transmission of rabies from skunks to humans has been documented.
A rabies vaccine has been licensed in the USA for use in ferrets; recommendations
are for primary immunization at 3 months and booster immunizations annually.
The recommendations regarding a healthy ferret that bites a human are the same as
those for dogs and cats with respect to confinement and observation for 10 days, with
evaluation by a veterinarian at the first sign of illness.
Rat-bite fever as a result of ferret and weasel bites was reported in the medical
literature between 1910 and 1920. Only in a report of a weasel bite was there isolation
of an organism from the patient's blood.
Trichinellosis has been reported in people who ate inadequately cooked or raw liver,
spleen, blood and muscle of a badger.
Yersinia pestis is transmitted in epidemics from rats to humans via the rat flea,
Xenopsylla cheopis. Numerous rodents and other mammals serve as reservoirs of Y. pestis,
some of which have been responsible for cases of human plague. Similarly, tularemia
is widely distributed in nature and has been transmitted to humans by many different
Leptospirosis is commonly associated with skin or mucous membrane exposure to water
contaminated by the urine of rodents, including rats, mice and voles. It has rarely
been reported to be transmitted via rodent bite.
Other uncommonly reported bacterial infections following rodent bites include Pasteurella
multocida, the Pasteurella ‘SP’ group and sporotrichosis. Rat-bite fever can be due
to either Streptobacillus moniliformis or Spirillum minus. The former has been transmitted
to humans not only by wild rats but also by laboratory rats, mice and other rodents.
It is unclear how often rodents cause cases or outbreaks of human salmonellosis. There
have been multi-state outbreaks of human salmonellosis that originated in frozen ‘feeder’
mice that were fed to reptile and amphibian pets
and from pet rodents.
Given that Salmonella spp. are commonly recovered from rodent feces, the serotypes
commonly recovered from rodents are similar to those recovered from cases of human
disease, and as rodents often infest human dwellings, restaurants and food production
facilities, it is likely that rodents account for some fraction of human salmonellosis
Many of the tick-borne relapsing fevers have wild rodents as reservoirs. This is also
the case for Babesia microti, Lyme disease and human granulocytic anaplasmosis. The
reservoirs of Colorado tick fever include squirrels, chipmunks and other rodents.
Similarly, Powassan encephalitis, tick-borne encephalitis, and Omsk hemorrhagic fever
virus are transmitted via ticks and have small mammals as reservoirs. Leishmania spp.
often have rodents as reservoirs.
Those members of the Hantavirus genus that are known to cause hantavirus pulmonary
syndrome (HPS) are carried by New World rats and mice, family Muridae, subfamily Sigmodontinae,
and are transmitted via the inhalation of rodent excreta or saliva or, rarely, via
rodent bite. In the USA and Canada, the viruses include Sin Nombre virus, the main
cause of HPS, transmitted by the deer mouse (Peromyscus maniculatus) and other less
common rodent-borne hantaviruses. In South America, viruses include Andes virus in
Argentina, Chile and Uruguay transmitted by the long-tailed pygmy rice rat (Oligoryzomys
longicaudatus), a virus for which there is epidemiologic evidence of person-to-person
transmission; Juquitiba virus in Brazil; Laguna Negra virus in Paraguay, transmitted
by the vesper mouse (Calomys laucha); and Bermejo virus in Bolivia. Additional hantaviruses
have been discovered as well. Hantaviruses that are associated with hemorrhagic fever
with renal syndrome in Europe and Asia include Hantaan virus, transmitted by the murine
field mouse (Apodemus agrarius); Dobrava virus transmitted by the murine field mouse
(Apodemus flavicollis); Seoul virus, transmitted by the Norway rat (Rattus norvegicus)
in Asia; and Puumala virus transmitted by the bank vole (Clethrionomys glareolus).
Arenaviruses are transmitted from rodents via the excreta and urine. These include
lymphocytic choriomeningitis virus, which is found worldwide and has been transmitted
to humans by hamsters
as well as mice; Machupo virus, which causes Bolivian hemorrhagic fever and is transmitted
by Calomys callosus; Junin virus, which causes Argentinian hemorrhagic fever and is
transmitted by Calomys spp.; Guanarito virus, which is found in Venezuela; Lassa fever
virus, which is found in Africa and is transmitted by the multimammate rat, Mastomys
natalensis; and a recently described New World arenavirus that caused three fatal
infections in California and shared 87% identity with the Whitewater Arroyo virus
at the nucleotide level.
Reservoirs of cowpox virus include several rodents. This is consistent with the epidemiology
of cowpox in which cat contact is implicated. Cowpox, or a similar virus, has also
been transmitted via rat bite.
A multi-state outbreak of more than 70 cases of monkeypox occurred in the USA following
the importation of exotic rodents from Ghana and affected people who had contact with
pet prairie dogs that had been in contact with the African rodents at an animal distributor.
Rickettsialpox has been associated with infestation of mice (Mus musculus) with mites
which serve as the vector for human disease.
Rodents serve as reservoirs for many other rickettsial diseases, including murine
typhus in which rats have historically been the reservoir, though in areas of California
and Texas cats and opposums serve that role; Rickettsia prowazekii, which has been
associated with flying squirrels;
scrub typhus, in which rats are hosts of the trombiculid mite vectors; and members
of the spotted fever group.
Although the issue of whether giardiasis is commonly zoonotic in origin is debated,
beavers may have been the source of an outbreak of water-borne giardiasis.
Ingestion of rodents has been associated with rare cases of trichinellosis, such as
following the ingestion of squirrel and bamboo rat.
There has been speculation on whether consumption of squirrel brains causes a spongiform
encephalopathy, but data are limited.
Eating fermented beaver has resulted in botulism.
Trichophyton mentagrophytes var. mentagrophytes is a common zoophilic dermatophyte,
infecting humans and domestic animals. Rodents are regarded as the reservoir of this
Lagomorphs (Rabbits, Hares)
Tularemia, also known as rabbit fever, has been acquired from rabbits and hares as
a result of cutaneous contact and skinning of the animals, presumably by entering
via microabrasions in the skin or via the conjunctiva, and following ingestion.4,
48 Transmission via infectious aerosol has been reported as a result of mowing over
Tularemia transmission to humans has not been reported from domesticated rabbits.
Although uncommon, eight cases of human bubonic plague from 1950 to 1974 were reported
as a result of contact (e.g. skinning) with rabbits and hares
in plague-endemic areas of the USA. Q fever has been transmitted to humans following
contact with wild rabbits.
A patient with Bordetella bronchiseptica respiratory infection was shown to be due
to a strain that was indistinguishable by pulsed-field gel electrophoresis from the
strain isolated from a respiratory tract isolate from one of 20 farm rabbits that
slept with a cat with which the patient had contact.
The raccoon ascarid, Baylisascaris procyonis, has caused cases, including fatal ones,
of meningoencephalitis, often with an associated cerebral spinal fluid (CSF) eosinophilia
and usually in young children who accidentally ingest infectious ova.
Ocular involvement has also been reported. Leptospirosis has been reported from contact
Rabies is common in raccoons, although transmission of the strain found in raccoons
to humans in the USA has only been rarely reported.
Leptospirosis is common among mongooses in Hawaii
and a number of Caribbean islands.
Rabies is quite common among many species of mongoose and accounts for a significant
number of cases of human exposure to rabies in the Caribbean. It is the principal
rabies reservoir in South Africa and it may be an important source of wildlife rabies
Hedgehog contact, notably with pet hedgehogs, has transmitted salmonellosis
and dermatophyte infections due to Trichophyton erinacei.
In an outbreak of leptospirosis in Italy in which 32 of 33 confirmed cases were contracted
by drinking water at the same water fountain, a dead hedgehog was found in a water
reservoir connected to the system, although isolation of Leptospira spp. from the
hedgehog was not attempted.
The Asian house shrew, Suncus murinus, may be infested with the oriental rat flea,
Xenopsylla cheopis, and infected with Yersinia pestis. It may well be important in
the maintenance of plague between epidemics. Insectivores also appear to be reservoirs
of tick-borne encephalitis and tularemia.
Marine Mammals (Seals, Sea Lions, Walrus, Whales, Dolphins, Porpoises, Manatees)
At the case report level, there are several infections that have been transmitted
from marine mammals to humans. Leptospirosis, which is commonly encountered in seals
and the California sea lion, was transmitted from an infected sea lion pup to a human.
Two people developed leptospirosis after performing a necropsy on a sea lion that
died of leptospirosis.
Human infection with Erysipelothrix rhusiopathiae has been reported among veterinarians
and veterinary students caring for or performing autopsies on cetaceans.
In these reports, the isolation of the organism was not made from the human cases.
Two of three people who cared for affected gray seals developed ‘single milker’s nodule-like
lesions’ on the fifth finger of the right hand. The lesions from the seal handlers
demonstrated virus particles that were identical to the virus particles from the seals'
pox lesions and were characteristic of the paravaccinia subgroup of poxviruses.
In 2005, a marine mammal technician who was bitten by a seal developed an orf-like
lesion that was ultimately demonstrated to be due to seal pox on the basis of polymerase
chain reaction (PCR) and sequencing of the amplified DNA.
Pulmonary tuberculosis due to a member of the Mycobacterium tuberculosis complex that
is similar to M. bovis has been transmitted from seals in a marine park in Western
Australia to a seal trainer who developed pulmonary tuberculosis 3 years after his
last exposure to the animals with an isolate of the Mycobacterium that could not be
distinguished from the seal isolates on the basis of DNA restriction endonuclease
Seal trainers are in very close contact with seals which, by barking and coughing,
are potentially able to transmit infection via the aerosol route.
Four people involved in necropsies of harbor seals from which influenza A virus A/Seal/Mass/1/80
(H7N7) was isolated developed purulent conjunctivitis but did not have detectable
antibodies in single serum samples 3–6 months after the exposure to the influenza
A virus isolated from the seals.
A seal that was known to be infected with the influenza A virus sneezed into the face
and right eye of a person who subsequently developed conjunctivitis from which the
virus was isolated.
Influenza A virus has also been isolated from cetaceans.
Numerous cases of ‘seal finger’ have been reported in people who have been bitten
or scratched by seals and from skinning or handling seals. Seal finger often responds
to tetracycline therapy. The etiologic agent has not been established. Other organisms
that have been transmitted via the bite of marine mammals include a single case report
of Mycoplasma phocacerebrale, which was isolated from the drainage material from a
patient's fingers and swabs from the seal's front teeth.
Consumption of whale, seal and walrus meat is not uncommon among the Inuit in Canada,
Alaska, Greenland and Siberia. There have been large epidemics of salmonellosis resulting
from consumption of whale meat from floating and beached whale carcasses that have
been used as the source of food. Trichinellosis (trichinosis) has been acquired following
the consumption of raw or undercooked walrus meat. The clinical presentation in arctic
trichinellosis due to Trichinella nativa differs from that of classic trichinellosis
caused by Trichinella spiralis in that the most prominent clinical symptoms in arctic
trichinellosis are gastrointestinal, with prolonged diarrhea.
Food-borne botulism, typically due to Clostridium botulinum type E, has been acquired
from the consumption of fermented foods including beluga whale meat, seal meat, seal
flippers and walrus meat.
Both experimental and naturally occurring leprosy in nine-banded armadillos has been
noted and there has been a body of literature (reviewed by Blake et al.
) that suggests that contact with armadillos may have been the source of leprosy in
some patients in the USA and Mexico. Sporotrichosis has been found to be highly associated
with armadillo contact in Uruguay.
Psittacosis is transmitted to humans not only via pet birds, but also via turkeys,
wild and domestic pigeons, ducks, and other birds.
Salmonellosis has been acquired from contact with birds and from consumption of birds
(e.g. chicken, turkey) and eggs.
Campylobacter jejuni and C. laridis infections have been associated with both the
consumption of birds and, interestingly, consumption of milk that has been pecked
by magpies (Pica pica) and jackdaws (Corvus monedula).
Erysipelothrix rhusiopathiae has been acquired from bird contact. Newcastle disease
virus of fowl, an occupational disease, causes an acute conjunctivitis that may be
associated with preauricular adenitis.
Histoplasmosis, often in large outbreaks, has been the result of inhalation of bird
Infection with Cryptococcus neoformans, which is known to be found in bird droppings,
has at the case report level been linked to exposure to pet birds
and fancy pigeons.
Avian strains of influenza A virus represent a global concern, as the host range of
the viruses may include humans. There exists the potential for pandemic influenza
as a result of the introduction of an avian virus with a hemagglutinin to which humans
For a detailed discussion of the risks associated with avian influenza please refer
to Chapter 172.
The epidemic of West Nile virus infection in the USA and Canada is largely attributable
to the introduction of this flavivirus into a new ecologic niche in wild birds in
Blackbirds, crows, other wild birds and domestic chickens are susceptible to this
viral illness and this forms the reservoir for this mosquito-transmitted infection
that is responsible for a potentially lethal form of viral encephalitis.
Tularemia has been, at the several case report level, acquired from wild birds. A
case of Crimean–Congo hemorrhagic fever in an ostrich farm worker who was involved
in the slaughter of ostriches, Struthio camelus, and handled the fresh blood and tissues
of the birds, has been reported. There were numerous adult Hyalomma ticks on the ostriches
and he likely was infected either directly due to skinning the ostriches or as a result
of the presence of the ticks on the ostriches.
In addition to the normal flora of the fish, a wound can become infected with environmental
bacteria. The species of bacteria that live in water are dependent on both salinity
and temperature. Estuarine and freshwater bacteria include members of the genera Vibrio,
Aeromonas and Plesiomonas. As a result, the etiologic agents isolated from an infected
wound from a fish bite, spine, or fin injury that occurs in salt water may well be
different from one that occurs in fresh water. The normal flora of teeth in salt-water
sharks includes, for example, Vibrio spp., including V. harveyi (formerly V. carchariae),
an organism that was the cause of infection following the bite of a great white shark.
By contrast, Edwardsiella tarda is commonly isolated from catfish injuries occurring
in fresh water. Other organisms that have caused wound injuries as a result of injuries
from fish include Aeromonas spp., Erysipelothrix rhusiopathiae, Mycobacterium marinum,
Mycobacterium terrae, Streptococcus iniae, Vibrio vulnificus and Vibrio vulnificus
serovar E (biotype 2; indole-negative) from eels.
Vibrio alginolyticus, Photobacterium damselae subsp. damselae (formerly Vibrio damsela),
Shewanella putrefaciens, Pseudomonas aeruginosa and Halomonas venusta have been isolated
from fish bites and injuries. It is not always clear whether the source of the organism
is the fish or the water.
Ingestion of fish or fish products can pose a significant risk of acquiring both bacterial
and parasitic infections unless the fish has been well cooked.
Vibrio spp., including V. fluvialis, V. hollisae, V. parahaemolyticus and V. cholerae
have all been associated with fish consumption, as has P. shigelloides. Eel consumption
has been associated with Photobacterium damselae subsp. damselae (formerly Vibrio
Listeria monocytogenes infections have been associated with the consumption of fish,
including vacuum-packed salmon and cold-smoked rainbow trout.
Fish-associated botulism is usually due to type E toxin and in the USA is most common
among Alaskans. Fermented fish eggs, fish eggs, home-marinated fish and dry salted
fish have all been implicated. Consumption of apparently fresh (unpreserved and unfermented)
fish in Hawaii resulted in three adults with botulism due to type B toxin.
Numerous parasitic infections have been reported following the consumption of raw,
undercooked, pickled and lightly or cold-smoked fish. Selected cestodes, trematodes
and nematodes acquired from the consumption of fish are listed in Table 74-3
Selected Parasites Transmitted Via Consumption of Fish
Type of Parasite
Types of Fish
Salmon, pike, perch, burbot
Mullet, tilapia, mosquito fish
Salmon, tuna, herring, mackerel, others
Cod, pollock, haddock, salmon, Pacific rockfish
Killifish, estuarine fish, minnows
Freshwater, estuarine fish
Freshwater, estuarine fish
Contact with amphibians has rarely transmitted salmonellosis, but has transmitted
sparganosis due to Diphyllobothrium (Spirometra) mansoni via the use of contaminated
frog flesh as a poultice (reviewed by Huang and Kirk
) and, rarely, intraocular Alaria spp., as reported in a woman with a long history
of frog collection and food preparation.
Ingestion of frogs has transmitted sparganosis. Infection with the trematode Fibricola
seoulensis occurred after 10 Korean soldiers ate raw or undercooked flesh of snakes
or frogs during survival training.
Two cases of intraocular infection with an Alaria spp. occurred in Asian-Americans
in California who consumed cooked frogs' legs in Chinese dishes.
Frogs' legs have a very high rate of contamination with Salmonella.
There is a published report of transmission of leptospirosis to two zoo employees
in which the most likely source was an ill polar bear cub.
There are few published reports on infections following bear bites. A man shot and
killed a grizzly bear in Alaska and scratched his left index finger on one of the
bear's teeth while removing the bear's tongue, resulting in a Mycobacterium chelonae
subsp. abscessus infection.
In multiple reports, consumption of undercooked bear meat has caused trichinellosis.
Bear steaks are often served rare, in part because they are somewhat ‘tough’ if they
are fully cooked. Bears are known to have a high rate of toxoplasmosis and the possibility
of a dual infection (trichinellosis and toxoplasmosis) in a person who ingested undercooked
bear meat has been reported.
Note that acute hypervitaminosis A occurs following the ingestion of polar bear liver.
Large Herbivores (Elephants, Rhinoceroses)
The few infections transmitted to humans include M. tuberculosis from elephants,
M. bovis from rhinoceroses
and an orthopoxvirus (possibly cowpox) from elephants to humans. It is likely that
many cases of tuberculosis in elephants, which are almost all due to M. tuberculosis,
are due to human-to-elephant transmission. In the USA, approximately 3% percent of
elephants are infected with M. tuberculosis.
References available online at