ZOONOTIC DISEASES: From Dogs to Humans
Bruno B. CHOMEL, DVM, PhD
The pleasures of dog ownership are certainly evident by the popularity of pet dogs in the
human population. Such a relationship with dogs started with their domestication in the Mesolithic
times. This brought many advantages, but also placed human beings at a greater risk for exposure to
dog parasites and pathogens. For example, it has been hypothesized that measles, which today is a
specific viral human disease, could have been derived from a close related virus of dogs, the
distemper virus, which is specific to dogs at present. Conversely, the discovery of parvovirus
infection in dogs in the late 1970s has raised concern on the role of dogs in the transmission of that
agent to humans as well as the potential role of dogs in the transmission of rotavirus and coronavirus.
Several parasitic, mycotic and infectious agents can infect both human beings and dogs, and are
therefore called zoonoses. There are more than one hundred and fifty zoonoses, but only a few are
associated with pets. However, some of them are widespread and others can be severe to fatal.
Prevalence of zoonoses transmitted from pets to humans is rather difficult to estimate and will
depend on numerous factors: number of infected animals, mode of transmission of the agent,
behavioral characteristics of the owners, and existing measures of prevention. Usually, children will
be at greater risk than adults, because of their closer physical contact with household pets and their
own behavior, including pica and exploration of the environment through putting objects in their
mouth. A brief review of current concepts of dog-associated human diseases is useful to provide
objective information to the dog owner and pet care and management.
Among the large variety of viral diseases that affect dogs, rabies is the only one, which is
particularly dangerous for human beings. No epidemiological data have supported the hypothetical
role of dog gastrointestinal viruses (coronaviruses, rotaviruses and parvoviruses), in the etiology of
Rabies - The dog is certainly a major animal species associated with rabies and its transmission to
humans. Fortunately, rabies is a rare disease in humans in the United States. Since canine rabies has
been controlled, the incidence of human rabies, excluding cases acquired abroad, has fallen from 43
(0.03 per 100,000) in 1945 to less than 1 per year (<0.001 per 100,000) in the 1980s. Although
rabies in the United States is mainly a wildlife disease affecting raccoons, skunks, foxes, and bats,
humans are probably at greater risk of acquiring rabies from a rabid dog, as dogs account for a large
majority of bite incidents reported in this country. In a review of dog rabies cases in 1988 in the
United States, most dog rabies cases occurred in young dogs (57% in dogs 1 year or less), dogs
considered as pets (84% of the cases), and mostly from a rural environment (85%). More
importantly, virtually all rabid dogs were never vaccinated, or their vaccination status was unknown.
The number of rabid dogs decreased from 182 in 1992 to 89 in 2001. In 2001, there were 89 rabies
cases in dogs. Texas (16 cases) and by Puerto Rico (13 cases) reported the largest numbers of cases
of rabies, followed by Georgia (6 cases), North Carolina (6 cases). Twenty-four states, the District of
Clolumbia and New York city did not report any rabid dogs.
When introduced to the victim's wound by a bite, the rabies virus will multiply locally at the
wound site, and then will invade the peripheral nerve(s) supplying that area. The virus migrates
along the nerves to reach the central nervous system, and radiates further through the nerves in
various organs, including the salivary glands. The virus is shed in the saliva and can be transmitted
to a new victim through a bite. The incubation of rabies varies from a few days to several months,
and the virus can be shed in the saliva a few days prior to the appearance of any clinical neurological
signs. This is the main reason why a dog, which bites a human, is quarantined for ten days. If the
dog is healthy ten days after the bite incident, one can assume that the dog was not shedding the virus
at the time of the bite, and consequently, the bite victim does not need a rabies post-exposure
treatment (a series of 5 doses of 1.0 ml of vaccine injected intra muscularly on day 0,3,7,14, and 28).
Rabies is mainly characterized by neurological and behavioral disorders. During the initial
prodromic phase, the dog is anxious, nervous, and suffers changes in personality. After 2 or 3 days,
the furious or paralytic form will start. In the furious form, lasting 1-7 days, the dog shows
irritability, aggression, hypersensitivity, disorientation, and sometimes grand mal seizures. In the
paralytic or dumb form, lasting 1 to 10 days, paralysis will affect one or more limbs. Paralysis then
progresses to affect the entire nervous system. Cranial nerve paralysis, especially laryngeal paralysis
is often the first recognized sign. Death occurs within 10 days.
Prevention of dog rabies is based on vaccination of susceptible animals, confinement of
animals, quarantine of biting dogs and removal of stray animals. Recommendations for state and
local rabies vaccination and control measures are published yearly by the National association of
State Public Health Veterinarians. All states require rabies vaccination in dogs. Interstate travel
usually requires possession of a health certificate and a proof of rabies vaccination. Sixteen rabies
vaccines are currently marketed for dogs in the United States and should be administered according
to the manufacturer's instructions. Puppies should be vaccinated at three months of age and
revaccinated one year later at fifteen months, after which they should receive annual or triennial
boosters. If dogs with a current rabies immunization are exposed to a rabid animal, they should be
revaccinated immediately, then confined and observed for 90 days. Unvaccinated animals are
usually euthanized or may be placed in strict isolation for 6 months and vaccinated one month before
Animal bites - An estimated 1 to 2 million animal bites occur in the United States every year and
dogs account for 75 to 90% of all animal bites requiring medical attention. Children are more likely
to be bitten than adults, and males are twice as likely to be bitten by dogs as females. It is estimated
that only 3 to 5 percent of dog bites will become infected. Dogs account for about 80% of animal
inflicted bites. In more than 70% of the cases, people are bitten by their own animal or from a
Although most bacteriological studies of dog bite wounds have focused on Pasteurella
multocida, a wide range of pathogens may be present in these wounds, including Staphylococcus,
Streptococcus, Moraxella, Bacillus, Neisseria (N. weaveri), Weeksella zoohelcum, Eikenella
corrodens, Proteus mirabilis, Pseudomonas aeruginosa and CDC alphanumeric aerobic gram-
negative rods (Capnocytophaga canimorsus (formerly DF-2), Group IIj, Group EF-4).
Pasteurellosis - Pasteurellosis of man is commonly associated with dog bites and even more
frequently with cat bites. Pasteurella are commensal bacteria isolated from the oral cavity of dogs
and cats. Carriage rates of Pasteurella in dogs ranges from 22% to 81%, but a recent study indicated
that pathogenic strains were found in 28% of the dog tested (versus 77% of the cats). Pasteurella
canis is the most common isolate from dog bites and Pasteurella multocida subspecies multocida
and P. septica were the most common isolates of cat bites (Talan et al., 1999). Several new bacterial
species have been isolated from dog and cat bites, including Reimerella anipestifer (from 2 cats),
Bacteroides tectum and Prevotella heparinolytica (dog and cat bites). Swelling, inflammation and
intense pain at the bite site a few hours after the exposure are the typical symptoms. Penicillin is the
antibiotic of choice for treatment. Patients are more frequently treated with a combination of a -
lactam antibiotic and a -lactamase inhibitor. Untreated affection can lead to severe complications,
including septic arthritis and osteomyelitis.
Capnocytophaga canimorsus and other disgonic fermenter bacteria. These organisms are common
bacteria of the oral cavity of carnivores. They are usually of low virulence, but can cause septicemia
in immunocompromized patients, such as splenectomized persons, people under chemotherapy or
those suffering from AIDS.
CDC Group NO-1: A new pathogen associated with dog and cat bite wounds: Over the past 23
years (1974-1997), 22 fastidious bite wound isolates submitted to CDC have been designated
nonoxidizer group 1 (NO-1). They are fastidious nonoxidative gram negative rods. Of the 22 bite
victims, half of them were males, but they were much younger (median age:18.3 yrs) than the femal
cases (39 yrs). 15 (68%) of the strains were isolated from dog and 4 (18%) from cat bites.
Other bacterial diseases can accidentally be transmitted by dog bites, such as brucellosis (B.
suis), tularemia, leptospirosis, tuberculosis and infection caused by Erysipelothrix insidiosa.
Campylobacteriosis - Campylobacter jejuni/coli is a leading cause of human enteritis. Fever,
headache, abdominal pain and severe watery to bloody diarrhea usually lasting less than a week are
the main symptoms. Food animals, especially poultry, are the major reservoirs of the organisms, and
human infection usually occurs following consumption of contaminated, untreated surface water,
unpasteurized milk or undercooked meat. However, evidence indicates that contact with infected
dogs, especially diarrheic dogs can increase risk of acquiring the infection. Prevalence of infection
varies from few percent in healthy dogs to 50% to 75% in diarrheic dogs and puppies. Puppies are
more likely to acquire the infection and show clinical signs (watery diarrhea lasting 3 to 7 days).
Infection can also occur after contact with healthy dogs, which are intermittently shedding the
organism. It is estimated that approximately 6% of enteric campylobacteriosis is transmitted from
pet animals. Control and prevention of zoonotic infection depends on interrupting contact with
contaminated materials. Infected animals should be isolated from other animals and from children.
Hands should be washed after handling the pet, pet's toys, feeding ustensils and premises should be
disinfected (bleach, quaternary ammonium compounds). Campylobacter upsaliensis has been
reported to cause gastroenteritis in humans. In dogs and cats, prevalence rates are ranging from 28 to
82%. In a cross-sectional study in Denmark (Hald and Madsen, 1997), 29% (21) of the 72 healthy
puppies (11-17 weeks old) and 5% (2) of 42 healthy kittens tested were infected with Campylobacter
(dogs: C. jejuni: 76%, C. upsaliensis 19% and 5% of C. coli).
Salmonellosis - Salmonellosis is another enteropathogen which can be transmitted from infected
dogs. Most human cases of salmonellosis are food borne; however, 3% of human cases could be pet
associated. Young children are at risk of developing salmonellosis from close contact with pets and
failure to properly wash their hands after handling animals. In humans and in dogs, the disease is a
gastroenteritis characterized by fever, nausea, vomiting, abdominal pain and a watery diarrhea. After
an infection, dogs may shed the organism for 3 to 6 weeks. Strict hygiene and antibiotic therapy,
when necessary, should be recommended.
Other gastrointestinal infections that might accidentally be transmitted by dogs are: Yersinia
enterocolitica and Y. pseudotuberculosis (see chapter on rodent-borne zoonoses), Helicobacter sp.
and Giardia and cryptosporidiosis (see below).
Helicobacter bizzozeronii – a species of Helicobacter frequently found in dogs and closed to H.
heilmannii has been cultured from a human. Thus, H. bizzozeronii may have zoonotic potential.
Helicobacter sp. accounts for 0.2% to 4% of human gastritis cases (Jalava et al., 2001).
Vector borne zoonoses
Lyme disease - Lyme disease, also called Lyme borreliosis, is a major tick-borne zoonosis in the
United States, especially in the eastern part of the country. Several thousand human cases are
reported every year to the Centers for Disease Control. The illness is a complex multisystem
disorder that commonly leads to chronic neurological sequelae and arthritis. The disease is caused
by Borrelia burgdorferi, a tick transmitted spirochete. The first large human outbreak described in
this country occurred in Lyme, Connecticut, in 1975. The common ticks involved in the
transmission of the disease are Ixodes scapularis on the East coast, which are commonly infected
(more than 50%) and Ixodes pacificus on the West coast, which has a much lower infection rate (1-
6%). In dogs, infection is often asymptomatic. After an incubation period of a few weeks to several
weeks, common signs are intermittent and painful lameness, and fever. In humans, the first sign of
Lyme disease, when present, is an early, expanding, round, red skin rash that develops around the
bite wound where the tick vector, usually long gone, had engorged. Cutaneous lesions are associated
with a flu-like syndrome. Weeks or months later, neurological, cardiac, and joint abnormalities
occur. Tetracycline is the antibiotic of choice for treatment of human beings and dogs. Dogs do not
play a direct role in the transmission of the disease to humans, but may carry infected ticks and bring
them into the household. Recently, a Lyme disease vaccine has been marketed for immunization of
healthy dogs and another one for humans, but it is still difficult to evaluate the efficacy of such
Rocky Mountain Spotted Fever and boutonneuse fever -
Rocky Mountain Spotted Fever (RMSF) is caused by Rickettsia rickettsii, which is
transmitted by tick bites to animals, especially dogs, and humans. Contamination of skin with
crushed tissues or feces of the tick may also cause infection. The disease is relatively common in the
mid western plains and the mid-Atlantic regions, where the major reservoir and vector is the
American dog tick, Dermacentor variabilis. The tick remains infective for life, commonly as long as
18 months. Vertical transmission (transovarial and transtadial) is the primary means of maintaining
infection in ticks. Dogs, two or three days after the infection will present with fever, depression and
decreased appetite. Neurological disorders (paresis, hearing loss, seizures) can also be observed.
Treatment requires the use of tetracyclines for 2 to 3 weeks. In humans, RMSF is characterized, after
3-12 days of incubation, by a flu-like syndrome, with fever, chills, muscle aches, nausea, vomiting
and photosensitivity. A cutaneous rash may occurs at the third to fifth day of illness on the hands,
wrists, ankles, feet and can spread to the rest of the body. When untreated, death can occur in 15 to
20% of the cases. Humans will get infected by a tick bite or a crushed tick. Dogs act as transient
hosts for tick vectors and serve as vehicle of infected ticks to the household.
Boutonneuse fever or Mediterranean spotted fever, caused by Rickettsia conori, is a tick
borne zoonosis which occurs in southern Europe. Humans and dogs get infected by the bite of the
dog tick, Rhipicephalus sanguineus. The infection is usually asymptomatic in dogs. Direct
transmission from dogs to humans do not occur. Dogs will bring or carry infected ticks that may be
passed on and bite humans. In humans, the most common symptoms are fever, a black spot or "tache
noir", and a maculopapular rash. Early treatment with tetracyclines usually leads to a rapid
improvement in clinical symptoms.
Human monocytic ehrlichiosis (HME) was first described in the United States in 1986. More than
800 cases have been reported since then, mostly from Southeastern and South Central States.
Human monocytic ehrlichiosis is an acute febrile illness. Symptoms are nonspecific and similar to
those of Rocky Mountain spotted fever, except skin rashes are rare. Cases occur during active tick
seasons, and most of the patients report being exposed to ticks, as the disease is primarily transmitted
by the lone star tick, Amblyomma americanum. Once considered as an Ehrlichia canis-like
organism, the etiologic agent has been determined by genetic analysis to be a new species, Ehrlichia
chaffeensis. A recent European epidemiological study indicated that human beings bitten by dog
ticks, Rhipicephalus, in endemic areas for E. canis were not reactive to the specific anti E. canis
antibody. No human case of ehrlichiosis has ever been related to an infected dog. A few cases of
monocytic erhlichosis caused by E. chaffeensis have recently been reported in dogs and similarly, a
human case caused by E. canis has been identify in a patient from Venezuela.
Human Granulocytic ehrlichiosis (HGE) is caused by Anaplasma (formerly Ehrlichia)
phagocytophila. It was first reported in the USA in 1994 from the northern Midwest. This infection
is also quite common in the North-East and the main vector is Ixodes scapularis. In California, the
infection is mainly transmitted by I. pacificus. It causes a severe disease in horses and humans, but
cases have also been reported in dogs.
The natural history of Ehrlichia ewingii is not completely known. However, dogs may be a reservoir
host and the lone star tick (Amblyomma americanum) may be an important vector. Canine
granulocytic ehrlichiosis caused by E. ewingii has been described in south central and southeastern
states, including Arkansas, Georgia, Mississippi, Missouri, North Carolina, Oklahoma, Tennessee,
and Virginia. To date, human cases have been observed in Missouri, Oklahoma, and Tennessee. It
has been demonstrated experimentally that the lone star tick is able to transmit the disease among
dogs. Other potential reservoirs and vectors remain to be identified.
Patients with ehrlichiosis generally visit a physician in their first week of illness, following an
incubation period of about 5-10 days after the tick bite. Initial symptoms generally include fever,
headache, malaise, and muscle aches. Other signs and symptoms may include nausea, vomiting,
diarrhea, cough, joint pains, confusion, and occasionally rash. In contrast to Rocky Mountain spotted
fever, rash is relatively uncommon in adult patients with HME, and is rarely reported with HGE.
However, rash has been described in approximately 60% of pediatric patients infected with E.
Plague - Plague, caused by Yersinia pestis, is an endemic disease of rodents in the Western United
States. In man, bubonic plague results from a flea-bite, usually from a rodent flea, but sometimes
from a cat or dog flea. In dogs, plague is usually a mild disease, characterized by a moderate fever
and enlarged lymph nodes. In endemic areas, plague antibody prevalence in pet dogs is very low
(less than 1%). The highest prevalence is observed in free roaming dogs, especially on Native
Americans Reservations. The plague bacillus is very sensitive to streptomycin.
Bartonellosis – Bartonella are Gram-negative bacteria that are found infecting a wide range of
mammals. They are usually infecting red blood cells. Bartonella henselae has been found
associated with Cat-Scratch Disease. The role of dogs in the transmission of B. henselae to human
has not been fully demonstrated. Dogs may be accidentally infected with B. henselae. In 2000, a
case of peliosis hepatis caused by B. henselae was diagnosed in a dog (Kitchell et al., 2000). In
1993, a dog was diagnosed with endocarditis caused by Bartonella vinsonii subsp. berkhoffii. Since
then, several cases of endocarditis, myocarditis and granulomatous rhinitis have been identified in
dogs. The first human case of endocarditis caused by B. vinsonii subsp. berkhoffii was reported from
Europe in 2000 (Roux et al., 2000). Infection in dogs is not very frequent (between 3-5% in the
general population), but seems more common (11%) in the southern of the USA (“sunbelt”)
(Honadel et al., 2001). Bartonella infections are usually vector-borne and ticks are highly suspected
as the vector of B. vinsonii subsp. berkhoffii.
Other bacterial zoonoses
Anthrax - Caused by Bacillus anthracis, can infect dogs. Chronic anthrax is more commonly seen in
dogs, which less susceptible than herbivorous animals. It is characterized by pharyngeal and lingual
edema. Treatment of choice is penicillin.
Bordetella bronchispetica - “kennel cough”. Causes kennel cough in dogs. Dogs, especially in
shelters, frequent carriers. Acute contagious respiratory infection of dogs. Disease is rare in
humans, mainly children or immunocompromised. Symptoms: Dogs: fever, nasal discharge,
sneezing, cough, lethargy, sometimes bronchopneumonia. Humans: a few cases in children
(whooping cough-like) and in AIDS patients: mild upper respiratory symptoms to severe pneumonia.
Diagnosis: culture of nasal swab, not easy. Treatment: Enrofloxacin, Doxycycline in severe cases.
Brucellosis - Dogs can be infected by various species of Brucella (B. melitensis, abortus, suis) and
transmit it accidentally to humans. In farm dogs in countries where brucellosis is endemic, orchitis,
epididymitis, abortion, arthritis can occur, but the infection is often subclinical. Dogs are also
infected by a specific biogroup, Brucella canis. Infected dogs have prolonged bacteremia. Since the
first human case reported to the Centers for Disease Control, more than 20 cases have been reported
in the U.S. Man is less susceptible to Brucella canis than to the other brucellae. In humans,
symptoms are characterized by chills, fever, sweat and joint pain. Treatment is long and requires the
use of doxycycline or tetracycline and streptomycine for at least 4 to 5 weeks.
Q fever – Caused by Coxiella burnettii. Ruminants are the main animal reservoir. In humans, can
cause flu-like symptoms, atypical pneumonia, hepatitis and endocarditis. An outbreak (3 human
cases of pneumonia) was associated with exposure to an infected parturient dog.
Leptospirosis - Human cases of leptospirosis are relatively rare in the United States (less than 100
cases per year in the 10 last years). Leptospirosis is mainly a water-borne disease, and major
reservoirs are rodents. Man is an accidental host that becomes infected trough occupational or
recreational exposure. Dogs are the natural carrier host for Leptospira canicola, and infected dogs
shedding the leptospires in their urine can infect humans by licking, or human can get infected when
petting the infected dog. Recently, many cases of leptospirosis have been reported in dogs, caused
by L. grippothyphosa, especially in the northeastern part of the USA and L pomona and L. bratislava
in California. The reservoirs are more likely to be raccoons, opossums and skunks. Some recent
reports seem also to indicate that several human cases occurring in the USA could be related to dog
exposure. Leptospira are very sensitive to penicillin, which is the most effective treatment in dogs
and humans. Other antibiotics used are doxycycline, ampicillin and enrofloxacin.
Tuberculosis - Dog tuberculosis is certainly a rare disease, mainly caused by Mycobacterium
tuberculosis. Most often human infection is the source of the dog infection. However, when
infected, the dog can shed the mycobacterium and infect other animals and humans. The recent
increase of human tuberculosis in the United States is of major public health concern and there is
some of potential pet infection and spread of the disease. Dogs get infected by infectious aerosols
from the tuberculous owner or by sniffing infectious sputum. In dogs, tuberculosis is clinically
characterized by a pleuropneumonia; unfortunately, clinical signs, such as weight loss and coughing,
are not specific. Diagnosis is a complex task, as skin test is not very reliable in the dog. Infected
dogs should be destroyed and not treated, as diagnosis is often late and treatment lasts for several
months, with the great risk of selecting multidrug resistant strains.
Canine scabies - Canine scabies (sarcoptic mange) is a non-seasonal, intensely pruritic, transmissible
infestation of the skin of dogs caused by the mite Sarcoptes scabei var. canis. The pruritus is due to
the mechanical irritation of burrowing mites plus the production of toxic and allergenic materials by
the mites. The primary lesions are erythematous papules, with secondary scaling, crusting and
excoriations. In humans, the classical lesion is the burrow, which consist of a linear scaling lesion
that is often vesicular. The lesions are very pruritic. Humans, especially children can become
infested after prolonged contact with the infested pet. Canine scabies is easily cured with weekly
application of scabicidal dips ( especially lindane).
Cheyletiellosis - Cheyletiellosis (Cheyletiella dermatitis) is a non-seasonal, variably pruritic,
transmissible infestation of the skin of dogs caused by mites from the genus Cheyletiella yasguri. In
dogs, cheyletiellosis is most often a clinical disorder in puppies. The parasite cycle is completed in
3 to 4 weeks. Clinical signs usually include some degree of dorsally distributed scaling, crusting,
and dermatitis. In humans, lesions begin as single or grouped erythematous macules, which rapidly
evolve into very itchy papules. The complete cycle does not occur in humans, thus human
infestations are self-limiting. Cheyletiellosis is easily cured in dogs with weekly application of
insecticides (pyrethrins or carbamates).
Helminthoses: Five helminthoses of the dog can be transmitted to humans. Three are rather
common, usually mild infestations: visceral larva migrans (roundworm larvae), cutaneous larva
migrans (hookworm larvae), Dipylidiasis. The fourth one, hydatid disease or echinococcosis, is a
seldom seen but potentially fatal parasitic disease in the United States. Strongyloidiasis is less
common in dogs and humans
Visceral larva migrans/oucular larva migrans: toxocariasis - Toxocariasis is a common
parasitic disease of dogs. Immature eggs of the dog roundworm (Toxocara canis) reach the soil in
the feces of infested dogs. After few days, mature embryonated eggs are infective for both dogs and
humans. They can remain infective in the soil for a prolonged period. In humans, risk of infection is
particularly high in young children that may ingest embryonated eggs while eating soil or playing in
feces-soiled areas. Embryonated eggs will hatch in the intestine of the children and the larvae will
migrate in various organs (liver, lung, muscle, eye [granulomatous retinal lesions=ocular larva
migrans] or sometimes central nervous system). Depending on the intensity of the infestation and
the localization of the larvae, symptoms range from pneumonitis, abdominal pain, skin nodules and
even visual deficiencies (ocular larva migrans) or convulsions. A third condition has been described
involving chronic weakness, allergic symptoms, abdominal pain and mild hyperesosinophilia
(Magnaval et al. 1994). Treatment with Diethylcarbamazine and thiabendazole decrease the number
of larvae, lessen symptoms and shorten convalescence times in patients with VLM. Prevention is
based on reducing access of children to areas likely to be heavily contaminated with animal feces.
Pet access to sandboxes should be forbidden and they should be covered when not used by children.
Regular worming of dogs, especially puppies, also contributes to the control of visceral larva
Cutaneous larva migrans and Tungiasis- The cutaneous localization of the canine hookworm
larvae (Ancylostoma spp.) can result in a pruritic creeping eruption in humans. These common
intestinal worms will shed eggs in the dog's feces. In warm, moist soils, the eggs will hatch and
produce infective larvae which can penetrate the skin of humans in contact with contaminated soil.
The larva produces a local papule at the site of entry and the larval tract can be seen in the skin, with
some itchy vesicles. Regular worming of dogs and banning dogs from playgrounds, especially
sandboxes, are useful measures to control the infestation in humans. Thiabendazole is effective both
orally and as topical suspension. Tungiasis is caused by the penetration of the female sand flea
Tunga penetrans into the epidermis and its subsequent hypertrophy. The infection occurs mainly in
the shade (under trees) in areas where pets prevail. The parasite is endemic in South and Central
America and sub-Saharan African countries. In the urban environment, dogs and cats act as
reservoirs for T. penetrans. In a slum in Noreth-East Brazil, 67% of dogs and 50% of cats were
found to be infected.
Dipylidiasis - Dipylidium caninum, also called tapeworm, is a common cestode that infests
dogs and cats. Adult worms reside in the host's intestine and gravid proglottids are excreted in the
stools. The parasite's life cycle requires larval development in fleas. It is completed when dogs or
cats ingest these intermediate hosts. Dipylidiasis affects mainly infants and young children who may
accidentally ingest an infected flea. Symptoms are characterized by digestive disorders, irritability.
Praziquantel is effective in killing the adult tapeworms. Flea control of pet is also an important
measure to prevent accidental infestation.
Hydatid disease or echinoccocosis - Hydatid disease is a rare disease in the United States,
but may be fatal. It is present in the Western United States, Alaska and Mexico. Dogs carry the
adult tapeworm which shed the eggs. If ingested by an intermediate host, especially sheep, or
accidentally man, the eggs hatch, penetrate the bloodstream and migrate throughout the body,
especially in the liver and lungs. Dogs get infested by ingesting hydatid cysts from infested
intermediate hosts (sheep viscera and offal). Man get usually infected by direct contact with an
infested dog (particularly children, if they don't clean their hands after petting or playing with an
infested dog). Indirect infestation can occur from contaminated water or raw vegetables. Control of
hydatid disease is based on worming infested dogs, preventing dogs from scavenging or eating
infected offal and hygienic control of slaughtering and disposal of infected viscera. Albendazole
shows promising results as a chemotherapeutic agent, especially with liver and peritoneal cysts.
Echinococcus multilocularis, a tapeworm of wild canids, especially foxes, can infest dogs
and has been reported mainly in Alaska, but has spread in the recent years in central North America.
Infected dogs have not yet been found in the contiguous United Sates; however, infected dogs are
considered the main source of human infection in Alaska. In infested areas, pet owners should wash
their hands after handling their pets, and control their diet.
Dirofilariasis: The dog heartworm, Dirofilaria immitis, is found worldwide in warm
climates. In the USA, canine and human dirofilariasis is most prevalent along the East Coast, Gulf
coast, Great Lakes and Mississippi river valley. Mosquitoes transmit the microfilarial form of the
parasite from dog to dog and from dog to human. In the canine host, the adult worm lives in the
right ventricle and pulmonary artery. Dogs are often asymptomatic, but may suffer hemoptysis or
heart failure. In human beings, larvae cannot develop into adults; most die before reaching the heart.
Symptoms are rare but may mimic thromboembolic pulmonary embolism. Human infection should
be considered in the differential diagnosis of solitary lung nodule.
Strongyloidiasis: Infection of dogs with Strongyloides stercoralis is generally less
common than with other helminths. Infected animals may be asymptomatic, but sever infestation
can lead to severe diarrhea and bronchopneumonia. Eggs of Strongyloides can hatch in the intestine
after being laid by an adult female worm. Larvae are passed in the feces and are directly infective for
dogs, cats and humans. In humans, there can be auto-infestation where the larvae hatch in the
intestine and then penetrate the intestinal lining, leading to re-infection. Humans can contract
infection from other humans as well as dogs. In humans, mild infestation is associated with
abdominal pain and diarrhea alternating with constipation. Massive infestation can lead to migration
of the worm through the body resulting in fever, liver tenderness, nausea, vomiting, weight loss and
severe diarrhea. In immunocompromised persons, it can lead to a disseminated, lifethreatening
infection. (Robertson and Thompson, 2002).
Chagas disease or American trypanosomiasis - Infection by Trypanosoma cruzi occurs from the
southern United States to Argentina and Chile. In the southern United States, where infected vectors
and sylvatic reservoirs exist, very few human cases have been reported. Chagas disease is usually
transmitted to humans by triatomines, especially Triatoma infestans. In poor rural and urban areas of
Central and South America, dogs and cats play an important role as reservoir in the epidemiological
cycle; but transmission to humans is done trough a triatomine. Dogs may develop a disease similar
to humans with an acute phase (fever, cardiac disorders, palpebral oedema, neurologic alterations)
and a chronic phase with myocarditis.
Leishmaniasis - visceral leishmaniasis, or kala-azar, caused by Leishmania donovani infantum is an
infection common in some areas of the world, especially in mediterranean countries and the Middle
East. Infection of dogs and humans occurs through the bite of a phlebotomine fly (sand fly) vector.
In endemic areas, dogs are frequently infected and represent a suitable reservoir because they offer
the vector direct access to the parasitized macrophages of their cutaneous lesions. Until recently,
most cases observed in dogs and humans in the United States had been acquired abroad, but some
cases of Leishmania donovani infantum acquired in the United States have been reported in dogs in
California, Texas and Oklahoma. Since November 1999, outbreaks of visceral leishmaniasis have
been recognized in foxhound kennels throughout the USA (62 foxhound kennels in 21 states and 2
Canadian provinces; Schantz et al., 2001). No human cases have been reported to be associated with
dog cases, so far. The route of Leishmania spp transmission in foxhounds in this country remains
unknown. Infants and young children are the most affected in endemic areas. In dogs, cutaneous
lesions (depilated areas, small ulcerations) are seen on the nose, earflap and back, few months after
the insect bite. Dogs do not respond well to drug treatment and must often be euthanatized when
infected. Successes have been obtained by using Pentostam (pentavalent antimony compounds),
Pentamidine, Allopurinol, Ketoconazole, Amphotericin B and Pentostam-Nifurtamox.
Cryptosporidiosis and Giardiasis: These protozoan pathogens are common in the environment and
cause diarrhea and abdominal pain in both humans and animals. To date the role of dogs in human
infection has not been fully demonstrated. A dog genotype of Cryptosporidium has been identified in
Australia and the USA, that may have zoonotic potential in immunocompromised people (Pieniazek
et al., 1999). Giardia duodenalis is the most common pathogenic intestinal parasite of humans
throughout the world, with a prevalence of 2-7% (Robertson and Thompson, 2002). Giardia lamblia
may also be zoonotic and similar genotypes have been isolates from humans and domestic animals,
including dogs (van Keulen et al., 2002)
Ringworm - Dermatophytosis, also called ringworm, is a common, transmissible, superficial fungal
infection of dogs and humans. It is a mycotic disease of keratinized areas of the body (hair, skin,
nails). The most common agents of dermatophytosis in dogs are Microsporum canis and
Trichophyton mentagrophytes. It is a very common infection in dogs. The disease is transmitted to
man by direct contact with infected animals or indirectly by spores in the hair or scales shed from
such animals. In dogs, cutaneous lesions are often discrete and localized. Alopecia can be observed
and the lesions are moderately pruritic. In humans, ringworm will affect the scalp or the body. On
the scalp, it begins with a papule, the hair becomes brittle, and the infection spreads in a wider circle,
leaving scaly bald patches. On the body, there are similar lesions, with a tendency to form rings with
reddish borders. Treatment is based on oral administration of griseofulvin for at least 4 weeks,
and/or topical anti-fungal solution.
Coccidioidomycosis – Valley fever. Dog can be infected by inhalation of windborne arthrospores of
the fungus (Saprozoonosis). Dogs are not a source of human infection. Symptoms are similar in
humans and dogs: iincubation:1-4 weeks. Flu-like symptoms, pneumonia (cough, fever, chest pain).
Disseminated form with granulomatous lesions. Treatment: ketoconazole.
Disease transmission from dogs to humans is rather uncommon if pet owners follow basic
hygiene rules. Special attention should be given to young children who may be more likely in close
contact with the pet and its environment. Regular deworming and vaccination of dogs are important
preventive measures that a pet owner should follow carefully.
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Proceedings: Int. Canine Leishmaniasis Forum, Crete, Greece, 2001. pp 4-13