Zoonotic Diseases in Dogs
Dr. Douglas Brum
The following list includes the most common and most significant zoonotic diseases: Visceral larval migrans is caused by the roundworm Toxocara cati or Toxocara canis. Children become infected after ingesting the eggs, from a contaminated environment.
Cutaneous larval migrans is caused by the hookworm Ancylostoma braziliense or Uncinaria stenocephala. Transmission occurs as the larvae penetrate the skin, which may cause severe itching and skin lesions in people.
Dipylidiasis or tapeworm infection. The most significant tapeworm infection is caused by Echinococcus granulosus and E. multilocularis. It is only rarely reported, but is significant since it can cause internal cystic masses in people and animals that can be fatal. It is most prevalent in sheep ranching areas and dogs usually become infected through the ingestion of sheep entrails or contaminated fecal material.
Toxoplasmosis is a protozoan infection whose main host is the cat, but it can infect many different species. It is one of the most common zoonotic diseases, but people are generally not infected through contact with a cat; ingestion of raw or under cooked meat is the most common method of transmission.
Cryptosporidiosis is also a protozoan organism that can cause diarrhea in domestic animals and people. Infection in people is usually self-limiting, except in the immunocompromised, where it can be fatal.
Giardia is a protozoan in the intestines of most animals. It can cause diarrhea in people and animals. Some animals may harbor the parasite, but display no symptoms. Animals and people usually acquire the disease by drinking stagnant water infected with giardia cysts.
Dirofilariasis, or heartworm disease, is caused by a parasitic worm that invades the animal's heart by way of the mosquito. Both cats and dogs can be affected, but it is much more common in dogs.
Brucellosis is a significant bacterial disease in breeding dogs. Infection occurs during breeding or through exposure to reproductive secretions or milk. People can become exposed through these secretions, although infection is rare.
Leptospirosis infection is most significant in dogs, but may occur in many mammals. Infection with the bacteria can lead to severe kidney and liver disease, with fever and bleeding tendencies. Exposure to infected urine, tissue or blood can lead to infection in people. Most infections occur due to contact with urine-contaminated water.
Salmonella and Campylobacter are probably the most common gastrointestinal bacterial infections, although, infection in people usually is through contaminated food (especially undercooked eggs) or water rather than pets. Infection in animals and people occurs through contact with infected stool. Both organisms may cause diarrhea, abdominal cramping, fever and dehydration.
Cat-scratch disease (cat-scratch fever, Bartonellosis) is caused by the organism Bartonella. Cats do not show any clinical signs, but carry the organism. People become infected when scratched by an infected cat.
Group A streptococcal infections are important to mention mostly due to misconceptions about the disease. This is the bacteria that causes strep-throat in people, and people are the natural reservoir for the organism. Dogs (and rarely cats) become infected from people, and then are usually are asymptomatic (not ill).
Q fever is caused by the bacteria Coxiella burnetii. Cats become infected through the bite of an infected tick. The disease is usually asymptomatic in cats, but it can cause spontaneous abortions. People may become exposed if the organism becomes airborne during parturition (giving birth) or from fetal and placental tissue.
Rabies has a high fatality rate. Although rare in people in the United States, it can infect any mammal, usually via bite wounds. The main reservoirs of the virus are raccoons, skunks, and bats, not dogs and cats.
Mycotic (fungal) Causes
Dermatomycosis (ringworm) infection in caused by the fungal organism Microsporum canis. It causes skin lesions and itching in both humans and animals. Transmission is through direct contact.
Sporotrichosis (Rose grower's disease) is caused by the fungal organism Sporothrix schenckii. People and animals can become infected through traumatic penetrating wounds.
Disease Requiring Intermediate Hosts for Transmission
Lyme disease is caused by the organism Borrelia burgdorferi and requires an infected tick (usually the deer tick) for transmission.
Rocky Mountain spotted fever and Ehrlichiosis are rickettsial diseases caused by Rickettsia rickettsi and Ehrlichia canis respectively. Ticks transmit both, and the diseases cause similar clinical signs.
Plague is caused by the bacterium Yersinia pestis. Rodents are the main reservoir, and fleas transmit the disease. Dogs usually have only mild signs, but cats may have severe signs causing death. The disease is rare in the United States, but is occasionally seen in the southwest.
Tularemia is caused by the bacterium Francisella tularemia. Rabbits and rodents are the main reservoir and the disease is transmitted by blood sucking insects (ticks), or through the ingestion of infected meat.
Leishmaniasis is a protozoal infection that occurs most often in the tropics. It is transmitted by the sand fly, but the mode of transmission in this country is not completely understood.