Intestinal parasites are common cause of diarrhea in cats: Giardia may be transmitted to humans

Barbara Hinney and her colleagues from the Institute for Parasitology at the University of Veterinary Medicine, Vienna, screened 298 faecal samples taken from cats across Austria for single-cell intestinal parasites, so called enteric protozoa. The samples came from private households, catteries and animal shelters. Of the 298 cats sampled, 56 tested positive with at least one intestinal parasite.

Multi-cat households often affected

A significantly higher rate of positive samples was registered in households with more than one cat. Households with kittens are also more at risk. “Young animals must first come to terms with the pathogen and are not yet immune, which makes it possible for the pathogen to persist more stubbornly. When the animals excrete the parasite via faeces, they infect other cats. This gives households with more than one cat a higher risk of infection,” explains first author Hinney.

Transmission from cats to humans not excluded

Giardia infect small intestines and were the most commonly found parasite with more than 12 per cent positive samples. The parasites are ingested as cysts and reproduce in the small intestine. The cysts are then reintroduced into the environment when excreted with the animal faeces. Giardia infections are asymptomatic in many cats. In some cases, however, an infection can result in diarrhea, nausea and abdominal pain.

“We mostly found species of Giardia that occur only in cats. There was one species that also exists in humans. The possibility of transmission from cats to humans can therefore not be excluded,” Hinney explains.  

Persons with compromised immune systems are especially at risk. “Most human Giardia infections occur through human-to-human transmission. Infections are common during trips to warm countries such as India. The infection then often occurs via the drinking water,” says Hinney.

Hygiene in catteries

“Giardia cysts are highly resistant and can be very difficult to get rid of. Recurrent infections are therefore possible even after successful medicinal treatment,” Hinney explains.

It is necessary to maintain certain hygienic standards in order to successfully eliminate Giardia in cats. The cysts of Giardia can survive quite well in moist and warm environments. Hinney therefore recommends washing blankets and towels which the animals have had contact with at temperatures of at least 60 degree Celsius. Drinking bowls and food dishes should be washed regularly with hot water and dried. As Giardia can be transmitted through the water, cat faeces should always be disposed with the household waste and not in the toilet.

It is not always possible to eliminate a Giardia infection even with strict adherence to these hygienic measures. If a cat continues to excrete Giardia despite medical therapy without exhibiting any symptoms, veterinarians and medical doctors can help determine if continued treatment makes sense. It should be considered, however, that infected animals remain a source of infection for others even if not ill themselves.

Additional causative agents of diarrhea found

The parasitologists also found Tritrichomonas blagburni in one cat. This parasite was only recently described as pathogenic. An infection causes diarrhea and flatulence in the animals. The pathogen is not transmissible to humans, however.

Twelve cats were infected with coccidia. An infection with this parasite is most often seen in young animals. Five animals tested positive for Cryptosporidium; the species that were found can only infect cats.

“Animals with severe cases of diarrhea lose a lot of fluid, so rehydration is the most important therapy for diarrheal illnesses. Medicines exist for some of these infections and, in the case of coccidia, can even be taken prophylactically,” says Hinney.