Protozoal Diseases in Cats

Protozoa are single-celled organisms that are not visible to the naked eye but can be seen easily under a microscope. Protozoa are usually carried by and live in water. A fresh stool specimen of infested cat is required to identify the adult parasite or its cysts (called oocysts), because mostly these disease causing protozoal agents are not usually identified by the standard fecal flotation techniques. Here is a brief summarized overview of some most commonly infesting protozoans of cats.

  • Giardia Species
  • Toxoplasma gondii
  • Cystoisospora felis (Coccidiosis)
  • Tritrichomonas foetus (Trichomoniasis )

Protozoal Diseases in Cats


This infestation is known as “Giaediasis” and it is caused by a protozoan of the Giardia species. Cats have their own species-specific strain of Giardia. Cats acquire the infection by drinking water from streams and other sources that are contaminated with infective cysts. Most infections in adult cats are subclinical. Young cats and kittens can develop a diarrhea syndrome characterized by the passage of large volumes of foul-smelling & watery stools. The diarrhea maybe acute or chronic, intermittent or persistent, and may be accompanied by sudden weight loss. Diagnosis is made by finding the protozoan or its characteristics cysts in saline smears of freshly passed stool. Smears from rectal swabs are also satisfactory. A negative smear does not exclude giardia, as cysts are shed only intermittently with gap of 1-2 days. Three negative fecal smears collected at least two days apart should be obtained before the diagnosis is excluded. Serology tests (ELISA and IFA) are now available.

Cats do not seem to develop an immunity to giardiasis, so prevention includes cleaning up areas of stagnant water where the protozoa may flourish and/or keeping cats away from those areas. The indoor environment should be thoroughly washed and cleaned as well.

Treatment of Giardiasis in Cats:

Giardiasis responds well to Flagyl (Metronidazole).

Because Flagyl causes developmental malformations in the fetus, it should not be administered to pregnant queens.

Metronidazole also prevents bacterial overgrowth and may influence existing immune disorders in the intestines. Other effective drugs are available, such as Fenbendazole. There is now a vaccine available for giardiasis, but it is rarely recommended because the disease is usually mild and responds well to treatment.


This disease is caused by the protozoan Toxoplasma gondii. Cats are likely to acquire the infection by consuming infected meat of birds or rodents or, rarely, by ingesting oocysts in contaminated soil. Cats are the primary host for this obligate intracellular parasite (a parasite that can only exist inside the living cell of another organism), but it can infect other warm-blooded animals and human beings. Toxoplasma gondii has its own zoonotic reputation.

Evidence strongly suggests that cats (and people) can also get the disease from eating raw or undercooked pork, beef, mutton, or veal or unpasteurized dairy products that contains toxoplasma organisms. In cats, the oocysts develop in the intestines and are passed out in the feces, so the feces of infected cats present another source of infection. These infective oocysts are only passed for a very short time after initial exposure.

Cats and humans can transmit toxoplasma in utero to their unborn offspring.

Feline intestinal toxoplasmosis is usually asymptomatic. When symptomatic, it affects the brain, spinal cord, eyes, lymphatic system, and lungs.

The most common signs are:

  • Loss of appetite, lethargy,
  • Cough
  • Rapid breathing.
  • Visual and neurological signs may be evident

Other signs are fever, weight loss, diarrhea, and swelling of the abdomen. Lymph nodes may enlarge. Kittens may exhibit encephalitis, liver insufficiency, or pneumonia. Prenatal infection may be responsible for abortion, stillbirths, and unexplained perinatal deaths, including the fading kitten syndrome. Many cats that show clinical signs are concurrently infected with feline immunodeficiency virus (FIV) or feline leukemia virus (FeLV).

The finding of T. gondii oocysts in the cat’s stool indicates the cat is currently infective to other cats and people. Serologic tests (including ELISA) will show whether a cat has ever been exposed. A positive test in a healthy cat signifies that the cat has acquired active immunity and is therefore not a source of human contamination.

To prevent this parasite, cats should not be fed raw meat or allowed to hunt. They also should not be given unpasteurized dairy products. If you have an indoor cat who eats only cat food, she’s not likely to ever be infected.

Treatment of Toxoplasmosis in Cats:

Antibiotics such as clindamycin are available to treat active infection and prevent the intestinal phase of oocyst shedding.

Toxoplasma gondii & Pregnant Women:

About half the human adult population shows serological evidence of having been exposed in the past. Men and women with protective antibodies probably will be immune to infection. However, the disease is a particular hazard when a pregnant woman without prior immunity is exposed to it. Immunocompromised people are also at risk.

Toxoplasmosis infection in a pregnant woman can result in abortion, stillbirth, and birth of babies with central nervous system infection. Cats are the only animals who pass on the infectious stage of this parasite through their feces, and this has given rise to the incorrect assumption that pregnant women should not have cats.

If you are pregnant, it is not necessary to get rid of your cat! The majority of human cases—by a wide margin—come from eating raw or undercooked meat, particularly lamb or pork. Unpasteurized dairy products can also be a source of infection. Wash fresh vegetables carefully, because oocysts can also cling to bits of soil. And wear gloves while gardening to avoid contact with infected soil.

Pregnant women can be tested to determine if they have had prior exposure, in which case they have acquired immunity and there is no risk. They can also take precautions to avoid contact with fecal material from cats by wearing gloves when gardening and cleaning the litter box. Prevent the disease in your cat by keeping the cat from roaming and hunting. Wear disposable plastic gloves when handling the cat’s litter. Remove stools every day from the litter box. Dispose of the litter carefully so that others will not come into contact with it. Clean and disinfect litter boxes often using boiling water and a diluted bleach solution. Cover children’s sandboxes when not in use to keep them from being used as a litter box by stray cats.

Cook all fresh meat, both yours and your cat’s, maintaining a temperature of at least 150°F (65.5°C, medium well). Wash your hands with soap and water after handling raw meat. Clean all kitchen surfaces that have been in contact with raw meat.


Coccidiosis usually targets young kittens shortly after weaning, although adult cats can also be affected. The disease is highly contagious. Immunity following recovery from infection is very short-lived.

Cats who recover often become carriers and shed adult oocysts in their feces.

There are several species of coccidia. Only Cystoisospora felis (formerly known as Isospora felis) is directly transmitted by fecal contamination from cat to cat. Other species use birds and animals as intermediate transport hosts. These species complete their life cycle when the transport host is eaten by the cat.

Kittens acquire Cystoisospora felis from mothers who are carriers. Five to seven days after ingesting the oocysts, infective cysts appear in the feces. Much of the life cycle takes place in the cells lining the small intestines. Diarrhea is the most common sign of infection. The feces are mucuslike and stained with blood. In severe cases, a bloody diarrhea may develop. These cases are complicated by weakness, dehydration, and anemia.

Coccidia can be found in the stools of kittens without causing problems, until some stress factor, such as overcrowding, malnutrition, weaning problems, an outbreak of ascarids, or shipping reduces their resistance.

Normal fecal flotations technique will easily detect these parasites.

Treatment of Coccidiosis in Cats:

Offer a bland diet and encourage fluid intake. A severely dehydrated or anemic cat may need to be hospitalized for fluid replacement or blood transfusion. Kittens are more likely to require intensive care than adult cats.

Supportive treatment is important, since in most cases the acute phase of the illness lasts about ten days and the cat then recovers. Sulfonamides and nitrofurazone are the antibiotics of choice. Known carriers should be isolated and treated. Cat quarters and runs should be washed daily with disinfectants and boiling water to destroy infective oocysts.


Trichomoniasis is caused by the protozoan Tritrichomonas foetus, an anaerobic protozoa. In cats, T. foetus infects and colonizes the large intestines, and causes chronic, recurrent diarrhea, sometimes stained with blood or mucus. Infection is most commonly seen in kittens and cats from catteries, where, possibly, the organism is spread among cats by close contact.

Diagnosis is by fecal examination. And more specifically it can be diagnosed by using some advance techniques i.e. PCR.


Treatment with various antiprotozoal drugs is usually unsuccessful. Most cats will slowly overcome the infection on their own. However, this can take nine months or more. It appears that most infected cats continue to shed low levels of the organism in their feces for many months after the diarrhea has resolved.