Coccidiosis in Cats

What is coccidiosis?

Coccidiosis is an intestinal tract infection caused by a single-celled organism (protozoa) called coccidia. Cystisospora species are the most common type of coccidia affecting cats. 

Coccidia live in the intestinal tract and can cause diarrhea, so they are often confused with intestinal worms, but coccidia are not worms. They are microscopic parasites that live within the cells that line the intestine.

How did my cat become infected with coccidia?

Your cat likely became infected with coccidia from swallowing oocysts (immature coccidia) that are found in cat feces and any environment contaminated with feces. Infected cats pass oocysts in the feces. These oocysts are resistant to a wide variety of environmental conditions and can survive for some time on the ground.

Under the right conditions of temperature and humidity, these oocysts become infective. The more mature form of oocysts is infectious to other mammals as well, such as mice. 

If your cat swallows the oocysts, they mature in the intestine to complete the life cycle. If a mouse swallows the oocysts, they encyst in the mouse’s organs, and your cat may become infected by eating the infected mouse.

Kittens are commonly diagnosed with coccidiosis. After birth, kittens can be infected by exposure to their mother’s feces, especially with kittens’ tendency to explore. Coccidiosis is of particular danger for kittens since their immune system is underdeveloped. If the mother is shedding oocysts, her babies can ingest them during nursing.

What are the clinical signs of coccidiosis?

The most common clinical sign of coccidiosis is diarrhea, but most cats infected with coccidia do not have any clinical signs. When coccidial oocysts are found in the stool of a cat without diarrhea, they are generally considered a transient, insignificant finding. However, in kittens and debilitated adult cats, coccidiosis may cause severe, watery or mucousy diarrhea, dehydration, abdominal distress, loss of appetite, and vomiting. In severe cases, death may occur.

How is coccidiosis diagnosed?

Coccidiosis is diagnosed by performing a microscopic examination of a stool sample. Infection with some of the less common coccidial parasites may be diagnosed with a blood test.

How is coccidiosis treated?

The most common drug used to treat coccidiosis is a sulfa-class antibiotic, sulfadimethoxine (Albon®). It is typically administered for 5-20 days. Some formulations of this medication are pleasant tasting and most cats will readily accept them. If the sulfa drug is not effective, other treatments are available, including sulfa antibiotics combined with another drug, amprolium (Albac/Amprol Hi-E®), or off-label use of ponazuril (Marquis®) or toltrazuril (Baycox®). Additional supportive treatments may be needed if diarrhea and dehydration occur.

Cats are frequently reinfected from the environment, so disinfection is important. The oocysts are resistant to environmental conditions and disinfectants. Diluted chlorine bleach is effective as a disinfectant (one cup or 250 mL of bleach mixed with one gallon or 3.8 L of water). Be sure to test clean a small area of affected materials since bleach can damage many surfaces. Steam cleaning may also be used to destroy oocysts. Be sure to remove your pet’s feces from the environment as quickly as possible to prevent reinfection.

Can I get coccidiosis from my cat?

The most common species of coccidia in cats does not infect humans. However, less common species of coccidia can potentially infect humans. One species, called Cryptosporidium, may be transmitted to people, especially those with compromised immune systems. Cryptosporidium has also been found in public water supplies in some major cities.

Another coccidian organism, Toxoplasma, is of particular concern to pregnant women because of the potential to cause birth defects. However, most human cases of toxoplasmosis are the result of eating contaminated meat as opposed to contact with cat feces (see handout: Toxoplasmosis).

These two coccidian parasites pose an increased health risk for immunosuppressed people (i.e., patients with immunosuppressive illnesses, those taking immune suppressant drugs, cancer patients, and the elderly). Good hygiene and proper disposal of cat feces are important in minimizing the risk of transmission of all feline parasites to humans. Although there is a risk of the cat transmitting these two parasites to humans, it does not require removing the cat from a home except in very rare instances, since transmission can be prevented by practicing good hygiene.