Coccidia are single-celled protozoa that act as intestinal parasites in a wide range of animals. They live within the cells lining the host’s intestinal tract, causing an infection called coccidiosis. The concern over whether these parasites can transfer from a cat to a person relates to zoonotic potential—the ability of a disease to jump from animals to humans. Assessing this risk requires understanding the specific type of parasite involved and its biology.
Understanding Coccidia in Felines
The Coccidia species most commonly found in cats belong to the genus Cystoisospora, specifically Cystoisospora felis and Cystoisospora rivolta. Infection begins when a cat ingests the parasite’s infective stage, known as a sporulated oocyst, from a contaminated environment. Oocysts are microscopic, thick-walled structures shed in the feces.
Once shed, oocysts must undergo sporulation to become infectious, a process that takes 6 to 16 hours depending on environmental conditions. Cats can also contract the infection by consuming transport hosts, such as mice or rodents, which have ingested the oocysts. The parasite then completes its life cycle within the cat’s intestine, multiplying and damaging the intestinal lining.
Many adult cats infected with Coccidia show no outward signs of illness and shed the oocysts asymptomatically. When symptoms do occur, they are generally seen in young kittens or cats with weakened immune systems. The damage to the intestinal cells results in gastrointestinal distress, most commonly presenting as watery or mucus-containing diarrhea. In severe cases, this can lead to dehydration, weight loss, and lethargy, which is serious for small kittens.
The Specific Risk of Cat-to-Human Transmission
The Cystoisospora species of Coccidia found in cats pose virtually no risk to human health. These parasites are highly host-specific, meaning they have evolved to complete their life cycle only within the feline species. The Coccidia that infect cats cannot establish a sustainable infection in the human intestinal tract.
This host specificity means that even if a person accidentally ingested a sporulated oocyst of C. felis from cat feces, the parasite would not be able to develop and cause disease. This contrasts sharply with other intestinal parasites that are easily transmitted between species. Therefore, the presence of typical feline Coccidia in a cat does not classify the animal as a source of infection for a healthy person.
Confusion arises because Coccidia describes a broader group of protozoa, some of which are zoonotic. Two other coccidian parasites found in cats, Toxoplasma gondii and Cryptosporidium, are transmissible to humans.
Toxoplasma gondii is a concern for pregnant women and immunocompromised individuals, but human infection is far more often acquired by consuming undercooked meat or contaminated soil than by direct contact with cat feces. Cryptosporidium is another coccidian that causes gastrointestinal illness in humans, and cats can occasionally shed the species that infects people.
However, the risk of acquiring Cryptosporidium directly from a cat is generally low compared to exposure from contaminated water sources or other infected individuals. It is important to differentiate these specific zoonotic parasites from the common, non-transmissible Cystoisospora species.
Essential Hygiene Practices for Cat Owners
While common feline Coccidia is not a direct threat to human health, general hygiene practices are important for responsible pet ownership to prevent the spread of potential fecal-oral pathogens. The infectious oocysts of Cystoisospora are shed in the cat’s feces and only become infective after they sporulate in the environment. This sporulation process typically takes several hours, providing a window for waste removal.
Daily and prompt scooping of the litter box is an effective method for parasite control, removing oocysts before they become infectious. Waste should be disposed of in sealed bags, and the litter box should be cleaned regularly. Handwashing with soap and warm water immediately after handling the litter box, cat feces, or garden soil is the most effective preventative measure against accidental ingestion of any parasite.
The oocysts are highly resistant to many common chemical disinfectants. Effective cleaning of contaminated surfaces, such as the litter box, typically requires a diluted bleach solution (one part bleach to ten parts water) or steam cleaning, as high temperatures destroy the oocysts. Furthermore, preventing cats, especially those that go outdoors, from hunting prey like mice helps break the chain of infection, as these animals can be transport hosts.