Ask a Vet: How Common and Contagious Is Coccidia?


I recently received a question from a reader who was in the process of purchasing a Bengal kitten. She was notified by the breeder that the kitten had tested positive for coccidia. The breeder was working to purchase medication to treat the kitten, but there had been a bit of a delay.

The reader had several concerns about the kitten’s future, the nature of the parasite, and its potential to spread to the cat she already owned. Would the delay lead to permanent intestinal damage from the parasites? Could the parasites spread to her other cat (a 14-month-old Bengal) by way of the owner’s clothing? If the kitten were treated and then tested negative for the parasite, would that mean that the kitten truly no longer was infected with it?

The reader is not alone in having questions about coccidia. Coccidiosis is very common in kittens.

Coccidia are microscopic parasites that live in the gastrointestinal tract of both cats and dogs. Cats and dogs each have their own form of coccidia — cats can’t catch the parasite from dogs, and vice-versa. There are no known reports of coccidia spreading from cats or dogs to people.

Diarrhea is the most common symptom of coccidiosis. Severe infections may lead to dehydration and emaciation. However, once a coccidia infection has been eliminated, the symptoms usually resolve completely. Coccidia commonly occurs simultaneously with other intestinal parasites such as roundworms. Such so-called co-infections often lead to more serious symptoms than would be caused by either parasite on its own.

Coccidia can be spread through environmental contamination or through predation. The parasites are capable of surviving for extended periods of time outside of cats’ bodies. Therefore, contact with areas contaminated by shedding cats can lead to new infections. The parasites also are capable of living in the muscles of prey species such as mice. Cats therefore can become infected as a result of hunting behavior.

Treatment of coccidia has the potential to be frustrating. Only one medication, sulfadimethoxine (Albon) is labeled for the treatment of the parasite. However, in my experience Albon doesn’t seem to work terribly well, and many pets require repeated or extended courses of it before recovery occurs. Another medication, ponazuril, seems to work much better. However, some vets are reluctant to use it because it’s not labeled for pets. Other old-school vets simply haven’t heard of it.

This description of coccidia makes the parasite sound quite frightening. Since environmental contamination is a common source of infection, and since infected cats can shed very large quantities of the parasites, it is easy to get the impression that a diagnosis of coccidia should be a nightmare for any cat owner.

Fortunately, it rarely works out that way. It’s a matter of the immune system to the rescue. It turns out that in practice coccidia appear basically to be opportunistic pathogens. Coccidia is a common cause of diarrhea in kittens, whose immune systems aren’t fully developed and therefore aren’t capable of fending the bugs off. Diarrhea and other symptoms of coccidia infection are very rare in adult cats with competent immune systems.

Armed with this information, it is possible to answer some of the reader’s questions. Long-term intestinal damage is not common after infection with coccidia. I have heard of animals that were symptomatic for months before the infection was cleared, and they have generally not gone on to suffer any lingering gastrointestinal symptoms.

If the kitten is shedding large numbers of coccidia, it is theoretically possible for them to be spread by so-called fomites such as clothing, bedding, and grooming materials. Thus, there is a chance of the parasite being spread from the kitten to the cat who already lives in the house even if they’re not in contact with each other. However, in practice this is not likely to occur as long as the kitten is kept quarantined for a while after his arrival (which is always a very good idea, even when healthy individuals are introduced to a new house) and as long as basic hygiene rules are followed.

A 14-month-old cat is on the border between kittenhood and adulthood, and I rarely see coccidia infections in cats more than a year old. Therefore there is a significant chance that the older cat’s immune system is fully competent, which means he probably won’t catch the parasite in any case.

The most common test for coccidia is evaluation of a stool sample that has been prepared in a special manner that helps to concentrate parasites and their eggs. The test is somewhat crude compared to sophisticated DNA tests or protein assays, which are available for many diseases and infections. The stool sample is prepared and then evaluated microscopically for parasites. If parasites are seen, then the sample is positive. If none are seen, then it is declared to be “NPS,” short for “no parasites seen.”

NPS is not the same thing as negative. If no parasites are seen, there may be no parasites in the gastrointestinal tract. Or there simply may have been no (or very few) parasites in the particular stool sample that was tested.

It is therefore impossible to prove that any animal is completely free of parasites — it’s not possible to prove a negative. However, if no parasites are found in stool samples, especially if they are tested repeatedly, then it is safe to say that the individual being tested is not shedding large numbers of organisms. When large numbers of organisms are shed it is easy to find them.

Since the organisms need to be shed in order to spread, a kitten whose stool is NPS on repeated evaluations is unlikely to spread coccidia to any other animals.

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Got a question for Dr. Barchas? Ask our vet in the comments below and you might be featured in an upcoming column. (Note that if you have an emergency situation, please see your own vet immediately!)

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