Many species of coccidia infect the intestinal tract of cats and dogs. All species appear to be host-specific. Cats have species of Isospora, Besnoitia, Toxoplasma, Hammondia, and Sarcocystis. Dogs have species of Isospora, Hammondia, and Sarcocystis. Neither dogs nor cats have Eimeria.

Hammondia has an obligatory 2-host life cycle with cats or dogs as final hosts and rodents or ruminants as intermediate hosts, respectively. Hammondia oocysts are indistinguishable from those of Toxoplasma and Besnoitia but are nonpathogenic in either host. (see also Besnoitiosis, see Sarcocystosis, and see Toxoplasmosis.)

The most common coccidia of cats and dogs are Isospora. Some Isospora spp of cats and dogs can facultatively infect other mammals and produce in various organs an encysted form that is infective for the cat or dog. Two species infect cats: I felis and I rivolta; both can be identified easily by oocyst size and shape. Almost every cat eventually becomes infected with I felis. Four species infect dogs: I canis, I ohioensis, I burrowsi, and I neorivolta. In dogs, only I canis can be identified by the oocyst structure; the other 3 Isospora overlap in dimensions and can be differentiated only by endogenous developmental characteristics.

Clinical coccidiosis, although not common, has been reported in kittens and puppies. In kittens, it is seen primarily during weaning stress. The most common clinical signs in severe cases are diarrhea (sometimes bloody), weight loss, and dehydration. Usually, coccidiosis is associated with other infectious agents, immunosuppression, or stress.

Treatment may be unnecessary in cats because they usually spontaneously eliminate the infection. In clinically affected cats, trimethoprim-sulfonamide (30–60 mg/kg/day for 6 days) can be used.

In kennel conditions when the need for prophylaxis might be predicted, amprolium is said to be effective, although it is not approved for use in dogs. In severe cases, in addition to supportive fluid therapy, sulfonamides such as sulfadimethoxine (50 mg/kg the first day and 25 mg/kg/day for 2–3 wk thereafter) can be used. Sanitation is important, especially in catteries and kennels, or where large numbers of animals are housed. Feces should be removed frequently. Fecal contamination of feed and water should be prevented. Runs, cages, and utensils should be disinfected daily. Raw meat should not be fed. Insect control should be established.

Last full review/revision March 2012 by Peter D. Constable, BVSc (Hons), MS, PhD, DACVIM