Coccidia are single celled protozoan parasites that are found in the small intestine of dogs and cats. There are many different species of coccidia (Isospora species) that can affect dogs, cats and people. In dogs and cats, coccidiosis is diagnosed using fecal floatation (looking at the stool sample under the microscope) to check for eggs (oocysts). Yellowish, watery diarrhea is the most common symptom; however in severe cases, the pet may have lost weight, be dehydrated, and may not want to eat. Fortunately, once diagnosed, it's easy to treat with 2 daily doses of a prescription medication. A stool sample is then reexamined in 2-3 weeks to make sure the infection is cleared completely.
This is what we see under the microscope.
Cats can be infected with toxoplasma gondii, a type of coccidia, which may be dangerous to people, particularly pregnant women and their developing baby, as well as people whose immune system is weakened. They become infected after ingesting the organism from rare or undercooked meat, such as birds and rodents carrying the parasite. Dogs can also be infected with toxoplasma gondii, but the protozoan doesn't reach the same infective stage in dogs that is reaches in cats and therefore dogs can't transmit the organism to people. It is difficult to diagnose, as the oocysts are only shed for about 1-3 weeks and that makes checking a stool sample for cysts unlikely to produce an accurate diagnosis. Antibody testing is one way to determine if a cat has been infected. Cats that test positive are unlikely to pose a threat to humans, as they have already shed the infected oocysts. The only time a cat can pass the parasite to people is when cats are passing the cysts in their feces.
If toxoplasma gondii is suspected in a cat and there is either a pregnant woman or immunosuppressed person in the household, it should be quarantined from 1-3 weeks. In general, pregnant women should not scoop litter boxes as a precaution or clean the box twice daily since it takes 24 hours from the time the stool is passed before the parasites become able to inject people. Human infection can cause abortion, and birth defects. Vigilant hand washing after scooping litterboxes is important for all cat owners, especially if the cats are indoor/outdoor and hunt. One of the more common treatments for toxoplasmosis is clindamycin, although it depends on what other symptoms the cat is currently exhibiting.