Most cats will come in contact with coccidia sometime in their life. The majority of adult cats are immune to the infectious disease that coccidia can cause, called “coccidiosis”. Kittens under six months of age and cats suffering from conditions that hinder their immune system may contract coccidiosis. This rare infection can cause serious effects and, in extreme cases, may even be fatal. Kittens who are infected with coccidiosis are contagious and can infect the rest of the litter. The most common parasite to cause coccidiosis in cats is Isospora  felis. Veterinary attention is needed to ease symptoms and rid the cat of the parasitic infestation.

Coccidia are a group of single-celled parasites called “protozoa”. Cats are susceptible to infection from a number of these parasites, including Isospora, Toxoplasma, Sarcocystis, Besnoitia and Hammondia. Coccidia lodge in the intestinal wall and form cysts. Some of these protozoa require more than one host to complete their development. Once inside the body, it can take up to two weeks for the parasites to mature and begin to reproduce. Coccidia are found throughout the world.

Kittens may start to show symptoms of coccidiosis from the ages of two weeks to six months. The stress of the weaning process can leave a kitten vulnerable to developing a parasitic infection. Signs to watch for are as follows:

To become infected with coccidia, a cat must come into direct contact with the parasite. Kittens are often exposed to the protozoa from their mother's feces (as adult cats often contain the parasites without showing any symptoms). All known causes of parasite exposure are listed below.

Susceptibility is increased in cats with immune deficiencies or who are experiencing stress.

If your cat or kitten begins to exhibit any of the symptoms of coccidiosis, bring it to a veterinary clinic or animal hospital immediately. Be prepared to provide the cat's full medical history, especially if it is an adult cat with immune system issues. The veterinarian will perform a complete physical examination of the cat, watching for known signs of coccidiosis. 

The most common way to diagnose a parasitic infection in a cat is by taking a sample of the cat's feces and sending it for microscopic examination. During this examination, larval or adult coccidia may be identified. As these protozoa are exceptionally small, if a microscopic examination comes back negative, there is no guarantee that your cat or kitten is not infected. Blood work will be run, including a complete blood count and a biochemical profile to assess the cat's overall condition. Certain parasites may also be identified via blood smears. If the infected cat is an adult, feline viruses that negatively affect the immune system, such as feline immunodeficiency virus and feline leukemia virus, should be tested for. 

In some kittens or adult cats, coccidiosis may spontaneously go away on its own. In severe cases, both symptomatic and causative treatments may be needed.

A course of antibiotics such as Sulfadimethoxine, Trimethoprim-Sulfonamide or Amprolium can stop the coccidia from reproducing. Up to two weeks of oral administration is needed.

If the infected cat has become severely dehydrated, hospitalization and intravenous fluids may be needed to stabilize its condition. 

Be sure to isolate your adult cat or kitten from other cats during antibiotic treatment. Reinfection can easily happen, so extra sanitation measures should be taken. Clean all litter boxes at least once a day. Most coccidia need at least 24 hours outside of a host to infect another animal, so removing feces from the litter daily can prevent the parasites from re-entering your cat. Disinfect the litter boxes weekly using hot water and bleach. 

Take extra care when monitoring the health of kittens to identify cases of coccidiosis before the infection has progressed too far. Test any pregnant cats for protozoa so that kittens may be treated after birth. Most coccidia can not spread to humans. The most common coccidia, I. felis poses no threat to owners. Infections of Toxoplasma or Cryptosporidium may present a small risk to pregnant women and any human who has a suppressed immune system.