Oocysts, like those shown above, are passed in stool. The oocysts begin to mature or “sporulate” in the environment After they have adequately matured, they become infective to any host (dog or cat) that accidentally swallows them. Coccidia are swallowed when a pet grooms/licks the dirt off itself. In some cases, sporulated oocysts are swallowed by mice and the host is infected when it eats the mouse. Coccidia infection is especially common in young animals housed in groups (in shelters, rescue areas, kennels, etc.)

A puppy or kitten is not born with the coccidia. However, once born, the puppy or kitten is frequently exposed to its mother's feces and if the mother is shedding the infective cysts in her feces, then the young animals will likely ingest coccidia. Since young puppies and kittens (usually those less than six months of age) have little immunity to coccidia, the organisms reproduce in great numbers.

The sporulated oocyst breaks open and releases eight sporozoites. These sporozoites find intestinal cells and begin to reproduce inside them. Ultimately, the cell is so full of these internal parasites that they burst, releasing “merozoites” which seek out other intestinal cells and the process begins again. Thousands of intestinal cells can become infected and destroyed as a result of swallowing a single oocyst. As the intestinal cells are destroyed in larger numbers, intestinal function is disrupted and a bloody, watery diarrhea results. The fluid loss can cause significant dehydration in a very young or small pet.

A routine fecal test is a good idea for any new puppy or kitten whether there are signs of diarrhea because young pets often have internal parasites. The above illustration demonstrates coccidia oocysts seen under the microscope in a fecal sample. Coccidia are microscopic and can only be detected under a microscope. Small numbers of coccidia can be hard to detect and parasites may not be evident until later in the course of the condition. Several fecal tests may need to be performed to find the exact cause of the diarrhea.

Once coccidian is detected your veterinarian can give your pet a medication like sulfadimethoxine (Albon) or trimethoprim-sulfadiazine (Tribrissen), which can inhibit coccidial reproduction. Once the numbers stop expanding, it is easier for the patient’s immune system to fight the parasitic intestinal infection. The time it takes to clear the infection depends on how many coccidia organisms there are and how strong the patient’s immune system is. A typical treatment course lasts for 21 days, but more severe cases may require more than one treatment. An infected pet should have another fecal exam after the treatment for coccidia to make sure the treatment has been effective.

While there are species of coccidia that can infect people (Toxoplasma and Cryptosporidium), the Isospora species of dogs and cats are not infective to people. This is an easily transmitted disease, especially in an environment with a large number of pets in a small area like a kennel, shelter, or breeding facility. Other pets may become infected from exposure to infected fecal matter. Any dog or cat can contract this intestinal parasite, but coccidia is usually an infection of the young (the immature immune system tends to let the coccidia infection reach large numbers). Prompt removal of feces helps prevent continued environmental contamination.

Because coccidia is spread by the feces of carrier animals, it is very important to practice strict sanitation. All fecal material should be removed from the environment. Housing needs to be such that food and water cannot become contaminated with feces. Clean water should be provided at all times. Most disinfectants do not work well against coccidia. Steam cleaning, immersion in boiling water or a 10% ammonia solution are the best methods to kill coccidia that have contaminated inanimate objects. Coccidia can withstand freezing.

To control coccidiosis:

1. Isolate the infected dog from any other dogs to keep from spreading the illness.
   
   
2. Treat the animal with medication prescribed by your veterinarian.
   
   
3. Dehydrated dogs may be put on intravenous fluids (IV) which will generally require a stay at the veterinarian's clinic.
   
   
4. Remaining dogs that may have been exposed to the infected dog should also be treated with the same medication as a precautionary measure.
   
   
5. Thoroughly clean any area where the infected dog may have been. A solution of eight ounces of bleach mixed with one gallon of water should be sprayed on the area and allowed to sit 20 minutes. Rinse the bleach solution thoroughly with water and allow to completely dry before returning any dogs to the area.
   
   
6. Bathe all dogs, infected or not, to remove any fecal matter that may be on them.