A common cause of diarrhea in puppies, and less commonly adult dogs, is a protozoal parasite called coccidia. Coccidia are single-cell organisms that enter cells of the small intestine and affect their ability to function properly, leading to the condition coccidiosis. There are several different groups of coccidia that can infect your dog, but the most common type is the group Isospora.
Coccidia are shed in an infected dog’s feces in a protected form called an oocyst, which is resistant to damage and can survive in the environment for extended periods of time. Under ideal temperature and humidity conditions, these oocysts become infective to certain animals. The oocysts may be present in water, contaminated grassy areas or other materials that your dog may consume. Dogs can also become infected by eating other animals, such as mice, that have ingested the oocysts. Once the oocysts are swallowed, they release sporozoites that invade the intestinal cells and can cause signs of illness.
It is possible for your dog to be infected with coccidia but show no signs of disease, particularly if he is an older dog. This is referred to as a sub-clinical infection. Even if your dog is not showing symptoms, it is still possible for him to pass the oocysts in his feces and therefore infect other dogs. Young puppies and dogs with suppressed immune systems are at much higher risk of coccidiosis compared to healthy adult dogs. Puppies are often infected before they even enter their new homes, particularly if housed in unsanitary environments. If your puppy is infected, the most common symptoms are diarrhea that can be watery or bloody, vomiting and signs of pain in the abdomen. In some cases, the diarrhea can be so severe that your puppy can become dehydrated very quickly. If you notice any of these symptoms, take your puppy to the vet immediately.
Coccidiosis is diagnosed by examination of the fecal matter under a microscope. The oocysts can be identified through either a fecal float or a direct smear. Your veterinarian may perform this examination due to clinical symptoms that are affecting your puppy, or as part of a routine wellness check when your pup is first brought home. If your puppy is not showing signs of illness, it may be possible for him to clear the infection on his own and a repeat fecal examination may be performed in the future. However, if your puppy is experiencing diarrhea or any other symptoms, treatment is recommended to eliminate the infection.
The most common treatment for coccidiosis is a sulfa antibiotic that is usually prescribed for five to 14 days. This medication may need to be repeated in cases of severe infection. Additional drugs are available if the initial therapy is unsuccessful. A very important part of clearing the infection is keeping your puppy’s environment very clean. If he is allowed to come in contact with infected feces, even while undergoing treatment, he can easily reinfect himself and the treatment will need to start again. Fortunately, once the infection is cleared the prognosis for a full recovery is excellent.