Coccidia (Coccidiosis)

by Race Foster, DVM and Marty Smith, DVM
Drs. Foster & Smith, Inc.

What are coccidia?

Coccidia are small protozoa's (one-celled organisms) that multiply in the intestinal tracts of dogs and cats, most commonly in kittens and puppies less than six months of age, in adult animals whose immune system is suppressed or in animals who are stressed in other ways (e.g., change in ownership, other disease present).

In cats and dogs, most coccidia are of the genus called Isospora. Isospora canis and I. ohioensis are the species most often encountered in dogs; I. felis and I. rivolta are the most common in cats. Regardless of which species is present we generally refer to the disease as coccidiosis. As a puppy or kitten ages it tends to develop a natural immunity to the effects of coccidia. As an adult it may carry coccidia in its intestines, shed the cyst in the feces, but experience no ill effects.

How are coccidia transmitted?

A puppy or kitten is not born with the coccidia organisms in its intestine. 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 them and coccidia will develop within their intestines. Since young puppies and kittens, usually those less than six months of age, have no immunity to coccidia, the organisms reproduce in great numbers and parasitize the young animal's intestines. Oftentimes this has severe effects.

From exposure to the coccidia in feces to the onset of the illness is about 13 days. Most puppies and kittens who are ill from coccidia are, therefore, two weeks of age and older. Although most infections are the result of spread from the mother, this is not always the case. Any infected kitten or puppy is contagious to other puppies and kittens. In breeding facilities, shelters, animal hospitals, etc., it is wise to isolate those infected from those that are not.

What are the symptoms of coccidiosis?

The primary sign of an animal suffering with coccidiosis is diarrhea. The diarrhea may be mild to severe depending on the level of infection. Blood and mucous may be present, especially in advanced cases. Severely affected animals may also vomit, lose their appetite, become dehydrated, and in some instances, die from the disease.

Most infected kittens and puppies encountered by the authors are in the four to twelve week age group. The possibility of coccidiosis should always be considered when a loose stool or diarrhea is encountered in this age group. A microscopic fecal exam by a veterinarian will detect the cysts confirming a diagnosis.

What are the risks?

Although many cases are mild it is not uncommon to see severe, bloody diarrhea result in dehydration and even death. This is most common in animals who are ill or infected with other parasites, bacteria or viruses. Coccidiosis is very contagious, especially among young kittens and puppies. Entire kennels and catteries may become contaminated with puppies and kittens of many age groups simultaneously affected.

What is the treatment of coccidiosis?

It should be mentioned that stress plays a role in the development of coccidiosis. It is not uncommon for a seemingly healthy puppy or kitten to arrive at its new home and develop diarrhea several days later leading to a diagnosis of coccidia. If the puppy or kitten has been at the new home for less than thirteen days then it had coccidia before it arrived. Remember the incubation period (from exposure to illness) is about thirteen days. If the puppy or kitten has been with its new owner several weeks, then the exposure to coccidia most likely occurred after the animal arrived at the new home. The authors merely point this out as they have been involved in legal cases as to who was responsible for the cost of treatment, the breeder or new owner. Usually coccidia was present only to surface during the stressful period of the puppy or kitten adjusting to a new home.

Fortunately coccidiosis is treatable. Drugs such as sulfadimethoxine (Albon), trimethoprim-sulfadiazine (Tribrissen) and amprolium (Corid) have all been effective in the treatment and prevention of coccidia. Because these drugs do not kill the organisms, but rather inhibit their reproduction capabilities, elimination of coccidia from the intestine is not rapid. By stopping the ability of the protozoa to reproduce, time is allowed for the puppy's own immunity to develop and remove the organisms. Drug treatments of five or more days are usually required.

How is coccidiosis prevented or controlled?

Because coccidia is spread by the feces of carrier animals, it is very important to practice strict sanitation. All fecal material should be removed. 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; incineration of the feces, and steam cleaning, immersion in boiling water or a 10% ammonia solution are the best methods to kill coccidia. Coccidia can withstand freezing.

Cockroaches and flies can mechanically carry coccidia from one place to another. Mice and other animals can ingest the coccidia and when killed and eaten by a cat, for instance, can infect the cat. Therefore, insect and rodent control are very important in preventing coccidiosis.

The coccidia species of dogs and cats do not infect humans.

There are many different species of coccidia but for dogs and cats, but the
most common infections are with coccidia of the genus Isospora (pictured here).
The information presented here pertains to Isospora species

What on Earth are Coccidia?

Coccidia are single celled organisms that infect the intestine. They are microscopic parasites detectable on routine fecal tests in the same way that worms are but coccidia are not worms and they are not visible to the naked eye. Coccidia infection causes a watery diarrhea which is sometimes bloody and can even be a life-threatening problem to an especially young or small pet.

Where do Coccidia Come From?

Oocysts (pronounced o'o-sists), like those shown above, are passed in stool. In the outside world, the oocysts begin to mature or “sporulate.” After they have adequately matured, they become infective to any host (dog or cat) that accidentally swallows them.

To be more precise, coccidia come from fecal-contaminated ground. They 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.) This is a common parasite and is not necessarily a sign of poor husbandry.

What Happens Inside the Host?

The sporulated oocyst breaks open and releases eight sporozoites. These sporozoites each finds an intestinal cell and begins to reproduce inside it. Ultimately, the cell is so full of what are called “merozoites” that it bursts releasing the merozoites which seek out their own intestinal cells and the process begins again. It is important to note how thousands of intestinal cells can become infected and destroyed as a result of accidentally swallowing a single oocyst.

As the intestinal cells are destroyed in larger and larger numbers, intestinal function is disrupted and a bloody, watery diarrhea results. The fluid loss can be dangerously dehydrating to a very young or small pet.

How Are Coccidia Detected?

A routine fecal test is a good idea for any new puppy or kitten whether there are signs of diarrhea or not as youngsters are commonly parasitized. This sort of test is also a good idea for any patient with diarrhea. The above illustration demonstrates coccidia oocysts seen under the microscope in a fecal sample. Coccidia are microscopic and a test such as this is necessary to rule them in.  It should be noted that small numbers of coccidia can be hard to detect so just because a fecal sample tests negative, this does not mean that the pet is not infected. Sometimes several fecal tests are performed, especially in a young pet with a refractory diarrhea; parasites may not be evident until later in the course of the condition.

How is Coccidiosis Treated?

We do not have any medicine that will kill coccidia; only the patient’s immune system can do that. But we can give medicines called “coccidiostats” which can inhibit coccidial reproduction. Once the numbers stop expanding, it is easier for the patient’s immune system to “catch up” and wipe the infection out.  This also means, though, that the time it takes to clear the infection depends on how many coccidia organisms there are to start with and how strong the patient’s immune system is. A typical treatment course lasts about a week or two but it is important to realize that the medication should be given until the diarrhea resolves plus an extra couple of days. Medication should be given for at least five days total. Sometimes courses as long as a month are needed.

The use of sulfa drugs in pregnancy can cause birth defects. Sulfa drug use can also lead to false positive test results for urine glucose.

Can People or Other Pets Become Infected?

While there are species of coccidia that can infect people (Toxoplasma and Cryptosporidium, for example), the Isospora species of dogs and cats are not infective to people. Other pets may become infected from exposure to infected fecal matter but it is important to note that this is usually an infection of the young (i.e. the immature immune system tends to let the coccidia infection reach large numbers where the mature immune system probably will not.) In most cases, the infected new puppy or kitten does not infect the resident adult animal. 

Website designs by Swiftwater Innovations Copyright © 2002 - All Rights Reserved

Updated 01-01-04