What is Coccidia?

Coccidia is a single-celled organisms that infects the intestine. They are microscopic protozoal parasites detectable on fecal tests. They are not worms but protozoa and infect through shedding of cysts.

Coccidia requires different anti-parasitic medication then what’s used for parasitic worms. Coccid is also not visible to the naked eye. 

Coccidia infection causes a watery diarrhea that is sometimes bloody and can be a life-threatening problem to an malnourished, young or very small pet.

There are many different species of coccidia but for dogs and cats, the most common infections are with coccidia of the genus Isospora. Dogs and cats each have their own coccidia species and cannot infect each other, nor can they infect people.

These are infectious Coccidia oocysts
These are infectious Coccidia oocysts 

Where do Pets get it?

Coccidia infection comes from consuming oocysts (pronounced o’o-sists). Oocysts are passed in  an infected animal’s stool. Once in the outside world, oocysts begin to mature and go through stages leading to an  infective stage. If this stage is consumed by a new host, infection results. The main mechanism of infection is fecal-oral (feces to mouth) transmission.

Alternatively, a host (such as a mouse, fly, cockroach or other insect) can become infected by eating an oocyst only to be in turn consumed by another host (a dog or cat). This would represent another way for a dog or cat to become infected.

Oocysts become infective in only 12-36 hours. Because of this, it is important to remove stool as quickly as possible from the pet’s environment to prevent contamination.

Housing animals in groups, leads to more stool exposure which, in turn, increases the risk for coccidia infection. Coccidia are common parasites and infection is not necessarily a sign of poor husbandry.

What Happens after the Host Consumes the Oocyst?

Coccidia lifecycle

This is quite a life cycle for a tiny organism but the short version is that the oocyst breaks open and releases eight sporozoites. These eight sporozoites go on to infect intestinal cells where they divide rapidly, eventually developing into a new stage called a merozoite. 

The merozoites divide and reproduce rapidly, filling up the intestinal cell until it bursts. A multitude of merozoites are released when the cell bursts and they go on to infect and similarly destroy more and more intestinal cells. When enough intestinal cells are destroyed, in three to 11 days, bloody watery diarrhea and disease result.

Merozoites divide and reproduce asexually but eventually a sexual generation of coccidia results in microgamonts, which are male, and macrogamonts that are female.

They merge and create an oocyst, which is what started the whole thing in the first place. The oocyst passes in stool where it can infect a new host and the life cycle begins again.

How are Coccidia Detected?

A fecal test is a good idea for any new puppy or kitten whether there are signs of diarrhea or not as youngsters commonly have parasites.

This sort of test is also a good idea for any patient with diarrhea and is recommended at least once a year for healthy dogs and cats as a screening test.

The above photograph shows coccidia oocysts seen under the microscope in a fecal sample. Coccidia are microscopic and a test such as this is necessary for diagnosis. Small numbers of coccidia can be hard to detect, so just because a fecal sample tests negative, this doesn’t mean the pet isn’t infected.

Sometimes several fecal tests are performed, especially in a young pet with a refractory diarrhea (one that won’t go away); parasites may not be evident until later in the course of the condition.

How is Coccidia Treated?

There are two common treatments used for Isospora infections in pets: sulfa drugs (the traditional treatment) and coccidiocidal medications (newer treatment).

The most common medicines used against coccidia are called coccidiostats. They inhibit coccidial reproduction. Once the numbers stop expanding, it is easier for the patient’s immune system to catch up and wipe out the infection.

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. In dogs and cats, sulfa-based antibiotics are the most commonly used coccidiostats.

There are newer medications that actually kill the coccidia outright: ponazuril and toltrazuril, both actually being farm animal products that can be compounded into concentrations more appropriate for dogs and cats.

These medications are able to curtail a coccidial infection in only a few doses and have been used in thousands of shelter puppies and kittens with no adverse effects.

Their use is becoming more popular used in kennels, catteries, and animal shelters and you may be pleasantly surprised to find one of them in stock at your regular veterinary office.

Cleaning the environment

Decontamination of the home environment may also be recommended by your veterinarian. Since the oocysts are resistant to most commonly used disinfectants, prompt removal of all stool then scrubbing any soiled areas with a detergent such as dilute bleach will be the best environmental measure. 

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