Coccidiosis In Chickens: Transmission, diagnosis, and treatment

Published on Thu, 07/31/2014 - 11:22am

As a poultry owner, understanding common diseases is an essential tool to prevent and treat outbreaks. Avian intestinal coccidiosis is a common protozoal gastrointestinal (GI) parasite that primarily affects young chickens. Clinical signs include mucus-like or bloody diarrhea, dehydration, anemia, listlessness, ruffled feathers, stunted growth, and death. Coccidiosis is also commonly associated with a drop in egg production.

Chickens can carry nine different types of coccidia, making it all the more important to understand that clinical disease is dependent on which species of coccidia are present and in what quantities. The presence of a few coccidial eggs or oocysts may not equal a diagnosis of the disease.

These differences and subtleties can be difficult for poultry owners who simply want to know if their chickens have coccidia. Add to this the difficulty controlling coccidiosis in mixed-aged flocks—where older, “healthy” chickens can shed coccidial oocysts in their feces and infect the younger chicks—and things become complicated.

This article will give you the information about the biology and epidemiology of coccidiosis you need to control and, if necessary, treat infections.

Coccidiosis 101
Coccidiosis refers to protozoa, or single-celled organisms, from the genus Eimeria. Chickens have nine different and well characterized species of coccidia. In contrast, there are seven different species of Eimeria that can infect turkeys. Interestingly, each species of Eimeria is unique because exposure to one species of coccidia does not appear to afford protection to others. It can also parasitize a specific portion of the chicken’s GI tract while causing slightly different pathological and clinical signs. 

For example, Eimeria maxima causes bleeding in the middle of the small intestines and is considered moderately pathogenic. In contrast, Eimeria tenella causes severe inflammation of the cecum and is considered highly pathogenic. Because no anticoccidial medication is effective against every species of coccidia, identification is key for treatment and control. 

Coccidial oocysts are found in areas contaminated by fecal matter. Chickens become infected when they inadvertently ingest these oocysts off of the ground. Once in the intestine, the eggs develop and eventually infect the cells of the chickens’ GI tract. Once inside the chickens’ GI cells, the coccidia transform into a new sexual stage and reproduce, eventually breaking down the GI cell. 

This is how a single oocyst can infect and destroy thousands of intestinal cells. As more and more of the intestinal cells are infected and subsequently destroyed, clinical signs like diarrhea and decreased growth become more and more apparent. As coccidia are shed in the feces, the resulting spores can remain viable for months. Once ingested by another chicken, the life cycle begins again. 

It is important to recognize that coccidia are common in the poultry environment and their presence is not necessarily a sign of poor care. In fact, if chickens are exposed to moderate numbers of oocysts, they will typically develop immunity towards that species. The primary way to maintain low to moderate amounts of coccidia is by keeping the chicken’s substrate, or litter material, dry.

Infection is via the fecal-oral route. Under the right environmental conditions—such as increased moisture—the oocysts can contaminate all areas of the chicken’s environment, including feed, litter, and soil, all while remaining viable for months. Consequently, controlling substrate and litter moisture levels becomes essential. 

The substrate or litter material should be “friable,” meaning it should clump in your hand but also crumble easily. If the litter is too dry, it can become a particulate that is inhaled by the chickens—and their owners. If it’s too wet, it will clump and not come apart. Also, wet litter may have a strong ammonia smell which can cause coccidial overgrowth and other flock management problems. Make sure moisture is controlled during the rainy season and around leaky waterers. 

Like us, birds are more susceptible to disease if they are immunosuppressed from another illness or stress. For example, sexually immature chickens that have the immunosuppressive condition infectious bursal disease, or IBD, are more likely to become infected after being exposed to coccidia. Likewise, intestinal coccidiosis may predispose birds to other concurrent intestinal infections such as necrotic enteritis, salmonellosis, and certain viral intestinal infections. This makes it even more essential to create a healthy environment for your chickens. 

Humans can transmit coccidiosis, too, through shoes and equipment. If we go to visit our neighbor’s chickens, we can carry diseases back and forth between the flocks. To sidestep this, limit access to your flock and be smart about visiting others. In the commercial poultry industry, it’s standard practice to wear booties and hair nets, wash your car before and after your visit, and wait at least 24 hours before visiting a new flock of birds. 

Many of us who have dogs and cats are familiar with detecting coccidia and other intestinal parasites on an annual visit to our small animal veterinarian. Typically, a fresh stool sample will be collected and viewed under a microscope. However, because coccidia, like many GI infectious diseases, are intermittently shed in the feces, a negative test does not mean the animal is not infected. Due to the potential for false negatives coupled with the possibility of coccidial transmission to the remainder of the flock, birds with clinical signs are typically euthanized to complete a thorough post-mortem examimation in order to appropriately treat and protect the remainder of the flock.

In a postmortem examination, a veterinarian will open up the GI tract and look for lesions that are consistent with coccidia (see Figure 1 on page 23). Finally, the veterinarian will collect a sample of the intestine and look at the material under the microscope. A definitive diagnosis can be made from this examination. 
It is important to remember that because coccidia is so prevalent, it is often found in the feces or intestines of chickens at necropsy. The significance of that finding is weighed against the visual and microscopic damage to the intestines. 

If one or two of your chickens were euthanized and diagnosed with coccidia, what should you do? If the chickens all share the same environment, treat the remainder of your flock with Amprolium (0.024 percent of the active ingredient in drinking water for three to five days). 

Sulfa drugs (like sulfamethazine administered at 0.1 percent for two days) are also effective, but shouldn’t be used in layers. It is important to contact the Food Animal Residue Avoidance Databank ( for any drug to find up to date information on withdrawal times for eggs and meat. Administration of water dispersible vitamin A and K supplements may also enhance recovery.

It is important to remember that no anti-coccidial is effective against all the different strains of coccidia and that over time, coccidia can become drug resistant. As a result, the above-mentioned drugs should only be used to treat an affected flock and not as a preventative program. If for some reason anti-coccidials are used regularly, consider using a rotation of different anti-coccidials. 

Disease prevention is always more desirable than treatment—this is especially true for backyard poultry. Commercial producers have several inherent advantages with respect to prevention, including enhanced biosecurity, more effective cleaning and disinfection practices, and better access to vaccines. Even so, there are several relatively simple prevention methods that should be utilized by all poultry owners to reduce coccidia in the environment and the risk of coccidia infection in your chickens. Specific prevention measures include: 

  • Controlling moisture with the appropriate installation and management of watering systems. Specifically, using nipple drinkers to reduce spillage of water onto litter instead of bell and trough drinkers.
  • If at all possible, periodically move the location of your chickens. Any area that is consistently covered with manure will eventually have a high load of bacteria, viruses, and parasites—like coccidia. Leaving land fallow for several weeks is one of the most effective ways to reduce the pathogen load in the environment. 
  • Including anticoccidials—such as medicated feed—into diets at recommended levels will prevent clinical infection. This is very important for the first month of the chick’s life since her immune system hasn’t fully developed. 
  • Good biosecurity: Coccidial oocysts are normally introduced into new facilities through contaminated equipment. Full immunity is not reached in chickens until approximately seven weeks of age.

Can I get sick from my chicken’s coccidia?
Coccidiosis is a common problem for most mammalian species—including humans. Fortunately, the species of coccidia that infects chickens is not capable of causing infection in people. 
Still, it’s important to understand that there are several other diseases which chickens carry that can make people sick, including some serotypes of the bacteria Salmonella as an example (see “Backyard Bugs” on page15 to learn more). To keep from spreading infection, it is essential to always wash your hands after working with chickens. 

Don’t make perfect the enemy of good
Some practices that backyard owners use—such as mixed-aged flocks and lack of access to coccidial vaccines—can make coccidia control a challenge. It is important to recognize these challenges while maximizing efforts to lessen the presence of coccidia in your chickens and their environment. 

Continue your education about coccidia and other avian diseases. Reach out to private veterinarians with an interest in poultry. Track down your local state and USDA animal health veterinarians. Email or call your friendly cooperative extension university faculty member. Also, identify your state’s diagnostic laboratory service—many times they offer heavily discounted or free diagnostic services for your backyard flock. 

Figure 1: Gross image of the intestinal tract of a chicken infected with coccida. (Inset image:) Microscopic image of coccidia. Gross image courtesy of Dr. Gabriel Sentíes-Cué. Microscopic image from Mike the chicken vet (