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Avian Coccidiosis

Coccidiosis is a common parasitic disease, caused by infection with Eimeria species (coccidia). Chickens become infected by swallowing the organism's eggs from the surrounding environment. Once swallowed, coccidia replicate in the cells of the bird, which in the process causes extensive damage to various organs within their bodies. The parasites are maintained and continue to spread to other birds by their ability to reproduce sexually inside the bird, forming eggs. The eggs are passed out of the bird through their droppings, and contaminate the surrounding environment. Other chickens become infected by ingesting these eggs.

Chickens who have previously been infected with coccidia, may develop immunity to the specific species in their environment. However, if their immune system is lowered due to infection with another disease, stress, or exposure to a new species of coccidia, they may develop coccidiosis. Outbreaks in flocks often occur when birds are stressed, overcrowded, and living in poor sanitary conditions. Even seemingly healthy flocks may be infected with coccidia, without showing any signs of disease.

There are at least 7 different species of Eimeria (coccidia) that affect chickens which include E. acervulina, E. brunetti, E. maxima, E. mitis, E. necatric, E. praecox and E. tenella. Different species of coccidia target specific organs and areas of the body---such as the intestinal tract, kidneys, liver, and some throughout the body in red blood cells.

Epithelium damage caused by Eimeria causes leakage of proteins including plasma into the the bowel. This not only interferes with their ability to digest nutrients, but also greatly increases their risk of developing Necrotic enteritis (NE), allowing Clostridium perfringens to replicate rapidly.

Coccidia Life Cycle

Eimeria (coccidia) are maintained in flocks through a complex life cycle. Chickens become infected initially by eating sporulated oocysts (coccidia "eggs"), present in the environment. Once infected with the parasite, these chickens will shed the oocysts (eggs) produced by the organism, thus continuing to contaminate the environment. Eimeria have a short life cycle, varying between 4 to 6 days depending on the species.
Oocysts (eggs) can survive for up to 18 months in the environment under optimal soil moisture and temperature conditions.

Symptoms of Coccidiosis

Signs of coccidiosis vary somewhat depending on the number and species of Eimeria present, site of infection, and the age and overall health status of the bird. Dysentery is a common sign that occurs during severe cases of coccidiosis---consisting of the appearance of blood and mucus in the feces. Affected birds may also appear fluffed up and depressed (will show decreased activity levels and disinterest in normal chicken activities). They may loose weight or show reduced weight gain if affected during early growth.

How Coccidiosis is Diagnosed

Coccidiosis is diagnosed through a fecal test on the chicken's droppings. Eimeria eggs can be identified when the feces is looked at with a microscope. A Complete Blood Count (CBC) may show decreased red blood cell and total protein level counts in affected birds.

Coccidiosis Treatment

When young chickens are exposed to Eimeria early on, as long as there are not excessive levels present in the environment, they will usually develop a natural immunity, without any treatment necessary. Emphasis should be placed on keeping their environment as clean and dry as possible.

If excessive levels of Eimeria eggs are present in the environment (such as what would happen when birds are overcrowded), and/or birds become stressed, they will likely require treatment. When adult chickens are introduced into a new environment, without having prior exposure to the particular species of Eimeria while younger, they will not have developed immunity and be very vulnerable to the disease.

When treatment is necessary, there are a wide range of different options available--referred to as anticoccidial drugs. These include Toltrazuril, Amprolium, and Sulphonamides. When Toltrazuril is administered, it is important NOT to concurrently give supplements that contain vitamin B, for it will override the effects of the drug. Since Eimeria have been known to develop a resistance to anticoccidial drugs, it is important to check the chicken's droppings following treatment, to evaluate whether it was effective. Treatment with chlortetracycline has also been shown to be effective.

Clinical Signs

Pale comb
Change in droppings (water, mucous, and blood)
Loss of appetite
Ruffled feathers
Loss of condition
Pasty whitish soiling around the vent
Stunted growth rate


  • History
  • Clinical signs
  • Fecal exam - Identification of oocysts under microscopy.
  • CBC


AmproliumMost be given for 5 days straight to be effective.
Toltrazuril6 mg/kg added to drinking water for 2 days.
Sulphonamides2-3 days of daily treatment and repeated in 5 days.
Supplemental vitaminsMany anticoccidial drugs interfere with the chickens ability to absorb important nutrients; also helps boost their immune system to help them fight off the infection.
AntibioticsMay be needed in some cases depending on the severity of the disease.
Supportive care
Environmental modificationsImprove sanitary practices by regularly cleaning the environment where birds are kept, minimizing risk of fecal contamination in feeders and waterers, and expand enclosure or coop area if overcrowding birds.



  • Clean, disinfect, and refill waterers with fresh water daily, to prevent buildup of potentially pathogenic organisms. Position them so as to minimize water spillage onto bedding litter, as moisture promotes the growth of cocci.
  • Do not overcrowd
  • Don't keep birds in the same enclosed area for extended lengths of time, rotate them periodically to another area
  • Keep chickens of different ages separated
  • Practice good sanitation and minimize accumulation of feces by cleaning at least once a week.
  • Design roost areas over screened dropping pits for feces, to minimize contact birds have with feces.
  • Provide apple cider vinegar in the drinking water (1 tablespoon per 5 gallons of water)
  • Purchase resistant poultry breeds, such as the New Hampshire, Rhode Island Red or Leghorns

Scientific References

Good Overviews


Age Range

Coccidiosis occurs most frequently inchickens between 4 to 5 weeks of age.

Risk Factors

  • Overcrowding
  • Mixing chickens of different ages together
  • Unsanitary living conditions (large accumulation of feces)
  • Stress (recent transport, change of ownership or flock mates, sudden temperature change, bullying, stalking predators, improper handling, injury, etc.)
  • Concurrent disease
  • Poor immune status
  • Introduction of a new chicken into the flock
  • Letting chickens recovering from an illness or injury back out into the flock prior to finishing the course of medication