Coccidiosis is a very common parasitic disease of chickens 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. previous infection 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. Usually, chickens are affected by coccidia which destroy the lining of the bowel in the gastrointestinal tract, where the disease is referred to as intestinal coccidiosis. Chickens can also be infected my multiple species of coccidia at the same time.
How Coccidia Affect Chickens
The severity of the disease in affected chickens varies from mild to severe, depending on the levels of coccidia present, site of infection, and the age and health status of the bird. When damage occurs to the lining of the bowel, it causes problems with the chicken's ability to digest food and properly absorb the nutrients. This may cause the chicken to loose weight, or show reduced weight gain of infected during growth as young birds. Damage to the lining of the bowel wall will also cause fluid to weep into the bowel, resulting in decreased red blood cell and total protein level counts in affected birds. These birds often tire quickly and may become out of breath after exercise. Chickens affected with coccidia are more susceptible to secondary infections, since it lowers their immunity.
Coccidia Life Cycle
(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 coccidia present, site of infection, and the age and overall health status of the bird. In young chickens, under 6 months of age, affected birds may appear fluffed up in their appearance, show decreased activity level, and may develop green or watery droppings. They may show reduced weight gain or when affected as adults, lose weight. Chickens may tire easily during minimal activity and may develop secondary infections.
How Coccidiosis is Diagnosed
Coccidiosis is diagnosed through a fecal test on the chicken's droppings. Coccidia eggs can be identified when the feces is looked at with a microscope.
When young chickens are exposed to coccidia 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 coccidia are present in the environment, 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 coccidia 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 coccidia 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.