Coccidiosis is a 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.
Chickens who have previously been infeted 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
(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.
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.