Avian coccidiosis is an intestinal tract infection caused by several species of the protozoan parasite Eimeria
(sometimes referred to as coccidia). Most infections involve multiple species of Eimeria
destroying different regions of intestinal epithelial tissue of the bird. Although over 1000 species of Eimeria
have been identified across numerous animal species, there are nine Eimeria
that are of main concern for chickens. The species of Eimeria
reported as highly pathogenic are E. acervulina, E. brunetti, E. maxima, E. mitis, E. necatric, E. praecox
and E. tenella
. Mildly pathogenic species include E. acervulina, E. mitis,
and E. mivati
, whereas E. praecox
and E. hagani
are considered to be the least pathogenic. 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. The severity of the infection (and resulting damage to the chicken's gastrointestinal tract) depends on the number of oocysts ingested and the general health and immunity of the bird.
Chickens become infected by ingesting sporulated oocysts (coccidia "eggs") from the surrounding environment. Chickens who have previously been infected, may develop immunity to the specific species of Eimeria
in their environment. However, if their immune system is lowered due to infection with another disease, stress, or exposure to a new species of Eimeria
, 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 Eimeria
, without showing any signs of disease.
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.
The resulting damage caused by Eimeria
to the chicken's intestinal lining results in the leakage of proteins, including plasma into the the bowel. This not only interferes with the ability to digest nutrients, but it also greatly increases their risk of developing Necrotic enteritis (NE)
, allowing Clostridium perfringens
to replicate rapidly.
Eimeria Life Cycle
are maintained in flocks through a complex life cycle. Chickens become infected initially by ingesting the oocysts present in the environment. Once infected with the parasite, these chickens will shed the oocysts 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 can survive for up to 18 months in the environment under optimal soil moisture and temperature conditions.
Symptoms of Coccidiosis in Chickens
Signs of coccidiosis in chickens varies 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 when infections are severe---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 in Chickens
Coccidiosis is diagnosed in chickens 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 for Chickens
Treatment of coccidiosis involves several important components:
- Anticoccidial agents. It is initially important to control the coccidia with an anticoccidial agent such as amprolium or toltrazuril, in accordance with the manufacturers recommendations.
- Antibiotics: It is important to control secondary bacterial growth by concurrently administering antimicrobials such as tylosin or amoxicillin. When coccidiosis damages the intestinal wall, it leaves the bird more at risk of developing secondary infections, such as necrotic enteritis.
- Supportive care: It is very important to keep the bird hydrated and comfortable.
- Environmental/Management Changes. Slow down oocyst sporulation within the environment where birds live by regularly cleaning the area where chickens live, by removal of the feces and soiled bedding, ensuring it is kept dry (perhaps install better drainage or roof to prevent rain), and/or rotate birds to different areas often. Do not overcrowd birds.
There has been an increased emergence of drug-resistant strains of Eimeria
, especially after prolonged uses of the drug. Therefore, it is important to conduct a follow up fecal test following treatment, to evaluate whether the drug was effective against the particular strains of Eimeria