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Coccidiosis in poultry

Causes of coccidiosis in poultry and other bird species, its clinical signs, and how to prevent and treat it. Coccidiosis in poultry is one of the most common diseases in the world. It causes economic losses due to mortality rate, low body weight, and expenses related to preventive and curative control, while making birds susceptible to necrotic enteritis as well. Worldwide annual losses have been estimated at more than US$3 billion due to coccidiosis in poultry and other avian species.

The reasons

Protozoan parasites of the genus Eimeria cause coccidiosis. They are obligate intracellular parasites with complex life cycles, including sexual and asexual stages. In poultry, Eimeria parasites affect the intestines, making them susceptible to other diseases (necrotizing enteritis) and reducing this organ’s ability to absorb nutrients. Modern poultry production practices facilitate the spread of this disease in poultry farms. The disease is transmitted between poultry farms by mechanical vectors, such as insects and wild birds. Although Eimeria eggs (oocysts) can be transported mechanically by wild birds, these parasites are host-specific and therefore wild birds do not act as a biological reservoir. The life cycle of Eimeria parasites begins with the ingestion of mature oocysts. Each oocyst egg consists of four sporophytes, and each sporophyte contains two sporophytes. Bile salts and the enzyme chymotrycin stimulate the release of sporophyte from the oocyst. Once released, the sporophyte invades the intestinal cells and begins the stage of asexual development called fission propagation. After a variable number of asexual cycles, gametes form and sexual development (gametogenesis) begins. The sexual stage ends with the production and release of oocysts into the intestinal cavity. Once released into the environment, the oocyst must produce spores to become infective. The sporulation process typically takes 2 to 3 days, depending on environmental conditions (Waldenstedt et al., 2001).


In general, good natural immunity is acquired after infection with Eimeria parasites in poultry. Therefore, coccidiosis is usually considered a disease of young animals. However, acquired immunity is specific for each species of Eimeria parasite and does not provide cross-protection between species (except for some cross-protection between E. maxima and E. brunetti). Moreover, cross-protection between strains of the same species is often partial (Long, 1974), which is of practical importance for the selection and use of live vaccines against Eimeria parasites in different geographical locations.

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