In spite of much research to advance the control and treatment of this disease, it remains the most costly disease of the poultry industry.
Coccidiosis is caused by microscopic animals called coccidia.
There are many species of coccidia that can infect fowl, domestic animals and humans. Each species of coccidia is host specific and does not infect a wide variety of animals. After an outbreak of a specific species of coccidia, the flock will develop a resistance to the exposed coccidia species but remain resistant to other infective species. This means that a flock may experience several outbreaks of coccidiosis, each being caused by a different species of coccidia. Chickens are susceptible to any of nine coccidia species, turkeys are susceptible to seven species and quail are susceptible to at least four different species of coccidia.