Despite recent advances in control and treatment, the disease remains one of the principal causes of economic loss to the poultry industry. Coccidiosis is caused by minute, microscopic animals called coccidia. There are a number of species of coccidia, each of which produces a distinct disease process. Following an outbreak of coccidiosis, a flock will be protected against subsequent exposure to the species which produced the outbreak, but it will remain susceptible to other species. This means a given flock may have several outbreaks of coccidiosis, depending on the number of coccidia species in an area and exposure to them.
Coccidiosis is transmitted by direct or indirect contact with droppings of infected birds.
When a bird ingests coccidia oocysts, the organisms invade the intestinal tract lining where they produce tissue damage while undergoing reproduction. Within a week after ingesting coccidia oocysts, an infected bird sheds descendant coccidia in its droppings. So great is the reproductive potential that a single organism may produce about a million descendants. This means that contamination can build up rapidly, even in a new poultry house. These changes occur in 24 to 72 hours if the litter is warm and damp.