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Coccidiosis Management for Natural and Organic Poultry

Life Cycle and Types of Coccidia

Knowing how coccidia develop helps to understand and control the disease. Coccidiosis is caused in poultry by a one-celled parasite of the genus Eimeria. The life cycle of Eimeria takes about four to seven days to complete. It begins when active “oocysts” are picked up by the bird and swallowed. An “oocyst” is a capsule with a thick wall protecting the parasites. They “sporulate” or become infective if moisture, temperature, and oxygen become conducive to growth. After a bird eats the oocysts, coccidia imbed in the intestinal lining and multiply several times, damaging tissue.

A coccidial infection differs from bacterial and viral infections because coccidia are “self-limiting” and usually stop multiplying before killing the bird.

Coccidia are parasites, so they get their nutrients from the chicken host. The multiplications eventually stop, usually before causing death of the bird. The bird sheds the parasite in its droppings. These new oocysts can infect other birds. See the box “Coccidial Multiplication” for further details on coccidia’s complex life cycle.

Coccidical Multiplication

Coccidia are very prolific parasites. A single sporulated oocyst can have a big impact when eaten by a chicken. Each oocyst has four sporocysts in it, and each sporocyst has two sporozoites in it. The digestive tract releases the eight sporozoites from the oocyst, and they move into the cell lining of the digestive tract. Inside the cell, the parasite divides and invades more cells. There may be several generations of asexual multiplication; however, this stage is self-limiting and eventually stops. Finally, a sexual stage occurs in which male and female organisms unite and form new oocysts that are protected by a thick wall. These oocysts are shed in the feces. See Coccidia Life Cycle Diagram below.

Coccidiosis is usually a disease of young birds, but birds can be infected at any time if never before exposed. Coccidia populations take time to build to dangerous levels, therefore outbreaks usually occur when birds are between 3 and 8 weeks of age. Coccidiosis goes hand-in-hand with gut diseases, because it damages the gut and allows bacteria to enter and cause secondary infections. Coccidia are “species-specific” – coccidia that affect chickens do not affect other livestock, and vice versa (see Species-Specific Parasites box).

Species-Specific Parasites

Almost all livestock are affected by different types of coccidia. Each type of coccidia infects only one species of livestock – each is “species-specific.” There are seven different Eimeria that infect chickens, but only three cause most of the trouble in the U.S.: Eimeria tenella, Eimeria maxima, and Eimeria acervulina. Immunity to one type does not provide immunity for other types. Turkeys, ducks, geese, and other types of poultry are all infected by different types of coccidia.
Chicken coccidia species:
Eimeria acervulina
Eimeria maxima
Eimeria tenella
Eimeria necatrix
Eimeria mitis
Eimeria brunetti
Eimeria praecox
Turkey coccidia species:
Eimeria adenoeides
Eimeria meleagrimitis
Eimeria gallopavonis
Eimeria dispersa

Typical life cycle of coccidia in birds

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