Coccidiosis is one of the least understood of all avian diseases. The key to preventing Coccidiosis is to have a programme that will keep the disease under control, yet allow sufficient immunity to develop. Because the oocysts that cause Coccidiosis are present everywhere, it is virtually impossible to be free of this disease.
Coccidiosis is caused by a Protozoan, which is a microscopic single-celled animal. When the Protozoa multiply in the bird's intestine, infection takes place causing intestinal damage. Cells that line the intestine and are used for digestion and conversion of feed into Amino Acids and other nutrients are destroyed by the ever-multiplying Coccidia. Some species of Coccidia can and do cause severe damage to the intestinal lining and therefore make it difficult for the bird to absorb the necessary nutrients to nourish its body.
There are at least nine species of Coccidia known to infect chickens. Every animal is affected by some species of Coccidia. All species of Coccidia are host specific. This means that Coccidia that are capable of infecting chickens will not infect Turkeys and vice versa. Five of the nine species of Coccidia that infect chickens can be very aggressive and cause permanent intestinal damage if not properly controlled. Each of these species resides in a particular section of the intestines. Emeria acervulina resides in the upper part of the small intestine and is usually found in birds that are eight weeks of age and older. EIrieria necatrix, usually found in the middle areas of the small intestine, is responsible for the intestinal bleeding often seen with Coccidiosis and it usually attacks young birds. Emeria tenella resides in the Caecal tonsil or blind pouches of the intestine and causes what is called Caecal Bloody Coccidiosis and is usually found in birds that are between five to eight weeks of age. Emeria brunetti does its damage in the lower small intestine and the Cloaca or rectum of the bird. Emeria maxima causes intestinal damage in the middle to lower portions of the small Intestine.
Coccidiosis is spread by contaminated feed and droppings from infected birds. The infectious oocysts that cause Coccidiosis can be carried by man, litter, contaminated equipment and free flying birds. The main source of infection is the chicken itself. Birds that are infected with Coccidiosis will pass great numbers of infectious oocysts in their droppings. Even a bird that has recovered from a Coccidiosis outbreak will remain infectious, as they are never really free of the disease. The oocysts are capable, under the right conditions, of surviving in the soil for periods of one year or longer. The oocysts that cause Coccidiosis thrive in wet surroundings and are easier to control if litter and/or the ground is in a drier condition. It takes approximately four to seven days for an Infection to take place in the intestines. It takes constant re-exposure to the infectious oocysts in order for immunity to Coccidiosis to develop. Immunity is not permanent nor is it guaranteed for the life of the bird. Immunity depends on constant re-exposure to the infectious oocysts; if re-exposure is not accomplished then immunity will be lost. There is no cross immunity among the different species of Coccidia. This means that in order for birds to develop immunity to all nine species of Coccidia they would have to be exposed to sufficient numbers of oocysts from all nine species. They would then have to be constantly re-exposed to all nine species of Cocci in order for immunity to be maintained. The severity of a Cocci outbreak will depend upon the numbers of oocysts that are ingested by the birds and their overall health and conditioning.
