Written by Dr. Balkar Bains
It may be difficult to know exactly who came first; the chicken or the Coccidia species. However, it can be said with certainty that the development and expansion of poultry flocks has accompanied the survival of all coccidia strains. Here we discuss the basics of coccidiosis.
What is coccidiosis?
Coccidiosis is an intestinal infection in chicken caused by a group of intracellular parasites belonging to the genus Eimeria. Among the seven Eimeria species known to cause intestinal infections in poultry, four of those cause severe enteritis and mortality. Therefore, in reality, coccidiosis refers to seven different intestinal infections with each infecting a different part of the intestine with some overlap.
Eimeria strains are host specific and their invasion of intestinal cells is also site specific. Prevalence and survival of all Eimeria strains is closely linked to the environment, density of chicken population and the completion of its two-phase life cycle.
The Eimeria reproduction commences in the intestinal cells and completes in the chicken droppings voided in the litter.
The first phase of the reproduction cycle begins with the chicken passing a large number of oocysts in its feaces. The environment change from internal to external is essential for the further development of the parasite. The development of oocysts requires oxygen, humidity and a temperature range about 20 to 25 degrees Celsius. The litter in the chicken house is ideal for oocyst survival and its further development. The exogenous phase is usually complete in approximately three days and oocysts remain infectious for several months in the natural poultry environment.
The second phase of the coccidia reproduction cycle begins when a chicken ingests sporulated oocysts from contaminated litter, feed or water. The gizzard action and various enzymes and bile salts present in the intestinal contents breaks down the outer coating of the oocyst and that releases developing progeny in the lumen of the intestine.
Depending upon the coccidia strains, the released progeny invade cells lining the intestine on a specific site and multiply within that ruptures the cell. The escaped progeny from the ruptured cells may infect more cells lining the intestine. This process may be repeated for a few more generations of the coccidia resulting in over whelming infection and death of the host chicken.
Some of the emerging progeny may differentiate into male and female forms resulting in the production of oocysts that are passed in the chicken droppings, and the reproduction cycle continues.
Spread of infection
Oocysts can survive for long periods in hot and humid environments but not in excessively hot and dry conditions. The relocation of chicken litter through various means remains a good source of spreading oocysts to other farms and poultry houses.
Following coccidiosis infection in a flock, the surviving chickens develop some degree of immunity to protect against future infections for limited period. The protection is only limited to the Eimeria strain that caused the infection. There is no cross protection against infection by other Eimeria strains.
Clinical signs of coccidiosis
Coccidiosis most commonly occurs in young chickens but is rarely observed in chickens under two weeks of age. The clinical signs of coccidiosis in chickens are directly linked to the Eimeria strain and the level of infection at any given time. Eimeria strains that invade and destroy the deeper layers of the intestinal cells may cause bleeding and mucus production that is passed in droppings. The affected chickens appear depressed, stop eating feed and drinking water, seek isolation, have ruffled feathers and loss of weight. A significant mortality is often experienced in cases of severe infections.
Subclinical coccidiosis is caused by Eimeria strains that do not infect and destroy the deeper cells lining the intestine. The main signs of infection include depressed growth rate, adverse feed conversion efficiency and loss of weight.
Clinical signs of coccidiosis among chickens are not sufficient for a definitive diagnosis except where the presence of mucus and blood in the feaces is suggestive of the disease. A postmortem conducted by a professional is often warranted for a definitive diagnosis.
Treatment of coccidiosis
Treatment is aimed at the most susceptible second phase of the life cycle of Coccidia. The most effective treatment of chickens with clinical signs is to administer medication via drinking water. Sick chickens may not eat feed but will most likely drink water. The course of medication varies from 3 to 5 days continuously to achieve desired results.
Prevention of coccidiosis
Good sanitation of the poultry house and its environment is paramount to eliminate oocysts. Feed medication with approved anticoccidials is very effective in the prevention and control of infections. An appropriate coccidian immunity program using approved medicated feed is very effective. Approved vaccination administration has also been practiced with some success.
Dr Balkar Bains has extensive experience in poultry farming in Australia and throughout Asia from a diagnostic lab and field perspective. With particular focus on optimizing health of broiler and breeder flocks, hatchability and fertility problems in the hatchery, hygiene and food safety issues, and disease prevention and treatment strategies.