Coccidosis in Poultry1

Coccidiosis is one of the oldest and most widely known parasitic diseases of poultry. Coccidiosis is caused by protozoans (a type of microscopic one-cellular animals) known as Eimeria that invade the cells in a chicken's or a turkey's intestine. The bird's ability to absorb nutrients suffers, which results in loss of weight or death. Coccidia can also damage the immune system and leave poultry more vulnerable to pathogens like Salmonella.

Each Eimeria parasite is able to infect only one host (for example, chicken or turkey, but not both), and they each attack different parts of the intestine in their specific host. These protozoan parasites are particularly difficult to combat because several different species of Eimeria exist in the field. Poultry may develop immunity to one type, but become infected with a different species because the immunity that develops after infection is also specific to only one species.

Coccidiosis organisms develop little eggs (oocysts) in the intestine that are passed in the droppings and can then infect other poultry in the same pen. If birds are held on wire floor, they cannot get in contact with droppings and will generally remain free of coccidiosis. Wet litter and warm temperature induce a heavy coccidiosis infection in the litter. That's why many coccidiosis outbreaks occur in the springtime (May, June).

Many avian diseases, including coccidiosis, are currently controlled by drug therapy. Producers add a number of anticoccidial drugs (coccidiostats) to commercial feed to combat the problem. Preventively, drugs are given in the chicks starter and grower feed, from day-old until 12-15 weeks of age. However, they are increasingly ineffective as drug-resistant coccidia strains rapidly develop.

All of the observed effects of coccidiosis are related to disruption of the epithelial cells lining the intestine by the release of parasite stages. While infection with high doses of some Eimeria species (E. tenella, E. necatrix) may cause death to chickens, usually the effects are insidious and are not apparent to the poultry farmer until the chickens are sent to market. The main effects that cause economic losses are a decreased weight gain due in part to the malabsorption of nutrients through the gut wall. This effect causes an increased feed conversion ratio, which is the amount of feed converted into body weight, because feed that is consumed is used inefficiently. Chickens that are infected with high levels of coccidia display symptoms such as droopiness and emaciation and may never achieve weight gain equal to their uninfected counterparts.

If chickens appear sick and ruffled from coccidiosis, get a diagnosis at a diagnostic laboratory. It can be made quickly and medication started immediately. Contact your county extension office for information about Cornell diagnostic services.

1 Sources: University of Connecticut Cooperative Extension Poultry Diseases; USDA-ARS Healthy Animals Newsletter Issue 10, 2002.

Last updated May 29, 2015