Coccidiosis is one of the most important poultry diseases worldwide.
What is the cause?
It is caused by a protozoal parasite that multiplies in the gut, specific to different hosts. Not all species of coccidia are harmful but there are five of the Eimeria species pathogenic to chickens, five in turkeys, three in geese, three in ducks, and three in pheasants.
What are the signs of infection?
Enteritis – that is inflammation of the intestine - is present in all coccidia infections and usually accompanied by diarrhea which may or may not have mucus and blood in it. Poor growth, depression, emaciation, and impaired feed conversion is common and mortality can be increased.
How it is transmitted?
The infective oocyst - coccidia egg - is eaten with droppings by the bird and then multiplies over about 7 days within the gut, thousands of new oocysts resulting from just one ingested oocyst. The bird then sheds the infective oocysts and the cycle
Day-old chicks do not get immunity from their mother. Birds of any age are susceptible, but most acquire infection early in life which gives them some immunity. Immunity is best kept strong by a low level of infection, which is what happens in the free-range.
Birds kept or reared on litter are more at risk when the coccidia has conditions that suit it such as wet litter. If the birds are also stressed by environmental factors such as cold, overcrowding, and poor ventilation then disease results. The oocysts are very resistant to destruction, either by disinfectants or by drying out, and can survive for months or years.
The coccidia species have different areas of the gut which they prefer, some producing bloody diarrhea, high levels of mucus, white diarrhea, and others stunting growth.
Infection can show from 3-6 weeks of age and infective oocysts can be transported by people looking after the birds. Older birds can become infected if either their immunity has been reduced due to being kept on a wire floor thus no access to droppings and therefore no trickle infection and then put onto the litter, or if environmental stressors reduce their immunity. The birds generally look hunched and depressed with or without blood in the droppings.
What is the economic impact of coccidiosis?
This disease is very common and unless controlled has a severe economic impact. Even low levels of infection cause ill thrift and loss of production with increased mortality.
What is the treatment of Coccidiosis?
Anticoccidial drugs can be used. Free-range reduces the incidence of disease while still providing trickle infection to boost immunity.
Temperatures above 56ºC and below freezing are lethal to oocysts, as is desiccation. Oocysts can stay in sheds despite disinfection unless a specific oocidal ("egg-killing") disinfectant is used.
What is the importance of Vaccination?
The better treatment and prevention for chickens is vaccination. This contains species of coccidia that are weakened so that they cause the chicken to mount an immune response but not to become infected.