Coccidiosis is one of the most important poultry diseases worldwide and is ubiquitous, the only limit to the distribution of this disease is the distribution of the hosts. 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.
A protozoal parasite which 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.
Enteritis (inflammation of the intestine) is present in all coccidia infections and usually accompanied by diarrhoea which may or may not have blood in it. Poor growth and impaired feed conversion is common and mortality can be increased.
Parasitic phase: the infective oocyst (coccidia egg) is eaten by the bird and then multiplies over about 7 days within the gut, thousands of new oocysts resulting from just one ingested oocyst. Non-parasitic phase: excreted in the droppings, the oocysts then take 2 days to mature (ideal conditions 25-30ºC and moist) before being ready for the next host to eat.
Dayold 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 on free-range. Birds kept or reared on litter are more at risk when the coccidia has conditions which suit it such as wet litter. If the birds are also stressed by environmental factors (cold, overcrowding, 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 species of coccidia have different areas of the gut which they prefer, some producing the expected bloody diarrhoea, some producing high levels of mucus, sometimes white diarrhoea, 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 (no access to droppings and therefore no trickle infection) and then put onto litter, or if environmental stressors reduce their immunity. The birds generally look hunched and depressed with or without blood in the droppings.
Clinical signs plus a faecal sample containing oocysts and/or post mortem where the intestines are dark purple and the laboratory finds stages of the coccidia in the lining of them.*