Coccidia are prozoan parasites that invade the lower small intestine, caecum and colon, causing damage to the mucosa and submucosa of the intestine. Spore-like oocysts, highly resistant to environmental conditions and disinfectants, are shed in faeces. The disease is often subclinical but may cause enteritis, dysentery and straining in severly affected animals. There are many species of coccidia. Coccidia are host specific meaning that different species infect sheep, goats and cattle.
The life cycle of coccidia involves a multiplication phase in the intestinal lining. Cysts are passed in the faeces and contaminate pasture. Massive intake of cysts can occur where animals congregate at feeding and watering points.
Coccidia are probably present in many animals after weaning and often cause little or no disease. Disease is usually confined to young animals on heavily stocked wet pastures, and may be exacerbated by stress or concurrent disease. Occasionally it is seen in older animals when subjected to stress and heavy challenge as may occur when animals are gathered in high density assembly yards in preparation for export. Sporadic cases may be seen on ships if a coccidiostat has not been incorporated into pellets.
When disease does occur, animals may show signs of tenesmus (straining to urinate or defaecate), and acute scouring may occur for a few days. Diarrhoea is yellow-brown to black and may be stained with fresh blood. There may be loss of appetite, severe dehydration, and weight loss.
Complete recovery from an acute disease episode may take several weeks during which affected animals may display varying levels of reduced appetite and poor weight gain.
Severe disease and death may occur under heavy exposures and when animals are compromised by other conditions such as heavy worm burdens.
Differential diagnoses include other causes of diarrhoea such as salmonellosis, gastrointestinal parasitism and bovine virus diarrhoea virus infection (cattle).
Laboratory confirmation requires a sample of faeces from affected animals for counting of oocysts. At necropsy, collect sections of small and large intestine in buffered formalin for histology.
Sulphadimidine is effective either by injection or drench. Sulphadimidine may be added to the drinking water but it may be difficult to ensure animals drink enough to receive effective levels of treatment.
In older animals or where the clinical disease is less severe, animals may be left to recover spontaneously.
In feedlots where coccidiosis has occurred repeatedly, feeds containing carefully measured concentrations of sulphadimidine or ionophores (monensin, lasalocid) may be used. Provide feed and water off the ground and minimize opportunities for animals to access surface water and spilt feed. There is no risk of spread of infection from one species to another (goats to sheep or cattle), and therefore no value in separating sheep from goats as part of control or prevention measures. Rotation of pens either between sheep and goats or to allow spell periods between successive uses, may help reduce build up of oocysts.