Clinical Signs

Sick birds huddle together, adopt a ball position, their eyes half-closed or closed, their dirty feathers ruffled, and their wings drooping. This state is accompanied by a loss of appetite, weight loss and diarrhoea, either bloody or not, depending on the species responsible. These symptoms are not specific to coccidiosis but the farmer or farm technician links them to the disease immediately if they occur in chicks aged three to four weeks.

Two types of coccidiosis may be observed :

1. Caecal coccidiosis due to E. tenella. As the caeca do not play a major role in digestive function, this coccidiosis is only important during a clinical disease. It is then characterised by loss of appetite and bloody diarrhoea and the consequences may be devastating because of the high resulting mortality rates.

2. Intestinal coccidiosis due to any of the other six species. They are generally less severe, although mortality or blood in droppings may be observed in infections due to E. maxima, E. necatrix and E. brunetti.

Clinical intestinal coccidiosis is characterised by loss of appetite (even anorexia), poor zootechnical performance (retarded and uneven growth and weight loss), or diarrhoea, varying with the degree of infection. Parasitic development may disturb digestive function as slowed gut movement, intestinal oedema, disorders of absorption and use of nutrients.

Absorption of nutrients is disturbed throughout the intestine but mainly in the duodenum and jejunum. Intestinal coccidiosis may also damage the general metabolism (e.g. protein synthesis) and affect laying (laying ceases, or eggs are smaller or discoloured to some degree, with a thinner shell) or production (increase in the feed consumption index, poor pigmentation in yellow chickens, poor uniformity, development of pathogenic contaminants in the digestive flora).

Subclinical infections are not without their impact on the physiology of the host and may be the cause of poor zootechnical performance and/or economic losses because of the poor quality of the product such as depigmentation (yellow birds look pale), and poor uniformity.

With vaccination and/or use of efficacious anticoccidials, deaths due to coccidiosis are rare; the disease is characterised by poor growth, a poor feed conversion ratio (FCR), and intestinal lesions which are sometimes difficult to identify.