E. maxima

E. maxima is located in the middle part of the intestine, on either side of Meckel's diverticulum, and frequently ascends into the duodenum. In severe infections, it may extend to the distal ileum as far as the junction of the caeca. The prepatent period is five to six days.

The lesions are characterised by petechiae, which are easier to recognise on the serous membrane than on the mucous membrane. The presence of orangey mucus in the digestive contents demonstrates the involvement of the mucous membrane.

The degree of pathogenicity does not always correlate with the severity of the lesions. First- and second-generation meronts are small and contain only a dozen merozoites. Their development in the epithelial cells at the peak of the villi does not have any serious effects on the chicken. However, the very large gamonts, in hypertrophic cells, occupy a sub-epithelial position and may spread more deeply during severe infections. Tissue damage is therefore mainly due to gamogony. It is delayed and of short duration.

The lesions disappear as rapidly as they appear.

The effects of an E. maxima infection are significant for pigmentation and growth.

An E. maxima infection is followed by the establishment of strong and lasting immunity.

According to Johnson and Reid (1970) the lesions are difficult to score for this species. The lesion scores should be established six or seven days after infection.

Score 0: No macroscopic lesion.

Score 1: Small red petechiae may appear on the serous membrane of the middle intestine. There is no distension or thickening of the intestine, although small quantities of orange mucous may appear.

Score 2: The serous membrane may be punctuated by numerous red petechiae. The intestine may be full of orange mucous and may or may not be distended. The intestinal wall is thickened.

Score 3: The intestine is distended and the wall is thickened. The mucous membrane is rough and the intestinal contents contain pinpoint clots and mucous.

Score 4: The intestinal wall may be distended throughout almost its entire length. The intestines contain numerous blood clots and digested red blood cells which give them a characteristic colour and putrid odour; the wall is greatly thickened. Score 4 is given to dead chickens.