E. necatrix

This species has a particular feature compared with the six other species in chickens: it performs its merogony in the middle intestine on either side of Meckel's diverticulum and its gamagony in the caeca.

The sporozoites invade the lamina propria before reaching the epithelial cells of the crypts of Lieberkühn where they develop. The tissue lesions appear between days 4 and 7 p.i., and they are due to the second-generation meronts (meronts II) which give the intestine a characteristic pepper-and-salt appearance.

The lesions are accompanied by distension throughout the length. The intestine may be distended to twice its normal diameter in heavy infections. The white dots visible through the wall of the unopened intestine are filled with enormous meronts II which may reach 60 to 80 mm in diameter. The diagnosis is facilitated by the presence of these lesions which are characteristic of the species. Although easily recognisable on the mucousal side, the meronts are so deep in the mucous membrane that it is easier to extract them by digging into the serous membrane in order to observe them. Meronts of other intestinal species do not exceed 30 mm in diameter. The most severe lesions are observed on release of the merozoites II. The intestinal lumen may then contain fresh blood, or partially coagulated blood and mucous.
The merozoites II migrate to the caeca and develop into third-generation meronts and gamonts. The meronts II, which are small, are confined to the epithelial cells. They contain few merozoites, and cells hosting three or four meronts are often observed. Gamagony and the oocysts' development take place in the caeca without producing distinctive lesions. Scraping the caeca shows oocysts which look like those of E. tenella but are more rounded.

The prepatent period is six days.

The clinical symptoms most often observed are a decrease in feed consumption and weights, bloody faeces and the decline of egg production in laying hens. Death may occur before clinical signs appear. With moderate infections, the symptoms last longer than with E. tenella infections because the sporozoites and merozoites do not all develop at the same time. Healing of the intestine may require several days. The recovery of the chickens is slow, maybe 15 days or more. Chickens which survive the infection become resistant to reinfection.

Score 0: No macroscopic lesion.

Score 1: Small petechiae and white spots can easily be observed on the serous membrane. The damage is difficult to see on the mucousal side. 

Score 2: Numerous petechiae are visible on the serous membrane; the middle intestine is slightly distended.

Score 3: Substantial haemorrhages in the intestinal lumen; the serous membrane is covered with red petechiae and/or white spots. The serous membrane is rough and thickened with numerous punctiform haemorrhages. The normal intestinal contents have disappeared: distension extends to the lower half of the small intestine. The chickens are prostrate, and stop feeding and drinking. Blood appears in the feaces. The zootechnical consequences are significant: weight loss and poor feed conversion.

Score 4: The extent of the haemorrhages gives the intestine a dark colour: the intestinal contents consist of red or brown mucous. Distension may spread along the entire length of the intestine. Score 4 is assigned to dead birds.