E. acervulina

E. acervulina is without doubt the most widespread species of coccidia in the chicken. Its prepatent period is four days. It colonises the duodenal loop and the very characteristic lesions, white ladder rung spots (stuffed with gamonts and oocysts), may spread into the jejunum and ileum in severe infections.

This species is not very pathogenic in terms of mortality. The stages of development are localised in the epithelial cells above the nucleus. This superficial location does not induce losses from death, however, E. acervulina may be the cause of substantial morbidity and this species is well known for promoting the establishment of Clostridium perfringens.

After an experimental infection, the disease is characterised by reduction of feed consumption (or even anorexia), decrease in weight gain and the appearance of diarrhoea three days after the infection (3 days p.i.). On the fourth day p.i., the oocysts are excreted with the droppings. The duration of the excretion or patent period is seven to nine days.

The weight losses observed are not only due to the decrease of feed consumption but also to the interference of the parasites with the digestion, absorption and digestive use of nutrients. During weak or moderate infections, the reduction in absorption at the duodenal level may be compensated for by an increase in absorption in the jejunum or even in the ileum.

A dose of 5 x 10⁵ sporulated oocysts of E. acervulina may cause significant losses of proteins and other nutrients and may, because of poor feed efficacy, affect live weight very severely although not causing deaths.

A very weak dose of only 200 oocysts has no effect on zootechnical performance (live weight, feed conversion index) but may cause poor pigmentation in yellow chickens, resulting in the downgrading of the product and a substantial loss for the farmer. This poor pigmentation is due to impaired absorption of carotenoid pigments; it depends on the severity of the infection. Measurement of plasma or serum colour is a criterion which can be used to judge the efficacy of anticoccidials in the control of E. acervulina infection.

Immunity against this species develops slowly.

Score 0: No macroscopic lesion.

Score 1: The white patches are scattered and confined to the duodenum. They contain oocysts in the process of formation. These lesions are elongated, transversal and at a 90 degree angle to the main axis of the intestine like the rungs of a ladder. These lesions may be seen on the serous membrane and mucous membrane of the duodenum. There may be a maximum of up to 5 lesions per cm². An infection scored 1 has no impact on zootechnical performance but causes slight discoloration of the serous membrane and depigmentation of the skin in yellow chickens.

Score 2: The lesions are much closer together but not coalescent; they may extend to 20 cm below the duodenum in 3-week-old chicks. The intestinal walls are not thickened. The contents of the digestive tract are normal.  A slight reduction in weight gain may be observed.

Score 3: The lesions are more numerous, and small. They become coalescent and the mucous membrane appears to be covered with a coating. The intestinal wall is thickened and the contents are liquid. The lesions may extend to the diverticulum of the yolk sac or Meckel's diverticulum. The changes in the intestinal wall result in disorders of absorption, hence the appearance of diarrhoea, the loss of colour in the serous membrane and consequences for zootechnical performance.

Score 4: The mucous membrane is greyish. The lesions form completely coalescent colonies. Congestion may be confined to little petechiae or, during very severe infections, the entire mucous membrane may be bright red. The individual lesions in the upper part of the intestine can no longer be distinguished. The typical ladder rung lesions appear in the middle part of the intestine. The intestinal walls are greatly thickened, and the intestine is filled with a creamy exudate which contains a large number of oocysts. Score 4 is assigned to chicks which die of coccidiosis.