Histopathology, immunohistochemistry and ultrastructure of the intestine of Leuciscus cephalus (L.) naturally infected with Pomphorhynchus laevis (Acanthocephala)

The histopathology, immunohistochemistry and ultrastructure of the alimentary canal of chub Leuciscus cephalus (L.), from the River Brenta, naturally infected with the acanthocephalan Pomphorhynchus laevis Müller 1776, was studied and described. Of 62 chub specimens examined, 54 (87%) were infected with P. laevis; the intensity of infection ranged from 5 to 130 parasites per host, and a density of 8 P. laevis per square centimetre was common. Examination of histological material of infected chubs revealed that both male and female acanthocephalans deeply penetrated all layers of the gut wall by means of their slender neck, bulb and proboscis. As a result, a capsule was formed around the bulb and proboscis on the external surface of the host intestine. In parasitized chub, four main types of reaction against the body of acanthocephalan were recognised. P. laevis caused local damage to the intestinal wall, eliciting catarrhal-erosive enteritis in the lumen and a fibroblastic-collagenous and fibro-epithelioid encapsulation in its thickness with tissue zonation according to the depth of parasite penetration. Furthermore, eosinophilic granular cells (EGCs) within the inflammatory tissue were identified by immunohistochemical methods and use of transmission electron microscopy.