Histopathology in Leuciscus cephalus (Pisces: Cyprinidae) resulting from infection with Pomphorhynchus laevis (Acanthocephala).

The histopathology present in Leuciscus cephalus Risso 1826 from the River Po, naturally infected with the acanthocephalan Pomphorhynchus laevis Müller 1776, was studied and described. The parasite was only found within the host's digestive tract, and a density of 10 P. laevis per square centimeter was common. On histological examination it was noticed that both male and female parasites penetrated deeply through all the layers of the host digestive tract by means of their slender neck, bulb and proboscis; thus the bulb and proboscis become encapsulated beneath the serosa and mesentery. As a result, the presence of a capsule was noticed on the external surface of the host digestive tract. P. laevis caused local damage to the intestinal wall, and the parasite elicited an intense host reaction. The response of L. cephalus at the attachment site of the acanthocephalan was hyperplasia of host connective tissue, with cellular infiltration. In a few hosts, the presence of a fibrous nodule on the outer surface of the alimentary canal was observed.