Pathological manifestation of the Acanthocephalus dirus in Thunnus albacares

ObjectiveTo describe the pathological manifestation of the Acanthocephalus dirus (A. dirus) infestation in Thunnus albacares (T. albacares) from southeast coast of India.MethodsThe parasite-infested fishes were collected from Nagapattinam landing centre of Tamil Nadu from southeast coast of India. The Acanthocephala morphology, gross pathology, histopathology and histochemistry were investigated.ResultsT. albacares were severely infested with A. dirus, the group of Acanthocephala attached to the posterior region of the intestine. The adult worm proboscis was cylindrical and the length and width ranging between 2.7–6.4 mm and 0.8–1.3 mm, respectively. Histopathologically, the infested intestinal mucosal epithelium, stratum granulosum, lamina propria, muscular and serosa layers were highly degraded. The lesions were infiltrating with basophil-like inflammatory cells. The parasite-affected lesions were histochemically positive for alcian blue, azo dye, toluidine blue and oil red O.ConclusionsThis is the new host for the parasite A. dirus in T. albacares. On the basis of histological and histochemical findings, the lesions were highly damaged due to the parasitic infestation. The high density of the parasite and severe penetration of the proboscis into the intestinal tissues are the main reason for the pathogenicity in the host.