Pathological manifestation of the Acanthocephalus dirus in Thunnus albacares

Objective: To describe the pathological manifestation of the Acanthocephalus dirus (A. dirus)\udinfestation in Thunnus albacares (T. albacares) from southeast coast of India.\udMethods: The parasite-infested fishes were collected from Nagapattinam landing centre of\udTamil Nadu from southeast coast of India. The Acanthocephala morphology, gross pathology,\udhistopathology and histochemistry were investigated.\udResults: T. albacares were severely infested with A. dirus, the group of Acanthocephala\udattached to the posterior region of the intestine. The adult worm proboscis was cylindrical\udand the length and width ranging between 2.7–6.4 mm and 0.8–1.3 mm, respectively.\udHistopathologically, the infested intestinal mucosal epithelium, stratum granulosum, lamina\udpropria, muscular and serosa layers were highly degraded. The lesions were infiltrating with\udbasophil-like inflammatory cells. The parasite-affected lesions were histochemically positive\udfor alcian blue, azo dye, toluidine blue and oil red O.\udConclusions: This is the new host for the parasite A. dirus in T. albacares. On the basis of\udhistological and histochemical findings, the lesions were highly damaged due to the parasitic\udinfestation. The high density of the parasite and severe penetration of the proboscis into the\udintestinal tissues are the main reason for the pathogenicity in the host