Co‐infection of infectious myonecrosis virus and Enterocytozoon hepatopenaei in Penaeus vannamei farms in the east coast of India

Abstract

Diseases caused by infectious pathogens are common in grow-out shrimp culture. The emergence of two shrimp diseases viz. infectious myonecrosis virus (IMNV) and hepatopancreatic microsporidiosis which is caused by Enterocytozoon hepatopenaei (EHP), has resulted in substantial economic losses to shrimp farmers in India. Based on previous reports of IMNV disease outbreaks in a small cluster of farms, an attempt was made to study the horizontal spread of this disease along the east coast of India, by active surveillance in four districts of Andhra Pradesh and Tamil Nadu. The present investigation reports the cases of co-infection of IMNV and EHP in Penaeus vannamei shrimp farms in India. Among the 12 ponds investigated, shrimp in four ponds were infected only with IMNV; a single pond was infected with EHP and seven ponds with shrimp harbouring both the pathogens. Shrimp affected by IMNV exhibited white discolouration on the abdominal segments. The EHP-positive pond did not exhibit any apparent clinical signs. The co-infected shrimp exhibited clinical lesions of both IMNV and EHP. Histopathology revealed that the hepatopancreas of shrimp with signs of slow growth, showed cytoplasmic developmental stages of EHP in the tubular epithelial cells and sloughing of infected cells, releasing spores in the tubular lumen whereas, IMNV affected shrimps had shredding of muscle fibres, coagulative necrosis with haemocytic infiltration in striated muscles and hypertrophy of lymphoid organ (LO). Both the infections were further confirmed by PCR as well as sequencing.