Classical Runt Deformity Syndrome Cases in Farmed Penaeus vannamei Along the East Coast of India

Abstract

Infectious hypodermal and haematopoietic necrotic viral disease caused by the infectious hypodermal and hematopoietic necrosis virus (IHHNV), a member of the Family Parvoviridae, Genus Penstyldensovirus, is the smallest known shrimp penaeid viruses. This viral disease poses a threat to shrimp farming as it causes runt deformity syndrome in Penaeus vannamei and thereby causing economic loss to the farmers. An analysis was carried out in various P. vannamei farms (n=350) along the East Coast of India from 2013-2018, and it was found that 30 farm samples positive for IHHNV. The shrimps in these farms exhibited classical IHHNV clinical signs like deformed sixth abdominal segment, deformed rostrum, cuticular roughness and wrinkled antennae. There was a wide size variation in growth among the affected farms. These samples on histological analysis showed prominent intranuclear, Cowdry type A inclusion bodies characteristic of IHHNV. The inclusion bodies observed were in the tissues of the ectodermal hypodermal epithelium of fore- and hindgut, mesodermal origins like haematopoietic organs, antennal gland and lymphoid organ. All the samples were positive for IHHNV by PCR using OIE primers. An experiment was conducted in P. vannamei (n=100) to study the disease transmission wherein, the animals were fed orally by the infected IHHNV tissue, and it was found that the animals got the infection by day five. The experimentally infected animals did not exhibit the classical IHHNV symptoms as that was seen in animals in the farming conditions.