Detection of nervous necrosis virus RGNNV genotype in pearl gentian grouper (Epinephelus lanceolatus male x E. fuscoguttatus female) fry imported to Thailand

Abstract

Nervous necrosis virus (NNV) is a deadly virus that affects more than 120 fish species worldwide, but there is little information about it in Thailand. In August 2019, a population of pearl gentian grouper fry imported to Thailand experienced mass mortality. The diseased fish exhibited darkening, floating on the water surface, sleepy behaviour, and erratic swimming. We received a set of samples for disease diagnosis. PCR analysis revealed that these samples were positive for NNV but negative for Megalocytivirus ISKNV and Ranavirus. Sequencing the viruss genome and phylogenetic analysis revealed that it is a member of the red-spotted grouper nervous necrosis virus (RGNNV) genotype. In situ hybridization using an NNV-specific probe revealed localization of the virus in the vacuolation lesions of the central nervous system (brain and spinal cord) and the retina of infected fish. The virus was successfully isolated from tissue homogenate from diseased fish using the E-11 cell line. This study identified NNV (RGNNV genotype) as a virus associated with massive die-offs in imported pearl grouper fry in Thailand. Considering the infectious nature of the virus and its broad host range, appropriate biosecurity measures are needed to prevent any loss to the marine aquaculture industry. HighlightsO_LIThis study reports detection of NNV in grouper larvae imported to Thailand C_LIO_LIThe virus was assigned to the RGNNV genotype, which is the most extensively distributed genotype C_LIO_LIHistopathology revealed a pathognomonic lesion of NNV C_LIO_LIISH using an NNV-specific probe revealed localization of NNV in the CNS and retina C_LIO_LIThe virus was successfully propagated from diseased fish using the E-11 cell line C_LI