Detection and genetic analysis of infectious spleen and kidney necrosis virus (ISKNV) in ornamental fish from non-clinical cases: First report from India

Abstract

Infectious spleen and kidney necrosis virus (ISKNV), a type species of the genus Megalocytivirus, poses a threat to ornamental fish trade as most cases show nonspecific symptoms, thus making timely diagnosis challenging. Apparently health molly (Poecilia sphenops) and angelfish (Pterophyllum scalare) collected from two distinct geographic localities of India were screened for four genera under Iridoviridae, Megalocytivirus i.e, ISKNV, turbot reddish body iridovirus (TRBIV) and red seabream iridovirus (RSIV); ranaviruses and Singapore grouper iridovirus; and Lymphocystivirus through molecular approach. In total seven numbers out of 35 samples (20%), ISKNV genome fragments were detected. A PCR assay using major capsid protein (MCP) gene was standardised to detect and differentiate infections within the Megalocytivirus genus, even without aid of sequencing. This forms the first report of ISKNV infection in ornamental fish from India. Moreover, the ISKNV infection was confirmed by PCR and sequence analysis of MCP and ATPase genes. The sequence of these genes showed that Indian isolate being 99-100% similar to the complete genome or reference strain of ISKNV. Phylogenetic reconstruction demonstrated the present strain belonging to ISKNV genotype I. Furthermore, structural stability of the MCP revealed this strain was more stable than ISKNV genotype II, RSIV and TRBIV at 25{degrees}C and pH 7.0. Thus, strong pan-India surveillance is recommended to reduce trade risk.