Investigating the mechanism of heat-shock protection in ISKNV-infected tilapia brain cell line

Abstract

Infectious spleen and kidney necrosis virus (ISKNV) is the causative agent of a fatal disease in many fish species, resulting in mass mortalities and significant economic losses. Since its introduction to Ghana in late 2018 and in the absence of effective vaccines, the crude practice of heat-shock treatment (HST) on deliberately exposed cultured tilapia fingerlings was widely adopted by farmers to control the disease in Ghana with some apparent success. This study investigated the interplay between the expression of heat-shock proteins (HSPs) and viral replication during ISKNV infection. An in vitro experimental challenge study which involved deliberate infection with ISKNV and subsequent exposure of primary Oreochromis niloticus (tilapia) brain cell lines to HST at 48 hours post-infection was carried out. The ISKNV was confirmed by Oxford Nanopore Sequencing of the full major capsid protein (MCP), while the species identity of the cell line was confirmed by Sanger sequencing of the cytochrome C oxidase (COX1) genomic region. The test groups and control groups were screened at various time points for viral proliferation and HSP marker expression using quantitative PCR (qPCR). Exposure to heat shock significantly increased HSP 90 and 47 expressions by fourfold and sixfold, respectively, with a concomitant 10-fold decrease in viral load as compared to the non-heat-shock group. Viral apoptosis gene ORF 005L was significantly downregulated following increase in HSPs expression. This initial finding implies that HST may play an important role in suppressing viral replication through the apoptosis regulatory gene ORF 005L. This information will contribute to the understanding of the beneficial effect of heat-shock therapy used in control of the viral pathogen in aquaculture. Further studies in controlled in vivo experiments will give more clarity to the general effect of this treatment on tilapia growth and ISKNV persistence in infected fish populations.