Reassortant viruses threatening fish aquaculture

Abstract

Aquaculture provides more than half of fish destined for human consumption worldwide. In aquaculture, infectious diseases triggered by viruses are amongst the major cause of mortality of farmed fish. The cohabitation of different virus strains in the same geographical area opens the possibility to natural reassortment. Virus reassortment is a characteristic recombination process of segmented viruses in which different viruses merge their genome by the shuffling of complete segments. This is possible when two or more viral strains are cohabitating into a single host, boosting their probability to concatenate their viral cycles, getting to pack segments from distinct parental strains. Cohabitation of different viruses in a geographical area, and therefore the possibility of natural reassortment, has been aided by the increment in the transport of eggs and larvae between facilities around the world. Reassortant viruses have been described to show special tropisms for fish species opposed from those affected by parental virus strains, entailing an emerging threat for aquaculture but also for wild populations. To date, outbreaks of reassortant strains of infectious pancreatic necrosis virus, nodavirus (NNV), infectious salmon anaemia virus and tilapia lake virus have been described. Unfortunately, only the characterization of reassortant NNV has been explored. The aim of this review is compiling the information available concerning reassortant viruses affecting fish species of relevance for aquaculture highlighting their potential impact for the sector. Additionally, recent research advances in host-NNV interaction are also included.