Diversity of viruses in freshwater fish mortality events

  

Soumesh K. Padhi 1,2, Vikash K. Singh 1,3, Isaiah Tolo 1,2, Sunil K. Mor 1,3, Nicholas B. D. Phelps 1,2

1 Minnesota Veterinary Diagnostic Laboratory and Department of Veterinary Population Medicine, University of Minnesota, 1333 Gortner Avenue, St. Paul, MN, 55108; 2 Minnesota Aquatic Invasive Species Research Center and the Department of Fisheries, Wildlife, and Conservation Biology, College of Food, Agriculture, and Natural Resource Sciences, University of Minnesota, St. Paul, MN 55108

ABSTRACT

Viral metagenomics has emerged as the most advanced approach for conducting quantitative surveys to explore the diversity of viral communities without the need for host-contextualized cultivation or universally conserved marker genes. Metagenomics also has relevance for improving diagnostic approaches and the discovery of novel viruses affecting fish aquaculture. The broad-spectrum understanding of viral diversity to the ecological and evolutionary patterns is considered an essential factor for the investigation of emerging viruses. Here we present a metagenomic analysis comparing viral communities present in wild North American fishes from naturally occurring mortality events. The goal of this study was to analyze virome composition, diversity, and abundance with respect to host species, and tissue tropism. We have collected samples from 39 mortality events representative of seven fish families i.e., Centrarchidae, Clupeidae, Cyprinidae, Esocidae, Ictaluridae, Moronidae, Percidae. The brain, gill, kidney, and spleen tissue homogenates were used to extract total nucleic acid. The RNA and DNA libraries were sequenced using HiSeq 2500 High-output 2x125-bp run. The raw sequenced data were analyzed using an in-house bioinformatics pipeline. Viral reads were classified into known orders and families with reference to the NCBI non-redundant protein database. Among all fish species sampled, we found the presence of following viral families: Anelloviridae, Astroviridae, Circoviridae, Herpesviridae, Iridoviridae, Nodavirdae, Parvoviridae, Picornavirales, Poxviridae, Reoviridae, and Totiviridae. The Herpesvirales, Nodavirdae, and Totiviridae were specific to common carp (Cyprinus carpio) fish mortality events. The difference in viral composition in different tissue types was observed. Interestingly, a novel poxvirus was detected in black crappie (Pomoxis nigromaculatus) mortality samples. Several divergent viruses have been discovered, and further analysis is under active investigation. Overall, this study highlights viral diversity in fish species that are to date unexplored, which provide insights into virus ecology and help inform the rational development of future prevention and control strategies for major infectious disease threat.