Characterization of a Novel Orthomyxo-like Virus Causing Mass Die-Offs of Tilapia.

Eran Bacharach,Adam Nitido,James Ng,Asaf Berkowitz,Toby Bloom,Jorge Del Pozo,Rachel Zamostiano,Mady Hornig,Sandra Cathrine Abel Nielsen,Hugh Ferguson,Michael C Zody,W Ian Lipkin,Nora C Toussaint,Japhette Esther Kembou Tsofack,Thomas Briese,Avi Eldar,André Corvelo,Nischay Mishra

doi:10.1128/mbio.00431-16

Eran Bacharach, Adam Nitido + Show 16 more

Open Access

https://doi.org/10.1128/mbio.00431-16

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Abstract

ABSTRACTTilapia are an important global food source due to their omnivorous diet, tolerance for high-density aquaculture, and relative disease resistance. Since 2009, tilapia aquaculture has been threatened by mass die-offs in farmed fish in Israel and Ecuador. Here we report evidence implicating a novel orthomyxo-like virus in these outbreaks. The tilapia lake virus (TiLV) has a 10-segment, negative-sense RNA genome. The largest segment, segment 1, contains an open reading frame with weak sequence homology to the influenza C virus PB1 subunit. The other nine segments showed no homology to other viruses but have conserved, complementary sequences at their 5′ and 3′ termini, consistent with the genome organization found in other orthomyxoviruses. In situ hybridization indicates TiLV replication and transcription at sites of pathology in the liver and central nervous system of tilapia with disease.

Highlights

Tilapia are increasingly important to domestic and global food security
Ferguson and colleagues described a disease in farmed Nile tilapia in South America that differed from that caused by the Israeli virus in that pathology was focused in the liver rather than in the central nervous system [12]
Overlapping predicted open reading frames (ORFs) in contigs from different assemblies were used to correct for frameshift errors and to infer the longest possible ORF

Summary

Introduction

Tilapia are increasingly important to domestic and global food security. Comprising more than 100 species, Nile tilapia (Oreochromis niloticus) is the predominant cultured species worldwide [1]. Eyngor and colleagues investigated outbreaks in Israel and reported a syndrome comprising lethargy, endophthalmitis, skin erosions, renal congestion, and encephalitis and demonstrated transmissibility of disease from affected to naive fish. They cultured a virus from infected fish in E-11 cells (cloned subculture of snakehead fish cell line), demonstrated sensitivity to ether and chloroform, and obtained a sequence specific for disease through cDNA library screening that predicted a 420-amino-acid (aa) open reading frame (ORF) with no apparent homology to any nucleic acid or protein sequence in existing databases. Our findings suggest that TiLV represents a novel orthomyxo-like virus and confirm that it poses a global threat to tilapiine aquaculture [12, 13]

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