Evidence for Cross-Species Transmission of Covert Mortality Nodavirus to New Host of Mugilogobius abei.

Jing Wei Hao,Jun Li,Guang Ming Fu,Xiao Ping Li,Xiu Hua Wang,Xiao Dong Bian,Shuang Liu,Song Wen Sang,Qing Li Zhang,Ting Ting Xu

doi:10.3389/fmicb.2018.01447

Abstract

Viral covert mortality disease (VCMD), caused by covert mortality nodavirus (CMNV), is a newly emerging disease affecting most cultured shrimp and other crustaceans, but not fish. However, we discovered for the first time that Mugilogobius abei, a common marine fish collecting from shrimp farming ponds and surrounding coastal waters in China, was tested to be CMNV positive based on reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay. Further investigation based on the quantitative RT-LAMP assay indicated that 39% individuals of sampled M. abei were CMNV positive. Sequencing and alignment of sequences revealed that the partial RNA-dependent RNA polymerase gene of CMNV isolated from M. abei shared 98% homology with that from the original CMNV isolates. Histopathological analysis showed that CMNV infection in M. abei could induce extensive skeletal muscle necrosis, nervous tissue vacuolation in retina of eye and cerebellum of brain. Positive signals were verified in skeletal muscle, eye, brain and intestine by in situ hybridization (ISH) with CMNV probes. Under transmission electron microscope (TEM), CMNV particles were further visualized in the cytoplasm of neurogliocytes, granulocytes and myocytes in the CMNV positive samples diagnosed by ISH. All findings suggested that CMNV, a typical alphanodavirus originated from shrimp, could switch their hosts to fish by cross-species transmission. Meanwhile, the results reminded us to pay close attention to the high risk of CMNV to use fish as intermediate or new host as well as potentially spread or cause epidemic among cultured marine fish.

Highlights

Nodamura virus (NoV) was the first identified species in the Nodaviridae and it was originally isolated from mosquitoes (Culex tritaeniorhynchus) sampled from the village of Nodamura near Tokyo of Japan in 1956 (Scherer and Hurlbut, 1967; Scherer et al, 1968; Tesh, 1980)
Following the clue of covert mortality nodavirus (CMNV) positive of the M. abei sample determined by reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay, we demonstrated the naturally infection of M. abei with CMNV based on a comprehensive investigation by using molecular histopathological, in situ hybridization (ISH) and transmission electron microscopic (TEM) assays in the present study
These findings indicated that all 6 M. abei samples were CMNV positive despite of their resources (Figure 1)

Summary

Introduction

Nodamura virus (NoV) was the first identified species in the Nodaviridae and it was originally isolated from mosquitoes (Culex tritaeniorhynchus) sampled from the village of Nodamura near Tokyo of Japan in 1956 (Scherer and Hurlbut, 1967; Scherer et al, 1968; Tesh, 1980). Over 25 members have been identified, which belong to two Genus, Alphanodavirus. Cross-Species Transmission of Covert Mortality Nodavirus and Betanodavirus (Andrew et al, 2011). All alphanodaviruses were isolated in nature from insects and NoV is the type species of the alphanodavirus genus (Johnson et al, 2003). The alphanodaviruses can infect insects, whereas NoV is a unique one that can lethally infect mammals (Scherer et al, 1968; Johnson et al, 2004). All betanodaviruses were isolated from larvae, juvenile or adult marine fish, in which they cause “viral nervous necrosis” or “viral encephalopathy and retinopathy” associated with abnormal behavior and high mortalities (Andrew et al, 2011). Previous reports confirmed that betanodaviruses are pathogenic to fish and can result in significant problems for the marine fish aquaculture industry (Chi et al, 2001; Ucko et al, 2004; Walker and Winton, 2010)

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