AUTHOR=Xu Tingting , Fan Yuding , Jia Tianchang , Wang Chong , Wang Wei , Li Jun , Zhang Qingli , Yao Cuiluan 

TITLE=Investigation on Natural Infection of Covert Mortality Nodavirus in Large Yellow Croaker, Larimichthys crocea

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 9 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.789128

DOI=10.3389/fmars.2022.789128

ISSN=2296-7745

ABSTRACT=Covert mortality nodavirus (CMNV) recently became more prevalent, severely affecting farmed shrimps, as well as other invertebrates and teleost fish, in the coastal areas of China. For better understanding of its prevalence and susceptibility of CMNV in large yellow croaker Larimichthys crocea, an epidemiological survey was carried out in the main producing areas (Ningbo, Zhejiang, China, and Ningde, Fujian, China) and its offshore feeding grounds in the Southern Yellow Sea. Cultured L. crocea individuals showed clinical symptoms such as anorexia, abnormal swimming was collected and diagnosed for CMNV infection by using RT-nPCR assay. The positive rates for CMNV in the collected L. crocea samples from Ningbo, Ningde, and the Yellow Sea were 14.29% (4/28), 20.00% (7/35) and 16.67% (1/6), respectively. Furthermore, CMNV diagnosis using Taqman RT-qPCR yielded positive rates of 25.00% (7/28), 22.86% (8/35) and 16.67% (1/6) respectively in the above-mentioned samples, and with a range of 12.73 to 3108.33 of CMNV copy numbers/μg of total RNA. Phylogenetic tree analysis based on the RdRp and capsid protein genes showed that CMNV isolates from L. crocea samples were clustered tightly with the original isolate of CMNV from Penaeus vannamei. The histopathological studies indicated that severe cellular necrosis occurred in the heart, liver, spleen, eye, and gill of naturally infected fish. Stronger positive signals for CMNV specific-probes appeared in the necrotic cells and tissues in the in situ hybridization (ISH) analysis. Transmission Electron Microscope (TEM) revealed the presence of many 30 nm in diameter of CMNV-like viral particles. The purified CMNV suspension could cause a significant cytopathic effect (CPE) in epithelioma papilloma cyprini (EPC) cells, and resulted in forming typical inclusion bodies, as well as visible CMNV particles around the lysed EPC cells under the TEM. Taken together, all results of the present study demonstrated that L. crocea is susceptible to CMNV. The prevalence of CMNV and its potential impacts on the wild population of L. crocea deserve further investigations.