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China

Research—New Iridescent Virus

 

From Abstract: A newly discovered iridescent virus that caused severe disease and high mortality in farmed Litopenaeus vannamei in Zhejiang, China, has been verified and temporarily labeled “Shrimp Hemocyte Iridescent Virus” (SHIV).  Histopathological examination revealed basophilic inclusions and pyknosis in hematopoietic tissue and hemocytes in gills, hepatopancreas, periopods and the tail muscle.  Using viral metagenomics sequencing, researchers obtained partial sequences, annotated as potential iridoviridae.  Phylogenetic analyses using amino acid sequences of major capsid protein (MCP) and ATPase revealed that it is a new iridescent virus, but it does not belong to the five known genera of Iridoviridae.  Transmission electron microscopy showed that the virus exhibited a typical icosahedral structure with a mean diameter of 158.6 ± 12.5 nm.  Challenge tests of L. vannamei via intermuscular injection, per os and reverse gavage all exhibited 100% cumulative mortality rates.  The in situ hybridization showed that hemopoietic tissue, gills and hepatopancreatic sinus were positively reacting tissues.  Additionally, a specific nested PCR assay was developed.  PCR results revealed that L. vannamei, Fenneropenaeus chinensis and Macrobrachium rosenbergii were SHIV-positive, indicating a new threat to the shrimp farming industry in China.

 

Observation and Detection of Diseased Shrimp: The samples of L. vannamei collected from the pond with massive die-offs exhibited obvious clinical signs, including empty stomach and guts, pale hepatopancreas and soft shells.  The shrimp samples were tested and demonstrated to be free of whitespot syndrome virus (WSSV), yellowhead virus (YHV), Taura syndrome virus (TSV), infectious hypodermal and hematopoietic necrosis virus (IHHNV) and Vibrio parahaemolyticus.

 

Discussion: In partially infected shrimp, the clinical symptoms of SHIV infection include slight loss of color, empty stomach and guts, soft shells and slightly reddish bodies in one-third of individuals.  These symptoms are not similar to those caused by the infection with putative iridovirus in penaeid shrimp.

 

Conclusions: Through isolation, reinfection and histopathological characterization, researchers say that SHIV is a new virus in the Iridoviridae family and a pathogen of L. vannamei.  Additionally, they developed an ISH assay and a nested PCR method for the specific detection of SHIV.

 

Sources: 1. The Shrimp List (a mailing list for shrimp farmers).  Subject: [Acuacultura-SLA] SHIV Vannamei.  From: Juan Aguirre (jxaquirre58@yahoo.com).  September 26, 2017.  2. PubMed.  Characterization of a New Member of Iridoviridae, Shrimp Hemocyte Iridescent Virus (SHIV), Found in White Leg Shrimp (Litopenaeus Vannamei).  A Free PMC Article (Full Text Free).  Liang Qiu, Meng-Meng Chen, Xiao-Yuan Wan, Chen Li, Qing-Li Zhang, Ruo-Yu Wang, Dong-Yuan Cheng, Xuan Dong, Bing Yang, Xiu-Hua Wang, Jian-Hai Xiang and Jie Huang (Corresponding Author, nc.ca.irfsy@eijgnauh, Qingdao Key Laboratory of Mariculture Epidemiology and Biosecurity, Key Laboratory of Maricultural Organism Disease Control, Ministry of Agriculture, Function Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao, 266071, China).  Sci Rep. (11834. doi: 10.1038/s41598-017-10738-8, PMID: 28928367).  September 19, 2017.

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