Characterization of a new member of Iridoviridae, Shrimp hemocyte iridescent virus
(SHIV), found in white leg shrimp (Litopenaeus vannamei)
Iridoviridae is a family of large icosahedral viruses with diameters in the range from 120 to 300 nm, which may even be up to 350 nm (e.g. genus Lymphocystivirus). e virion core contains a single linear double stranded DNA (dsDNA) molecule of 140–303 kbp, a value that includes both unique and terminally redundant sequences. is family of viruses is characterized by its wide host spectrum, including invertebrates (such as insects), poikil- othermic vertebrates, such as fish, amphibians and reptiles. Based on their particle sizes, host range, DNA cross-hybridization, the presence of a methyltransferase, and the sequence of major capsid protein (MCP), family Iridoviridae is subclassified into five genera, including Iridovirus, Chloriridovirus, Ranavirus, Lymphocystivirus, and Megalocytivirus. Viruses of the genera Iridovirus and Chloriridovirus primarily infect insects while the spe- cies of genera Megalocytivirus and Lymphocystivirus are associated with sh hosts. Viruses of genus Ranavirus are known to cause disease in amphibians, reptiles, and n sh. Furthermore, it was reported that some viruses of Iridoviridae, such as a Irido-like virus in marine crab Macropipus depurator, could infect crustaceans, Sergestid iridovirus (SIV) in sergestid shrimp Acetes erythraeus, a putative iridovirus in penaeid shrimp Protrachypene. Recently, an iridescent virus was identified from pill bug and freshwater lobster Cherax quadricarinatus.
Fig.1. SHIV challenge test. Challenge animals showed pale hepatopancreases and empty guts
Fig. 2. Histopathological features of Davidson’s alcohol-formalin-acetic acid (AFA) xed L. vannamei in sample 20141215 (a,c,e and d). Black arrows show the basophilic inclusions while white arrows show the karyopyknotic nuclei. (a) Haematoxylin and eosin (H&E) staining of the hematopoietic tissue; (b) H&E staining of gills; (c) H&E staining of the sinus in hepatopancreas, and (d) H&E staining of periopods
A newly discovered iridescent virus that causes severe disease and high mortality in farmed Litopenaeus vannamei in Zhejiang, China, has been veri ed and temporarily speci ed as shrimp hemocyte iridescent virus (SHIV). Histopathological examination revealed basophilic inclusions and pyknosis in hematopoietic tissue and hemocytes in gills, hepatopancreas, periopods and muscle. Using viral metagenomics sequencing, we 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 does not belong to the ve 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 (n = 30)(v-v) and 143.6 ± 10.8 nm (n = 30)(f-f), and an 85.8 ± 6.0 nm (n = 30) nucleoid. 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 the positively reacting tissues. Additionally, a speci c nested PCR assay was developed. PCR results revealed that L. vannamei, Fenneropenaeus chinensis, and Macrobrachium rosenbergii were SHIV-positive, indicating a new threat existing in the shrimp farming industry in China.
(Qiu et al., 2017)
Qiu, L., Chen, M.-M., Wan, X.-Y., Li, C., Zhang, Q.-L., Wang, R.-Y., Cheng, D.-Y., Dong, X., Yang, B., Wang, X.-H., Xiang, J.-H., Huang, J., 2017. Characterization of a new member of Iridoviridae, Shrimp hemocyte iridescent virus (SHIV), found in white leg shrimp (Litopenaeus vannamei). Scientific Reports. 7, 11834.
1/ the impact of SHIV on shrimp industry of Vietnam
--> The SHIV infected shrimps are showing the symptoms that are similar to AHPND. Probably, SHIV has been present in Vietnam even thought there are no scientific evidences. Thus, the development of detection kit for this pathogen is very necessary. As a result, the shrimp industry of Vietnam will be protected from SHIV.