Abstract
In this study, ridgetail white prawns—Exopalaemon carinicauda—were infected per os (PO) with debris of Penaeus vannamei infected with shrimp hemocyte iridescent virus (SHIV 20141215), a strain of decapod iridescent virus 1 (DIV1), and via intramuscular injection (IM with raw extracts of SHIV 20141215. The infected E. carinicauda showed obvious clinical symptoms, including weakness, empty gut and stomach, pale hepatopancreas, and partial death with mean cumulative mortalities of 42.5% and 70.8% by nonlinear regression, respectively. Results of TaqMan probe-based real-time quantitative PCR showed that the moribund and surviving individuals with clinical signs of infected E. carinicauda were DIV1-positive. Histological examination showed that there were darkly eosinophilic and cytoplasmic inclusions, of which some were surrounded with or contained tiny basophilic staining, and pyknosis in hemocytes in hepatopancreatic sinus, hematopoietic cells, cuticular epithelium, etc. On the slides of in situ DIG-labeling-loop-mediated DNA amplification (ISDL), positive signals were observed in hematopoietic tissue, stomach, cuticular epithelium, and hepatopancreatic sinus of infected prawns from both PO and IM groups. Transmission electron microscopy (TEM) of ultrathin sections showed that icosahedral DIV1 particles existed in hepatopancreatic sinus and gills of the infected E. carinicauda from the PO group. The viral particles were also observed in hepatopancreatic sinus, gills, pereiopods, muscles, and uropods of the infected E. carinicauda from the IM group. The assembled virions, which mostly distributed along the edge of the cytoplasmic virogenic stromata near cellular membrane of infected cells, were enveloped and approximately 150 nm in diameter. The results of molecular tests, histopathological examination, ISDL, and TEM confirmed that E. carinicauda is a susceptible host of DIV1. This study also indicated that E. carinicauda showed some degree of tolerance to the infection with DIV1 per os challenge mimicking natural pathway.
Highlights
The iridescent virus family Iridoviridae contains large icosahedral double-stranded DNA viruses, which is divided into two subfamilies (i.e., Alphairidovirinae and Betairidovirinae) and composed of five known genera: Lymphocystivirus, Megalocytivirus, Ranavirus, Chloriridovirus, and Iridovirus
The results showed that all Decapod iridescent virus 1 (DIV1) negative prawns of the IM and per os (PO) groups survived and all prawns of control of intramuscular infection (CIM) and showed that all DIV1 negative prawns of the IM and PO groups survived and all prawns of CIM and control of per os (CPO) groups were DIV1 negative
Results of Loop-Mediated Isothermal Amplification (LAMP) primer specificity assay showed that the reactions were only positive for DIV1-infected shrimp, while the reactions were negative for white spot syndrome virus (WSSV), VpAHPND, infectious hypodermal and hematopoietic necrosis virus (IHHNV), 3.4
Summary
The iridescent virus family Iridoviridae contains large icosahedral double-stranded DNA viruses, which is divided into two subfamilies (i.e., Alphairidovirinae and Betairidovirinae) and composed of five known genera: Lymphocystivirus, Megalocytivirus, Ranavirus, Chloriridovirus, and Iridovirus. Lightner and Redman reported another suspected iridescent virus in penaeid shrimp Protrachypene precipua [5]. Reported that a suspected iridescent virus was observed in lymphoid cell cultures from the Chinese white shrimp Penaeus chinensis in 1999. The range of susceptible hosts is an important part of epidemiology and pathogen ecology It is of significant concerned for international trade and control of the disease. E. carinicauda accounts for one-third of the total yields of polyculture ponds in the eastern China [12] It is a species of wild prawns and commonly exists in the ponds farming M. rosenbergii or penaeid shrimp. E. carinicauda in intensive shrimp farming ponds, verifying its susceptibility to DIV1 is a prerequisite for evaluation of the potential transmission routes and possible reservoirs of DIV1 in the nature. A combination of TaqMan real-time PCR, histopathological observation, in situ DIG-labeling-loop-mediated DNA amplification (ISDL), and ultra-thin transmission electron microscopy were used to confirm the infection with DIV1 in E. carinicauda
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