Wenzhou shrimp virus 8 (WzSV8) detection by unique inclusions in shrimp hepatopancreatic E-cells and by RT-PCR

Abstract

The genome sequence of Wenzhou shrimp virus 8 (WzSV8) (GenBank record KX883984.1) was described in 2015 from wide screening for RNA viruses in aquatic animals. A closely related sequence (GenBank record OK662577.1) from the whiteleg shrimp Penaeus vannamei was deposited in 2021 under the name Penaeus vannamei picornavirus (PvPV). In 2022 another closely related sequence (GenBank accession: OP265432) was submitted under the name Penaeus vannamei solinvivirus (PvSV). In 2021, prior to the publication of PvPV and PvSV, we used an RT-PCR method devised from the sequence of KX883984.1 (described herein) to screen for WzSV8 in specimens of cultivated shrimp. Samples that gave positive RT-PCR results were subsequently tested by in situ hybridization (ISH) analysis to identify virus target tissues. Several tissues gave positive ISH results within morphologically normal nuclei. Thus, these tissues were of no use for diagnosis of WzSV8 by normal histological analysis. However, unique basophilic, cytoplasmic inclusions within vacuoles in tubule epithelial cells of the shrimp hepatopancreas (HP) were also found in the same WzSV8-positive shrimp specimens, sometimes accompanied by a smaller eosinophilic inclusion. We call these Lightner double Inclusions (LDI) that can be considered pathognomonic for diagnosis of WzSV8 infection when detected using the light microscope. Such abnormal WzSV8 inclusions could be seen scattered throughout the HP. However, the presence of vacuoles, and especially those containing viral inclusions, is highly abnormal in E-cells. Thus, focusing attention on the E-cell region of the HP for such features, serves as a useful approach in facilitating more rapid detection of WzSV8 infections in shrimp. Although no current proof of WzSV8 is the cause of disease, it is important to investigate new viruses and related tissue anomalies, even from normal cultivated shrimp, to determine whether they may have any relationship to significant negative effects on the production.