Highly lethal Vibrio parahaemolyticus strains cause acute mortality in Penaeus vannamei post-larvae

Abstract

A new lethal disease, commonly known as the “glass post-larval disease”, occurs in many shrimp hatcheries in China since late 2019. This disease affects 6– 12-day-old post-larvae of Penaeus vannamei and leads to over 90% mortality within 24– 48 h after the first sign of abnormal individuals. The typical gross clinical signs include an empty digestive tract and pale or colorless hepatopancreas, which result in a translucent look of diseased animals. Here, by applying per os infection study, we show that the “glass post-larval disease” is caused by an infectious agent. Three highly lethal Vibrio parahaemolyticus strains, vp-HL-201910, vp-HL-202005, and vp-HL-202006 are isolated from naturally infected post-larvae collected from different farms. They are very closely related to each other since their 16S rRNA and thermolabile hemolysin genes are identical. These strains reproduce the same pathology in experimental animals and can be successfully re-isolated. The normal structure of hepatopancreas tubule and midgut epithelium is seriously damaged by the representative strain vp-HL-202005. A comparison study suggests that vp-HL-202005 is ~1000 times more virulent than the strain causing acute hepatopancreatic necrosis disease. Moreover, the bacteria-free sonicate supernatant of vp-HL-202005 induces the same symptom in post-larvae shrimp, which strongly suggests that the pathology is caused by a bacterial toxin(s). These findings demonstrate that the “glass post-larvae disease” is caused by a specific type of highly lethal V. parahaemolyticus. Thus, we rename it “highly lethal Vibrio disease” (HLVD). HLVD is a serious threat to shrimp aquaculture.