Prevalence investigation of translucent post-larvae disease (TPD) in China

In early 2020, the shrimp farming in China suffered a severe setback due to an outbreak of the translucent post-larvae disease (TPD) in Penaeus vannamei. The emerging disease was caused by a hypervirulent strain of Vibrio parahaemolyticus (VpTPD). Although some progress has been made in understanding virulence factors of VpTPD, the diversity and prevalence of TPD pathogen are still unclear. Therefore, this study was undertaken to systematically investigate the epidemiology of TPD in China. In this study, potentially pathogenic bacteria present in naturally infected shrimp samples were isolated, identified, and preserved firstly. The further investigation showed that different Vibrio species carrying the key virulence genes of VpTPD can infect post-larvae of P. vannamei and cause TPD, revealing the diversity of TPD pathogens, and the pathogenic Vibrio strains has been temporarily named as Vibrio causing TPD (VTPD). In addition, epidemiological surveillance based on TaqMan qPCR detection and histopathology techniques analysis showed that VTPD positive samples were detected in most shrimp aquaculture ponds in different shrimp aquaculture provinces of China, with prevalence rate exceeding 50% in some areas. And seawater cultured species such as P. vannamei and P. japonicus were more sensitive to VTPD and were more likely to be infected or carry it. Freshwater cultured shrimp such as Macrobrachium rosenbergii and Procambarus clarkii may not be affected by VTPD. However, shrimp bait organisms are still at risk of carrying or being infected with VTPD. The result suggests that VTPD is still prevalent and spreading in coastal shrimp farming areas in China, with a high risk of transmission. This effort of present study provided a basic epidemiological understanding as well as important technical insights for prevention and management of emerging shrimp diseases.