Abstract:
Scale drop disease (SDD) caused by a novel Megalocytivirus, scale drop disease virus (SDDV), has been reported causing severe economic losses for affected farmed Asian seabass (Lates calcarifer) in Southeast Asian countries. Detection of SDDV is currently relied on lethal samples. Therefore, this study aimed to detect SDDV from non-lethal samples (blood, mucus and caudal fin) of both clinically sick and healthy Asian seabass during the disease outbreak, using semi-nested PCR method. The result revealed that the prevalence of SDDV in blood and mucus were 100% from both clinically sick (n=15) and healthy fish (n=5). Blood samples were then used for non-lethal surveillance of SDDV in the asymptomatic fish collected from the same farm 13 months after the disease outbreak. The results showed that 1/20 blood samples were tested positive for SDDV. Co-infections of SDDV and Vibrio harveyi were also detected from the fish tissues. Interestingly, this study also revealed that two-gill ectoparasites, Lernathropus sp. and Diplectanum sp., collected from affected fish during the disease outbreak were all tested positive for SDDV, indicating that these parasites are a useful non-lethal sample type for non-lethal detection of SDDV. In summary, non-lethal samples offer great advantages in the diagnosis and monitoring of SDDV infection in economically important farmed Asian seabass and possibly broodstock.