RESUMO
Background and Aim: Malaysia has more than 630 culturists who are involved in the ornamental fish industry and culture 250 species, including local and exotic species. Among these viruses, megalocytiviruses have been associated with severe systemic diseases and economic losses in ornamental fish. The intensity of Megalocytivirus infection in Pterophyllum scalare in Malaysia remains unknown. Thus, this study aimed to investigate the occurrence of Megalocytivirus while discovering its associated risk factors and the genotypes of its causative agents in an ornamental fish farm in Malaysia. Materials and Methods: Seven broodstock pairs of P. scalare were used in this study to follow the life stages of fish, from egg to market size. Water samples and other samples, such as mucus swabs, gill swabs, P. scalare eggs, fries, juveniles, snails, snail eggs, live feed (Tubifex worms and Moina spp.), sediment samples, and wild fish, were collected periodically for initial environmental sampling from day 0 to day 60. Nested polymerase chain reaction amplifications were performed for megalocytivirus-related sequences. The phylogenetic tree, including the sampled causative agents of megalocytiviruses, was inferred from the major capsid protein genes of all known Iridoviridae species. Pearson's correlation coefficients were calculated to determine the strength of the correlation between the presence of megalocytiviruses in P. scalare samples and the associated risk factors. Results: A total of 312 out of 935 pooled and individual samples tested positive for the presence of Megalocytivirus-related sequences, except snail eggs and wild fish (Poecilia reticulata). No clinical symptoms were observed in any fish samples. Megalocytivirus-associated viruses detected in water samples indicate horizontal transmission of the virus. All the nucleotide sequences found in this study had high nucleotide identities of 95%-99 % and were closely related to Megalocytivirus genotype I infectious spleen and kidney necrosis virus. Risk factors associated with Megalocytivirus include water temperature, dissolved oxygen (DO), pH, ammonia, nitrate, nitrite, and the life stages of P. scalare. High Megalocytivirus infection was detected when the water temperature, DO, and pH were high in P. scalare, high water temperature and nitrate in the water samples, and the same rate of Megalocytivirus infection in P. scalare fry and juveniles. Conclusion: This is the first study to confirm the existence of different possible routes of megalocytivirus distribution in ornamental fish farms in Malaysia. Nevertheless, the connection between the mode of transmission and the risk factors for this virus needs to be explored further to recognize the evolution and potential new host species.
RESUMO
Iridoviruses, especially megalocytiviruses, are related to severe disease resulting in high economic losses in the aquaculture industry worldwide. The ornamental fish industry has been affected severely due to Megalocytivirus infections. Megalocytivirus is a DNA virus that has three genera; including red sea bream iridovirus, infectious spleen and kidney necrosis virus, and turbot reddish body iridovirus. Megalocytivirus causes non-specific clinical signs in ornamental fish. Cell culture, histology, immunofluorescence test, polymerase chain reaction (PCR) assay, and loop-mediated isothermal amplification assay have been used to diagnose megalocytiviruses. Risk factors such as temperature, transportation (export and import), and life stages of ornamental fish have been reported for the previous cases due to Megalocytivirus infections. In addition, other prevention and control methods also have been practiced in farms to prevent Megalocytivirus outbreaks. This is the first review of megalocytiviruses in ornamental fish since its first detection in 1989. This review discusses the occurrences of Megalocytivirus in ornamental fish, including the history, clinical signs, detection method, risk factors, and prevention measures.
