Genetic, Phylogenetic, and Serological Analysis of a Getah Virus Strain Isolated from Culex tritaeniorhynchus Mosquitoes in Nagasaki, Japan in 2022.

Overview

• Researchers isolated and analyzed a new strain of Getah virus (GETV) from mosquitoes in Nagasaki, Japan, in 2022.
• The study examined the genetic relationships and vaccine effectiveness against this strain, finding it closely related to Chinese strains and confirming the current vaccine’s effectiveness.

Background on Getah Virus (GETV)

• GETV is a mosquito-borne virus classified within the Alphavirus genus and Togaviridae family.
• It primarily affects horses and pigs, causing symptoms such as fever, rash, edema (swelling) in horses, as well as fatalities and pregnancy disorders in pigs.
• Outbreaks have been reported occasionally in Asia, with endemic areas expanding, especially in countries like Japan, China, India, and in the broader Asia-Oceania region.

Objective of the Study

• The main goal was to isolate and genetically analyze a new strain of GETV found in Culex tritaeniorhynchus mosquitoes collected in Nagasaki Prefecture, Japan, in 2022.
• The study aimed to determine the phylogenetic relationships of this strain with previously known GETV strains.
• Additionally, the study evaluated whether the current equine GETV vaccine, based on strain MI-110, would provide immunity against the newly isolated strain.

Methods and Analyses

• Mosquitoes (Culex tritaeniorhynchus) were collected from Nagasaki Prefecture in 2022 and tested for GETV presence.
• Genetic sequencing was performed on the isolated strain, named 22IH8, to analyze its viral genome.
• Phylogenetic analysis compared the 22IH8 strain to other known GETV strains from Japan, China, and other regions.
• Protein sequences were examined to identify specific amino acid substitutions and compare them to those found in Chinese strains.
• Serological tests assessed the neutralization ability of antiserum against vaccine strain MI-110 when exposed to the 22IH8 strain.

Key Findings

• Strain 22IH8 was genetically closer to Chinese GETV strains than to Japanese strains previously isolated during the 2010s.
• Some amino acid changes in viral proteins of 22IH8 matched those in Chinese strains, suggesting a geographic or evolutionary linkage.
• These results support the hypothesis that the 22IH8 strain recently entered Japan from mainland Asia, signifying a cross-border movement of the virus.
• The antiserum developed from the vaccine strain MI-110 showed a high neutralizing effect against 22IH8, implying the current vaccine remains effective for horses in Japan.

Implications of the Research

• Monitoring and genetic characterization of GETV strains are essential to track viral spread and mutations.
• The identification of new strains like 22IH8 indicates ongoing virus movement across regions, potentially increasing the risk of outbreaks.
• Despite genetic differences, the current vaccine appears to provide sufficient protection against emergent strains, supporting continued use in equine populations.
• Findings emphasize the importance of continued surveillance of mosquito-borne viruses and vaccine efficacy to manage animal health risks.

Conclusion

• The study isolated a novel GETV strain from mosquitoes in Nagasaki, closely related to Chinese strains, indicating recent introduction from mainland Asia to Japan.
• The current horse vaccine strain MI-110 remains effective in neutralizing this new strain, highlighting its ongoing utility in Japan’s equine disease prevention efforts.
• Continuous genetic, phylogenetic, and serological monitoring are recommended to promptly detect changes that may affect disease dynamics or vaccine performance.