Surveillance of Encephalitis-Causing Arboviruses in Horses in South Korea

Serological Evidence of Arboviruses in Horses During West Nile Fever Monitoring Surveillance in Southeastern Brazil

Many human arboviruses are also pathogenic for horses, and some of these have emerged recently. A descriptive cross-sectional observational study was conducted to assess the prevalence of West Nile virus (WNV) and other arboviruses among 77 horses on the rural properties of the Espirito Santo state, Brazil. Serum samples were screened for arbovirus-reactive antibodies using the hemagglutination inhibition technique and subsequently a plaque reduction neutralization test for the confirmation of exposure from sera was used to detect heterotypic immune reactions. Overall, the total antibodies against at least one arbovirus of Alphavirus, Flavivirus, and Orthobunyavirus genera were detected in 39 (50.6%) animals. The antibodies to Phlebovirus were not detected in any sample. When the 24 WNV hemagglutination inhibition (HI)-positive samples were tested by the plaque-reduction neutralization test 90%, 9 (32.1%) were positive for WNV antibodies and 14 (50%) for Saint Louis encephalitis virus. Our findings indicate that the region provides ideal conditions for the emergence of arboviruses, reinforcing the need for further surveillance of mosquito-transmitted diseases in domestic animals.

Genotype-specific neutralizing antibody titers against Japanese encephalitis virus genotypes 1 and 3 in horses immunized with a genotype 3 vaccine

Purpose

Japanese encephalitis is one of the most important mosquito-borne and zoonotic diseases in Asia and the Pacific region. Although the dominant Japanese encephalitis virus (JEV) genotype has shifted from G3 to G1 in Korea since 1990, a G3 strain (Anyang 300) has been used in vaccines for horses for almost 40 years. This study aimed to investigate the seroconversion rates and geometric mean titers (GMTs) of virus-neutralizing antibodies (VNAs) against JEV G1 and G3 in horses immunized with the G3 vaccine.

Materials and Methods

Serum samples of 1,231 horses immunized with the Anyang 300 vaccine were collected in 2018. VNA titers against JEV KV1899 (G1) and Anyang 300 (G3) were measured in all serum samples using the virus neutralization test. Titers were analyzed according to blood sampling time (prior to and following annual revaccination), age, and region.

Results

Rates of VNA titer >10 were 45.1% and 77.8% for G1, and 49.1% and 82.9% for G3 in samples taken before and after revaccination, respectively. GMTs of genotype-specific VNAs against JEV G1 and G3 were 8.3 and 11.6 before revaccination and rose to 27.2 and 65.4 following revaccination. Overall sero-positivity did not significantly differ between genotypes, but GMTs significantly differed among genotypes and sampling times. No significant difference was found in GMTs among age groups or regions.

Conclusion

Genotype-specific neutralizing antibody titers against JEV G1 and G3 differed significantly in horses immunized with the G3 vaccine. Antigenic differences between genotypes could reduce the vaccine's efficacy, requiring the development of a new vaccine.