# Molecular and Serological Surveillance of Mosquito-Borne Viruses in Racehorses or Mosquitoes From Horse Farms in Shanghai, China, 2022

## TL;DR

This study monitored mosquito-borne viruses in Shanghai racehorses and mosquitoes, finding Getah virus as the main threat.

## Contribution

The study provides the first systematic surveillance of mosquito-borne viruses in Shanghai racehorses and mosquitoes.

## Key findings

- GETV was detected in four mosquito pools and two strains were isolated and classified as genotype III.
- GETV antibody positivity in horses was 28.6%, with higher rates in older horses and during autumn.
- JEV had a 12.6% seroprevalence, while WNV and AHSV showed no antibody presence in horses.

## Abstract

Getah virus (GETV), Japanese encephalitis virus (JEV), West Nile virus (WNV), and African horse sickness virus (AHSV) are mosquito-borne viruses threatening the health of racehorses. However, the systematic surveillance of these viruses among Shanghai racehorses remains lacking. Therefore, molecular and serological surveillance was conducted for these viruses in racehorses and mosquitoes at horse farms in Shanghai, China, during 2022 to assess their prevalence. Among 11,140 mosquitoes collected from seven farms across four districts, Culex tritaeniorhynchus and Anopheles sinensis were identified as the dominant species. RT-qPCR detected GETV in four mosquito pools (FX1-6, PD1-32, PD1-45, and PD1-57) and JEV in three pools (SJ1-4, PD1-22, and JS1-9), while WNV and AHSV remained undetected. Two GETV strains (SH202201 and SH202202) were isolated and phylogenetically classified as genotype III (GIII). Serological surveys of 182 horse serum samples revealed an overall GETV antibody positivity rate of 28.6%. The positivity rate demonstrated significant age-dependency (41.7% in horses >15 years) and seasonal variation (45.1% in autumn vs. 12.1% in spring). JEV seroprevalence rates were 12.6%, exhibiting significant seasonal differences. No antibodies positive for WNV and AHSV were detected. These results indicate that the threat of WNV and AHSV to racehorses in Shanghai is currently very small, while GETV represents the primary arboviral risk. Implementing targeted surveillance for GETV during high-risk seasons (autumn) and in key regions (Fengxian), while enhancing surveillance for JEV, WNV, and AHSV, is crucial for safeguarding equine health and promoting the sustainable development of the equestrian industry.