# Enhanced surveillance to assess the presence of Sindbis and Batai virus in mosquito populations at an urban zoo in the United Kingdom

## TL;DR

This study monitored mosquitoes at London Zoo to check for two emerging viruses, but found no evidence of their presence in the UK.

## Contribution

The study provides baseline data on SINV and BATV absence in UK mosquitoes, using a zoo as a sentinel site for arbovirus surveillance.

## Key findings

- No SINV or BATV was detected in 8477 mosquito specimens collected over 18 months.
- Culex pipiens/Culex torrentium mosquitoes dominated the sample, making up 97.5% of specimens.
- London Zoo is identified as a potential sentinel site for future arbovirus monitoring in the UK.

## Abstract

Sindbis virus (SINV) and Batai virus (BATV) are emerging zoonotic arboviruses with a growing number of detections in Europe. Recent SINV outbreaks in northern Europe and high BATV seroprevalence in sheep, goats, and cattle in Germany emphasise the threat they pose to both animal and human health. Despite their presence in countries of similar latitude and climate, neither of these viruses have been detected in the UK.

Zoos are strategic sentinel sites for disease surveillance because they are well monitored and possess a high diversity of animal species. Located in southeast England, where the climate and vector prevalence may provide suitable conditions for viral emergence, London Zoo was selected as the sampling site for SINV and BATV prevalence in mosquito samples between September 2022 and January 2024. In 2020, it was also the first location where Usutu virus was detected in the UK. Adult mosquitoes were collected during host-seeking and overwintering seasons while larvae were collected in the summer months.

A total of 8477 mosquito specimens were analysed, representing all mosquito stages, i.e. including host-seeking and overwintering mosquitoes as well as adults that had emerged from larvae. Mosquitoes of the Culex pipiens/Culex torrentium complex were the most abundant, accounting for 97.5% of the total. Molecular analysis using quantitative polymerase chain reaction was performed to test for SINV and BATV; however, none of the samples tested positive.

These results suggest that neither SINV nor BATV actively circulated in the sampled area during the study period. The findings provide baseline data for arbovirus surveillance in the UK, particularly at London Zoo, which is home to diverse bird populations that might be potential sentinel populations for viral emergence. Future studies that obtain molecular and serological data on birds or mammals housed at the zoo would complement our surveillance efforts on the emergence or prevalence of SINV and BATV in the UK. This study focused on a single location, but extending sampling and monitoring to other sites across the UK, especially in the southeast, is crucial to strengthening the UK’s preparedness and response strategies in case SINV and BATV emerge in the country in the future.

The online version contains supplementary material available at 10.1186/s13071-025-07149-4.