# Transmission routes of cluster 3 Tembusu virus in ducks and chickens

## TL;DR

This study shows how a new strain of Tembusu virus spreads in ducks and chickens, highlighting the role of mosquitoes and direct contact in transmission.

## Contribution

The study provides first-time laboratory evidence of mosquito-mediated TMUV transmission and clarifies species-specific transmission routes.

## Key findings

- TMUV SD infects both ducks and chickens, but only ducks shed the virus through throat and cloacal swabs.
- Direct transmission occurs in ducks without mosquitoes, but chickens require mosquitoes for transmission.
- Viral excretion through respiratory and digestive tracts is critical for TMUV's direct contact transmission.

## Abstract

Tembusu virus (TMUV) is an emerging mosquito-borne flavivirus, primarily transmitted by Culex spp. mosquitoes. The 2010 outbreak of TMUV in ducks revealed that the virus had acquired direct contact and aerosol transmission routes, enabling its rapid spread in duck farms. Recently, cluster 3 TMUV has increasingly been isolated from chickens, ducks and geese. In this study, we examined the pathogenicity and transmission routes of the cluster 3 TMUV Shandong 2021 (SD) strain in ducks and chickens. Our results show that TMUV SD can infect both species, but only in ducks could TMUV be detected in throat and cloacal swabs. In ducks, the virus can spread without mosquito involvement to co-housed naïve birds, demonstrating direct transmission capability. Conversely, no virus shedding and direct transmission were observed in chickens, suggesting that mosquitoes are required for virus transmission between chickens. Indeed, Culex pipiens mosquitoes could become infected by biting chickens infected with the TMUV SD and transmit the virus to naïve chickens. Our results, for the first time, provide direct evidence that TMUV can be transmitted by mosquitoes in a laboratory setting. Furthermore, our findings indicate that viral excretion through the respiratory tract and/or digestive tract is essential for direct contact transmission of TMUV, which is a critical factor in the epidemic spread of TMUV. These insights into the transmission dynamics of a cluster 3 TMUV emphasize the importance of effective vector control and biosecurity measures in managing and preventing outbreaks.