Beyers et al. 2025. Evidence of Limited Laboratory Infection of Culex tarsalis (Diptera: Culicidae) by Usutu Virus. Vector-Borne and Zoonotic Diseases 25(1) https://doi.org/10.1089/vbz.2024.0054
Background: Usutu virus (USUV) is an emerging flavivirus, closely related to West Nile virus (WNV), that has spread into Europe from Africa. Since Culex tarsalis Coquillett is an important vector for WNV transmission in the United States, we tested the ability of USUV to replicate in and be transmitted by these mosquitoes. Materials and Methods: USUV was used to infect 3-4 day-old Cx. tarsalis with 5.6 to 7.5 log10 pfu/ml in goose bloodmeals. Saliva, heads, and bodies were collected on day 13 or 14 and analyzed by RT-qPCR for detection for USUV vRNA. Blotting paper punches were also collected daily to assess viral transmissibility. Results: The low and high dose blood meal resulted in 0% and 19.6% of the mosquitoes having established infections, respectively. All of the high dose females had a dissemination of USUV RNA to the heads and none of the filter papers had detectable USUV RNA, but five of the capillary saliva collections were positive, representing 45.5% of the infected mosquitoes.
Conclusions: Limited infection of Cx. tarsalis was observed when exposed to bloodmeals with greater than 10^7 pfu/mL of USUV, indicating this vector is not likely to have a key role in transmission of the virus. Note: USUV caused frequent epiornitics in blackbirds in Europe, but has not produced noticeable human disease, unlike WNV before its introduction into North America.