Byers, NM, et al. Evidence of Limited Laboratory Infection of Culex Tarsalis (Diptera: Culicidae) by Usutu Virus. VECTOR-BORNE AND ZOONOTIC DISEASES Volume 00, Number 00, 2024. DOI: 10.1089/vbz.2024.0054
Abstract
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 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 is in the same Japanese encephalitis complex within the family Flaviviridae as WNV and SLEV. Cx. tarsalis is considered a potential vector of JEV based on vector competence studies [Reeves & Hammon. 1946. J. Exp. Med. 83: 185]. Because USUV causes extensive mortality in blackbirds, it is possible that mosquitoes could be exposed to higher blood meal titers in nature than used in these experiments. Also useful to remember that Cx. tarsalis is less suseptible to WNV than SLEV, and yet WNV is more prevalent because of its higher titers in infected avian hosts.