Laboratory evidence on the vector competence of European field-captured Culex theileri for circulating West Nile virus lineages 1 and 2

Abstract

Background Culex theileri (Theobald, 1903) is distributed in Afrotropical, Paleartic, and Oriental regions. It is a mainly mammophilic foodwater mosquito that is involved in the transmission of West Nile virus (WNV, renamed as Orthofavivirus nilense by the International Committee on Taxonomy of Viruses [ICTV]) in Africa. This virus is a mosquito-borne favivirus that is kept in an enzootic cycle mainly between birds and mosquitoes of the Culex genus. Occasionally, it afects mammals including humans and equines causing encephalopathies. The main purpose of the present study was to evaluate the vector competence of a European feld-captured Cx. theileri population for circulating WNV line‑ ages (1 and 2). Methods Field-collected Cx. theileri larvae from Sevilla province (Spain) were reared in the laboratory under sum‑ mer environmental conditions. To assess the vector competence for WNV transmission, 10–12 day old Cx. theileri females were fed with blood doped with WNV lineages 1 and 2 (7 log10 TCID50/mL). Females were sacrifced at 14and 21- days post exposure (dpe), and their head, body, and saliva were extracted to assess infection, dissemination, and transmission rates, as well as transmission efciency. Results A Culex theileri population was experimentally confrmed as a highly competent vector for WNV (both line‑ ages 1 and 2). The virus successfully infected and disseminated within Cx. theileri mosquitoes, and infectious virus iso‑ lated from their saliva indicated their potential to transmit the virus. Transmission efciency was 50% for lineage 1 (for both 14 and 21 dpe), while it was 24% and 37.5% for lineage 2, respectively. There was barely any efect of the midgut infection barrier for lineage 1 and a moderate efect for lineage 2. The main barrier which limited the virus infection within the mosquito was the midgut escape barrier. Conclusions In the present study, the high transmission efciency supports that Cx. theileri is competent to transmit WNV. However, vector density and feeding patterns of Cx. theileri mosquitoes must be considered when estimating their vectorial capacity for WNV in the feld. Keywords West Nile virus, Culex theileri, Vector competence, Arbovirus, Transmission