Assessing vector competence of mosquitoes from northeastern France to West Nile virus and Usutu virus

Abstract

West Nile virus (WNV) and Usutu virus (USUV) are two arthropod-borne viruses that circulate in mainland France. Assessing vector competence has only been conducted so far with mosquitoes from southern France while an increasingly active circulation of WNV and USUV has been reported in the last years. The main vectors are mosquitoes of the Culex genus and the common mosquito Culex pipiens. Here, we measure the vector competence of five mosquito species (Aedes rusticus, Aedes albopictus, Anopheles plumbeus, Culex pipiens and Culiseta longiareolata) present in northeastern France. Field-collected populations were exposed to artificial infectious blood meal containing WNV or USUV and examined at different days post-infection. We show that (i) Cx. pipiens transmitted WNV and USUV, (ii) Ae. rusticus only WNV, and (iii) unexpectedly, Ae. albopictus transmitted both WNV and USUV. Less surprising, An. plumbeus was not competent for both viruses. Combined with data on distribution and population dynamics, these assessments of vector competence will help in developing a risk map and implementing appropriate prevention and control measures.

Molecular Xenomonitoring (MX) allows real-time surveillance of West Nile and Usutu virus in mosquito populations

“…In addition, the detection of WNV in Ae. albopictus echoes recent findings that this urban and anthropophilic mosquito species is able to transmit WNV and USUV under experimental conditions 38 . Unlike Culex mosquitoes, this invasive species has been reported to have strict mammalian orientated feeding preferences 39 and an avian component is a prerequisite for amplification of these viruses prior to infection of mosquitoes.…”

Aedes albopictus is a competent vector of five arboviruses affecting human health, greater Paris, France, 2023

“…Engorged mosquitoes were maintained at 28 °C until examination. WNV-infected mosquitoes, samples were titrated on Vero cells [10]. After 5 days at 37 °C, lytic plaques were counted after staining with a solution of safranine (0.5% in 10% formaldehyde and 20% ethanol).…”

“…For USUV-infected mosquitoes, samples were titrated on C6/36 cells [10]. After 5 days at 28 °C, cells were fixed with 3.6% formaldehyde, washed and hybridised with anti-flavivirus monoclonal antibody (MAB10216, Millipore), and revealed by using a fluorescent-conjugated secondary antibody (A-11029, Life Technologies).…”

“…In France, Culex pipiens is the main vector but Ae. albopictus is an experimentally competent mosquito [10]. While they are considered dead-end hosts, WNVinfected humans develop a mean viraemia of 10 4.4 RNA copies/mL [19] which can be technically insufficient to infect mosquitoes [20].…”

Circulation of West Nile Virus and Usutu Virus in Europe: Overview and Challenges

“…It would, therefore, appear that mammals living in the wild are naturally exposed to On the European continent, the main vector of these viruses is the Culex pipiens mosquito [7][8][9]. Experimental vector competence has nevertheless been demonstrated by Aedes albopictus, as well as natural carriage [10][11][12]. USUV was also identified in Aedes japonicus japonicus mosquitoes [13].…”