Vector competence of Belgian Anopheles plumbeus mosquitoes for West Nile virus under different temperature conditions

Belgium will likely be confronted with the introduction of West Nile virus (WNV) in the near future, as its presence in neighboring countries has been documented, and the high abundance of Culex pipiens, the main vector of this virus, has been documented in Belgium as well. Other mosquito species, such as Anopheles plumbeus, could also play a role in disease transmission. Anopheles plumbeus is a tree hole-breeding species whose habitat is expanding to urban sites, thus increasing its contact with humans. Only limited data are available on the vector competence of this species for arboviruses, let alone WNV. Such knowledge is important with respect to risk assessments and a preparedness plan in case a WNV introduction in Belgium takes place.

A vector competence study with field-collected Belgian Anopheles plumbeus mosquitoes for WNV (lineage 1) was performed under different temperature conditions: a constant 25 °C, 25/20 °C, and 25/15 °C day/night temperature gradient.

At 14 days post-blood-feeding, the different temperature conditions did not impact the infection rate, ranging between 24% and 29%, nor the viral load in the gut, indicating a similar level of viral replication. Interestingly, statistically significant differences in virus dissemination from the gut to secondary tissues were observed between the different conditions. At a constant temperature of 25 °C, WNV was detected via quantitative reverse transcription polymerase chain reaction (RT-qPCR) in the saliva of one mosquito, resulting in a transmission efficiency of 1.6%. In contrast, no WNV was detected in the saliva under gradient conditions. WNV could not be isolated from the RT-qPCR positive saliva sample.

Since no proof could be found of infectious WNV being present in the saliva of Anopheles plumbeus under any temperature condition, this species cannot be considered a competent vector on the basis of our results. As also only a low viral RNA load was detected by RT-qPCR in one saliva sample at the 25 °C condition, we conclude that Anopheles plumbeus will probably play no role in WNV transmission in Belgium, especially under temperature conditions that more closely reflect the current Belgian climate (25/15 °C) or what could occur in the future (25/20 °C) during the vector season.