Not all West Nile virus lineages behave alike: dose-response differences between lineages 1 and 2.

The globally distributed arbovirus West Nile virus (WNV) is expanding across Europe, with rising numbers of human cases and an increasingly broad geographic distribution. Transmitted primarily by Culex mosquitoes, WNV lineages 1 and 2 are pathogenic to humans, yet their differences in transmission dynamics remain unclear. As vertebrate hosts develop varying viremia, mosquitoes encounter a wide range of viral doses, which may influence transmission. Here, we investigated the dose-response differences between the lineages in Cx. pipiens biotype pipiens, Cx. torrentium, and Aedes albopictus. Mosquitoes were fed increasing titers of one strain of either WNV lineage, and infection and transmission were assessed after 14 days at 24 °C. Lineage 2 required lower infectious doses while causing higher transmission. Notably, Cx. torrentium was identified as a highly competent vector for lineage 2. These findings highlight important differences between WNV lineages, improve our understanding of dose-dependent transmission, and therefore support refined risk assessments in Europe.