What are the West Nile virus vectors in southern France?

The epidemiological cycles of West Nile virus (WNV) include birds as amplifying hosts, mosquitoes as vectors and humans and equines as sensitive dead-end hosts. Although WNV infection is often asymptomatic, it can lead to encephalitis in sensitive hosts. Its emergence in the Americas, where it causes thousands of clinical cases (mainly in the United States) has sparked the current interest in this virus. In France, WNV caused epizootics including several human cases in the beginning of the 1960s before it disappeared for 35 years. Since 2000, however, it has caused epizootics in the Camargue and sporadic human and/or equine cases in other parts of the Mediterranean coast. This paper reviews the studies conducted in recent years; our aim is to identify the vector species in southern France. Bird, human and horse-baited trap collections were conducted to identify the potential vectors. Mosquito exposure to virus under natural conditions was assessed by testing field-collected individuals for the presence of WNV Experimental infections allowed us to evaluate the susceptibility of potential vectors to infect with, amplify and transmit WNV These studies show that Culex modestus and Culex pipiens can be considered the principal WNV vectors in the Camargue wetlands, while Culex pipiens is probably the only vector in the dry coastal areas. After vector identification, a risk assessment for each species covering the appropriate time and space is necessary to propose prevention and control methods. Various approaches under development for these purposes, using modelling and remote sensing tools, are briefly described.