West Nile virus in Europe: waiting for the start of the epidemic?
In: Emerging pests and vector-borne diseases in EuropeSearch for other papers by Marion Koopmans in
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The recent changes in West Nile virus (WNV) epidemiology, with incursions into the New World and reporting of increased neuroinvasive disease, have raised concerns that this might happen in Europe as well. Recent studies suggest that a single viral mutation may have resulted in increased virulence specifically for American crows, raising viraemic levels above the critical threshold for mosquitoes present in North America. This illustrates the complexity of predicting by extrapolation what could happen in Europe, a conclusion that has led us to undertake a systematic review of available information from a surveillance perspective. Surveillance studies undertaken since the late 1990s have shown that WNV is present in parts of Europe, particularly but not exclusively in wetland areas. Continued reporting of human or animal cases in subsequent years suggests that in some areas the virus is enzootic, but the picture is far from complete. The fact that additional cases are often found in these areas when active surveillance is done indicates that there is significant underreporting. Whether or not birds, arriving from Central Europe, could establish a sylvatic cycle resulting in an outbreak of WNV in Western Europe will, among other factors, depend on mosquito species present, their activity, and feeding behaviour in late autumn. Consequently, climatic changes that shift the balance of ecological factors towards one favouring the start and maintenance of the transmission cycle may increase the risk of WNV outbreaks in the future, although at present we consider this risk to be low. In addition, several other, largely unknown, factors play a role in the epidemiology of WNV as well. Therefore, monitoring of WNV presence in areas with occasional illness reports should continue but a more coordinated effort is needed to provide a reliable risk map of WNV for Europe that can be used for public health preparedness.