Epidemiology of West Nile in Europe and in the Mediterranean Basin~!2009-11-17~!2009-12-11~!2010-04-22~!

Abstract

Abstract:In the last 30 years several cases of West Nile (WN) virus infection were reported in horses and humans in Europe and in the Mediterranean Basin. Most of them were determined by strains of the Lineage 1 included in the European Mediterranean/Kenyan cluster. Strains of this cluster are characterised by a moderate pathogenicity for horses and humans and limited or no pathogenicity for birds. In recent years, however, WN cases determined by strains grouped in the Israeli/American cluster of Lineage 1 or in the lineage 2 have been reported in Hungary and Austria. The role of migrating birds in introducing new viruses to Europe has been often demonstrated. The migratory birds, which may be infected in their African wintering places, carry the virus northward to European sites during spring migrations. In the past, the virus introduction determined occasional cases of WN. In the recent years, new epidemiological scenarios are developing. In few occasions it has been evidenced the capability of WNV strains of overwintering by using local birds and mosquitoes. Species of Culex amongst mosquitoes and magpies (Pica pica), carrion crows (Corvus corone) and rock pigeons (Columba livia) amongst resident birds are the most probable species involved in this hypothetical WND endemic cycle.

Climate change impacts on West Nile virus transmission in a global context

“…At the same time, it is important to note that, in some cases, extremely high temperatures begin to slow down mosquito activity. For example, temperatures above 308C reduced larval survival of Culex tarsalis [44] and slowed WNV growth in Culex univittatus [45].…”

Recent progress in West Nile virus diagnosis and vaccination

“…Mosquito species from other genera are also susceptible to infection. There is now indirect evidence that WNV is transported by migratory birds to the temperate areas of Europe during spring migration [26-28]. Mammals are less important than birds in maintaining transmission cycles of the virus as viremia is too low in most of the mammal species to reinfect mosquitoes.…”

Usutu Virus

“…It is unclear to what extent natural selection has already taken place in these species that migrate to Africa for the winter, so that despite a possible infection with viremia, the animals do not develop the disease and survive the infection. Such bird species would thus be in a position to spread the virus [12,52,53,54]. …”