West Nile Virus diffusion in temperate regions and climate change

West Nile virus (WNV) is a member of the Japanese
encephalitis serocomplex, which was first described
in 1937 as neurotropic virus in Uganda in 1937. Subsequently, WNV was identified in the rest of the oldworld and from 1999 in North America.
Birds are the primary hosts, and WNV is maintained
in a bird-mosquito-bird cycle, with pigs as amplifying
hosts and humans and horses as incidental hosts. WNV
transmission is warranted by mosquitoes, usually of the
Culex spp., with a tendency to spill over when mosquitoes’ populations build up. Other types of transmissions
have been described in endemic areas, as trough transplanted organs and transfused blood, placenta, maternal milk, and in some occupational settings.
WNV infections in North America and Europe are
generally reported during the summer and autumn.
Extreme climate phenomena and soil degradation are
important events which contribute to expansion of
mosquito population and consequently to the increasing number of infections. Draught plays a pivotal role
as it makes foul water standing in city drains and catch
basins richer of organic material.
The relationship between global warming and WNV
in climate areas is depicted by investigations on 16,298
WNV cases observed in the United States during the
period 2001-2005 that showed that a 5°C increase in
mean maximum weekly temperature was associated
with a 32-50% higher incidence of WNV infection.
In Europe, during the 2022 season, an increase of WNV
cases was observed in Mediterranean countries where
1,041 cases were reported based on ECDC data. This
outbreak can be associated to the climate characteristics reported during this period and to the introduction
of a new WNV-1 lineage.
In conclusion, current climate change is causing an increase of mosquito circulation that supports the widest spread of some vector-borne virus including WNV
diffusion in previously non-permissible areas. This
warrant public health measures to control vectors circulation to redu