Duration:
West Nile Virus is a zoonosis with several avian species acting as a reservoir, and mosquitoes of the Culex pipiens species acting as a vector. Humans become infected when bitten by the vector: they develop viraemia, but they are only symptomatic in a small percentage of cases, mostly elderly patients, with predominantly febrile/pauci-symptomatic features. However, 1% of infected patients may develop a severe neurological condition, linked to the virus’ neuro-invasiveness. To date, the neurological condition has no treatment, and leads to lethality in 10-20% of patients. No vaccine is currently available, and there is also a risk of transmission via transfusion. Consequently, West Nile virus (WNV) belongs to the group of diseases that should be subjected to One Health multidisciplinary surveillance and tested in blood donors.
The virus has been endemic in Lombardy since 2008, and there is a robust surveillance system in place that can detect viral circulation in animals using traps distributed throughout the region for monitoring mosquitoes (activated on 1 June each year and tested every 15 days) and culling birds, which are then tested for WNV. Over the course of the surveillance period, it has been observed that the appearance of the first human cases in a territory is preceded by the detection of animal positivity for West Nile virus (WNV). Consequently, a province is only defined as being at risk of infection when WNV is found in animal species, and only after this the region commence testing donors and alerting Emergency Rooms to the possible presence of neurological WNV cases.
In the context of current surveillance, an element that is not sufficiently considered is climate. However, climate plays a fundamental role in determining the evolution of WNV seasonality, as it favours the mosquito directly (in terms of abundance, survival, reproduction, etc.), but also WNV replication and its possibility of becoming endemic, which is linked to reservoir bird migrations and the presence of mosquitoes. Furthermore, in the context of climate change and the emergence of arboviruses in Europe, it is crucial to incorporate climate information into surveillance systems in order to effectively monitor areas at risk of virus spread.

Project Leader
- University of Milan

Partners
- University of Pavia

Funding
Goal
To assess the influence of climate on West Nile Virus (WNV) infection during the decade 2013-2022.
Objectives
- To evaluate the potential integration of the climate component into surveillance models.
- To incorporate climate data for predictive purposes according to climate trends for the next future.
Activities
- Collection of scientific background and data;
- Statistical evaluations to define a model that explains the correlation mathematically.
Impact
- Initial graphical observations of time series showed the presence of correlations between climatic trends, in particular temperature, and cases of positivity in animals and humans. This is consistent with observations reported in the literature from other regions of Italy and internationally.