What happens to mosquitoes in the winter?
An Italian task force, led by the Department of Public Health and Infectious Diseases, has launched a citizen-science project to obtain a spatial and temporal mapping of the most dangerous species of mosquitoes now present in our territory through a new version of the "Mosquito Alert" app. First goal: to discover, thanks to citizens' reports, where mosquitoes go during the winter.
Mosquitoes are not what they used to be. In Italy and Europe, in recent decades, globalisation and climate change have led to the spread of exotic mosquito species once confined to tropical regions; first and foremost the famous tiger mosquito (Aedes albopictus), but also other lesser-known species, such as the Japanese (Aedes japonicus) and Korean mosquito (Aedes koreicus). These species have not only changed our lives because of their aggressive, daytime biting behaviour but have created the conditions for the transmission of exotic viruses capable of causing serious diseases in humans. To combat this dangerous insect, a national task force has been created in Italy. The task force is coordinated by the Molecular Entomology Group of the Department of Public Health of Sapienza University of Rome, with the collaboration of the Italian National Institute of Health (ISS), MUSE - Science Museum, Trento, Italy, the Istituto Zooprofilattico Sperimentale delle Venezie and the Alma Mater Studiorum University of Bologna. The project is part of the development and optimisation of surveillance and monitoring strategies for invasive mosquito species promoted by the European project "Aedes Invasive Mosquito" COST ACTION (AIM-COST). The project, coordinated by the Sapienza group, involves researchers and professionals from 41 countries.
The working group can rely on the valuable contribution of Mosquito Alert, a free application for mobile phones, through which every citizen can send reports and photographs of mosquitoes. Mosquito Alert has been active since 2014 in Spain and, thanks to over 18,000 sightings sent by a large network of volunteers, it has been able to quickly detect the expansion of the tiger mosquito to northern regions, which had until recently remained free, and the presence of new invasive species. Mosquito Alert is now an international phenomenon thanks to two projects funded by the European Community - AIM-COST Action and Versatile Emerging Infectious Disease Observatory (VEO) - which bring together 46 countries in Europe and neighbouring regions. The application has been updated and translated into 17 languages. Through the new version, users can send photos of mosquitoes (alien or not) and report bites they received. Through a task force of more than 50 entomological experts, the images are identified and archived to allow a large-scale assessment of the spread and seasonality of the different species. It would be impossible to obtain this kind of data using conventional entomological tools scattered in various residential areas of the countries currently analysed.
The presence of mosquitoes should not be underestimated. In 2017 a chikungunya virus epidemic, caused by the tiger mosquito, caused hundreds of infections in Lazio and Calabria, central and southern Italy, and in recent weeks the first 10 native cases of the most fearsome dengue virus have been recorded in Vicenza, northern Italy. Transmission of these viruses from infected travellers coming from endemic tropical regions has now become the norm in many European countries.
These cases are in addition to those of a virus endemic to our territory - the West Nile virus - transmitted by the local nocturnal mosquito (Culex pipiens). In recent years a worrying increase has been observed, probably linked to a particularly favourable climate which has enabled the spread.
According to data from the European Centre for Disease Prevention and Control (E-CDC), in 2020 there were 29 cases of West Nile virus in Italy and 1,688 cases in Europe, with 13 deaths.
"Italy is certainly one of the European countries where the risk of a worsening of vector-borne diseases is higher - says Beniamino Caputo in charge of the Italian task force. We think that Mosquito Alert can represent a truly significant step forward towards the surveillance of new invasions and spatial and temporal mapping of the most dangerous species of mosquitoes now present on our territory.
To help citizens understand the meaning and importance of the contribution we expect from them, we have created a website specifically to provide basic information on biology, health risks and mosquito control, including a section dedicated to Mosquito Alert".
However, does it really make sense to engage in this effort now that the summer season (for us, but also mosquitoes) is coming to an end? "Absolutely yes," explains Caputo, "we do not know much about mosquitoes’ behaviour during the colder months. We know that the tiger mosquito produces hibernating eggs that will hatch next spring, but we also know that adults of this species and Culex pipiens are also reported in winter. Only with the active contribution of citizens will we be able to understand how important this phenomenon is in the various regions and use it to develop more effective control strategies. Furthermore, the data we hope to receive in the coming weeks will help us calibrate and optimise the system for the coming year. Next spring, we will certainly summon once again all those citizens who want to help us in the fight against these annoying and dangerous enemies!".