Why is it important to track the expansion of invasive mosquito species?

• They transmit diseases that represent more than 17% of all infectious diseases globally, according to the World Health Organization
• NEIKER is working on a programme to evaluate the expansion of invasive mosquito species in the Basque Country, for example tiger mosquitoes
• This tracking programme is coordinated by the Public Health Division of the Basque Ministry of Health and has participation from the main Basque city councils and NEIKER’s Department of Animal Health

Mosquitoes are insects found in most parts of the world. There are around 3,500 species, although only some of these are responsible for transmitting diseases to human beings and animals. According to the World Health Organization (WHO) vector-borne diseases, such as those transmitted by mosquitoes, represent more than 17% of all infectious diseases globally and cause more than 700,000 deaths every year.

A large part of these diseases mainly affect populations with fewer resources, in tropical and subtropical regions. Nevertheless, globalisation and climate change are causing some species of mosquitoes, such as the tiger mosquito (Aedes albopictus) we already know, to move and settle in different parts of the world, leading to the emergence of diseases in regions that had not had cases before. Their monitoring and tracking has become the best way to launch measures to control their expansion.

In the case of the Basque Country, NEIKER, member of the Basque Research and Technology Alliance (BRTA), has been working since 2013 alongside the public institutions to track invasive mosquito species. The tracking programme has evolved over the years, with the number of municipalities sampled growing gradually. In 2022, all municipalities with populations over 10,000 are being sampled.

Active monitoring to detect invasive species of mosquitoes, like the tiger mosquito (Aedes albopictus), is often focused at ports and airports, as well as throughout road networks and urban centres with high vehicle affluence, which act as pathways for the species to disperse.

As explained by Ana García and Jesús Bandarika, researchers from NEIKER’s Department of Animal Health, “this monitoring aims to evaluate the possible expansion of these mosquitoes in urban and periurban areas. We’re looking for areas conducive to these invasive mosquito species to rule out or confirm their presence. If we do find them, we will report the findings to the authorities so they can implement control measures”.

Expansion in Gipuzkoa and Bizkaia

One of the invasive mosquito species included in the monitoring programme is the tiger mosquito (Aedes albopictus). It is a mosquito from south-east Asia, where it has a significant role in the transmission of viruses such as dengue, chikungunya and zika. It was detected in the Basque Country for the first time in the municipality of Irun (Gipuzkoa) in 2014.

Since then, and as sampling efforts have expanded, the mosquito has been found to be increasing in a number of municipalities in Gipuzkoa and Bizkaia, and occasionally in Araba”, García added.

“It has expanded widely around the world, mainly through passive transport of eggs or larvae via freight traffic (tyres, etc.) and has adapted perfectly to temperate climates. Its eggs can survive and remain viable for months with no water and are able to withstand temperatures of -4°C”, García explained.

Continuous tracking of this species of mosquito, which tends to bite people as well as other mammal species, has given NEIKER researchers insight into its breeding sites.

Specifically, tiger mosquitoes breed in small volumes of water, so controlling and/or eliminating water points (drums, tyres, containers, sewers, gutters, etc.) both in public and private spaces is paramount, because their breeding grounds are often found in these small pools of water.

In some cases, regular people are the ones detecting these and other invasive species of mosquitoes by reporting them on citizen platforms like Mosquito Alert.

New invasive species

But the tiger mosquito is not the only invasive mosquito species being monitored by this tracking programme. There is another species known as the Asian bush mosquito (Aedes japonicus) and its presence in Spain was confirmed for the first time in Asturias by a report made on Mosquito Alert in 2018. The following year it was found in Cantabria. In 2020 it was detected in the three historic territories of the Basque Country and in 2021 it was shown to already be well distributed in Gipuzkoa and Bizkaia.

Like the tiger mosquito, Aedes japonicus is also highly invasive and has adapted well to a number of different ecological niches, including, it would seem, colder climates.

“In nature, holes appear in trees and there are many other cavities where small amounts of water can collect, although these mosquitoes also use artificial containers, especially used tyres and larger containers like troughs”, Barandika specified.

However, this species of mosquito is not considered high risk as a vector of pathogens, though it does occasionally feed on human blood, especially in areas with a great deal of vegetation and wooded areas.

“Some laboratory studies have shown that it may be a good transmitter of certain viruses, like West Nile, but to date no cases of natural virus transmission to humans have been confirmed”, García underscored.

“In addition to Aedes albopictus and Aedes japonicus, in Europe three other invasive mosquito species have been identified (Ae. koreicus, Ae. aegypti and Ae. atropalpus). Consequently, we are on the alert to detect their possible emergence in the Autonomous Community of the Basque Country”, remarked Barandika.

The invasive mosquito monitoring programme is coordinated by the Public Health Division of the Basque Ministry of Health. In addition to this support, the programme is also being worked on by major Basque city councils and NEIKER’s Animal Health Department, which has co-funding from the Spanish government’s Division of Public Health, Quality and Innovation programme “Entomological Monitoring at Airports and Ports Against Imported Vectors of Exotic Infectious Diseases and Monitoring of Potential Native Vectors of Said Diseases”.