Multiple species of native mosquitoes may be involved in Usutu virus circulation and maintenance in temperate zones

Imagine the natural world as a giant, invisible highway system where tiny travelers—viruses—hop from one host to another. Usually, these viruses stay within their own "neighborhoods," like birds passing a cold to other birds. But sometimes, a virus decides to take a detour, jumping into a new territory or finding a new way to travel. This is the world of "arboviruses" (short for arthropod-borne viruses). Think of mosquitoes not just as annoying biters, but as the delivery trucks of this viral highway. They pick up a virus from a bird, fly around, and drop it off at a new location, potentially even to humans. Scientists care deeply about this because when these viral trucks start driving in new areas, especially as the climate changes and cities grow, they can cause outbreaks of diseases that make people and animals very sick. One such virus, the Usutu virus, has been making headlines in Europe, and understanding exactly which "trucks" are carrying it is the key to keeping our roads safe.

In this study, a team of scientists acted like high-tech traffic cops, setting up traps across England to catch and inspect the local mosquito fleet. They were investigating the Usutu virus, which was first spotted in the UK in 2020 and has since become a permanent resident in Southeast England. The big question was: Who is actually driving this virus around? While everyone suspected the common house mosquito (Culex pipiens) was the main culprit, the researchers wanted to know if other native mosquito species were also part of the crew, helping the virus survive and spread through the temperate British climate.

The team spent two years (from March 2023 to February 2025) setting up traps in 30 different spots, from wetlands to cities, catching a massive total of 32,054 mosquitoes representing 21 different species. They then put these mosquitoes into groups (pools) and scanned them for the virus's genetic fingerprint. The results were a bit like finding out that the virus isn't just being carried by one specific delivery truck, but by a whole mixed fleet. They found Usutu virus RNA in 116 of the mosquito pools, which is about 3.2% of the groups they tested.

The most frequent "drivers" were indeed the Culex pipiens mosquitoes, confirming they are the primary engine of the virus's spread. However, the study found that the virus was also hitching rides on at least 12 other species. Some of these were surprising, including the Anopheles claviger and Culex modestus. These are important because, unlike the house mosquito that mostly sticks to birds, these other species are known to bite both birds and mammals (including humans). This suggests they might act as "bridge vectors," capable of carrying the virus from the bird population over to people. The researchers also discovered that the virus is circulating in two different genetic lineages (families): the "Africa 3.2" family, which has been there since the 2020 start, and a "Europe 3" family, which appears to be a second, previously unnoticed arrival that is now spreading alongside the first.

The study also looked at the weather, acting like a meteorologist for the virus. They found that 2023 was a "perfect storm" year for the virus, with warm, humid weather that kept the mosquitoes active and the virus happy, leading to a high number of detections. In contrast, 2024 was a bit more chaotic with rain and cooler temps, and the virus detections dropped. Interestingly, they even found the virus in mosquitoes that had survived the winter in a dormant state, suggesting the virus can hibernate and wake up again in the spring, rather than needing to be re-imported every year.

Ultimately, this paper suggests that the Usutu virus in England is more complex than we thought. It's not just one mosquito species doing all the work; it's a network of many native species working together, some of which might be able to bite humans. While finding the virus in a mosquito doesn't prove that mosquito can definitely transmit it to a human, the fact that so many different types were carrying it suggests the virus is well-established and widespread. The researchers emphasize that keeping a close eye on all these different mosquito species, not just the famous ones, is crucial for predicting where the virus might go next and how to protect both wildlife and people.