A deadly mosquito-borne virus is spreading through southern England, raising alarm among scientists and conservationists about the future of one of Britain’s most cherished songbirds the blackbird.
The Usutu virus, which was first identified in Africa and only detected in the UK in 2020, has now been confirmed across large swathes of southern England. Linked to significant declines in blackbird populations in Greater London, the virus is being closely monitored by researchers concerned that climate change could accelerate its spread.
A Rising Threat from Infected Mosquitoes
“We’ve seen that the virus has spread further than we thought it might do, and it’s persisted,” said Dr Arran Folly from the Animal and Plant Health Agency (APHA), which is leading the research into the disease’s spread.
Usutu is transmitted by infected mosquitoes and primarily affects birds, especially blackbirds, which appear to be highly vulnerable. Since its arrival in Britain, scientists have recorded a roughly 40% drop in blackbird populations in some areas of Greater London, particularly since the 2020 summer heatwave when the virus was first identified in the region.
Dr Folly warns that this outbreak may be an early signal of things to come. “In the future we might get other viruses that are transmitted by mosquitoes emerging in the UK,” he added.
What Is the Usutu Virus?
- Usutu was first discovered in southern Africa more than 50 years ago.
- It spread to Europe in the early 1990s and arrived in the UK in 2020.
- The virus primarily affects blackbirds but has also infected horses and humans in other countries.
- There have been no reported human cases in the UK, and the virus is considered low-risk to people.
The virus causes neurological symptoms in birds and can lead to death. In mainland Europe, Usutu has caused mass die-offs in some areas, particularly among blackbirds. So far, similar widespread mortality has not been observed in the UK, but scientists remain cautious.
Climate Change and the Expanding Range of Mosquitoes
One key driver behind the virus’s spread is changing climate conditions. Warmer temperatures, prolonged summers, and heavier rainfall are creating more favourable environments for mosquitoes to thrive in regions that were once too cool or dry for them.
This has turned Europe, including Britain, into a potential breeding ground for mosquito-borne diseases. “Climate change is giving these insects opportunities to move into new territories,” said Dr Folly.
Tracking the Spread and Gathering Data
Usutu has now been recorded in wild birds as far west as Dorset and as far north as Cambridgeshire. However, blackbird numbers remain healthy in many rural and northern areas. To better understand regional impacts and detect emerging patterns, scientists at APHA have teamed up with the British Trust for Ornithology (BTO).
They are calling on members of the public to help by counting blackbirds in their gardens throughout the summer. These citizen science efforts will provide vital information on blackbird distribution and behaviour.
“They’re beautiful birds intelligent, friendly and they have the most beautiful song,” said Lucy Love, a BTO garden birdwatch ambassador. “And we cannot lose them they’re a vital part of our ecosystem.”
Conservation Amid Multiple Threats
Blackbirds, one of the most common garden birds in the UK, are already facing numerous threats, including habitat loss, pesticide use and broader environmental changes. The added stress of a novel virus only increases the urgency for conservation action.
To mitigate the spread of mosquito-borne diseases like Usutu, experts highlight the importance of monitoring wildlife health, reducing breeding grounds for mosquitoes, and ensuring robust climate action to curb temperature extremes.
While the blackbird population overall remains stable in many regions, the emergence of Usutu is a stark reminder of how quickly ecological conditions can change. Ongoing research, public vigilance and a coordinated response will be key to protecting Britain’s wild birds in a warming world.
