The effect of rising temperatures is likely to speed up the arrival of mosquito-borne diseases in the UK, experts warn.
While not blaming the anticipated arrival of chikungunya, dengue fever and West Nile virus in the UK in the next decades entirely on climate change, the effect of rising temperatures is likely to accelerate it, say the authors, two experts from the Emergency Response Department at Public Health England.
Dr Jolyon Medlock and Professor Steve Leach report their concerns and the evidence they base them on in a review published in The Lancet Infectious Diseases journal.
They warn that vector-borne diseases are rising and spreading across Europe. The last decade has seen malaria arrive in Greece, West Nile virus in eastern Europe, and chikungunya in Italy and France.
The paper follows a United Nations report in December 2014 that warned dengue poses a serious threat to large parts of Europe and South America.
Both the UN report and the new review say that currently these regions are too cold to allow larvae and eggs of the dengue-carrying mosquitoes to survive the winter. But as global temperatures rise, these areas will become smaller.
Prof. Leach says climate change is one of several factors that are driving the increase in vector-borne diseases in the UK and Europe. He notes that other factors that should be considered include socioeconomic development, urbanization, migration, widespread change in land use.
Used tires are an ideal breeding ground for disease-carrying mosquitoes
Public Health England has been monitoring seaports, airports and even motorway service stations for signs of disease-carrying mosquitoes. So far, they have not found any non-native mosquitoes in the UK, but Dr. Medlock says a better system is needed to monitor imported used tires, a favored place for mosquitoes to lay their eggs.
- Dengue fever is caused by any one of four related viruses spread through mosquito bites
- There are no vaccines against dengue and the only protection is to reduce the risk of being bitten by mosquitoes
- Dengue currently infects 400 million people a year and is a leading cause of death in the tropics and subtropics.
Used tires are a good example of where it is not just the change in climate but also human activity that increases the spread of vector-borne diseases.
Used tires are an ideal breeding ground for several species of disease-carrying mosquitoes. They fill with leaf litter and rain, making conditions right for mosquito larvae to grow.
For example, in the US, they have been targeted as an entry point for vector-borne diseases since the mid-1980s when a substantial breeding population of Asian Tiger (Aedes albopictus) mosquitoes was discovered in Houston, TX. These mosquitoes are known carriers of dengue and chikungunya viruses.
The US authorities concluded it was likely the insects arrived from Japan as eggs deposited in used tires.
Medlock and Leach suggest that increased rainfall and milder climate are likely to spur the Asian Tiger mosquito to breed and expand in the UK, particularly in the south of England.
Climate change models predict chikungunya virus spread in London by early 2040s
The authors note that climate change models predict that by the early 2040s, conditions will be suitable for 1 month of chikungunya virus transmission in London, and up to 3 months in southeast England by the early 2070s.
And just a 2°C rise in temperature is enough to extend the active season for dengue-carrying mosquitoes by 1 month, and increase their geographical spread by up to 30% by 2030, they add.
There are already several mosquitoes in the UK capable of spreading West Nile virus. At present the number of mosquitoes that bite humans (the Culex species) is too low, but rising temperatures could alter this, warn the authors, who also note that a number of sites harboring Culex modestus - the number 1 carrier of West Nile virus in Europe - have been found recently in Kent. Prof. Leach concludes:
"Lessons from the outbreaks of West Nile virus in North America and chikungunya in the Caribbean emphasize the need to assess future vector-borne disease risks and prepare contingencies for future outbreaks."
The paper's release is planned to coincide with the Impact of Environmental Changes on Infectious Diseases 2015 meeting that is taking place in Sitges, Spain, this week.