Climate change could allow disease-carrying mosquitoes to spread across Western Europe

15 Mar 2019

Invasive species: an Asian tiger mosquito. (Courtesy: James Gathany/CDC)

Climate change could allow disease-carrying Asian tiger mosquitoes to spread across Western Europe, say two independent groups of researchers. The insects are known to spread more than 20 diseases including yellow fever, chikungunya, dengue, and Zika – which could become more common in the region.

According to a new study by Soeren Metelmann of the University of Liverpool and colleagues in the UK, almost all of England and Wales could be warm enough for the species by the 2060s. Meanwhile, an international team including Moritz Kraemer at the University of Oxford has done an independent study that predicts that the mosquito will spread throughout Europe over the next 30 years.

Successful invader

To understand how the mosquito could spread further in the UK, Metelmann and colleagues created a model that combines detailed knowledge of the life cycle of the mosquito with UK climate predictions from NASA for the period 2060–2069. The climate data covers two carbon-emission scenarios: one sees emissions peak in 2040, while emissions continue to rise in the other. Originally from East Asia, the insect is a highly-successful invasive species and is now found on every continent except Antarctica. It has been spreading across Europe since the 1970s. It is established as far north as Germany and the mosquito has been spotted in south-east England. In the last decade, there have been outbreaks of chikungunya in Italy, showing that the spread of such mosquito-borne viruses within Europe is possible.

Under median predicted temperature rises, the model indicates that southern England and the English Midlands could support populations of Asian tiger mosquitoes by the 2060s, for both emissions scenarios. If the higher emissions scenario occurs and NASA’s maximum predicted temperature rise happens, then all of England and Wales along with parts of Scotland and Ireland would be suitable for the mosquitoes.

In their study, Kraemer and colleagues predict the future global distribution of the mosquito using 17 climate change models combined with data on historical mosquito spread and forecasts of human movement.

Describing their results in Nature Microbiology, the team says that they expect the Asian tiger mosquito to have spread across Europe by 2050, encompassing large areas of France and Germany and also patches of England, Wales, Scandinavia, and the Baltic states. Initially, the expansion is expected to be independent of climate change, but later dispersals will be driven primarily by environmental change. By 2080 the team predicts that the Asian tiger mosquito will be in 197 countries worldwide, with 20 of those detecting its presence for the first time.

Urbanization and humidity

Kraemer told Physics World that much of the expansion “can be attributed to increasing temperatures, but other factors like urbanization and humidity also play key roles”. He adds, “We show that human movements are of crucial importance. Humans transport mosquitoes in all stages – adult, eggs, larvae – to new locations where they can establish new populations.”

This is not a new phenomenon. In the summer of 1865, there was an outbreak of yellow fever in South Wales when a similar species of mosquito arrived on a boat from Cuba. At least 27 people were infected and 15 died. Metelmann says that it has always been possible for tropical mosquitoes to be introduced into the UK in warm summer months and survive – and even breed – for a few weeks before disappearing in the winter. But his team’s latest research shows that in the near future such introductions could lead to the establishment of resident populations that survive the winter.

Metelmann adds that the arrival of Asian tiger mosquitoes does not necessarily mean the arrival of the diseases they carry, but it makes it “more likely”. The biggest risk is mosquito-borne diseases brought in by travelers. “If this mosquito establishes in the UK and we get introductions by traveling cases of chikungunya, for example, and the mosquitoes bites the traveler it could then get transmitted locally,” Metelmann explains.

While current monitoring and control strategies are sensible, preventing the establishment of Asian tiger mosquitoes in the UK in the long term will become more and more challenging as conditions become more suitable, Metelmann says. He suggests that the future focus could instead be on techniques to stop the mosquitoes from transmitting viruses and other actions, such as vaccination.

22/3/2019 physicsworld.com