Increasing temperatures over the next several decades will expand the seasonal window of opportunity for mosquitos to transmit dengue fever in Europe, putting much of the continent at risk for an epidemic, according to a research paper in EBioMedicine.

“This study shows that, by the end of 2099, most major cities in Europe would have a climate suitable for dengue transmission. Athens, Rome, Nice, Paris, London, Amsterdam, Berlin and Stockholm will be affected,” says co-author Kristie Ebi, professor of global health and environmental and occupational health sciences at the University of Washington School of Public Health and a visiting professor at Sweden’s Umeå University, where the study was conducted.

The dengue virus is transmitted by female mosquitoes, mainly of the species Aedes aegypti and Aedes albopictus. These mosquitos also transmit the Zika virus. “Dengue fever is one of the most common mosquito-borne diseases worldwide, with about 390 million cases per year,” Ebi says.

While dengue is a public health issue mostly seen in tropical and sub-tropical climates, new evidence suggests temperate areas are increasingly vulnerable. The Umeå study is the first of its kind to look at how increasing mean temperatures and daily temperature variations correspond with the ability for a mosquito to transmit the disease between humans.

In general, warmer temperatures increase virus reproduction and transmission, and the rate in which the female mosquitos bite. “Unless health systems are prepared, it is very likely that climate change will increase the number of cases of dengue fever,” Ebi says. “Risks later in this century would be lower under scenarios with lower greenhouse gas emissions.”

Also taking part in the study were researchers from Nanyang Technological University in Singapore and the University of Sao Paul, Brazil.