Study warns of spread of chikungunya

DEBILITATING ILLNESS: Higher temperatures due to the climate crisis and invasive mosquitoes mean the tropical disease could expand further northward in Europe

• The Guardian

An excruciatingly painful tropical disease called chikungunya can now be transmitted by mosquitoes across most of Europe, a study has found.

Higher temperatures due to the climate crisis mean infections are now possible for more than six months of the year in Spain, Greece and other southern European countries, and for two months a year in southeast England, it said.

Continuing global heating means it is only a matter of time before the disease expands further northward, the scientists said.

The analysis is the first to fully assess the effect of temperature on the incubation time of the virus in the Asian tiger mosquito, which has invaded Europe in the past few decades.

The study found the minimum temperature at which infections could occur is 2.5°C lower than previous, less robust, estimates, representing a “quite shocking” difference, the researchers said.

Chikungunya virus was first detected in 1952 in Tanzania and was confined to tropical regions, where there are millions of infections a year. The disease causes severe and prolonged joint pain, which is extremely debilitating and can be fatal in young children and older adults.

A small number of cases have been reported in more than 10 European countries in the past few years, but large-scale outbreaks of hundreds of cases hit France and Italy last year.

“The rate of global warming in Europe is approximately double the rate of global warming at global scale and the lower temperature limit for virus spread matters a lot, so our new estimates are quite shocking. The northward expansion of the disease is just a matter of time,” said Sandeep Tegar of the UK Centre for Ecology and Hydrology (UKCEH) and lead author of the study.

“Twenty years ago, if you said we were going to have chikungunya and dengue in Europe, everybody would have said you were mad: These are tropical diseases. Now everything’s changed. This is down to this invasive mosquito and climate change — it really is as simple as that,” Steven White, also a researcher at the center.

“We’re seeing rapid change and that’s the worry. Up until last year, France had recorded 30-odd cases of chikungunya over the last 10 years or so. Last year, they had over 800,” he said.

The virus was carried by travelers from French overseas territories in the tropics where there were outbreaks, including Reunion.

The Asian tiger mosquito (Aedes albopictus), which bites during the day, is moving northward across Europe as temperatures rise. It has been detected in the UK, but is not yet established. There are costly vaccines for chikungunya, but the best protection is to avoid being bitten.

“This study is important because it indicates that transmission [in Europe] might become even more evident over time,” said Diana Rojas Alvarez, who leads the WHO’s team on viruses transmitted by insect and tick bites.

Chikungunya can be devastating, with up to 40 percent of people still experiencing arthritis or very severe pain after five years, she added.

“Climate has a huge impact on this, but Europe still has the chance to control these mosquitoes from spreading any further,” she said.

Community education on removing the still water where mosquitoes breed is one important tool, while wearing long, light-colored clothing and using repellent prevents bites.

Health authorities also need to set up surveillance systems, she said.

The study, published in the Journal of Royal Society Interface, used data from 49 earlier studies on chikungunya virus in tiger mosquitoes to determine the incubation time across the full range of temperatures for the first time.

The study found the cut-off temperature for transmission is 13°C to 14°C, meaning infections can occur for more than six months of the year in Spain, Portugal, Italy and Greece, and for three to five months of the year in Belgium, France, Germany, Switzerland and a dozen other European countries.

The minimum temperature was previously estimated at 16°C to 18°C, meaning there is a risk of chikungunya outbreaks in more areas and for longer periods than previously thought.

The new work gives much more detailed information on the areas at risk.

“Identifying specific locations and the months of possible transmission will enable local authorities to decide when and where to take action,” Tegar said.

Outbreaks in Europe are sparked by infected travelers returning from tropical regions and being bitten by local tiger mosquitoes, which then spread the disease. Until now, Europe’s cold winters have stopped tiger mosquito activity and acted as a firebreak for the disease from one year to the next.

However, scientists are starting to see all-year-round tiger mosquito activity in southern Europe, meaning chikungunya outbreaks are likely to amplify as the continent warms.

The UKCEH team is investigating this issue.

“Our intuition is that we’re going to get much bigger outbreaks because you don’t have this natural firebreak,” White said.

There have not yet been any local transmissions of chikungunya reported in the UK, but there were a record 73 cases among people who contracted the virus abroad from January to June last year, almost three times higher than in the same period in 2024.

“It is important there is continued action to try to prevent the tiger mosquito from establishing in [the UK] because this highly invasive species is capable of transmitting several infections that can cause serious health conditions including chikungunya, dengue and Zika viruses,” White said.