Warmer climate can give Europe dengue fever

"Because we cannot stop travel between continents, the only safe way to prevent the spread of dengue fever is to prevent the establishment of mosquitoes that can carry the virus. For that, climate is a key factor," says Jing Helmersson, doctoral student at the Department of Public Health and Clinical Medicine at Umeå University.

In the course of her doctoral dissertation, Jing Helmersson has developed two mathematical models to calculate the potential of the dengue epidemic and dengue mosquito proliferation globally, with focus in Europe. It is partly concerns the mosquito's ability to transmit the dengue virus based on temperature, and partly on the density or establishment of the mosquitoes in relation to climate.

The most potent mosquito that can transmit the dengue virus is called Aedes aegypti. However, in order for a mosquito population in an area to become a carrier, the virus must first get there. That is where our travels across the world come into the picture. The risk that people unknowingly will carry the infection on is partly because dengue, as for some is mortal, in most cases does not give any symptoms at all. However, in order to spread the infection, a combination of viruses, the right kind of mosquitoes, the suitable season and the right environment for mosquito to develop, suitable temperature, rainfall and breeding sits are required. It is a combination of conditions that also alter with climate change.

Already today, the secondary dengue mosquito, Aedes albopictus, has established in the Mediterranean region. The primary dengue mosquito, Aedes aegypti, is on the verge of invading the southernmost parts of Europe. Jing Helmersson shows in her doctoral dissertation that if climate change is held within the framework of the Paris agreement on a maximum of two degrees of warming, the Aedes aegypti mosquito will only be provided the potential to spread in southern small regions of Spain, Portugal, Italy and Greece. However, if global warming continues beyond two degrees, dramatic expansion is predicted to take place so that parts of southern and central Europe risk being invaded by this type of mosquitoes and, as a consequence, dengue epidemics. This would concern large parts of France, Spain, Italy, Portugal, Greece and the Balkans.

"My conclusions underline the importance of keeping global warming within the two degree goal. Reducing the potential area and time window for the spread of dengue therefore, goes hand in hand with the reducing of carbon dioxide emissions," says Jing Helmersson.

Dengue fever is, according to the World Health Organization WHO, the world's most serious mosquito-born viral disease. The disease has so far been limited to some tropical and subtropical areas in Africa, Asia and Latin America. Only two local outbreaks are known to date in Europe, in Athens in 1927 and in Madeira 2012. Yet there is no effective vaccine against dengue that can be used in uninfected areas.

Jing Helmersson has previously obtained a doctorate in Physics from the University of Michigan.