Dengue in Europe: a disease of the tropics on the move?

For European citizens, thinking about dengue fever as a threat to public health in Europe might seem irrelevant… Indeed, the World Health Organisation considers dengue as “the fastest progressing vector-borne disease with more than 100 countries and half of world population at risk for dengue", but most of the 390 million dengue virus infections occurring every year, of which nearly 100 million are symptomatic and approximately half a million require hospitalization globally each year (1)”, are reported from the subtropical areas of our planet (1). Most European citizen might think there is nothing to worry about if they are not traveling to the tropics. But unfortunately this may no longer be true.

Firstly, dengue affects European citizens in their faraway lands. When thinking about Europe, it is always good to remember that some of the European countries (primarily France, the UK, the Netherlands, and Portugal) have oversea territories in inter-tropical areas, mainly in the Caribbean and Latin America, and to a lesser extent in the Pacific and Indian Oceans. In these overseas territories, we observe a rapidly expanding geographic distribution of vector infestation despite ongoing control efforts. Four virus stereotypes are circulating which means that people could potentially be infected several times.

In addition, several indicators are on the rise and are pointing to a worsening situation: these include the frequency and magnitude of epidemics, the levels of hospitalization and the number of severe forms of dengue.

But more surprisingly, dengue also affects Europeans in their continental land, and this is mainly due to two factors: the increase in international travels and warmer climate. In terms of travels, surveys by The European Network on Imported Infectious Disease Surveillance (TropNetEurop) have indicated a stark rise in the number of travelers coming back home infected (2). The impact of warmer climate can be summarised by the views of Jing Helmersson, doctoral student at the Department of Public Health and Clinical Medicine at Umeå University, which give us a good picture of the risks for dengue in Europe: “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 [...] Large parts of Europe can suffer from the dreaded dengue fever unless climate change is attenuated. The mosquito that can transmit the disease needs a certain temperature and humidity to spread. The only safe way to prevent the spread of dengue fever is to prevent the establishment of mosquitoes that can carry the virus.”

Dengue is a rapidly spreading global disease and the chances of this becoming a regular threat in Europe or parts of Europe should not be underestimated. Let's not forget that there was a time when malaria was rampant in parts of London. High temperatures recorded in continental Europe in 2018 and in other recent years is one example of the many factors which will have important consequences for vector and disease prevalence, including the increase in the risk of dengue. The focus should now turn to improving the surveillance, understanding and preparadeness for these evolving threats.

References

World Health Organization. Dengue and Severe Dengue Fact Sheet No. 117. Available at: http://www.who.int/mediacentre/factsheets/fs117/en/. Accessed April 2018.
Diseases of Environmental and Zoonotic Origin Team, ECDC. Dengue worldwide: an overview of the current situation and the implications for Europe. Euro Surveill. 2007;12(25)
Seyler T, Grandesso F, Le Strat Y, Tarantola A, Depoortere E. Assessing the risk of importing dengue and chikungunya viruses to the European Union. Epidemics 2009 Sep;1(3):175-84.
"Warmer climate can give Europe dengue fever." Umeå universitet. ScienceDaily. ScienceDaily, 1 February 2018. https://www.sciencedaily.com/releases/2018/02/180201092227.htm
Images via the ECDC