Abstract
Given the speed of air travel, diseases even with a short viremia such as dengue can be easily exported to dengue naïve areas within 24 hours. We set out to estimate the risk of dengue virus introductions via travelers into Europe and number of secondary autochthonous cases as a result of the introduction. We applied mathematical modeling to estimate the number of dengue-viremic air passengers from 16 dengue-endemic countries to 27 European countries, taking into account the incidence of dengue in the exporting countries, travel volume and the probability of being viremic at the time of travel. Our models estimate a range from zero to 167 air passengers who are dengue-viremic at the time of travel from dengue endemic countries to each of the 27 receiving countries in one year. Germany receives the highest number of imported dengue-viremic air passengers followed by France and the United Kingdom. Our findings estimate 10 autochthonous secondary asymptomatic and symptomatic dengue infections, caused by the expected 124 infected travelers who arrived in Italy in 2012. The risk of onward transmission in Europe is reassuringly low, except where Aedes aegypti is present.
Highlights
Arboviral diseases are on the rise, with dengue viral infections taking the lead[1]
We investigated the number of imported dengue-viremic travelers into 27 European countries based on the following variables: (1) the monthly dengue incidence in the exporting countries; (2) the monthly number of people leaving the airports of exporting countries and traveling to importing countries; (3) the expected monthly number of dengue-viremic travelers arriving at the importing countries. (4) the accumulated number of secondary cases in humans in the importing countries generated by the infected travelers from the exporting countries taking into account the vectorial capacity of Aedes mosquitoes in the importing countries over a one year period; and (5) the accumulated per capita risk of dengue infection in the population of the importing countries over one year caused by infected travelers arriving in that year
Our estimated number of importations tally with the reported importations of dengue in Europe, the numbers are slightly lower as we are focusing only on air passengers traveling to Europe still in the viremic phase[20,29]
Summary
Arboviral diseases are on the rise, with dengue viral infections taking the lead[1]. The distribution of Aedes aegypti and Ae. albopictus mosquitoes - the vectors for dengue- is the widest ever recorded; extensive in all continents, including North America and Europe, with over three billion people living in Aedes-infested countries or areas[2]. Given the speed of air travel today[19] and increase of travel to tropical and subtropical countries[19], diseases with short viremia such as dengue (around 7 days) can be exported to a dengue naïve areas within 24 hours, where mosquitoes may be able to feed on viremic blood, and transmit the virus on to other humans. The first large dengue outbreak in Europe that occurred in Madeira in 2012 as a result of importation of the virus via incoming viremic air passengers most likely from Venezuela[8] prompted us to study the extent of potentially dengue viremic travelers arriving in Europe as a whole in the same year and to estimate the probability of secondary transmission in Europe as a result of such importation. We set out to model the estimated numbers of dengue-viremic air passengers from dengue-endemic countries to 27 European countries and the subsequent risk of autochthonous transmission as a result of such importation
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