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Venezuela is the most likely country of origin for the dengue outbreak in Madeira in 2012: study

I covered the dengue fever outbreak on the Portuguese island of Madeira since the first locally transmitted cases were detected in early October 2012, both here at The Global Dispatch and on the Infectious Disease Examiner.

Image/U.S. Defense Mapping Agency

Image/U.S. Defense Mapping Agency

The British Health Protection Agency said that this is the first time that dengue fever has been reported in Madeira, although the vector for the disease, the Aedes aegypti mosquito, is established on the island.

So the question at the time was– where did the virus come from that infected some 2,100 people on Madeira resulting in dozens of cases introduced into 13 other European countries via travelers departing the tourist destination of Madeira?

Fascinating new research published recently in Eurosurveillance by authors from several institutions investigated the interconnectivity via air travel between dengue-endemic countries and Madeira, and compared available sequences against GenBank.

Image/CIA

Image/CIA

There were 22,948 air travelers to Madeira in 2012, originating from twenty-nine dengue-endemic countries; 89.6% of these international travelers originated from Venezuela and Brazil. We developed an importation index that takes into account both travel volume and the extent of dengue incidence in the country of origin.

The number of air travelers from Venezuela to Madeira was 15,884, almost four times higher than the 4,676 travelers from Brazil. Most of the air travelers from Venezuela boarded in Caracas, whereas in Brazil most travelers boarded in Sao Paulo and Rio de Janeiro.

Related story:Dengue in the Americas: Nearly 2.3 million cases, 1,244 deaths

The researchers said based on the importation index, their findings show that Venezuela is by far the most likely origin of the Madeira outbreak. The importation index was almost two times higher than for Brazil, the country with the second highest interconnectivity with Madeira.

Image/CDC

Image/CDC

Although the extent of dengue activity in Brazil is higher than that of Venezuela, the risk of introducing dengue from Brazil to Madeira is lower because of the lower overall interconnectivity via air travel between Brazil and Madeira.

As the outbreak in Madeira was first reported in October 2012, taking the extrinsic and intrinsic incubation time of the Aedes mosquitoes into account, the most likely time of importation into Madeira would have been between July to September 2012. Using the monthly index for July, August and September 2012, the importation index for Venezuela is seven times higher during this period than that for Brazil.

This is because at this time of the year Venezuela has higher dengue activity than Brazil; dengue is seasonal in most dengue-endemic countries. Their findings, based on the importation index, suggest that Venezuela is the most likely source of importation of dengue to Madeira in late summer 2012, just before the outbreak’s first reported case.

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About the Author

- Writer, Co-Founder and Executive Editor of The Global Dispatch. Robert has been covering news in the areas of health, world news and politics for a variety of online news sources. He is also the Editor-in-Chief of the website, Outbreak News Today and hosts the podcast, Outbreak News Interviews on iTunes, Stitcher and Spotify Robert is politically Independent and a born again Christian Follow @bactiman63

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