Re: Waiting for the tiger ? The Asian tiger mosquito in Europe
Status of _Ae. albopictus_ (Tiger Mosquito) in Europe
Date: Fri 9 Nov 2012
From: Paul Reiter [edited]
Well established
ProMED-mail stated [archive no. 20121107.1397801] that if a viraemic dengue patient were to travel to southern coastal France there is a risk of ongoing dengue transmission because _Aedes albopictus_ is established there. In truth, _Ae. albopictus_ is established in 21 European countries, from southern Spain to Romania and from Holland to southern Sicily and Malta. It is also well established in parts of southern Russia (where _Ae. aegypti_ is also present) as well as Israel, Lebanon, and Syria.
Aedes aegypti
Most of these populations have been entering winter diapause for several months, so adult numbers are considerably lower than, say, during the Italian chikungunya epidemic (transmitted by _Ae. albopictus_) in 2007, which began in June. In our studies (Institut Pasteur and EID Mediterannee) it is clear that adult populations of the species in Mediterranean France are already very low and oviposition has all but ceased. Madeira is an unlucky victim because the vector there is _Ae. aegypti_. If (when?) _Ae. aegypti_ returns to Europe we can expect repetitions of the great epidemics of the past, such as the dengue epidemic in Greece in 1927-28; clinical cases were estimated at one million people with about 1000 deaths.
Imported
The earliest infestation of _Ae. albopictus_ in Europe was detected in Albania in the 1970s. Today the species is present from the Adriatic to rugged mountainous regions near the Montenegro border, where snow lies on the ground for 3 months of the year. The political history of Albania suggests it was imported from China, its sole trading partner at the time; the species is well established as far north as Beijing and North Korea, which do not enjoy a Mediterranean climate.
Used tires
Infestations in the rest of Europe appear to have begun in 1990 in northern Italy; there is evidence that the species was introduced in used tires imported from Atlanta, Georgia (which is in the United States). The North American infestations, which also exhibit winter diapause, are believed to have come from Japan or other north Asian country, exported in used tyres.
Expand northwards
Given the origins of the European populations, there is little reason to suppose that _Ae. albopictus_ will not expand northwards. If climate is the sole confining factor this could mean at least as far north as Stockholm, in Sweden. The species is generally considered a poor vector of dengue in the field because it is not host-specific -- it feeds on many vertebrates that are not susceptible to the virus -- but it has certainly been the sole vector in some large epidemics. Again, if temperature is the limiting factor I see no clear reason why it could not transmit dengue in the regions of Europe where malaria, dengue, and yellow fever were transmitted in the past. This too would limit the northern range of transmission to central Sweden, Finland, and mid-latitudinal Siberia.
Dry season
Lastly, it is worth remarking that the majority of European tourists who visit tropical dengue-endemic regions do so at sites in the northern hemisphere during the European winter. Their visits are therefore roughly coincident with the dry season, when dengue transmission tends to be at its lowest.
It is small comfort that this asynchrony of transmission seasons may lessen the likelihood of introduction and autochthonous transmission; the sagas of the Asian tiger, dengue and chikungunya have become the quintessential examples of the globalization of vectors and vectorborne diseases.
The worst is yet to come.
[The European Commission is funding studies on _Ae. albopictus_, dengue and chikungunya to the tune of several million Euros. Principal among these are EDENext http://www.edenext.eu/, DengueTools http://www.denguetools.net/, and DENFREE http://www.pasteur.fr/ip/easysite/pasteur/en/press/press-releases/2012/denfree. A map of the current distribution of _Ae. albopictus_ (June 2012) can be seen at http://ecdc.europa.eu/en/activities...s/Aalbopictus-vbornet-maps-distr-june2012.jpg.]
--
Paul Reiter, PhD, FRES
Unite "Insectes et Maladies Infectieuses"
Institut Pasteur
25-28 rue du Dr Roux
75015 Paris
France
ProMED-mail
