Abstract
Following the outbreak of autochthonous chikungunya fever in humans in northern Italy, first reported 3 years ago (1) we have now witnessed two independent cases of autochthonous transmission of dengue fever and two cases of chikungunya fever in south-eastern France during September 2010. This worrying trend has raised serious concern among the health authorities, as Aedes albopictus, the Asian 'tiger mosquito', is the most likely transmission vector of both viruses, and this mosquito species is known to be spreading widely throughout many regions of southern Europe. The two cases of dengue fever occurred in patients (a 64-year-old male and an 18-year- old male) living in Nice in the same neighbourhood and know- ing each other. The two cases of chikungunya fever occurred in 12-year-old female patients also living in the vicinity of each other in Frejus, and attending the same high school. Both pre- sented with high fever, headache, lombalgia and arthralgia. These two patients lived in the same neighbourhood as the unique laboratory-documented imported case of the county, affecting a 7-year-old female patient returning from Asia. All four cases resulted in mild, self-resolving infections. The virological identification of these four cases of arbo- viral disease, with no travel history, and within the recorded area of dissemination of A. albopictus, along the 180-km region of the Mediterranean coast from Menton to Toulon (2): (i) demonstrates the first cases of autochthonous trans- mission of both viruses (dengue and chikungunya) in France; (ii) implies that A. albopictus, which is resident in this region, is the most likely competent vector for dengue virus (http:// www.sante-sports.gouv.fr/apparition-des-premiers-cas-auto chtones-de-dengue-en-france-metropolitaine.html); and (iii) raises important issues to be resolved in time for the next 'mosquito season', namely the adaptation of surveillance systems and the implementation of countermeasures to limit dispersal of the viruses and to limit the number of human cases of dengue or chikungunya fever. How alarmed should we be in Europe? Imported cases of dengue and chikungunya fever have long been reported in infected viraemic travellers (3) returning from tropical regions where the viruses are endemic or transiently epi- demic. Indeed, dengue virus ranks second only to the malar- ial parasite as an agent of systemic febrile illness in travellers to the tropics who are returning to Europe (4). However, during the past 5-10 years, the perceived risk of infection in Europe, particularly with these two arboviruses, has increased. This is because a competent mosquito vector was not previously present at a sufficient density in Europe to be able to initiate and generate secondary human cases of chikungunya or dengue fever among human populations. With the establishment and amplification of A. albopictus in Europe, and these cases of dengue and chikungunya fever in France, the perceived risk of epidemics caused by these viruses or other emerging arboviruses has increased dramati- cally. Consequently, in an attempt to prevent and monitor the appearance of autochthonous cases, the French authori- ties have elaborated a surveillance programme targeting both viruses in returning travellers during the summer period of vector activity (http://www.circulaires.gouv.fr/pdf/2010/05/cir_
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