Dengue fever in Europe: could there be an epidemic in the future?

Abstract

Dengue virus (DENV) is the arbovirus with the widest impact on human health. Although its dispersal is partially conditioned by environmental constraints that limit the distribution of its main vector (Aedes aegypti), DENV has been spreading geographically in recent times, but mostly afflicting tropical and subtropical regions. With no prophylactic vaccine or specific therapeutics available, vector control remains the best alternative to restrain its circulation. Moreover, the establishment of thriving vector populations in peri urban environments brings humans and viruses together, opening the possibility for the occurrence of unexpected outbreaks. Europe is no exception: such was the case of Madeira in 2012. In addition to its impact on the health of the local population, health services, and economy, this outbreak revealed how difficult it may be to control the circulation of pathogenic arboviruses, especially taking into consideration that Europe is already partially colonized by another DENV vector, Aedes albopictus.

Keywords:

• Aedes
• dengue fever
• dengue virus
• Europe
• flavivirus
• mosquitoes

Financial & competing interests disclosure

The authors would like to thank Fundação para a Ciência e a Tecnologia (Ministério da Ciência e Ciência-Portugal) for financial support of part of the work mentioned in this manuscript, with funding attributed to Unidade de Parasitologia e MicrobiologiaMédicas (PEst-OE/SAU/UI0074/2011) and project PTDC/SAU-EPI/115853/2009. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Dengue virus (DENV) accommodates a highly diverse assemblage of flaviviruses, transmitted to humans and non-human primates by Aedes mosquitoes. DENV form a serocomplex with at least four serotypes and numerous genotypes, with global dispersion, putting the millions of individuals mostly in tropical/subtropical regions at risk of infection.

• Different factors that include uncontrolled urban growth, rapid and global traveling, difficult-to-control vector spread, environmental degradation possibly impacted by climate change, all contribute to the global spread of DENV.

• DENV circulates in two ecologically distinct settings (sylvatic and urban), involving genetically distinct viral strains, vectors and hosts. Sylvatic maintenance of DENV in Europe is not probable due to environmental incompatibility and the absence of appropriate vectors. In urban setting, DENV is mainly transmitted by Ae. aegypti and Ae. albopictus. The latter has already extensively colonized considerably large areas of the European continental territory.

• Infection with DENV usually manifests as a self-limited febrile syndrome, the clinical evolution of which is difficult to anticipate, but may involve capillary permeability changes, hemorrhagic manifestations, shock and ultimately death. These outcomes are the result of the combination of viral and host susceptibility factors. These are mostly unknown for European citizens.

• At the present time, no antiviral drug or prophylactic vaccine has been licensed for DENV control. A tetravalent vaccine based on the 17D yellow fever genetic backbone has entered Phase III trials, with promising results.

• Until recently, sustained transmission of DENV in Europe had last been reported in the late 1920s. However, after sporadically autochthonous transmission had been identified in 2010 (involving Ae. albopictus), a large DENV outbreak occurred in Madeira in 2012 in association with an active Ae. aegypti population.

• Although the native entomological fauna of Europe is unlikely to participate in DENV dispersal in the continent, import/spread of Ae. aegypti aegypti to continental Europe or the possibility of Ae. albopictus advancing to most of the continent, associated with extensive traveling involving the circulation of viremic individuals (that may escape medical surveillance) turn the occurrence of DENV outbreaks into a real possibility, which has already been confirmed by sporadic autochthonous of DENV transmission.

• Despite the risk of sporadic outbreaks occurring (especially along the Mediterranean and Adriatic coasts), that of DENV becoming endemic in continental Europe is unlikely in the near future, at least as long as the establishment of Ae. aegypti aegypti is warded off.