Dengue and chikungunya: long-distance spread and outbreaks in naïve areas

Abstract

Mosquito-borne virus infections, such as dengue and chikungunya, are continuously expanding their geographical range. The dengue virus, which is known to be a common cause of febrile illness in tropical areas of the Old World, is now widespread in the Americas. In most affected areas, all the four dengue virus serotypes have circulated. Recently, small clusters of dengue have been identified also in Southern Europe during the hot season. The chikungunya virus, initially restricted to Central Africa, where is a common cause of sporadic cases or small outbreaks, and Asia, where it is used to cause large epidemics, has recently invaded new territories. After ravaging Indian Ocean Islands and the Indian subcontinent, CHIKV caused an outbreak in north-eastern Italy. Recently, chikungunya has reached the Caribbean, causing for the first time a large epidemic on the American continent. Although Aedes aegypti is the main vector of both viruses, Aedes albopictus, the Asian 'Tiger' mosquito, is now playing an increasingly important role, contributing to their spread in temperate climate areas. Hereby, we focus the attention on outbreaks of dengue and chikungunya occurring in previously disease-free areas and discuss factors associated with the long-distance spread of the vector-borne infections, such as mutations increasing viral fitness, climate change, urbanization, and globalization of humans and vectors.

Keywords: Aedes albopictus,; Arbovirus,; Chikungunya,; Dengue,; Global health.

Figure 1

Distribution of Aedes aegypti (orange area), Aedes albopictus (yellow area), or both (green area), and areas where dengue activity has been detected (dotted area). Circulation of all the four dengue virus serotypes has been identified in all affected continents. No details are given on small outbreaks occurred on the Hawaii and sporadic cases of dengue reported in France and Croatia are not reported in the map.

Figure 2

Distribution of Aedes aegypti (orange area), Aedes albopictus (yellow area), or both (green area), and areas where chikungunya activity has been detected. Chikungunya virus genotype (As = Asian, ECSA = East/Centre/South African, WAf = West-African) distribution and dates of recent outbreaks due to the ECSA (Indian Ocean) and Asian genotype (America) are also shown in the map. Sporadic cases of chikungunya reported in France are not reported in the map.