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    • As the epidemic expands in

    2018-10-30

    As the epidemic expands in scale and geographic range, a growing number of travellers are exporting ZIKV to other regions of the world, including Europe, where Aedes vectors are known to be present (Maria et al., 2016; Zammarchi et al., 2015; http://ecdc.europa.eu/en/healthtopics/vectors/vector-maps/Pages/VBORNET_maps.aspx, n.d.). In Europe, Aedes aegypti is known to exist on the island of Madeira, Portugal (http://ecdc.europa.eu/en/healthtopics/vectors/vector-maps/Pages/VBORNET_maps.aspx, n.d.) and in parts of Georgia and southwestern Russia, whereas Aedes albopictus is established along much of the Mediterranean coast (http://ecdc.europa.eu/en/healthtopics/vectors/vector-maps/Pages/VBORNET_maps.aspx, n.d.). While virus importation events could trigger epidemics in distant geographies where competent Aedes mosquito vectors exist, this risk has to date, been mitigated by winter temperatures in the northern hemisphere. Given the growing experimental and ecological evidence to suggest that Ae. albopictus may be a competent vector for ZIKV (Chouin-Carneiro et al., 2016; Grard et al., 2014; Li et al., 2012; Wong et al., 2013), health officials must plan for the possibility of locally acquired ZIKV infections in parts of Europe. The imminent arrival of summer in the northern hemisphere, when Aedes mosquito populations will peak and viral px12 within these vectors will be most efficient, could lead to autochthonous transmission, not unlike the recent localized and transient European epidemics of dengue and chikungunya (Angelini et al., 2007; Wilder-Smith et al., 2014). To assist public health decision-making, we (i) modeled the risks of ZIKV importation into Europe via airline travellers departing areas in the Americas where ZIKV activity has been confirmed or where suitable conditions exist for its transmission year round (Bogoch et al., 2016), (ii) used a temperature driven vectorial capacity model to quantify the potential for European Aedes mosquitoes to support autochthonous transmission of ZIKV, assuming that Ae. albopictus is a competent vector, and (iii) quantified the size of populations living in European areas where mosquito-borne transmission of ZIKV may be possible at the height of summer.
    Materials & Methods
    Results
    Discussion Since Ae. albopictus mosquitoes might prove to be competent vectors for ZIKV (Chouin-Carneiro et al., 2016; Grard et al., 2014; Li et al., 2012; Wong et al., 2013), the public, healthcare providers and public health officials across Europe could use these findings to identify regions at greatest risk for the importation of ZIKV, and its potential transmission within ecologically suitable areas. Although the volume of travellers arriving from the Americas to Madeira, Portugal is substantially lower compared to other major cities in continental Europe, the known occurrence of Ae. aegypti, a longer season with high vectorial capacity, the explosive epidemic of dengue fever in 2012 (Wilder-Smith et al., 2014), and the recent Zika epidemic in nearby Cape Verde (Attar, 2016), collectively highlight the potential for autochthonous transmission of ZIKV on this sub-tropical island. Our analysis highlights necessary, but not always sufficient conditions for autochthonous transmission of ZIKV. While the introduction of ZIKV into Europe, the presence of competent mosquito vectors, and suitable climatic conditions are all prerequisites for local mosquito-borne transmission, a multitude of other factors, including but not limited to, population density, housing conditions, and socioeconomic factors, could influence the likelihood of observing ZIKV epidemics, as seen with other arbovirus infections such as dengue (Clark, 2008; Reiter et al., 2003). Our model is founded on a number of assumptions, most notably that continental European strains of Ae. albopictus possess competence for the transmission of ZIKV. While there is growing evidence to suggest that Ae. albopictus can become infected with ZIKV under experimental conditions (Chouin-Carneiro et al., 2016; Li et al., 2012), empirical data on its role as a vector in nature exist (Grard et al., 2014), but are limited. Recent evidence from the Americas also suggests that Ae. aegypti and Ae. albopictus may be less competent vectors than anticipated (Chouin-Carneiro et al., 2016), and that other factors such as population density, immunologically naïve populations, additional modes of transmission (e.g. sexual (Oster et al., 2016; Foy et al., 2011)), and possibly even other mosquito species might play a role in this epidemic (Ayres, 2016). A key strength of our study is that our model\'s R0 outputs were comparable to estimates we derived using ZIKV surveillance data from the ongoing epidemic in the Americas. However, we assumed that our model, validated against ZIKV data from the Americas where Ae. aegypti is thought to be the primary driver for transmission, would be transferrable to a European setting where Ae. albopictus is the dominant vector.