Dispersal dynamics and surveillance of the invasive Asian tiger mosquito (Aedes albopictus) in Switzerland

Vavassori, Laura. Dispersal dynamics and surveillance of the invasive Asian tiger mosquito (Aedes albopictus) in Switzerland. 2022, Doctoral Thesis, University of Basel, Associated Institution, Faculty of Science.


Official URL: https://edoc.unibas.ch/88533/

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Background: In the wake of increasing globalization and environmental change, invasive mosquito species have become an emerging threat in Europe. Aedes species have a high invasive potential and are passively displaced across the globe by international traffic and trade. At regional levels, adult mosquitoes are travelling along roads as hitchhikers in vehicles. The Asian tiger mosquito (Aedes albopictus) is one of the most invasive insect species and is a disease vector of considerable public and veterinary health relevance. In addition, its aggressive day-biting behaviour makes it a considerable nuisance for people. Over the last four decades, it has spread worldwide, starting from its Southeast Asian native range and reaching the southern part of Switzerland in 2003. Since then, the mosquito expanded its range across the country. Yet, it is not known which are the routes of introduction into Switzerland that contribute the most to the expansion, or if the Alps may act as barrier for the spread. Additionally, it is unclear how far this mosquito colonises new areas through active flight. Understanding mosquito movement at the regional scale is fundamental to improve mosquito surveillance, assess the risk of disease transmission, and to target vector control efforts.
Objectives: The overall aim of this PhD thesis was to understand the distribution of Ae. albopictus, to identify the drivers contributing to its spread in Switzerland, and to evaluate the use of new arbovirus surveillance tools. The specific objectives were:
(i) to investigate the introduction of invasive Aedes mosquitoes through a surveillance system along main Swiss traffic axes;
(ii) to estimate population density, age structure and active dispersal in established populations;
(iii) to describe the origin and the introduction routes into Switzerland;
(iv) to develop and evaluate a novel tool for the surveillance of imported mosquito-borne viruses through returning travellers.
Methods: We monitored the introduction of invasive Aedes species with specialized traps placed along the main traffic axes in Switzerland over six consecutive years. To understand population density, age structure and the movement through active flight we conducted a Mark-Release-Recapture study in areas with established mosquito populations in southern Switzerland. We marked individuals with fluorescent colours and recaptured them in traps positioned at different distances from the release points. To identify by which routes the Asian tiger mosquito arrived in Switzerland, we used > 4000 genome-wide single nucleotide polymorphisms obtained through next generation sequencing. These powerful genetic markers allow grouping of individual mosquitoes based on their ancestral relationships. Next, we identified viruses that are transmitted by mosquitoes and may be introduced to Switzerland testing a novel method of surveillance. We asked travellers to take sugar-baited FTA card kits to collect information about virus circulation at their travel destinations in Brazil. These cards collect arboviral RNA from mosquito saliva when it feeds on the sugar. The study participants were using the kits in conjunction with a mobile phone application in which they were asked to enter clinical symptoms suggestive of an infection, such as fever or swollen joints.
Results: We found three invasive Aedes species, Ae. albopictus, Ae. koreicus and Ae. japonicus in our survey throughout Switzerland. The marking and recapturing of the mosquitoes revealed that host-seeking Ae. albopictus females are flying 2.5 times further than previously assumed for European populations. Additionally, mosquitoes survive long enough for a virus to replicate and be transmitted in our study areas. Applying population genomics, we detected a weak genetic structure and high levels of genetic admixture in Switzerland. These findings support a scenario of passive dispersal facilitated by human travel along traffic routes. The genetic pattern suggests frequent re-introductions from Italy. We found evidence of an overwintering population north of the Alps showing that this mountain range does not prevent further northward spread. The new method we tested for arbovirus surveillance proved to be successful. We found arboviruses on the FTA card kits that travellers brought back from Brazil, suggesting that volunteers are an excellent way to collect data on arboviruses and that this simple sampling tool enables risk assessment of travel-associated virus importation to Switzerland.
Conclusion: The passive dispersal along traffic routes plays a fundamental role in the invasion of Ae. albopictus into Switzerland. Active flight of adult mosquito contributes at the smaller scale to the establishment of local populations. This dynamic of mosquito movement, together with the high gene flow between European populations, underlines the risk of continuous re-introduction events. Multiple sites in Switzerland are at risk of becoming starting points for the establishment of new populations and should, therefore, be closely monitored through continuous surveillance of mosquitoes and targeted control measures. Collaboration between country borders are fundamental to achieve successful mosquito surveillance and control.
Advisors:Müller, Pie and Utzinger, Jürg and Simard, Frédéric
Faculties and Departments:09 Associated Institutions > Swiss Tropical and Public Health Institute (Swiss TPH) > Department of Epidemiology and Public Health (EPH) > Vector Biology > Vector Research and Control (Müller)
UniBasel Contributors:Müller, Pie and Utzinger, Jürg
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:14749
Thesis status:Complete
Number of Pages:131
Identification Number:
  • urn: urn:nbn:ch:bel-bau-diss147494
edoc DOI:
Last Modified:03 Jul 2024 10:55
Deposited On:20 Jul 2022 15:04

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