Developing molecular barcoding and egg sampling tools to underpin vector surveillance in Great Britain

Abstract

Coined as ‘a huge global burden’, the surveillance of mosquito species considered high-risk for disease transmission is currently undertaken in almost every country on the planet. The monitoring of the, approximately 36, species native to Great Britain for their potential as disease vectors (of which 14 are considered to have significant vector potential in other countries) should also be included. Similarly, there is now an urgent need for effective surveillance in Britain for the two most rapidly dispersing and globally invasive species, Aedes (Stegomyia) albopictus (Skuse 1895), and Aedes (Stegomyia) aegypti (L. 1762). The former having swept across Europe since its introduction in 1990 bringing autochthonous outbreaks of dengue fever and chikungunya virus. For the surveillance of these species to be effective, however, a solid underpinning of strategies and tools must be available.
Here we attempt to improve the surveillance of native and invasive mosquitoes by undertaking the first large scale effort to collect and characterise all the species found in Britain, by using the mitochondrial barcoding genes, cytochrome c oxidase subunit I (COI) and internal transcribed spacer 2 (ITS2). A detailed analysis of both genes, as well as descriptions of the folded secondary RNA structures of ITS2, are also included. To gauge the taxonomic status of British species against those from across their range, data collected was compared to sequences from other countries. We collected samples of 28 species, those unaccounted for are currently considered rare, or have a questionable presence. Examination of COI and ITS2 suggests they are good predictors of species; however, high levels of intraspecific genetic variation were recorded in some (i.e. Aedes vexans), and too low to support others (i.e. Ochlerotatus annulipes / cantans and Oc. daciae / messeae). The addition of species range data indicated several distinct clusters within species groups over long distances, this could signify a need for taxonomic review and reclassification (i.e. Ae. vexans, Culex territans, Culiseta alaskaensis, Cs. morsitans). Most clear separations were between those that occupy Nearctic and Palearctic biogeographical regions.
Alarmingly, both Ae. albopictus and Ae. aegypti were discovered in England during the period of this study. A description of the post surveillance survey for the Ae. aegypti find is also included here. This discovery highlights a need to improve methods of detecting imported Aedes. Therefore, a study into the effectiveness of sticky tape as a cheap and tactile medium to test car tyres for mosquito eggs was also undertaken. This study suggests that affordable and rapid methods of surveying for invasives can be achieved, and although microscopic analysis of eggs collected in this manner is not possible, molecular identification is not prohibited. Additionally, the removal of eggs by adhesive tape does not prevent rearing of larvae for further analysis.
Underpinning the surveillance of important disease vectors, such as mosquitoes, by using the methods tested above, could be paramount to the avoidance of autochthonous transmission in Britain. However, their rapid dissemination into practice will be key to their future usefulness.

Date of Award	25 Feb 2020
Original language	English
Awarding Institution	Edge Hill University
Supervisor	CLARE STRODE (Director of Studies) & ANNE OXBROUGH (Supervisor)