Quantifying dengue transmission risk associated with vector species and location in Dhaka, Bangladesh

Between 1990 and 2013, globally, dengue virus (DENV) – transmitted by Aedes mosquitoes - caused ~10,000 deaths per year and was responsible for ~1.14 million disability-adjusted life-years in 2013 alone. In Bangladesh dengue outbreaks occur annually.

Despite research toward a vaccine, reducing Aedes populations remains the main strategy for DENV control. In some countries, Ae. aegypti-infected Wolbachia have been released to successfully reduce DENV incidence, but this relies on this species being necessary and sufficient for transmission. Therefore, it is essential to confirm the relative contribution of both Ae. aegypti and Ae. albopictus to transmission when considering this control method in new areas. More generally, vector control efforts are rarely applied evenly across a region and therefore locations of highest transmission risk also need to be identified. Cross-sectional household surveys quantifying immature or adult Aedes abundance are often used by researchers and control practitioners to implicate species and guide where to focus control efforts. Cromwell et al. (2017) however showed that even adult Aedes abundance was not a sufficient proxy for human DENV infection risk. This is likely in part because human factors, including movement, also influence contact between susceptible humans and infectious mosquitoes and vice versa. Indeed, between households and public sites, the level of repeated bites on the same individuals versus bites on different individuals may vary considerably with important implications for transmission risk across locations. Despite this, when dengue transmission risk is compared between locations, Aedes abundance, is usually the only indicator used. Failure to account for other heterogeneities when identifying high risk areas and vector species may have contributed to the current lack of support for vector control as effective against DENV. Indeed, in Bangladesh, entomological studies to inform DENV control have focused only on immature Aedes in households, but Aedes are day biting mosquitoes, therefore public sites must also be considered.

This project will quantify DENV transmission risk in public sites, including schools and work places, compared with households in Dhaka. Data will be collected on: i) adult Aedes aegypti and Ae. albopictus abundance using aspirators and odour-baited traps – including trial of a new heat trap that is as effective as a human-landing catch but without the inherent risks to the collector; ii) the number of different human DNA sequences in mosquito blood meals using nanopore sequencing as a proxy for the host population size accessible to Aedes; and iii) the proportion of adult mosquitoes infected with DENV using nanopore sequencing. These data will be used, in combination with data on the vector competence of Ae. aegypti and Ae. albopictus from Dhaka to parametrize mathematical models to quantify the relative transmission risk associated with location and species, accounting for variation in the number of humans available to Aedes populations, and the nonlinear dynamics of transmission. This will also allow analysis of the relationships between adult Aedes abundance and DENV infection prevalence in Aedes populations over time. Designing surveillance strategies informed by DENV transmission dynamics and greater focus on drivers of variation in the transmission process would improve the subsequent targeting of vector control which could be assessed using resulting models.

Where does the project lie on the Translational Pathway?

T1 – Basic Research AND T3 Evidence into Practice

Expected Outputs

This project will produce high quality REF returnable 3*/ 4* papers reporting the field data results and potentially vector competence experiments and then bringing these results together in a paper using modelling to determine the relative contribution of vector species and location to transmission risk. This project will also generate data to be used in collaborative applications to MRC for further Aedes-borne virus research in Bangladesh with colleagues at icddr,b.

Training Opportunities

The student will receive a unique combination of skills in: i) medical entomology; ii) nanopore sequencing and bioinformatics; iii) working at CL3/ arthropod infections and with support will gain exposure to the application of mathematical modelling in infectious disease epidemiology.

Skills Required

Basic knowledge of and strong interest in vector biology and arbovirus epidemiology

Key Publications associated with this project

LSTM Themes and Topics – Key Words

Malaria and other vector-borne diseases