Simulating an invasion: unsealed water storage (rainwater tanks) and urban block design facilitate the spread of the dengue fever mosquito, Aedes aegypti, in Brisbane, Australia.

Brendan J Trewin,Daniel E Pagendam,Myron P Zalucki,Hazel R Parry,Gregor J Devine,Nancy A Schellhorn,Jonathan M Darbro,Cassie C Jansen

doi:10.1007/s10530-021-02619-z

Abstract

Aedes aegypti (Linnaeus) was once highly prevalent across eastern Australia, resulting in epidemics of dengue fever. Drought conditions have led to a rapid rise in semi-permanent, urban water storage containers called rainwater tanks known to be critical larval habitat for the species. The presence of these larval habitats has increased the risk of establishment of highly urbanised, invasive mosquito vectors such as Ae. aegypti. Here we use a spatially explicit network model to examine the role that unsealed rainwater tanks may play in population connectivity of an Ae. aegypti invasion in suburbs of Brisbane, a major Australian city. We characterise movement between rainwater tanks as a diffusion-like process, limited by a maximum distance of movement, average life expectancy, and a probability that Ae. aegypti will cross wide open spaces such as roads. The simulation model was run against a number of scenarios that examined population spread through the rainwater tank network based on non-compliance rates of tanks (unsealed or sealed) and road grids. We show that Ae. aegypti tank infestation and population spread was greatest in areas of high tank density and road lengths were shortest e.g. cul-de-sacs. Rainwater tank non-compliance rates of over 30% show increased connectivity when compared to less than 10%, suggesting rainwater tanks non-compliance should be maintained under this level to minimize the spread of an invading Ae. aegypti population. These results presented as risk maps of Ae. aegypti spread across Brisbane, can assist health and government authorities on where to optimally target rainwater tank surveillance and educational activities.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10530-021-02619-z.

Highlights

Large epidemics of dengue historically plagued the east coast of Australia, where an estimated 70–90% of the human population were infected (Lumley and Taylor 1943)
We show that Ae. aegypti tank infestation and population spread was greatest in areas of high tank density and road lengths were shortest e.g. cul-de-sacs
While our results focus on the random variation of non-compliant rainwater tanks between suburbs, it is likely that distributions of key larval habitats within suburbs will vary across large cities

Summary

Introduction

Large epidemics of dengue historically plagued the east coast of Australia, where an estimated 70–90% of the human population were infected (Lumley and Taylor 1943). It has been suggested that large water storage containers, called rainwater tanks, maintained Aedes aegypti (Linnaeus) populations responsible for these epidemics (Hamlyn-Harris 1931; Lumley and Taylor 1943). When unsealed or ‘non-compliant’ with regulations, rainwater tanks are ideal habitat for all life-cycle stages of Ae. aegypti and have the potential to act as a major population source for disease vectors (Trewin et al 2020; Tun-Lin et al 1995). Rainwater tanks provide all the requirements for development of the species; reliable larval food resources, ideal temperature range and humidity, a surface for oviposition and resting, a permanent or semi-permanent source of water where larval density is unlikely to be restricted and close proximity to human hosts (Trewin 2018). The rapid rise of these permanent water storage containers has led to an increased risk of the reestablishment of Ae. aegypti in Brisbane, the largest urban centre in Queensland, Australia (Heersink et al 2015; Trewin 2018; Trewin et al 2013)

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