Research
Mosquitoes transmit a diverse array of disease-causing viruses including Zika, West Nile, chikungunya and dengue. The global incidence of dengue fever alone has increased drastically within the last few decades, with approximately 390 million infections occurring annually. Dengue virus (DENV) is transmitted by the mosquito, Aedes aegypti, whose geographic range continues to expand.
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The increasing rates of dengue fever are largely the result of two factors; the expansion of the mosquito’s geographic range as a result of warming temperatures to include tropical and temperate zones around the globe, and because of growing urbanization of the world’s population. This mosquito species thrives in and around crowded human habitation rather than more rural areas.
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My interest lies in understanding how changes in global climate, including factors such as temperature, humidity and precipitation may impact the rates of vector borne disease in humans. Ambient temperatures have been shown to alter mosquito lifespan, development and reproduction and the incubation period of the pathogen. This in turn can influence the rate of pathogen transmission. It has also been shown to influence the biting rate of the mosquito, its development, reproduction. All these factors, in turn, can have a substantial impact on the population dynamics of the vector, its range and thus pathogen transmission.
With changes in global mean temperature, and the escalating regularity of extreme thermal events- understanding the relationship between temperature and pathogen exposure is more important than ever. While there are some published studies of thermal performance of mosquito vectors, several key knowledge gaps remain.
Microbial Infection & Thermal Tolerance
The geographic range of the mosquito Aedes aegypti continues to expand, risking greater incidence of viral diseases including dengue (DENV), Zika, chikungunya, and yellow fever. One emerging solution to control these viruses is the release of the insect bacterium Wolbachia, whose infection in mosquitoes reduces virus transmission to humans. However, the effects of rising temperatures on the efficacy of this tool are unclear. I have studied whether DENV and Wolbachia can alter the thermal sensitivity of the mosquito Ae. aegypti by using a heat-based physiological assay. My work demonstrates that, separately, DENV and Wolbachia infections increase mosquito thermal sensitivity, causing more rapid death when mosquitoes are exposed to extreme heat. These findings demonstrates that future global projections of DENV transmission risk and of Wolbachia’s potential efficacy may need to consider the impact of these microbes on vector survival.
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Publications from this work:
Ware-Gilmore F, Sgrò CM, Xi Z, Dutra HLC, Jones MJ, Shea K, Hall MD, Thomas MB, McGraw EA. Microbes increase thermal sensitivity in the mosquito Aedes aegypti, with the potential to change disease distributions. PLoS Negl Trop Dis. 2021 Jul 22;15(7):e0009548.
Evolution of DENV under high temperatures
Temperature is considered one of the most important abiotic factors impacting mosquitoes and the viruses they transmit as it is able to impact a great variance of things including viral strains and populations, vector survival, population growth, genetic structure, susceptibility to viral infection, and virus structure and replication. Mosquito-borne viruses must be able to tolerate a range of temperatures, and successfully replicate as they must transition through two hosts]. Arboviruses are evolutionarily constrained, and transmission imposes a variety of fitness consequences.
In their vertebrate host, arboviruses replicate at temperatures ranging from 37°C to 44°C. From there, they face another hurdle as they switch to replicating within their inveterate host whose temperature is dependent on ambient temperature (ranging anywhere from 15°C and upwards). By inducing changes in these factors, temperature is likely a major factor modifying the properties of these viruses and their interaction with cellular components during replication. Silent mutations within these factors likely play a major role in the long-term adaption of these viruses to elevated temperatures.
This raises a number of questions about their thermotolerance capabilities and the effect of temperature on virus structure and dynamics, selection on temperature-adapted variants, and overall pathogenesis. To date, little is known about the ability of arboviruses to evolve their thermotolerance capacity.
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Thermal Disturbances & DENV infection Dynamics
Extreme weather events affect the development and survival of vectors and the disease-causing pathogens they transmit. In this chapter we will quantify the mosquito, Aedes aegypti, response to different heat shock disturbances based on prior thermal history from larval development. Thermal history is an important factor in species ability to inhabitant thermally challenging environments. Building off of the first chapter, we were also interested in adding viral infection as an interacting parameter to our ecological disturbance framework. In this chapter, we aim to understand how development at various thermal regimes influence a mosquito’s ability to cope with infection at high temperatures, and also how heat shock events may impact the progression of infection throughout the mosquito. In total, we wanted to understand the interactions between prior thermal acclimation, infection, and acute thermal stress on mosquito thermal performance.
