Dr Ellie Sherrard-Smith

Summary

I am a UKRI FLF Advanced Research Fellow focusing on infectious diseases. I am co-lead of the Malaria Network of Excellence and part of the malaria modelling group at ICL. I focus on integrated vector control for malaria. I consider how intervention impacts are sensitive to mosquitoes able to survive in the presence of insecticides used on mosquito nets or for indoor spraying, how mosquito behaviors and densities change seasonally and between communities, as well as how differences in human behaviors across communities relate to risk of mosquito bites. The aim of the work is to better understand these differences - to help guide policy decisions on the most effective and cost-effective combination of interventions - and best protect communities from malaria. I am very interested in transitioning to control methods that protect ecosystem processes and provide communities with the resilience to tackle malaria in the long-term.

 

MALARIA

 

Malaria remains a serious public health concern. The malaria parasite is transmitted between vertebrate hosts by Anopheline mosquitoes. Transmission stages are ingested during blood-feeding and develop into oocysts on the wall of the mid-gut. Sporozoites are released from oocysts and gather within the mosquito salivary glands before being injected back to the vertebrate host during a subsequent feed. Within the host, the sporozoites pass from the blood to the liver where they encyst. On rupturing, tens of thousands of blood-stage parasites are released per cyst which go on to reproduce asexually. Some of these asexual parasites will develop into gametocytes that can complete the life-cycle on transmission back to a mosquito.  

Vector Control

Mosquito control remains vital to the fight against malaria. Insecticide-treated nets (ITNs) and indoor residual spraying of insecticides (IRS) are used across malaria-endemic settings because mosquitoes tend to bite indoors and at night. These two interventions have reduced the burden of disease globally. Yet, malaria can be transmitted outdoors and through daytime hours too but to different degrees depending on social structure and mosquito species composition and behaviour in different settings. There is a growing concern that the effectiveness of ITNs is under threat from mosquitoes that are able to survive exposure to the principle active ingredient, pyrethroid insecticide. Nets with different mechanisms of action or partner actives are now available and we can understand their impact through systematically reviewing the available data testing the entomological impact of these interventions. There are also a number of innovations to target outdoor biting. Of particular interest is larval source management which could be an effective option particularly if natural predators or biodiverse habitat can be protected from exposure to toxins. We aim to understand how these different ideas not only kill mosquitoes, but also contribute to protecting patients from reinfection, reducing malaria transmission and averting cases. 

Transmission blocking vaccines

Transmission-blocking interventions (TBIs) aim to eliminate malaria by reducing transmission of the parasite between the host and the invertebrate vector. TBIs include transmission blocking drugs and vaccines which interrupt transmission by targeting sexual, sporogonic, and/or mosquito antigens. I work on a statistically robust empirical method for estimating TBI efficacy from population assay data which fits a hierarchical Bayesian model to multiple life stages of the parasite. This enables both host-to-vector and vector-to-host transmission to be a density-dependent process whilst accounting for stochastic fluctuations driven by superinfection and small sample sizes. Doing so increases the precision of intervention efficacy estimates to capture the impact of TBIs at suppressing parasite prevalence and density in secondarily infected hosts. 

 

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