Malaria Epidemiology and Transmission

Understanding malaria epidemiology is a critical component in properly targeting interventions and measuring their impact. In order to develop tools and devise strategies for malaria control and elimination, it is important to accurately characterize patterns in the transmission and burden of malaria, and to elucidate the complex relationship between the two.

Alongside efforts to map the burden of malaria across the globe, and to quantify the impact that interventions have had on reducing that burden over time, IHME researchers and partners are working to understand malaria transmission in a wide range of epidemiological settings, aiming to generate insights that will help decision-makers maximize the impact of interventions.

Focuses of our research include:

Spatial variation

Malaria epidemiology often varies widely over relatively small geographic areas, and this variation has implications for national programs as they seek to control and eliminate the disease: an intervention that works in one part of the country may have very limited impact in another. In countries nearing elimination, transmission is often sustained in malaria “hot spots” with large numbers of vectors or particularly vulnerable populations.

Additionally, infections imported by people traveling from outside of the country are a serious concern, particularly in areas where the potential for transmission is still high. In order to allocate their resources efficiently, countries aiming to eliminate malaria therefore have to answer important questions about where and why malaria is spreading, whether it is a result of endemic transmission or imported infections, and in which contexts it is most likely to be transmitted from person to person by mosquitoes.

Immunity

This picture is made more complicated by the relationship between transmission, infection, and disease: the number of infectious mosquito bites that actually cause malaria infections and the number of infections that go on to cause clinical symptoms can differ by location, season, and levels of immunity within a population. Immunity to malaria is a complex subject and we still have a lot to learn about it. Because immunity affects parasite densities within humans, it is an important factor shaping the transmission of malaria from people to mosquitos. In addition, people with high levels of immunity may not experience serious symptoms when they contract malaria, and so are often less likely to seek care. This can be a challenge when it comes to malaria surveillance, diagnosis, and treatment.

Antimalarial drugs

A further issue our research considers is the choice of drugs used to treat malaria and their effects on controlling transmission. Different drugs, for instance, target different stages of the malaria parasite life cycle, which in turn affects how infectious a person is to mosquitoes and, ultimately, other humans. Additionally, the mass administration of malaria drugs can be a useful tool in reducing transmission, as it reduces the infectiousness of large populations all at once, but for a strategy like this it is vital to know how best to deploy it, and to understand the mechanisms through which it works.

Understanding these complex, interconnected dynamics is crucial to effectively deploying control measures and maintaining progress against malaria. IHME’s work therefore aims to generate a clearer picture of heterogeneity in malaria epidemiology and how it varies across space and within populations. Researchers are developing models that can help countries in a process of stratification: subdividing them into areas that share common features affecting malaria transmission and analyzing individual-level transmission dynamics in order to identify hot spots. Their work also focuses on how factors such as immunity, care-seeking behavior, and different drug choices impact transmission, and their implications for reaching and sustaining elimination. This research aims to generate an evidence base that will allow for more effective prioritization of particular regions or populations for the deployment of interventions, in order to achieve the greatest impact.

Partners: University of California San Francisco (UCSF), The Marshall Lab at UC Berkeley, Infectious Diseases Research Collaboration (IDRC), International Centers of Excellence for Malaria Research (ICEMR), Sanaria, Flowminder Foundation