Developing methods to assess the impact of malaria interventions upon transmission and the progress towards elimination

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Malaria, an infectious disease transmitted by mosquitoes, is estimated to cause around 1 million deaths per year, with the majority of these deaths occurring in sub-Saharan Africa, primarily amongst young children. Over the last decade there has been an increase in funding from high-income countries and global agencies with the aim of reducing transmission and hence decreasing the burden of disease. This has resulted in the large-scale distribution of interventions of cheap and effective interventions such as the provision of protective bed nets and antimalarial medication in many parts of the world.Malaria is, however, a complicated disease. It is spread between humans by mosquitoes and people become more immune to the disease the more they are infected (and less immune when they are not). This makes it difficult to work out the progress that has been made in reducing transmission. For example, a 50% reduction in the number of mosquito bites would not necessarily produce a 50% reduction in the proportion of people with malaria. Moreover, as transmission is imperfect and requires an infected mosquito to survive until it becomes infectious to humans, it is not necessary to kill all mosquitoes or prevent all members of the population from being bitten to achieve elimination. In Western Kenya, particularly around the shores of Lake Victoria, malaria transmission remains intense, even in areas where bed nets have been used by the majority of the population for over a decade and despite the availability of effective anti-malarial medication for those with the disease. As a result, further intervention measures are currently being considered, including a forthcoming trial looking at the effects of testing all residents within a village for infection and giving highly effective anti-malarial medication to all those who test positive to infection in an attempt to break transmission. In order to better understand the progress towards this goal, and the implication the trial outcome has for malaria elimination more generally, it is important to understand where the trial started and where the trial ended in terms of transmission (i.e. the chances of an infected person passing infection to others via a mosquito), as this is the only reliable measure of the extent to which elimination is likely to be sustainable. In this project, Dr Patrick Walker, a researcher at the Department of Infectious Disease Epidemiology, Imperial College, will use mathematical models of the spread of malaria to estimate the changes in transmission that occur during this trial to assess the progress being made towards local elimination of the disease. This will first involve developing a statistical technique which is able to estimate changes in transmission intensity during a previous trial of protective nets in the same area This work will also allow him to investigate the extent to which the disease spreads from one village to another and how this is affected by the presence of nets within different areas. This technique will then be adapted and applied to the different arms of the drug trial, taking into account changes in transmission up to the beginning of the trial.In the event that the mass administration of anti-malarials proves effective as a tool for helping Western Kenya to eliminate malaria, this research will help to further define the criteria by which to judge where else in the world the intervention could be effective. Alternatively, if the intervention does not prove effective the work will provide an indication of the additional level of control required to achieve elimination. Moreover, monitoring whether transmission changes throughout the trial could provide an indication as to whether the effectiveness of anti-malarial drugs remains the same throughout the trial, which is an important consideration in light of concerns about drug resistance.