By Chris Drakeley
Malaria elimination is an explicit goal for a significant number of malaria-endemic countries, including some where nation-wide elimination may seem unrealistic but sub-national elimination is possible due to the natural heterogeneity of malaria transmission.
The Malaria Centre works in several African countries where transmission is uniformly low (The Gambia, Namibia, and South Africa), a number of south east Asian countries coping with varied parasite species, human movement and drug resistance (Cambodia, Malaysia, Philippines, Indonesia) and the only country in the Caribbean with indigenous transmission (Haiti).
These different study sites have in common a need to identify the driving forces behind persisting transmission, so that spatial and/or demographic foci (hot spots and hot pops) can be better understood and targeted. Work in Cambodia highlights the multifaceted nature of work required to understand ongoing transmission. Building on strong links with the national control programme, Malaria Centre researchers have investigated different approaches to identify and target infected individuals in the face of the threat of drug resistance. This involves proactive detection of infections, including among high-risk forest-goers, and attempting to increase efficacy by involving community members. These efforts are coupled with the evaluation of new rapid diagnostic tests with reportedly higher sensitivity in detecting individuals with low-density parasite infections, which have been implicated in the maintenance of transmission.
A key component for any intervention is the cost that would ultimately have to be borne by control programmes. Both the proactive infection detection in Cambodia and reactive household detection in the Gambia have core economic components that will help guide intervention choice. Similarly, rationalising choice and use of existing interventions is equally important. In South Africa, a study comparing targeted versus blanket IRS showed no difference in efficacy but a significant reduction in cost with targeted interventions.
The Malaria Centre at LSHTM has been at the forefront of investigating the use of specific antimalarial antibody responses as markers of exposure and transmission. Antibodies are longer-lived than infections in either mosquitoes or humans and therefore have unique potential as a marker of previous infection, particularly at low transmission. Malaria Centre projects located in Indonesia, South Africa and Haiti are examining the utility of serological markers of infection to describe hotspots of transmission, and to stratify areas for interventions. Studies in Namibia and The Gambia have extended the use of these markers to post-intervention evaluation, and in particular to include antigens that are associated with recent infections. This offers an alternative approach to measure incidence which has considerable potential for the future.