By Jackie Cook
Effective malaria surveillance, and the monitoring and evaluation of control and elimination efforts, are essential to track progress in malaria control and to know where best to target resources to maximise their impact. This is highlighted in the WHO’s Global Technical Strategy for Malaria 2016-2030 where surveillance constitutes one of three pillars identified as vital for the continued success of malaria control. The WHO highlights the importance of surveillance as a both core intervention, and as a way to prevent re-establishment of transmission. Work within the Malaria Centre covers both these aspects, along with important elements of surveillance research.
A wealth of malaria surveillance data has been collected from nationally representative household surveys, such as Malaria Indicator Surveys and Demographic and Health Surveys. An example within the Malaria Centre of a long running community-wide survey is the Bioko Island Malaria Project (Equatorial Guinea) in which large annual cross-sectional surveys chart longitudinal achievements of a control programme deploying extensive indoor residual spraying (IRS) and bed net distributions. The ongoing work has contributed data to enable evidence-informed deployment of intervention strategies in moderate to high malaria transmission areas. In contrast, in areas of low malaria prevalence alternative methods of detecting infections, such as the use of highly sensitive RDT pioneered by the PACES project in Cambodia, may be needed. The most commonly used RDT identify P. falciparum infections by detection of circulating HRP-2 antigen; however, work at LSHTM and elsewhere has shown that HRP-2 and HRP-3 deletions in P. falciparum are becoming more prevalent across the globe, potentially rendering RDTs less effective. We are compiling global genomic data regarding pfhrp2/3 deletions and exploring the consequences of HRP2 deletion for parasite fitness and virulence. An alternative to conducting surveillance by detection of parasites is to measure prevalence of parasite-specific antibodies circulating in the blood of people exposed to malaria. Within the Malaria Centre, researchers are exploiting newly optimised multiplex luminex assays and microarrays, with novel recombinant Plasmodium spp. antigens known to elicit short-term antibody responses, to assess malaria transmission dynamics, particularly in low transmission settings. These important new high-throughput methods enable the team to find areas that are most susceptible to re-establishment of transmission and to determine the distribution of emerging species, such as P. knowlesi.
Other key surveillance work within the Malaria Centre includes:
- the identification of substandard ACT being sold across sub-Saharan Africa and South East Asia, where P. falciparum resistance to artemisinin has been reported
- the development of tools to quickly and simply identify key inherited blood disorders such as HbC, HbS and G6PD which are associated with severity of disease, or play a role in disease management
- optimising data collection for confirmation of elimination, through identifying the relationship between passively collected data (which is often routine in preelimination countries) and community collected data (which can be logistically difficult to conduct)
- deploying methods established in veterinary science to establish certainty around measures of zero to help inform whether elimination has been achieved
- utilising alternative sampling strategies, such as easy access groups i.e. school children, or health facility attendees, to provide contribute information on malaria risk in the community without the need for logistically complicated surveys
- Integrating novel ways to map the precise location of cases within the community through readily available data, as a proxy for more logistically complicated surveys.