Effective strategies for preventing reestablishment of malaria in areas with recent elimination and high transmission potential

Abstract

Maintaining zero transmission after malaria elimination will be a challenging task for many countries where malaria is still endemic. When local transmission potential is high, and importation of malaria infections continues from neighboring areas with ongoing transmission, malaria programs must develop robust surveillance and outbreak response systems. However, the requirements for such systems remain unclear. Using an agent-based, spatial microsimulation model of two areas in southern Zambia, where elimination efforts are currently underway, we compare the ability of various routine and reactive intervention packages to maintain near-zero prevalence in the face of continued importation. We find that in formerly moderate-transmission areas, high treatment rate of symptomatic malaria is sufficient to prevent reestablishment of malaria. Routine redistributions of insecticide-treated nets and reactive case detection with antimalarial drugs cannot completely compensate for inadequate case management. In formerly high-transmission areas, excellent case management and maintenance of good bednet coverage are both required to prevent resurgence, and outbreak response with antimalarial drugs or additional vector control is also necessary. These results begin to describe the essential criteria for operations that successfully prevent reestablishment of malaria post-elimination and highlight the need for both long-term, sustainable excellence in primary care and comprehensive surveillance that feeds into rapid and flexible outbreak response. Author SummaryThe global community is working toward malaria elimination, but some areas will eliminate before others. Eliminated areas will need to develop intervention programs capable of preventing imported infections from leading to reestablishment, a particular challenge when transmission was previously very high. Past experience has shown that stopping elimination interventions leads to massive resurgence, but it is unclear which interventions must be continued, which can be stopped to conserve resources, and what new interventions should be deployed. Using a simulation model built to capture malaria transmission and intervention history of two areas that recently made enormous progress toward elimination, we tested how well different intervention programs were able to prevent reestablishment of malaria. We found that treating as many symptomatic cases as possible was the single most important intervention to implement. In some contexts, this intervention alone was sufficient to prevent reestablishment. Other areas with historically higher transmission required maintaining vector control to contain mosquito populations. Localized outbreak response with antimalarial drugs or additional vector control was also necessary and predicted to be a highly efficient use of resources. These findings provide quantitative guidance for policy-makers considering how to stratify eliminated areas and plan new operational modes for the post-elimination era.