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Tracking shifting malaria trends in Zambia

March 3, 2021: New research by EPI investigators examines why intervention strategies to mitigate malaria in Zambia began failing several years ago. In a twist, the mechanisms were predicted by a separate EPI investigator in different work published five years earlier.

New research connected to the medical geography unit in the University of Florida’s College of Liberal Arts and Sciences has uncovered shifting trends in malaria transmission in Zambia. As a standalone finding, this would not be too surprising as the presence of infectious diseases sometimes shift geographically over time. But what makes this finding so interesting is that a separate UF researcher predicted these changes five years ago.

A few years back, UF postdoctoral researcher Ubydul Haque was collaborating with UF geography professor Gregory Glass to develop affordable antimalarial interventions in Zambia. But after initial success, the past few years saw a resurgence of cases, which led the team to ask: Why?

Haque coauthored the new study, which published recently in the Nature Research journal Scientific Reports. The new research uses socioeconomic, spatial, and temperature data from 2000-2016 to model changes in the incidence of malaria in Zambia. The team found that targeted interventions designed to eliminate malaria in the country were working at the beginning of their study period. But around 2009, the incidence of malaria began to increase in some areas, despite the interventions remaining stable.

Areas where malaria had been stable began to see an increase in cases. And areas where malaria had already been increasing began to see this trend amplify. But areas where malaria had been declining saw an even more exaggerated decline:

Graphs showing seasonal changes in malaria incidence in Zambia

Panel A in the graph above shows seasonal incidence trends in areas with declining malaria transmission. Panel B shows seasonal incidence trends in areas where malaria transmission held constant in some quarters. Panel C shows seasonal incidence trends in areas where malaria transmission is increasing in all quarters.

The team attributed these changes to fluctuations in the climate, an observation that aligns with predictions made by UF medical geographer Sadie Ryan five years earlier in a separate paper. Both Ryan and Glass are professors in UF’s College of Liberal Arts and Sciences, and they are faculty in UF’s Emerging Pathogens Institute.

Ryan’s research predicted that areas of Africa suitable to malaria transmission would shift due to changes in both climate and projected human density. Places where malaria transmission occurred year-round would move from coastal West Africa to the Albertine Rift area, which is located roughly between the Democratic Republic of Congo and Uganda. And places with only seasonal transmission would shift toward sub-Saharan coastal areas. 

Haque coauthored a second paper that was recently published in PLOS-Computational Biology which describes a method of targeting regions with a high burden of malaria for rigorous control measures while maintaining a stable elimination effort in other areas. The work is meant to help governments adaptively manage seasonal changes in malaria transmission.