Lead Institution: Johns Hopkins University
Research Areas
The overall goals of the Southern Africa ICEMR are to study barriers to malaria control and elimination and inform national strategies. The Southern Africa ICEMR addresses these challenges in low, moderate, and high transmission settings in Zambia.
- In the low transmission setting in southern Zambia, ICEMR researchers study how malaria transmission is sustained at low levels and what strategies are needed to achieve elimination.
- In the moderate transmission setting in Ndola District in Zambia, ICEMR researchers will study why malaria is increasing in this peri-urban environment to inform control strategies.
- In the high transmission setting in northern Zambia, ICEMR researchers will continue to investigate why the standard package of malaria control interventions, including indoor residual spraying, insecticide treated bed nets, and community case management, have not led to a substantial reduction in malaria burden.
These research questions are addressed using a multidisciplinary approach that combines classical epidemiology, geospatial science, serosurveillance, parasite and mosquito genetics, and vector bionomics in each of the three transmission settings.
High (Nchelenge) Transmission Setting
Why are interventions ineffective and who is contributing to transmission?
- Area A – Epidemiology - Longitudinal cohort, community and HF surveillance
- Area B – Transmission - Gametocytemia, STR typing, volatomics, biting behavior, digital vector ID
Moderate (Ndola) Transmission Setting
Why is malaria increasing in peri-urban areas and how should interventions be deployed?
- Area A – Epidemiology - HF surveillance, human behavior, genomics
- Area B – Transmission – Emerging vectors, biting behavior
Low (Choma) Transmission Setting
Where are foci and introductions of malaria and how should it be monitored?
- Area A – Epidemiology - HF surveillance, hotspots, genomics
- Area B – Transmission – Serological surveillance, real-time forecast, data visualization for outbreak detection
Key Achievements
Understanding low-level transmission is critical to achieving elimination in southern Zambia.
ICEMR researchers documented a dramatic decrease in the burden of malaria in southern Zambia as reflected in a decrease in pediatric hospitalizations for severe malaria, a decrease in malaria incidence at health centers, and a decrease in parasite prevalence through community-based surveys. However, malaria transmission persists, likely through a combination of parasite importation and local transmission arising from pauci-symptomatic reservoirs and hot spots. The National Malaria Elimination Programme in Zambia uses a reactive test-and-treat strategy to identify and treat parasitemic individuals who do not present for care. Challenges with implementation and the failure to detect low level parasitemia by rapid diagnostic test (RDT) have reduced the effectiveness of this strategy. Although Anopheles arabiensis is known to be the major vector, understudied secondary vectors, with outdoor biting behaviors, also contribute to ongoing transmission. Persistent challenges to elimination include unknown relative contributions of imported vs. endemic transmission, asymptomatic reservoirs with low level parasitemia, and outdoor biting by secondary vectors.
Reference: Ippolito MM, et al. Scientific Findings of the Southern and Central Africa International Center of Excellence for Malaria Research: Ten years of malaria control impact assessments in hypo-, meso- and holoendemic transmission zones in Zambia and Zimbabwe. Am J Trop Med Hyg 2022;107(4 Suppl):55-67.
Understanding why standard control interventions have had limited impact in high transmission area of northern Zambia
Nchelenge District in northern Zambia represents one of the most challenging settings for malaria control because of the ecology, complex vector bionomics, and high parasite prevalence. Malaria transmission is intense, with transmission occurring throughout the year and parasite prevalence greater than 50 percent. Standard malaria control interventions, including spatially targeted indoor residual spraying, insecticide treated bed nets, and community case management, have not led to a substantial reduction in malaria burden.
Researchers investigated reasons for the limited impact of these interventions to guide alternative control strategies and found:
- Minimal impact on parasite prevalence and vector abundance following changes in insecticides for indoor residual spraying after the ICEMR identified high levels of resistance to pyrethroids in the major malaria vectors.
- Complex vector bionomics of the two major vectors Anopheles gambiae and Anopheles funestus, with Anopheles funestus peaking in abundance at the end of the rainy season.
- Minimal impact of IRS on parasite prevalence when conducted at the end of the rainy season to target the peak in Anopheles funestus abundance.
- High human mobility between sprayed and unsprayed areas using GPS tracking loggers that may diminish the impact of targeted indoor residual spraying.
The ICEMR continues to work with the National Malaria Elimination Programme and key partners to monitor the impact of interventions and plan new strategies, including malaria vaccine introduction.
Reference: Ippolito MM, et al. Scientific Findings of the Southern and Central Africa International Center of Excellence for Malaria Research: Ten years of malaria control impact assessments in hypo-, meso- and holoendemic transmission zones in Zambia and Zimbabwe. Am J Trop Med Hyg 2022;107(4 Suppl):55-67.
Regional Impact
For more than a decade, the ICEMR has operated with local partners across study sites in Zambia and Zimbabwe that range from hypo- to holoendemic and vary ecologically and entomologically. The burden of malaria and the impact of control measures were assessed in longitudinal cohorts, cross-sectional surveys, passive and reactive case detection, and other observational designs. Findings have helped elaborate the patterns and possible causes of sustained low-to-moderate transmission in southern Zambia and eastern Zimbabwe and recalcitrant high transmission and fatality in northern Zambia. Cryptic and novel mosquito vectors, asymptomatic parasite reservoirs in older children, residual parasitemia and gametocytemia after treatment, indoor residual spraying not timed to vector abundance, and stock-outs of essential malaria commodities, all in the context of intractable rural poverty, appear to explain the persistent malaria burden despite current interventions. These scientific findings led to new policies and action by the national malaria control programs and their partners in the selection of methods, materials, timing, and locations of case management and vector control. Studies of reactive case detection informed malaria elimination programming in southern Zambia, and time series analyses of entomological and parasitological data motivated several major changes to indoor residual spray campaigns in northern Zambia
Study Sites
View Associated sites for the Southern Africa ICEMR in Zambia in a larger map
Collaborating Institutions
- Macha Research Trust, Macha, Zambia
- Tropical Diseases Research Centre, Ndola, Zambia
Staff
Principal Investigator: William Moss, M.D., M.P.H.
Project Leads
- Mathew Ippolito, Johns Hopkins School of Medicine
- William Moss, Johns Hopkins Bloomberg School of Public Health