Endemicity response timelines for Plasmodium falciparum elimination

Area of Science:

• Epidemiology
• Mathematical Biology
• Public Health

Background:

• Scaling up malaria control and eradication efforts necessitate understanding timelines for changes in malaria endemicity.
• Previous malaria eradication programs relied on models that may not fully capture complex transmission dynamics.

Purpose of the Study:

• To critically review and extend epidemiological theory for Plasmodium falciparum parasite rate (PfPR) decline post-intervention.
• To establish timelines for malaria control and elimination using mathematical models considering factors like superinfection.

Main Methods:

• Reviewed epidemiological theory for PfPR decline, incorporating superinfection, heterogeneous biting, and aging infections.
• Utilized a range of mathematical models to simulate timelines for malaria control and elimination.
• Focused analysis on timelines from baseline to 1% PfPR and from 1% to elimination.

Main Results:

• Models incorporating superinfection predict a 2-3 year longer timeframe to reach 1% PfPR from a hyperendemic baseline compared to models ignoring it.
• Time to elimination is contingent on the level of transmission interruption and the modeled human population size.
• Post-1% PfPR decline shows proportional yearly reductions, with roughly equal time intervals to decrease from 10% to 1% and 1% to 0.1%, potentially accelerating with infection senescence.

Conclusions:

• The developed theory offers practical "rules of thumb" and timeframes for malaria control and elimination impacts.
• Global Malaria Eradication Programme timelines, based on simplified models, were optimistic and potentially inappropriate for diverse endemicity settings.
• Elimination timelines from 1% PfPR are influenced by population size and residual transmission, providing a theoretical basis for tailored strategies.