Measuring changes in Plasmodium falciparum census population size in response to sequential malaria control...

Area of Science:

• Malariology
• Population Genetics
• Epidemiology

Background:

• Assessing Plasmodium falciparum epidemiology and control traditionally focuses on human host infections.
• Measuring parasite population dynamics is crucial for understanding malaria transmission and intervention effectiveness.

Purpose of the Study:

• Introduce a novel endpoint, 'census population size,' for evaluating Plasmodium falciparum epidemiology.
• Develop a method to estimate parasite census population size using parasite genetic variation.
• Track changes in Plasmodium falciparum population size and genetic structure in response to malaria interventions.

Main Methods:

• Defined 'census population size' based on parasite variation (multiplicity of infection, MOIvar).
• Employed a Bayesian approach to estimate MOIvar from sequencing unique DBLα tag types of var genes.
• Monitored parasite population size and var diversity through indoor residual spraying (IRS) and seasonal malaria chemoprevention (SMC) in northern Ghana (2012-2017).

Main Results:

• Indoor residual spraying (IRS) significantly reduced parasite prevalence, transmission intensity, var diversity, MOIvar, and population size.
• Reductions in parasite metrics were temporary; populations rebounded after IRS cessation and introduction of SMC.
• Parasite populations rebounded across most age groups, except for young children (1-5 years) targeted by SMC.
• Despite interventions, Plasmodium falciparum populations remained large and maintained genetic characteristics of high-transmission systems, indicating resilience.

Conclusions:

• The 'census population size' offers a valuable new metric for malaria epidemiology and control assessment.
• Plasmodium falciparum exhibits significant resilience to short-term malaria interventions in high-burden settings.
• Targeted interventions like SMC may have differential impacts on parasite population structure across age groups.