The fight against malaria

In the documentary ‘The Fight against malaria’ we follow malaria researcher Teun Bousema, PhD candidate Daniel Ayo and their team at work in rural Uganda. The documentary illustrates the daily reality of scientific fieldwork in the fight against a cunning and ever-changing creature, the malaria parasite. 

One of their researches focuses on the effects of parasite mutations on infectivity, and findings have been published in The Lancet Infectious Diseases by Andolina, Chiara et al. Below is a brief reflection on this study addressing the sources of persistent malaria transmission in a setting with effective malaria control in eastern Uganda.

The hidden burden of asymptomatic malaria transmission poses a constant and looming threat to public health. The results of a large-scale longitudinal observational study, recently published in Lancet Infectious Disease, showed that school-aged children are the greatest contributors to malaria transmission.

This study aimed to investigate the contribution of different populations to the human malaria infectious reservoir. Gametocyte density plays a key role in facilitating transmission. Although there is no clear association between asexual parasite density and gametocyte density in symptomatic infections and a weak association in asymptomatic infections, the results of this study showed a gametocyte prevalence (via qRT-PCR) that is significantly higher in asymptomatic infections than in symptomatic infections.

Mosquito feeding assays showed that gametocyte density was strongly predictive of the proportion of mosquitos that became infected when feeding on a blood meal. However, gametocyte densities among gametocyte carriers differed between age groups with school-aged children (5-15 years) showing the highest densities. These school-aged children are therefore the mayor contributors to asymptomatic microscopy-detected infections, which are estimated to be responsible for 83.8% of the human infectious reservoir. 

The knowledge that school-aged children are the main reservoir is valuable information since to effectively eliminate malaria, it is the human infectious reservoir that must be targeted. School-aged children constitute a substantial portion of this reservoir, most likely because they have a higher complexity of infection and more persistent parasitaemia when compared to younger children or adults. Symptomatic malaria infections were uncommon and comprised only 0.6% of the human infectious reservoir.

School-aged children’s substantial role in the reservoir is likely due to their higher complexity of infection and more persistent parasitaemia compared to younger children or adults. Because they represent the largest hidden reservoir of infection, interventions should be directed toward school-aged children, ideally within the school setting. Such measures may include screening for infection, intermittent preventive treatment, and integrated vector control.