Understanding the Transmission Intensity of Plasmodium Falciparum in Lilongwe, Malawi

Abstract

The GlaxoSmithKline RTS,S vaccine has been undergoing Phase III trials to evaluate efficacy for protection from malaria, a disease infecting between 300-600 million people every year. As RTS,S is a transmission blocking vaccine, transmission intensity may be important in vaccine efficacy. Therefore, all trial sites conducted a concordant Malaria Transmission Intensity (MTI) study, from 2011-2013, to look at the prevalence of malaria by microscopy within the trial site. Malaria parasitemia prevalence is often used as a surrogate of transmission intensity. Unfortunately, it is known that microscopy can miss many, if not most, of malaria parasitemia in a population. Nucleic acid detection methods are more sensitive than microscopy, often detecting parasitemia counts below the detection limit of microscopy (called “submicroscopic” parasitemia). We use a real-time Polymerase Chain Reaction (RT-PCR) assay for pfldh on dried blood spots from 800 patient blood samples collected during the 2013 MTI study in Lilongwe, Malawi to determine the difference in prevalence of parasitemia between testing methods. We found that the addition of RT-PCR nearly tripled the number of participants with malaria detected (5.6% by microscopy vs. 14.3% composite microscopy or RT-PCR.). We then analyzed the malaria prevalence of submicroscopic parasitemia within specific demographic groups to identify risk factors associated with greater rates of parasitemia. This data suggests that transmission intensity within Lilongwe was greater than previously expected, which may have impacted vaccine efficacy, and that differences in transmission intensity may have differed significantly between demographics groups. Future studies should research the impact this has on vaccine effectiveness and how this can be utilized when redesigning the vaccine so that future versions can be more effective in reducing infections.Bachelor of Scienc