Effect of Single-course Malaria Chemoprevention on Clearance of and Protection from Plasmodium Falciparum Infection in the Presence of Resistance-associated Genotypes in Cameroon

The World Health Organization (WHO) recently published new malaria chemoprevention guidelines that included a recommendation for the provision of perennial malaria chemoprevention (PMC) with sulfadoxine-pyrimethamine (SP) to children resident in areas of high malaria transmission. PMC is the successor to an intervention originally known to as intermittent preventive treatment of malaria in infants (IPTi) that involved SP dosing of children at 2, 3 and 9 months of age during vaccination visits of the Essential Programme on Immunization (EPI) that coincide with the 2nd and 3rd doses of the DPT/Penta and measles vaccines. Under the new PMC guidelines, countries are now encouraged to increase the number and frequency of SP doses, and to extend the target age beyond the first year of life.1 Evidence supporting PMC comes in part from meta-analysis2 of six randomised placebo-controlled trials3-8 that demonstrated the protective effect of SP against clinical malaria, anaemia, hospital admissions due to malaria infection, and all-cause hospital admissions. Biomarkers of SP resistance, however, vary in different malaria-endemic settings and have been shown to compromise its protective effect.

In East and Southern Africa, Plasmodium falciparum parasites carry a high frequency of mutations in the Pfdhfr and Pfdhps genes with differing degrees of effect. In Mozambique, for example, SP was protective against malaria infection despite the Pfdhps A437G plus K540E double mutation circulating in over one-half, 52.3%, of P. falciparum (Pf) parasites. 5,9,10 In contrast, SP showed no protective effect in an IPTi trial in Northeastern Tanzania11 where 94.3% of Pf parasites had Pfdhps K540E. However, in this trial, the Pfdhps A581G mutation was also present in 55.0% of Pf parasites, forming the haplotype ISGEGA at codons 431, 436, 437, 540, 581 and 613.12 Thus, Pf appears to be highly resistant to SP where the A581G mutation is concurrently expressed with K540E. Fortunately, for PMC with SP there are few locations in East Africa where the combination of K540E and A581G circulate; most areas across Central, East and Southern Africa have parasites that contain the K540E without the A581G mutation (Pfdhps haplotype ISGEAA). The prevalence threshold of the ISGEAA haplotype at which SP is no longer protective is unknown. Indeed, there may not be an upper limit, although empirical studies are needed to confirm this.

In West Africa, specifically the Sahel region, there are emerging parasite genotypes that harbour a distinct haplotype of Pfdhps, VAGKGS,13,14 which lacks the K540E. These observations have come from molecular monitoring conducted alongside the delivery of intermittent preventive treatment of malaria in pregnancy (IPTp) with SP, and seasonal malaria chemoprevention (SMC) that targets children under 5 years of age with a combination of SP plus amodiaquine (AQ). The VAGKGS haplotype, and the related VAGKAS and VAGKAA, have been reported in 2-40% of Pf parasites in Cameroon, Chad, Niger and Nigeria. The current distribution of parasites harbouring these genotypes is only partially described, and the effect these mutations have on parasite susceptibility to SP remains unknown. Nevertheless, it is possible that parasites harbouring Pfdhps-VAGKGS pose a threat to the effectiveness of PMC with SP or other SP-containing chemoprevention strategies in some parts of the West African Sahel. Thus, there are two clear evidence gaps, one in East/Southern Africa and another in West Africa, which the PCPI (parasite clearance and protection from infection) protocol has been developed to fill. This particular version of the PCPI protocol has been written for use in Cameroon. Another PCPI protocol has been submitted for Zambia with different sample sizes, but with the same approach.

Our aim with the PCPI studies is to evaluate a single-dose of malaria chemoprevention where genotypes (Pfdhps haplotypes ISGEAA and VAGKGS) are associated with SP resistance among healthy and symptom-free children between 3-5 years of age with unknown parasite status. In Cameroon, our objective is to measure parasite clearance and protection from infection conferred by malaria chemoprevention over a 63-day period in the presence/absence of the Pfdhps I431V mutation.

The new WHO chemoprevention guidelines remove the upper age limit of 12 months so that countries may evaluate PMC among a broader range of ages. We selected an age range for eligibility from 3 years and 0 days to 4 years and 364 days with the rationale being that 3-4 years old are more likely to tolerate PMC dosing better than children 0-2 years old. They are also more likely to have some modest level of semi-immunity and, therefore, are less likely to develop a clinical episode of malaria during the follow-up period relative to children who are 0-2 years of age.