Across West and Central Africa, malaria remains the biggest killer of children under five. This area, from Senegal in the west to Sudan in the east, experiences highly seasonal transmission. By administering seasonal malaria chemoprevention (SMC) once a month for the four-month rainy season, evaluation through the ACCESS-SMC project provided evidence of substantial reductions in child malaria cases and deaths in hospital associated with malaria. This approach is currently used in thirteen countries in West and Central Africa. However, parasite resistance to SMC drugs across this region poses a potential threat to this intervention.
The ACCESS-SMC partnership, including researchers and national malaria programmes in seven countries, Malaria Consortium and Catholic Relief Services, working with researchers at LSHTM, investigated resistance to the SMC drugs deployed – sulfadoxine-pyrimethamine plus amodiaquine (SP-AQ). In 2016 and 2018 community surveys were conducted among children under 5 years and individuals over 10 years in districts implementing SMC with SP-AQ in Burkina Faso, Chad, Guinea, Mali, Nigeria, Niger and The Gambia, to collect dried blood samples for genotyping of P. falciparum. A large representative sample was taken in the same way in each country, the first time such comprehensive surveys have been undertaken in the subregion.
Molecular marker combinations known to be associated with drug resistance, haplotypes of P. falciparum genes pfcrt, pfmdr1, pfdhfr and pfdhps, were identified by PCR and sequencing, in order to estimate the prevalence of the key marker combinations and to determine if the prevalence has increased. No evidence of increasing resistance to the drugs was found but a resistance-associated haplotype of the parasite gene pfdhps is emerging in four countries - Mali, Niger, Nigeria and Chad.
The key markers of resistance were present at low prevalence, but the situation could change rapidly. There is an urgent need for further surveillance, as four years of SMC implementation have occurred since the samples described were collected. This should be done in the same locations using the same methods, to determine whether wide-scale deployment of SMC is driving resistance.
LSHTM first author, Dr Khalid Beshir, commented “The availability of modern technology with high throughput capability, and the concerted effort and effective collaboration of several institutions allowed us to successfully carry out this large-scale genotyping study”.
It remains critical for policy makers to commit to ongoing surveillance of SMC drugs to establish whether any threat to SP-AQ efficacy has arisen in these parasite populations since 2018.
Prevalence of Plasmodium falciparum haplotypes associated with resistance to sulfadoxine–pyrimethamine and amodiaquine before and after upscaling of seasonal malaria chemoprevention in seven African countries: a genomic surveillance study
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