Malaria prevalence of 18% found in this study was higher than 10% and 13% observed among pregnant women in another Kenyan coastal region (16) and the lake region in Tanzania (17), respectively, but significantly lower than 31% documented in the Kenyan lake regions (16). Therefore, the high burden of malaria in pregnancy remains of public health concern. As observed in this study and elsewhere (18–20), younger women in their first pregnancy are at greatest risk of infection and should be targeted with preventive and early treatment interventions.
IPTp-SP is an important prophylactic therapy recommended for prevention of malaria in high endemic African regions to reduce morbidity/mortality among pregnant women and adverse pregnancy outcomes (2).The emerging high Pf resistance to the SP is likely to render IPTp-SP prophylactic intervention ineffective. Similar to our findings, other studies have reported high prevalence (78%–97%) of quintuple PfDHFR/PfDHPS haplotype mutations in western Kenya (10,21). Studies elsewhere have documented quadruple mutations (65%) in Equatorial Guinea (22) and 48% in DRC (23), and triple mutations (92%) in Gabon (24) and 61–71% in Burkina Faso (25) as the most prevalent. Similar to India, where double mutation was the most prevalent (26,27), a study in Brazil reported double mutation as most prevalent but did not find quintuple or quadruple mutations (28).
Findings from this study demonstrated very high prevalence of SNPs at the two important genes that confer SP resistance. The high prevalence of 89% observed at PfDHFR51I in this study was similarly to (85%–100%) documented in western Kenya and elsewhere (10,21–24,29), but contrary to the 21% reported in India (26). Although a study in DRC reported a conservative prevalence of 60% (23) at 59R, other studies found slightly higher prevalence (87%–98%) at this codon (10,21,22,24,26,29), compared to 78% demonstrated in this study. In agreement with our study, investigations elsewhere found a prevalence of ≥97% at 108N (10,21–24,26,27,29). In contrast to average prevalence (66%–68%) reported in India and Gabon (24,26), prevalence of >90% at PfDHPS437G was reported in this study, western Kenya and parts of central Africa. (10,21–23,29). PfDHPS540E mutation is highly prevalent in Kenya (10,21), but rare in several countries, which have reported a prevalence of only 0–5% (22–24,29).
PfDHFR polymorphism at 51I, 59R and 108N combined mutations of 89% observed in this study was similar to 89–97% documented in western Kenya among pregnant women(10,21). Proportion comparable to these have been reported elsewhere: 97% in Uganda (8); 87% in Equatorial Guinea (22); 98% in Cameroon (29), and 93% in Senegal (30). These frequencies were higher compared to 48% detected in DRC (23) and 54 –74% in Burkina Faso (25,31). The high frequency (94%) of PfDHPS gene double mutation (437G and 540E) reported in this study concurs with findings from other studies in East Africa that reported 90–99% and 99% in western Kenya (10,21) and Uganda (8) respectively. However, double mutation in this gene are reportedly rare occurring with a prevalence of 4% in Equatorial Guinea (22), 1% in Burkina Faso (25),and 2% in DRC (23). An average mutation prevalence of 71.3% was seen at codon 540E in the coastal regions of Tanzania which was low when compared to the country prevalence of 92.4% (9).
Several studies have demonstrated that the differing degrees of antimalarial drug resistance are dependent upon the number and combination of mutations present (32). The PfDHFR/PfDHPS quintuple mutant, in either mixed or pure form, is the most clinically relevant molecular marker for SP resistance. In the East African region, the prevalence of molecular markers of SP resistance has been increasing since the emergence of the first resistance-conferring mutations in the 1950s (9). Therefore, continuous molecular surveillance will allow early detection of drug resistance susceptibility and high mutation prevalence within the PfDHFR and PfDHPS gene of the Pf parasite that reduce SP drug effectiveness as a prophylactic treatment for malaria in pregnancy (25). These finding show that there is high prevalence of PfDHFR/PfDHPS haplotype mutations believed to confer resistance to SP, the drug of choice for malaria prophylactic treatment in pregnant women. Our data aligned with findings in other parts of Kenya and other tropical regions in defining high prevalence of SP resistance markers within circulating Pf isolates.