BACKGROUND: Artemisinin-based combination therapy is the first-line anti-malarial treatment for uncomplicated Plasmodium falciparum infection in Angola. To date, the prevalence of polymorphisms in the pfk13 gene, associated with artemisinin resistance, and pfmdr1, associated with lumefantrine resistance, have not been systematically studied in Angola. METHODS: DNA was isolated from pretreatment and late treatment failure dried blood spots collected during the 2015 round of therapeutic efficacy studies in Benguela, Lunda Sul, and Zaire Provinces in Angola. The pfk13 propeller domain and pfmdr1 gene were sequenced and analysed for polymorphisms. Pfmdr1 copy number variation was assessed using a real-time PCR method. The association between pfmdr1 and pfk13 mutations and treatment failure was investigated. RESULTS: The majority of pretreatment (99%, 466/469) and all late treatment failure (100%, 50/50) samples were wild type for pfk13. Three of the pretreatment samples (1%) carried the A578S mutation commonly observed in Africa and not associated with artemisinin resistance. All 543 pretreatment and day of late treatment failure samples successfully analysed for pfmdr1 copy number variation carried one copy of pfmdr1. The NYD haplotype was the predominant pfmdr1 haplotype, present in 63% (308/491) of pretreatment samples, followed by NFD, which was present in 32% (157/491) of pretreatment samples. The pfmdr1 N86 allele was overrepresented in day of late treatment failure samples from participants receiving artemether-lumefantrine (p value 0.03). CONCLUSIONS: The pretreatment parasites in patients participating in therapeutic efficacy studies in 2015 in Angola's three sentinel sites showed genetic evidence of susceptibility to artemisinins, consistent with clinical outcome data showing greater than 99% day 3 clearance rates. The lack of increased pfmdr1 copy number is consistent with previous reports from sub-Saharan Africa. Although pfmdr1 NYD and NFD haplotypes were overrepresented in artemether-lumefantrine late treatment failure samples, their role as markers of resistance was unclear given that these haplotypes were also present in the majority of successfully treated patients in the artemether-lumefantrine treatment arms.

BACKGROUND: Recent anti-malarial resistance monitoring in Angola has shown efficacy of artemether-lumefantrine (AL) in certain sites approaching the key 90% lower limit of efficacy recommended for artemisinin-based combination therapy. In addition, a controversial case of malaria unresponsive to artemisinins was reported in a patient infected in Lunda Sul Province in 2013. METHODS: During January-June 2015, investigators monitored the clinical and parasitological response of children with uncomplicated Plasmodium falciparum infection treated with AL, artesunate-amodiaquine (ASAQ), or dihydroartemisinin-piperaquine (DP). The study comprised two treatment arms in each of three provinces: Benguela (AL, ASAQ), Zaire (AL, DP), and Lunda Sul (ASAQ, DP). Samples from treatment failures were analysed for molecular markers of resistance for artemisinin (K13) and lumefantrine (pfmdr1). RESULTS: A total of 467 children reached a study endpoint. Fifty-four treatment failures were observed: four early treatment failures, 40 re-infections and ten recrudescences. Excluding re-infections, the 28-day microsatellite-corrected efficacy was 96.3% (95% CI 91-100) for AL in Benguela, 99.9% (95-100) for ASAQ in Benguela, 88.1% (81-95) for AL in Zaire, and 100% for ASAQ in Lunda Sul. For DP, the 42-day corrected efficacy was 98.8% (96-100) in Zaire and 100% in Lunda Sul. All treatment failures were wild type for K13, but all AL treatment failures had pfmdr1 haplotypes associated with decreased lumefantrine susceptibility. CONCLUSIONS: No evidence was found to corroborate the specific allegation of artemisinin resistance in Lunda Sul. The efficacy below 90% of AL in Zaire matches findings from 2013 from the same site. Further monitoring, particularly including measurement of lumefantrine blood levels, is recommended.

Results from regular drug efficacy monitoring should always be interpreted in the context of the many limitations inherent to attributing apparent treatment failures to antimalarial resistance, as concisely summarized by Hamed and Kuhen (1). Notably, in study settings where direct supervision of the evening doses of artemether-lumefantrine (AL) is operationally infeasible or culturally unacceptable, low efficacy can also potentially be attributed to inaccurate dosing or underdosing. Details of how we strived to guarantee participant compliance with evening doses in lieu of direct supervision are found in our original report (2). Importantly, procedures were identical in both provinces, and we have no indication that participant adherence to the evening doses or food consumption guidelines was different in Zaire Province, where we found lower efficacy of AL. While lack of direct observation of doses and nonadherence to guidelines regarding food consumption with drug administration have been shown to be associated with lower blood lumefantrine levels, they have not been directly associated with decreased efficacy of AL (3, 4). | | While in vitro susceptibility testing requires infrastructure rarely found at drug efficacy monitoring sites, there is a long history of complementing clinical outcome data with testing for known molecular markers of resistance (5). Samples from treatment failures with mutations associated with resistance provide more evidence of resistance than clinical outcome data alone. In our study, the detection of pfmdr1 haplotypes previously associated with decreased sensitivity to lumefantrine (6) and the absence of mutations associated with artemisinin resistance in AL treatment failures support the hypothesis of lumefantrine resistance. | | Notably, the NFD and NYD pfmdr1 haplotypes predominated not only in recrudescent infections but also in reinfections in the AL arms. Contrary to Hamed and Kuhen's assertion, reinfections observed during follow-up do provide important data on efficacy. For the calculation of uncorrected efficacy, an important outcome for therapeutic efficacy studies, both reinfections and recrudescences are considered treatment failures. The reporting and interpretation of uncorrected efficacy results are standard components of drug efficacy monitoring for two primary reasons (7,–9). First, uncorrected efficacy estimates are not subject to the limitations and potential biases of using genotyping data to differentiate reinfection from recrudescence. Second, uncorrected efficacy results provide data concerning the posttreatment prophylactic effect of the partner drug in artemisinin-based combination therapies and thus the proportion of clients that will require retreatment, data of increasing interest to malaria control programs. The reinfection rates in the AL arms in Zaire and Uíge Provinces provide a good example of the potential utility of reinfection rates. The reinfection rate in Zaire (13%) was measured as more than twice the rate in Uíge (5.1%). This was despite our screening data, where 67% of the children screened tested positive for malaria in Uíge, compared to 53% in Zaire, indicating that transmission was almost certainly higher in Uíge at the time of our study. This unexpectedly high rate of reinfection in Zaire could therefore point to a parasite population that is less sensitive to lumefantrine and that consequently has a higher likelihood of successfully invading patients with subtherapeutic doses of lumefantrine following AL treatment (10). | | Finally, we would like to reaffirm that while certain screened children had parasitemia levels above 100,000 parasites/μl, only children with parasitemia levels between 2,000 and 100,000 parasites/μl were enrolled in the study, as described in Materials and Methods. Given that no children with parasitemia levels above 100,000 parasites/μl were enrolled in any of the study arms at either site, differences in hyperparasitemia rates between the Uíge and Zaire AL arms cannot explain the difference in efficacy as Hamed and Kuhen suggest.

The development of resistance to antimalarials is a major challenge for global malaria control. Artemisinin-based combination therapies, the newest class of antimalarials, are used worldwide but there have been reports of artemisinin resistance in Southeast Asia. In February-May 2013, we conducted open-label, nonrandomized therapeutic efficacy studies of artemether-lumefantrine (AL) and dihydroartemisinin-piperaquine (DP) in Zaire and Uige Provinces in northern Angola. The parasitological and clinical responses to treatment in children with uncomplicated P. falciparum monoinfection were measured over 28 days and the main outcome was PCR-corrected adequate clinical and parasitological response (ACPR) proportion on day 28. Parasites from treatment failures were analyzed for the presence of putative molecular markers of resistance to lumefantrine and artemisinins, including the recently identified mutations in the K13-propeller gene. In the 320 children finishing the study, 25 treatment failures were observed, 24 in the AL arms and one in the DP arm. The PCR-corrected ACPR proportion on day 28 for AL was 88% (95% CI: 78-95) in Zaire and 97% (91-100) in Uige. For DP, it was 100% (95-100) in Zaire, and 100% (96-100) in Uige. None of the treatment failures had molecular evidence of artemisinin resistance. In contrast, 91% of AL treatment failures had markers associated with lumefantrine resistance on day of failure. The absence of molecular markers for artemisinin resistance and the observed efficacies of both drug combinations suggest no evidence of artemisinin resistance in northern Angola. There is evidence of increased lumefantrine resistance in Zaire, which should continue to be monitored.