Increasing Prevalence of Artemisinin-Resistant HRP2-Negative Malaria in Eritrea.

Abstract

Although the clinical efficacy of antimalarial artemisinin-based combination therapies in Africa remains high, the recent emergence of partial resistance to artemisinin in <i>Plasmodium falciparum</i> on the continent is troubling, given the lack of alternative treatments. In this study, we used data from drug-efficacy studies conducted between 2016 and 2019 that evaluated 3-day courses of artemisinin-based combination therapy (artesunate-amodiaquine or artemether-lumefantrine) for uncomplicated malaria in Eritrea to estimate the percentage of patients with day-3 positivity (i.e., persistent <i>P. falciparum</i> parasitemia 3 days after the initiation of therapy). We also assayed parasites for mutations in <i>Pfkelch13</i> as predictive markers of partial resistance to artemisinin and screened for deletions in <i>hrp2</i> and <i>hrp3</i> that result in variable performance of histidine rich protein 2 (HRP2)-based rapid diagnostic tests for malaria. We noted an increase in the percentage of patients with day-3 positivity from 0.4% (1 of 273) in 2016 to 1.9% (4 of 209) in 2017 and 4.2% (15 of 359) in 2019. An increase was also noted in the prevalence of the <i>Pfkelch13</i> R622I mutation, which was detected in 109 of 818 isolates before treatment, from 8.6% (24 of 278) in 2016 to 21.0% (69 of 329) in 2019. The odds of day-3 positivity increased by a factor of 6.2 (95% confidence interval, 2.5 to 15.5) among the patients with <i>Pfkelch13</i> 622I variant parasites. Partial resistance to artemisinin, as defined by the World Health Organization, was observed in Eritrea. More than 5% of the patients younger than 15 years of age with day-3 positivity also had parasites that carried <i>Pfkelch13</i> R622I. In vitro, the R622I mutation conferred a low level of resistance to artemisinin when edited into NF54 and Dd2 parasite lines. Deletions in both <i>hrp2</i> and <i>hrp3</i> were identified in 16.9% of the parasites that carried the <i>Pfkelch13</i> R622I mutation, which made them potentially undetectable by HRP2-based rapid diagnostic tests. The emergence and spread of <i>P. falciparum</i> lineages with both <i>Pfkelch13</i>-mediated partial resistance to artemisinin and deletions in <i>hrp2</i> and <i>hrp3</i> in Eritrea threaten to compromise regional malaria control and elimination campaigns. (Funded by the Bill and Melinda Gates Foundation and others; Australian New Zealand Clinical Trials Registry numbers, ACTRN12618001223224, ACTRN12618000353291, and ACTRN12619000859189.).