Resistance to artemisinin-based combination therapy (ACT) in the <i>Plasmodium falciparum</i> parasite is threatening to reverse recent gains in reducing global deaths from malaria. While resistance manifests as delayed parasite clearance in patients, the phenotype can only spread geographically via the sexual stages and mosquito transmission. In addition to their asexual killing properties, artemisinin and its derivatives sterilize sexual male gametocytes. Whether resistant parasites overcome this sterilizing effect has not, however, been fully tested. Here, we analyzed <i>P. falciparum</i> clinical isolates from the Greater Mekong Subregion, each demonstrating delayed clinical clearance and known resistance-associated polymorphisms in the <i>Kelch13</i> (PfK13<sup>var</sup>) gene. As well as demonstrating reduced asexual sensitivity to drug, certain PfK13<sup>var</sup> isolates demonstrated a marked reduction in sensitivity to artemisinin in an <i>in vitro</i> male gamete formation assay. Importantly, this same reduction in sensitivity was observed when the most resistant isolate was tested directly in mosquito feeds. These results indicate that, under artemisinin drug pressure, while sensitive parasites are blocked, resistant parasites continue transmission. This selective advantage for resistance transmission could favor acquisition of additional host-specificity or polymorphisms affecting partner drug sensitivity in mixed infections. Favored resistance transmission under ACT coverage could have profound implications for the spread of multidrug-resistant malaria beyond Southeast Asia.
Antimicrobial agents and chemotherapy
Department of Life Sciences, Imperial College London, London, United Kingdom.