Artemisinin resistance surveillance is looking for the wrong signal in Africa

Design

systematic review of 96 studies across southeast Asia and Africa, 35 with genotype-linked clearance or ring-stage survival data

Population

Plasmodium falciparum infections with and without kelch13 mutations

Primary outcome

concordance between parasite clearance half-life and ring-stage survival by continent

Effect

southeast Asian kelch13 mutants showed prolonged clearance with concordant ring-stage survival; east African mutants showed faster clearance despite raised ring-stage survival

Artemisinin partial resistance is defined operationally by a prolonged parasite clearance half-life after treatment, a threshold derived in southeast Asia where kelch13 mutations produce exactly that. This review of 96 studies, 35 of them with genotype-linked clearance or ring-stage survival assay data, asked whether the definition transfers.

In southeast Asia it works: canonical kelch13 mutants clear slowly, and clearance half-life and ring-stage survival agree. In east Africa and the Horn of Africa the pattern breaks. Independently emergent kelch13 mutations there show raised ring-stage survival — the in vitro marker of artemisinin tolerance — while clearing at close to normal speed in patients. A surveillance system watching clearance half-life alone would record those infections as sensitive.

The authors' concern is timing rather than treatment. The Greater Mekong experience was that resistance was detected after it had spread widely and partner drugs were already failing. If African resistance is phenotypically quieter, the same delay is being built in — and delay is what allows resistant parasites to reach genetic fixation before policy responds.

• Treatment advice is unchanged: artemisinin-based combination therapy remains first line, and this is about surveillance definitions.
• A patient who clears parasitaemia on schedule has not ruled out a resistant parasite in an African setting.
• Partner-drug susceptibility matters as much as artemisinin susceptibility — most ACT failures are partner-drug failures.
• India's falciparum burden is concentrated in the north-east and tribal belts, and surveillance there uses the same thresholds; the same caution applies.
• Record and report day-3 parasitaemia where you can — it is the data that makes any of this visible.

Why it matters

If the definition does not fit, resistance will be detected late — which is exactly how it happened in the Mekong.

Don't overread it

This is a review of existing studies proposing a surveillance change, not new field data showing treatment failure in Africa.

The statistics, in plain English

This is a narrative systematic review, not a meta-analysis, so there is no pooled effect estimate to quote — the finding is a discordance between two measures rather than a difference between two groups. Ring-stage survival assay and clearance half-life measure different things: one is parasite biology in vitro, the other is the combined result of parasite biology, host immunity and initial parasite burden. In high-transmission African settings, acquired immunity clears parasites faster, which is a plausible reason the two measures diverge there and not in Asia.

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