In vitro cultured malaria hypnozoites leave a footprint of specific metabolites.

Plasmodium vivax malaria control and elimination is complicated by the presence of dormant liver stages, known as hypnozoites, that can reactivate weeks, months or years after infection giving rise to clinical and transmissible vivax malaria, without exposure to new infectious mosquito bites. Hypnozoite infection remains without symptoms and there are no diagnostic tools available to identify hypnozoite carriers. Such diagnostic tools are invaluable for precise mapping of the scale of the infection problem and for identifying individuals that would qualify for targeted drug treatment, to wipe out this hidden reservoir of malaria parasites. Targeted treatment would have considerable benefits as it would prevent the exposure of individuals without hypnozoites to the considerable side-effects of drugs such as Primaquine, which has a relatively high toxicity to people deficient in glucose-6-phosphate dehydrogenase. Here we present a Proof-of-Concept study aimed at identifying diagnostic markers for malaria hypnozoite infection, by combining in vitro Plasmodium cynomolgi hypnozoite cultures (an accessible proxy to P. vivax with nearly identical biology) with sensitive metabolomics. Specific hypnozoite-related metabolites have been identified in the supernatant of hypnozoite-enriched in vitro liver stage cultures. This suggests that, following in vivo validation of such metabolites in the P. cynomolgi/rhesus monkey model and subsequent in P. vivax-infected individuals, a rapid diagnostic test for hypnozoite infection may be developed.