Perturbation of Plasmodium vivax hypnozoite formation, growth and reactivation in vivo in a human-liver chimeric mouse

Plasmodium vivax eradication will necessitate an additional set of interventions to prevent and cure latent liver infection. Unlike P. falciparum, P. vivax can remain dormant in an infected persons’ liver for months to years before the parasite reactivates and causes clinical disease. While it is recognized that drugs, vaccines and mosquito interventions are all necessary to eradicate malaria, the eradication of vivax malaria will require not only preventing the formation of latent liver hypnozoites, but will also demand inactivation or removal of hypnozoites in persons presently infected. A better understanding of hypnozoite formation, persistence and reactivation will be needed to achieve this task. Here we show for the first time in vivo the effect of prophylactic antimalarials on P. vivax liver stage development to begin to understand the biology of hypnozoite growth and maturation. Using the liver-chimeric humanized mouse model, we show that treatment with primaquine during early liver stage development prevents hypnozoite formation and a treatment time-course highlights the point of true hypnozoite maturation, as latent parasites are refractory to absolute clearance in the liver. Hypnozoites continue to expand in size while the ER and apicoplast become larger, albeit without DNA replication. Treatment with MMV048, a pre-clinical candidate, is able to selectively kill and clear replicating schizonts from the liver when administered during the pre-erythrocytic growth cycle which allowed us to demonstrate the reactivation and blood-stage relapse of P. vivax hypnozoites. Using this model we are investigating transcriptional responses during the switch from early to mature hypnozoite, and persistent to reactivated, in an effort to identify potential drug targets and biomarkers of latent infection.