New study on the risk of Plasmodium vivax parasitaemia after Plasmodium falciparum malaria

Outside of sub-Saharan Africa, Plasmodium vivax is the most geographically widespread human malaria species. P. vivax and P. falciparum are co-endemic in areas such as Asia, the Americas and the horn of Africa. Following treatment of P. falciparum malaria, there is a high risk of recurrent P. vivax parasitaemia. This is thought to be due to reactivation of vivax malaria dormant liver stages which can occur weeks to months after the initial infection. Treatment using radical cure (which treats blood and liver stages) may be beneficial in some populations, however there are risks associated with this for those with a genetic disorder known as G6PD deficiency. The risk of vivax parasitaemia after falciparum infection and the underlying factors are not well understood.

The paper, which uses individual patient data from the WWARN Data Inventory aimed to identify populations in which a policy of universal radical cure, combining artemisinin-based combination therapy (ACT) with a hypnozoitocidal antimalarial drug, would be most beneficial.

Researchers collated and analysed data from 42 studies from 12 co-endemic countries enrolling 15,341 patients.

It was found that there was a high risk of recurrent vivax malaria after treatment of P. falciparum with all ACTs. However, there were significant variations between study populations and sites. For example, there was an increased risk of recurrence in regions where the duration between P. vivax relapses is short, such as south-east Asia. Furthermore, there was an increased risk of recurrent vivax malaria in patients who were slow to clear their initial P. falciparum infection, suggesting a host-parasite interaction may be triggering dormant liver stage P. vivax to reactivate.

Researchers concluded these P. vivax infections are most likely to be due to relapses, so could potentially be prevented with radical cure targeting both the blood and dormant liver stages of P. vivax. However, the benefits of this strategy are likely to vary considerably between geographical areas and would need to be coupled with appropriate G6PD testing. Further prospective clinical efficacy studies are needed to better determine the risks and benefits of this approach.

Read the full paper: The risk of Plasmodium vivax parasitaemia after P. falciparum malaria: An individual patient data meta-analysis from the WorldWide Antimalarial Resistance Network