The In Vitro Invasion Inhibition Assay (IIA) for Plasmodium vivax.

Plasmodium vivax is considered as the most widely distributed human malaria parasite outside Africa. Studies of P. vivax malaria have always been limited due to the lack of continuously in vitro-propagated parasite lines. Due to this limitation, studies on P. vivax have lagged behind that of P. falciparum, which is routinely maintained in in vitro blood-stage culture. This method allows for the short-term ex vivo culture of P. vivax blood stages and as such offers a wealth of opportunities to study the biology of the blood stages of the parasite. In this chapter we describe the in vitro erythrocyte invasion inhibition assay (IIA) for P. vivax, which can be used as a powerful tool for blood-stage vaccine screening. The major challenges of this assay are the purification of schizont-stage parasites and host reticulocytes. The purification methods for both P. vivax schizont-stage parasites and reticulocytes as detailed here have been developed and simplified. The protocols in this chapter have been optimized to ensure that IIA becomes a more feasible and reliable assay.