Transmission-blocking vaccine of vivax malaria

Malaria remains one of the leading causes of both morbidity and mortality of humans residing in tropical countries. For many malarious regions outside of Africa, development of effective transmission-blocking vaccines will require coverage against both Plasmodium falciparum and Plasmodium vivax. The genes coding for two potential P. vivax transmission-blocking antigens, Pvs25 and Pvs28, have been cloned. Mice vaccinated with yeast-produced recombinant proteins Pvs25 and Pvs28 adsorbed to aluminum hydroxide developed strong antibody responses against the immunogens. The development of oocysts in mosquitoes was completely inhibited when these antisera were ingested with the P. vivax Salvador (Sal) I strain-infected chimpanzee blood. In a large collection of P. vivax field isolates, we found only 5 nucleotide changes that would result in amino acid substitutions in Pvs25. In contrast, the Pvs28 gene had 22 nucleotide changes that would result in conservative amino acid substitutions. How the antigenic polymorphism of Pvs25 and Pvs28 would affect the efficacy of Sal I based vaccine remains to be elucidated. Clinical trials with Pvs25 and the P. falciparum ortholog Pfs25 are in preparation.