Low levels of polymorphisms and no evidence for diversifying selection on the Plasmodium knowlesi Apical Membrane...

Area of Science:

• Malariology
• Parasitology
• Vaccinology

Background:

• Plasmodium knowlesi, a zoonotic malaria parasite, poses a significant and increasing threat to human health in Southeast Asia.
• Apical Membrane Antigen 1 (AMA1) is a key candidate antigen for malaria vaccine development.
• Understanding the genetic diversity of AMA1 is critical for designing effective vaccines.

Purpose of the Study:

• To determine the genetic diversity of the ama1 gene in Plasmodium knowlesi isolates from human infections.
• To identify epitopes of AMA1 under strong immune selection.
• To assess the potential for a single-allele AMA1-based vaccine.

Main Methods:

• Sequencing of the ama1 gene from 52 P. knowlesi isolates obtained from human infections.
• Comparative sequence analysis of isolates from two geographically distinct regions in Sarawak.
• Analysis of genetic polymorphism, haplotype diversity, and mutation frequencies.

Main Results:

• Low levels of polymorphism were observed in the P. knowlesi AMA1 gene compared to P. falciparum and P. vivax AMA1.
• Only six polymorphic positions had a variance frequency higher than 10%, with only two positions showing multiple amino acid variants.
• Three high-frequency polymorphic sites in P. knowlesi AMA1 corresponded to invariant sites in P. falciparum and P. vivax AMA1.

Conclusions:

• The P. knowlesi ama1 gene is not under balancing selection, unlike its counterparts in major human malaria parasites.
• PkAMA1 is unlikely to be a primary target for protective humoral immune responses in its natural macaque hosts.
• The low genetic diversity of PkAMA1 supports the development of a single-allele AMA1-based malaria vaccine.