Contrasting sequence polymorphism and structural basis patterns of Plasmodium falciparum histidine-rich proteins 2/3 in Cameroon and India

The bulk of malaria rapid diagnostic tests (RDTs) target Plasmodium falciparum histidine-rich protein 2 (PfHRP2), but several reports have shown that sequence variations in this protein are associated with false-negative RDT results. The polymorphism of PfHRP2/3 was analyzed from Cameroonian and Indian P. falciparum isolates. Cameroon and India are two of eleven countries with the highest malaria burden. Exon 2 of  pfhrp 2/3 genes were PCR-amplified, and the amplicons were purified and sequenced. A total of 25 PfHRP2 and 12 PfHRP3 novel repeat type variants were found. The nature and organization of PfHRP3 sequences were quite similar between Cameroon and India. Some structurally unique PfHRP2/3 sequences, characterized by a high proportion of proline (5.8–10.3%) for PfHRP2, and two non-repeat regions for PfHRP3, were found in both countries. Most of the Cameroonian isolates belonged to group B (66.7%), while the Indian isolates belonged to group C (69.2%) (p=0.03). Three epitope motifs (AHHAHHA, HATDAHH, and YAHHAHHA) were found in all Cameroonian and Indian PfHRP2 sequences. Mutations observed in unique sequences were mainly associated with alterations of helical structures in the PfHRP2 C-terminal region. The high genetic diversity, epitope availability, and structural basis patterns found here could help develop the next generation of RDTs with improved quality.