Plasmodium falciparum histidine-rich protein 2 (PfHRP2) diversity in Ghana

Abstract

Background: In the absence of microscopy, Plasmodium falciparum histidine-rich proteins 2 (PfHRP2)-based rapid diagnostic tests (RDTs) are recommended for the diagnosis of falciparum malaria, particularly in endemic regions. However, genetic variability of the PfHRP2 gene threatens the usefulness of the test. This study aimed to investigate the diversity of PfHRP2 in malaria cases among children in Ghana. Methods:A cross-sectional study was conducted at the Adidome Government Hospital in the Volta Region of Ghana. A total of 50 children with mean age of 6.6±3.5 years and diagnosed of falciparum malaria were included. Blood samples were collected for complete blood count, malaria parasite identification and counting. DNA samples were amplified and sequenced. Nucleotide sequences were translated in silico to corresponding amino acids and the deduced amino acids sequences were analyzed for diversity. Results:The number of repeats and number of each repeat within PfHRP2 varied between isolates.Twelve rare PfHRP2 repeat types, two of which are previously unreported, were identified in this study. Our HRP2 sequence shared high similarity with isolates from Kenya. Using Baker's regression model, Group B was the highest occurring type (58.0%). Screening of all sequences for epitopes recognized by PfHRP2-specific monoclonal antibodies (mAbs), we found the predominant motif to be AHHAADAHH, which is recognized by the C1-13 mAbs. Conclusion:This study reports diversity of P. falciparum histidine-rich proteins 2 in samples from Ghanaian children with symptomatic malaria. We highlight the existence of extra amino acid repeat types which adds to the PfHRP2 antigenic variability. The findings of this study will contribute to the understanding of the performance of PfHRP2-based RDTs in the Ghanaian setting.accounting for not less than 20% of child deaths, 40% of child hospital admissions, and more than 50% of outpatient attendances [4][5][6][7].Although, microscopic examination of stained blood smears remains the gold standard for malaria diagnosis, its benefit is limited by the absence of adequate skilled personnel, and infrastructural and logistic resources, particularly in resource-poor areas [8]. To overcome this problem, the World Health Organization (WHO) included rapid diagnostic tests (RDTs), a relatively less expensive and easily accessible test, as one of the alternative testing systems for malaria diagnosis prior to the prescription of antimalarial drugs.Since its development in the 1990s, and with more than 200 currently available brands, there has been consistent reports of observable increase in malaria RDT sales worldwide [9,10]. Most of the malaria RDTs exploit the presence of P. falciparum Histidine-Rich Protein-2 (PfHRP2) for the detection of Plasmodium falciparum [11]. The presence of repetitive epitopes, that enable their detection by multiple antibodies, and their abundance in blood during the blood-stage of malaria infections has made the PfHRP2 protein a common antigenic target for RDTs [12,13].In 2010, Gh...