Low Prevalence of Deletions of the pfhrp2 and pfhrp3 Genes in Plasmodium falciparum Parasites in Freetown, Sierra Leone in 2015

Abstract

Sierra Leone relies heavily on histidine-rich protein 2-based diagnostics for malaria because of the high transmission of Plasmodium falciparum. During the 2015 recombinant vesicular stomatitis virus (VSV)-Zaire Ebola virus envelope glycoprotein (GP) vaccine trial, 77 participants with asymptomatic Plasmodium infection were enrolled, with all but four having P. falciparum malaria. Of the 73 participants with P. falciparum malaria, one infection (1 of 73, 1.4%; 95% CI, 0.03-7.4) showed P. falciparum with a pfhrp3 single deletion, and two P. falciparum infections (2 of 73, 2.7%; 95% CI, 0.03-9.6) showed pfhrp2/pfhrp3 dual deletions. This study shows evidence of pfhrp2- and pfhrp3-deleted parasites in Freetown, Sierra Leone. Additional studies for more precise estimates of prevalence are warranted.

Figure 1.

Laboratory assay workflow, reporting of pfhrp2 and pfhrp3 deletions, and relationship of histidine-rich protein 2 (HRP2) antigen levels to Plasmodium falciparum genotype. (A) Flow diagram for all blood samples included in this study with terminal boxes displaying pfhrp2 and pfhrp3 genotypes of selected samples. (B) Level of HRP2 and HRP3 antigen in blood samples for persons polymerase chain reaction negative for Plasmodium DNA (n = 444, blue circles), mono-infected with non-falciparum Plasmodium (n = 4, red diamonds), infected with wild-type P. falciparum (n = 71, black triangles), or infected with P. falciparum with a pfhrp2 deletion (n = 2, green squares). Red hashed line indicates threshold for assay signal indicating positivity for HRP2. Among the P. falciparum–infected participant samples, a single sample was determined be a pfhrp3 single deletion (pfhrp2+/pfhrp3–), and is indicated as the single shaded black triangle near the threshold line. Pf = Plasmodium falciparum.