Major Threat to Malaria Control Programs by Plasmodium falciparum Lacking Histidine-Rich Protein 2, Eritrea

Abstract

False-negative results for Plasmodium falciparum histidine-rich protein (HRP) 2-based rapid diagnostic tests (RDTs) are increasing in Eritrea. We investigated HRP gene 2/3 (pfhrp2/pfhrp3) status in 50 infected patients at 2 hospitals. We showed that 80.8% (21/26) of patients at Ghindae Hospital and 41.7% (10/24) at Massawa Hospital were infected with pfhrp2-negative parasites and 92.3% (24/26) of patients at Ghindae Hospital and 70.8% (17/24) at Massawa Hospital were infected with pfhrp3-negative parasites. Parasite densities between pfhrp2-positive and pfhrp2-negative patients were comparable. All pfhrp2-negative samples had no detectable HRP2/3 antigen and showed negative results for HRP2-based RDTs. pfhrp2-negative parasites were genetically less diverse and formed 2 clusters with no close relationships to parasites from Peru. These parasites probably emerged independently by selection in Eritrea. High prevalence of pfhrp2-negative parasites caused a high rate of false-negative results for RDTs. Determining prevalence of pfhrp2-negative parasites is urgently needed in neighboring countries to assist case management policies.

Keywords: Eritrea; HRP2; HRP2 deletion; HRP3; Plasmodium falciparum; RDTs; genetic diversity; genetic relatedness; histidine-rich protein 2 gene; histidine-rich protein 3 gene; malaria; malaria control programs; parasites; rapid diagnostic tests.

Figure 1

Location of study sites at Ghindae and Massawa Hospitals, Eritrea, for analysis of a major threat to malaria control programs by Plasmodium falciparum lacking histidine-rich protein 2. Inset shows the location of the study sites in Eritrea.

Figure 2

Plasmodium falciparum histidine-rich protein 2–based malaria RDT results and presence or absence of the pfhrp2/pfhrp3 genes, in relation to parasite density, orizontal lines indicate geometric means a,d Eritrea. Horizontal lines indicate geometric means, and error bars indicate 95% CIs. pfhrp, P. falciparum histidine-rich protein; RDT, rapid diagnostic test; – negative; +, positive.

Figure 3

Plasmodium falciparum HRP2 antigen levels in relation to presence or absence of pfhrp2/pfhrp3 genes and HRP2-based malaria RDT results, Eritrea. Horizontal lines indicate means, and error bars indicate SDs. HRP2, histidine-rich protein 2; pfhrp, P. falciparum histidine-rich protein; RDT, rapid diagnostic test; – negative; +, positive.

Figure 4

Number and frequency of Plasmodium falciparum haplotypes detected in patients at 2 hospitals, Eritrea, by hospital (A) and by pfhrp2-positive versus pfhrp2-negative parasite populations (B). pfhrp, P. falciparum histidine-rich protein; – negative; +, positive.

Figure 5

Genetic relatedness among Plasmodium falciparum parasite populations in Eritrea differing in pfhrp2 and pfhrp3 gene status (A) and comparison of parasite populations from Eritrea and Peru (B). Plots were produced by using Phyloviz software (24) at a cutoff value of 2 (minimum differences for 2 loci). Numbered circles indicate specific haplotypes. Circle sizes indicate number of samples with a particular haplotype. pfhrp, P. falciparum histidine-rich protein; – negative; +, positive.