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.

BackgroundRelatively large number of false-negative malaria rapid diagnostic test (RDT) results for microscopically confirmed Plasmodium falciparum cases were reported from five of the six administrative regions of Eritrea in 2015. This activated the Ministry of Health to conduct an initial exploratory investigation. The main objective of the investigation was to confirm the sensitivity of the RDTs in the field in microscopically confirmed malaria cases, identify the possible causes of the failure and recommend further actions to be taken.MethodsA team composed of the National Malaria Control Programme, National Medicines and Food Administration and Laboratory Unit of the Ministry of Health was established to confirm the sensitivity of the SD Bioline® RDTs. A ‘Malaria RDT quality monitoring form’ was prepared and distributed to 13 health facilities selected on availability of microscopy services, experienced laboratory personnel and malaria endemicity, to carry out preliminary investigation on the suspected RDT quality defect. In parallel, field visits to central and regional medical warehouses as well as selected health facilities were conducted to assess the storage conditions, handling and operator procedures. Furthermore, joint field assessment was conducted with the manufacturer, SD Bioline RDTs. During the time frame of 15 July 2015 to 19 January 2016, 65 microscopically confirmed patients were tested with Malaria RDTs SD Bioline Pf/Pv/Mixed Combo cassettes.ResultsA total of 65 blood specimens (50 P. falciparum, 13 Plasmodium vivax and 2 mixed) confirmed microscopically were tested against the available lots of malaria RDTs. Out of the 50 P. falciparum infected blood specimens, only 10 were confirmed positive with all the lots of PfHRP-2 detecting RDTs making the false negativity rate at 80% [41/51]. The false negative result for RDT targeting PfHRP2 antigen ranged from 65% [11/17] in Gash Barka region to 100% [12/12] in Northern Red Sea Region. In addition, supervisory visits undertaken by the study team have ruled out storage, handling and operator errors as causes of false negative results as the above parameter were found to be up to standards.ConclusionThe investigation confirmed high false-negativity rate in PfHRP-2 detecting RDTs and has ruled out quality of RDTs, storage, handling and operator error as causes of the reported problem. Therefore, molecular characterization of the P. falciparum is highly recommended to explore if parasite characteristics can be considered as causes of false negative results.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-017-1752-9) contains supplementary material, which is available to authorized users.

Background: Many health facilities in malaria endemic countries are dependent on Rapid diagnostic tests (RDTs) for diagnosis and some National Health Service (NHS) hospitals without expert microscopists rely on them for diagnosis out of hours. The emergence of P. falciparum lacking the gene encoding histidine-rich protein 2 and 3 (HRP2 and HRP3) and escaping RDT detection threatens progress in malaria control and elimination. Currently, confirmation of RDT negative due to the deletion of pfhrp2 and pfhrp3, which encodes a cross-reactive protein isoform, requires a series of PCR assays. These tests have different limits of detection and many laboratories have reported difficulty in confirming the absence of the deletions with certainty. Methods: We developed and validated a novel and rapid multiplex real time quantitative (qPCR) assay to detect pfhrp2, pfhrp3, confirmatory parasite and human reference genes simultaneously. We also applied the assay to detect pfhrp2 and pfhrp3 deletion in 462 field samples from different endemic countries and UK travellers.Results: The qPCR assay demonstrated diagnostic sensitivity of 100% (n = 19, 95% CI= (82.3%; 100%)) and diagnostic specificity of 100% (n = 31; 95% CI= (88.8%; 100%)) in detecting pfhrp2 and pfhrp3 deletions. In addition, the assay estimates P. falciparum parasite density and accurately detects pfhrp2 and pfhrp3 deletions masked in polyclonal infections. We report pfhrp2 and pfhrp3 deletions in parasite isolates from Kenya, Tanzania and in UK travellers. Interpretation: The new qPCR is easily scalable to routine surveillance studies in countries where P. falciparum parasites lacking pfhrp2 and pfhrp3 are a threat to malaria control.

Eritrea was the first African country to complete a nationwide switch in 2016 away from HRP2-based RDTs due to high rates of false-negative RDT results caused by Plasmodium falciparum parasites lacking hrp2/hrp3 genes. A cross-sectional survey was conducted during 2019 enrolling symptomatic malaria patients from nine health facilities across three zones consecutively to investigate the epidemiology of P. falciparum lacking hrp2/3 after the RDT switch. Molecular analyses of 715 samples revealed the overall prevalence of hrp2-, hrp3-, and dual hrp2/3-deleted parasites as 9.4% (95%CI 7.4–11.7%), 41.7% (95% CI 38.1–45.3%) and 7.6% (95% CI 5.8–9.7%), respectively. The prevalence of hrp2- and hrp3-deletion is heterogeneous within and between zones: highest in Anseba (27.1% and 57.9%), followed by Gash Barka (6.4% and 37.9%) and Debub zone (5.2% and 43.8%). hrp2/3-deleted parasites have multiple diverse haplotypes, with many shared or connected among parasites of different hrp2/3 status, indicating mutant parasites have likely evolved from multiple and local parasite genetic backgrounds. The findings show although prevalence of hrp2/3-deleted parasites is lower 2 years after RDT switching, HRP2-based RDTs remain unsuitable for malaria diagnosis in Eritrea. Continued surveillance of hrp2/3-deleted parasites in Eritrea and neighbouring countries is required to monitor the trend.

BackgroundEritrea, like most countries in sub-Saharan Africa, has expended much effort towards malaria control with the view of transitioning from reduction of the disease burden to elimination. This paper reports on the level of achievement as highlighted by the follow-on, malaria-endemic area representative, survey that aimed to provide data and to assess progress on malaria indicators and parasite prevalence at household level across the country.MethodsIn 2012, data were collected using a two-stage stratified cluster random sample of 1887 households in 96 clusters (villages in rural areas and census enumeration areas in urban centers) during a malaria indicator and prevalence survey in Eritrea. The survey determined parasite prevalence in vulnerable population groups and evaluated coverage, use and access to malaria control services. Standardized Roll-Back Malaria Monitoring and Evaluation Reference Group household and women’s questionnaires were adapted to the local situation and used for collection of data that were analysed and summarized using descriptive statistics.ResultsThe results of the survey showed that 90 % (95 % CI 89–91) of households owned at least one mosquito net. The proportion of the population with access to an insecticide-treated net (ITN) in their household was 55 % (95 % CI 54–56). The utilization of ITNs was 67 % (95 % CI 65–70) for children under 5 years and 60 % (95 % CI 58–63) for pregnant women (OR: 0. 73(95 % CI 0.62–0.85); P = 0.52). Only 28 % (95 % CI 26–30) of households were covered by indoor residual spraying (IRS) the previous year with significant heterogeneity by zoba (Debub 50 % (95 % CI 45–54) vs Gash Barka 32 % (95 % CI 28–36); OR = 0. 47 (95 % CI 0.36–0.61), P = 0.05). Malaria parasite prevalence was low; 1.1 % (95 % CI 0.9–1.3) in the general population and 1.4 % (95 % CI 1.0–2.0) in children under five and 0.7 % (95 % CI 0.4–1.1) among women aged 15–49 years. Only 19 % (95 % CI 15–26) of children under five had fever in the 2 weeks preceding the survey, with 61 % (95 % CI 54.1–67.1) seeking treatment from a health facility. Data on knowledge levels show that 92 % reported that malaria is transmitted by mosquitoes, 92 % mentioned that the use of mosquito nets could prevent malaria, 47 % knew malaria prevention medication, 83 % cited fever as a sign and symptom of malaria, and 35 % had heard or seen malaria awareness messages.ConclusionNotwithstanding confounders, the observed low malaria parasite prevalence could be associated with malaria intervention coverage, access and utilization as well as high and equitable knowledge levels in the population. This indicates that Eritrea is on the right track towards pre-elimination. However, technical and infrastructure capacity should be strengthened to facilitate implementation, surveillance, monitoring, and evaluation.