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

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.

Rapid diagnostic tests failing to detect Plasmodium falciparum infections in Eritrea: an investigation of reported false negative RDT results.

BACKGROUND: Relatively 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. METHODS: A 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. RESULTS: A 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. CONCLUSION: The 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.