Failure of rapid diagnostic tests in Plasmodium falciparum malaria cases among travelers to the UK and Ireland: Identification and characterisation of the parasites
Debbie Nolder, Lindsay B. Stewart, Julie Tucker, Amy Ibrahim, Adam Gray, Tumena Corrah, Carmel Gallagher, Laurence John, Edel O’Brien, Dinesh Aggarwal, Ernest Diez Benavente, Donelly A. van Schalkwyk, Gisela Henriques, Nuno Sepúlveda, Susana Campino, Peter L. Chiodini, Colin J. Sutherland, Khalid B. Beshir
Abstract
OBJECTIVES: Our objective was to systematically investigate false-negative histidine-rich protein 2 rapid diagnostic tests (HRP2-RDT) in imported Plasmodium falciparum malaria cases from travelers to the UK and the Republic of Ireland (RoI). METHODS: Five imported malaria cases in travellers returning to the UK and RoI from East Africa were reported to the PHE Malaria Reference Laboratory as negative according to histidine-rich protein (HRP2)-RDT. The cases were systematically investigated using microscopic, RDT, molecular, genomic, and in in vitro approaches. RESULTS: In each case, HRP2-RDT was negative, whereas microscopy confirmed the presence of P. falciparum. Further analysis revealed that the genes encoding HRP2 and HRP3 were deleted in three of the five cases. Whole-genome sequencing in one of these isolates confirmed deletions in P. falciparum chromosomes 8 and 13. Our study produced evidence that the fourth case, which had high parasitemia at clinical presentation, was a rare example of antigen saturation ('prozone-like effect'), leading to a false negative in the HRP2-RDT, while the fifth case was due to low parasitemia. CONCLUSIONS: False-negative HRP2-RDT results with P. falciparum are concerning. Our findings emphasise the necessity of supporting the interpretation of RDT results with microscopy, in conjunction with clinical observations, and sets out a systematic approach to identifying parasites carrying pfhrp2 and pfhrp3 deletions.