Abstract
Malaria rapid diagnostic tests (RDTs) play a critical role in malaria case management, surveillance and case investigations. Test performance is largely determined by design and quality characteristics, such as detection sensitivity, specificity, and thermal stability. However, parasite characteristics such as variable or absent expression of antigens targeted by RDTs can also affect RDT performance. Plasmodium falciparum parasites lacking the PfHRP2 protein, the most common target antigen for detection of P. falciparum, have been reported in some regions. Therefore, accurately mapping the presence and prevalence of P. falciparum parasites lacking pfhrp2 would be an important step so that RDTs targeting alternative antigens, or microscopy, can be preferentially selected for use in such regions. Herein the available evidence and molecular basis for identifying malaria parasites lacking PfHRP2 is reviewed, and a set of recommended procedures to apply for future investigations for parasites lacking PfHRP2, is proposed.
Highlights
Malaria rapid diagnostic tests (RDTs) play a critical role in malaria case management, surveillance and case investigations
Role of malaria rapid diagnostic tests (RDTs) Malaria remains endemic in 104 countries, representing a major public health problem in many [1]
One hundred and ten (110) of the 127 RDTs that are capable of diagnosing Plasmodium falciparum, target an antigen that is unique to P. falciparum, the histidine-rich protein 2 (PfHRP2)
Summary
Very low parasite densities/target antigen concentrations Prozone effect (hyperparasitemia/antigen overload). Not reported to date in field isolates, a frame shift in these genes could cause non-expression of the protein Based on these published findings, deletions of pfhrp occur because of chromosomal breakage and rejoin in the subtelomeric regions of chromosome 8. These false negative results will cause a major problem for malaria case management This effect is demonstrated in a recent study comparing sensitivities of several PfHRP2- and pLDH-based RDTs for detecting P. falciparum infections in health centres around Iquitos [23]. Incorrect or unsubstantiated reporting of parasites lacking pfhrp may unnecessarily trigger a costly change of RDT product ( there is no guideline as to what prevalence level should trigger this change), a process which requires significant logistic and financial support, as well as user retraining It may damage overall user confidence in RDTs. So far, the rarity of reports summarized in Table 2 suggests pfhrp deletion is not a major problem across broad areas; no systematic mapping has occurred. The requirement for a positive pan-band is because pan-bands are generally less sensitive than HRP2-test bands and a positive pan-band, and negative HRP2 test band makes the possibility of a false negative due to low parasite density less probable
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