While non-HRP2-based RDTs are in development to combat this problem, PCR and RT-PCR methods that target the essential 18S rRNA or coding genes have been used to find even pfhrp2-deleted parasites. Our lab's pan-Plasmodium 18S rRNA RT-PCR method can detect P. falciparum, P. vivax, P. ovale, P. malariae and P. knowlesi as well as Plasmodium species that only infect mice like P. yoelii and P. berghei. This high rate of conservation within and between Plasmodium species and the critical role of 18S rRNAs in eukaryotic biology make it less likely that field strains will evade an 18S rRNA RT-PCR based approach. Currently-approved RDTs detect parasites at densities down to ~100,000-200,000 parasites/milliliter, whereas 18S rRNA RT-PCR can detect parasites down to 10-20 parasites/milliliter. Thus, the RT-PCR approach is thousands of time more sensitive than currently-approved RDTs. However, next-generation RDTs are rapidly improving and this is a good thing because they can be used right at the point of patient care. We are actively using our RT-PCR tests to support field studies whose goals include improvement of new and better RDTs. Perhaps one day, RDTs will be able to find nearly all of the malaria parasites lurking in asymptomatic patients worldwide regardless of their pfhrp2 status.
Reference to the UNC paper: Parr et al. 2016. Pfhrp2 -deleted Plasmodium falciparum parasites in the Democratic Republic of Congo: A national cross-sectional survey. Journal of Infectious Diseases. jiw538 DOI: 10.1093/infdis/jiw538