Absence of Plasmodium falciparum Histidine-Rich Protein 2 and 3 (Pfhrp2/3) Gene Deletions in Rizal, Palawan, the Philippines.

Microscopy and rapid diagnostic tests (RDTs) are used in the Philippines as the gold standard for malaria diagnosis. However, parasites evading RDT detection have recently emerged in other settings as a result of deletions in Plasmodium falciparum histidine-rich protein genes (pfhrp2 and pfhrp3). Failure to detect and treat individuals carrying these deletions may result in increased malaria transmission and hinder elimination efforts. In addition to the implications for malaria elimination efforts, we emphasize that false-negative RDT results caused by pfhrp2/3 deletions pose a critical risk to patient outcomes, as individuals with active P. falciparum infections may go untreated. Sixty-three samples collected from Palawan, the Philippines, were interrogated for the presence of Plasmodium isolates and pfhrp deletions. All 63 samples were microscopically positive for P. falciparum. Although only 27 (43%) were positive for RDTs, all samples were confirmed free of pfhrp2 and pfhrp3 deletions by nested polymerase chain reaction (PCR) tests. RDT false negatives in the study were most likely caused by low parasite densities. Incorporating molecular monitoring of histidine-rich protein 2 deletions into routine malaria surveillance would improve assessments of the performance of the current RDTs and help strengthen strategies toward malaria elimination by 2030.