Short report: surveillance of hrp2/hrp3 deletions in Plasmodium falciparum within Haiti, 2021-2023, using RDTs

Malaria continues to be endemic within Haiti, despite numerous strategies to reduce its incidence. In 2012, malaria surveillance in clinical settings shifted away from microscopy to HRP2 based Rapid Diagnostic Tests (RDTs) as the primary form of screening. While this approach removes obstacles and delays associated with seeking skilled microscopy, the global emergence of malaria parasites containing HRP deletions has raised concerns of selective pressure and reduced sensitivity.

Stored RDTs from febrile patients presenting to clinics in the Ouest and Sud Departments of Haiti were collected between 2021-2023. Total nucleic acid (TNA) was extracted from the entire RDT test strip. TNA was tested for Plasmodium spp. 18S rRNA. Samples testing positive by the 18S rRNA were tested with a triplex assay targeting P. falciparum-specific genes Pfrnr2e2, Pfhrp2, and Pfhrp3. Only samples with successful amplification of Pfrnr2e2 were assessed for Pfhrp2 and/or Pfhrp3 deletions.

Of the 2,073 RDT samples analyzed, 193 were positive for Plasmodium spp. 18S rRNA, 49 of which came from negative RDTs (2.61% false-negative rate). Analyses of positive and negative RDT samples in which the Pfrnr2e2 gene successfully amplified resulted in 34 samples being Pfhrp2+/Pfhrp3- (33 from positive RDTs, 1 from a negative RDT), three samples being Pfhrp2-/Pfhrp3+ (all from positive RDTs), and three samples being Pfhrp2-/Pfhrp3- (2 from positive RDTs, 1 from a negative RDT). All deletions were reported in the Sud department. While samples with Pfhrp3 deletions were distributed throughout the Sud department, samples with Pfhrp2 deletions were located exclusively in Port-a-Piment, Les Anglais, and Tiburon.

These results, and the recent reports of Pfhrp2 gene deletions in the Dominican Republic, demonstrate a growing threat to the use of HRP2-based RDTs within Haiti and throughout the entire island of Hispaniola. Future studies making use of whole blood samples should be conducted to confirm these findings. Additional studies should also be conducted to continue monitoring the spread and persistence of these gene deletions by sampling different Departments within Haiti.