Persistent histidine-rich protein 2, parasite lactate dehydrogenase, and panmalarial antigen reactivity after clearance of Plasmodium falciparum monoinfection

Abstract

We tested 240 patients with Plasmodium falciparum monoinfection for persistent parasite antigenemia after successful standardized antimalarial therapy by using the ICT Malaria Pf/Pv and OptiMAL-IT assays that detect the malaria antigens Plasmodium falciparum histidine-rich protein 2 (HRP2) and parasite lactate dehydrogenase (pLDH), respectively, as well as a panmalarial antigen (PMA). The patients were screened for antigenemia on days 0, 3, 7, and 14 of follow-up. On day 0, all 240 patients showed positive reactivity with both assays. Of the 229 cases with negative parasitemia on day 3, persistent antigenemia was observed in 207 (90.4%) of the cases: 188 (82.1%) for HRP2 antigen and 75 (32.8%) for PMA. There was a gradual decrease in antigenemia on follow-up to day 14; however, the drop in reactivity to PMA was less than that for HRP2 antigen. In contrast to HRP2 antigenemia, there was a significant decrease in pLDH antigenemia to 38.4% and to 14.8% (PMA) on day 3 (P < 0.03). The pLDH antigenemia level dropped further to 14.8% on day 7. There was no significant association of persistent antigenemia with gametocytemia. One case with gametocytemia was negative for both the antigens. In conclusion, the OptiMAL-IT assay is more sensitive than the ICT Malaria Pf/Pv test for monitoring therapeutic responses after antimalarial therapy since the LDH activity ceases when the malarial parasite dies.

FIG. 1.

Percentage of cases with antigenemia as detected by ICT Malaria Pf/Pv assay (A) and OptiMAL-IT assay (B) on days 0, 3, 7, and 14 after antimalarial therapy. The cases were negative for asexual-stage parasites by microscopy of Giemsa-stained blood films. The ratio was expressed as the number of cases with persistent antigenemia for each antigen to the total number of cases (i.e., 229) negative for asexual-stage parasitemia.

FIG. 1.

Percentage of cases with antigenemia as detected by ICT Malaria Pf/Pv assay (A) and OptiMAL-IT assay (B) on days 0, 3, 7, and 14 after antimalarial therapy. The cases were negative for asexual-stage parasites by microscopy of Giemsa-stained blood films. The ratio was expressed as the number of cases with persistent antigenemia for each antigen to the total number of cases (i.e., 229) negative for asexual-stage parasitemia.

FIG. 2.

Relationship between gametocytemia and HRP2/PMA antigenemia. The cases were negative for asexual-stage parasites and positive for gametocytes by microscopy. The data present the numbers of cases with gametocytemia for each antigen on days 0, 3, 7, and 14 after antimalarial treatment.