Persistent ICT malaria P.f/P.v panmalarial and HRP2 antigen reactivity after treatment of Plasmodium falciparum malaria is associated with gametocytemia and results in false-positive diagnoses of Plasmodium vivax in convalescence

Abstract

A problem with rapid Plasmodium falciparum-specific antigen histidine-rich protein 2 (HRP2) detection tests for malaria is the persistence of antigen in blood after the disappearance of asexual-stage parasitemia and clinical symptoms, resulting in false-positive (FP) test results following treatment. The ICT P.f/P.v immunochromatographic test detects both HRP2 and a panmalarial antigen (PMA) found in both P. falciparum and Plasmodium vivax. To examine posttreatment antigen persistence with this test and whether persistent sexual-stage forms (gametocytes) are a cause of FP tests after treatment, we compared serial antigen test results with microscopy results from patients symptomatic with P. falciparum malaria in Indonesia for 28 days following treatment with chloroquine (CQ; n = 66), sulfadoxine-pyrimethamine (SP; n = 36), and artesunate plus sulfadoxine-pyrimethamine (ART + SP; n = 15). Persistent FP antigenemia following SP treatment occurred in 29% (HRP2) and 42% (PMA) of the patients on day 7 and in 10% (HRP2) and 23% (PMA) on day 14. The high rates of persistent HRP2 and PMA antigenemia following CQ and SP treatment were strongly associated with the presence of gametocytemia, with the proportion with gametocytes on day 7 posttreatment being significantly greater in those with FP results than in those with true-negative PMA and HRP2 results. Gametocyte frequency on day 14 post-SP treatment was also greater in those with FP PMA results. Following SP treatment, PMA persisted longer than HRP2, giving an FP diagnosis of P. vivax in up to 16% of patients on day 14, with all FP P. vivax diagnoses having gametocytemia. In contrast, PMA was rapidly cleared following ART + SP treatment in association with rapid clearance of gametocytemia. Gametocytes appear to be an important cause of persistent posttreatment panmalarial antigenemia in areas of endemicity and may also contribute in part to persistent HRP2 antigenemia following treatment.

FIG. 1

Microscopic findings (a and b) following chloroquine treatment of P. falciparum malaria, sulfadoxine-pyrimethamine treatment of patients who had received failed chloroquine treatment, and treatment with artesunate plus sulfadoxine-pyrimethamine. (a) Recurrence of asexual P. falciparum parasitemia following chloroquine treatment is shown. ∗, P. vivax asexual parasitemia was noted on day 28 in one sulfadoxine-pyrimethamine-treated patient and in two patients following treatment with artesunate plus sulfadoxine-pyrimethamine. (b) Proportion with P. falciparum gametocytemia in those negative for asexual-stage P. falciparum parasites on each day of follow-up. (c) Antigen persistence following chloroquine treatment. The proportion of all patients having HRP2 or panmalarial antigenemia on each day of follow-up is shown. (d) Antigen persistence following sulfadoxine-pyrimethamine treatment. The proportion of all patients having HRP2 or panmalarial antigenemia on each day of follow-up is shown.

FIG. 2

FP persistence of HRP2 and panmalarial antigenemia following treatment with chloroquine (a), sulfadoxine-pyrimethamine (b), and artesunate plus sulfadoxine-pyrimethamine (c) of symptomatic P. falciparum malaria. Results do not include true-positive results associated with asexual-stage parasitemia on microscopy and are expressed as FP antigen results, as a proportion of the total FP and true-negative results for each antigen on each day of follow-up.

FIG. 2

FP persistence of HRP2 and panmalarial antigenemia following treatment with chloroquine (a), sulfadoxine-pyrimethamine (b), and artesunate plus sulfadoxine-pyrimethamine (c) of symptomatic P. falciparum malaria. Results do not include true-positive results associated with asexual-stage parasitemia on microscopy and are expressed as FP antigen results, as a proportion of the total FP and true-negative results for each antigen on each day of follow-up.

FIG. 2

FP persistence of HRP2 and panmalarial antigenemia following treatment with chloroquine (a), sulfadoxine-pyrimethamine (b), and artesunate plus sulfadoxine-pyrimethamine (c) of symptomatic P. falciparum malaria. Results do not include true-positive results associated with asexual-stage parasitemia on microscopy and are expressed as FP antigen results, as a proportion of the total FP and true-negative results for each antigen on each day of follow-up.

FIG. 3

Frequency of P. falciparum gametocytemia on days 7 and 14 after treatment with chloroquine (a), sulfadoxine-pyrimethamine (b), and artesunate plus sulfadoxine-pyrimethamine (c) in those with FP immunochromatographic antigen tests (below the zero line) compared with those with true negative tests (above the zero line). ∗ indicates a significant difference (P < 0.05) using Fisher's two-tailed exact test.

FIG. 3

Frequency of P. falciparum gametocytemia on days 7 and 14 after treatment with chloroquine (a), sulfadoxine-pyrimethamine (b), and artesunate plus sulfadoxine-pyrimethamine (c) in those with FP immunochromatographic antigen tests (below the zero line) compared with those with true negative tests (above the zero line). ∗ indicates a significant difference (P < 0.05) using Fisher's two-tailed exact test.

FIG. 3

Frequency of P. falciparum gametocytemia on days 7 and 14 after treatment with chloroquine (a), sulfadoxine-pyrimethamine (b), and artesunate plus sulfadoxine-pyrimethamine (c) in those with FP immunochromatographic antigen tests (below the zero line) compared with those with true negative tests (above the zero line). ∗ indicates a significant difference (P < 0.05) using Fisher's two-tailed exact test.