Usefulness of Plasmodium falciparum-specific rapid diagnostic tests for assessment of parasite clearance and detection of recurrent infections after artemisinin-based combination therapy

Abstract

Background: Rapid diagnostic test (RDT) is an important tool for parasite-based malaria diagnosis. High specificity of RDTs to distinguish an active Plasmodium falciparum infection from residual antigens from a previous infection is crucial in endemic areas where residents are repeatedly exposed to malaria. The efficiency of two RDTs based on histidine-rich protein 2 (HRP2) and lactate dehydrogenase (LDH) antigens were studied and compared with two microscopy techniques (Giemsa and acridine orange-stained blood smears) and real-time polymerase chain reaction (PCR) for assessment of initial clearance and detection of recurrent P. falciparum infections after artemisinin-based combination therapy (ACT) in a moderately high endemic area of rural Tanzania.

Methods: In this exploratory study 53 children < five years with uncomplicated P. falciparum malaria infection were followed up on nine occasions, i.e., day 1, 2, 3, 7, 14, 21, 28, 35 and 42, after initiation of artemether-lumefantrine treatment. At each visit capillary blood samples was collected for the HRP2 and LDH-based RDTs, Giemsa and acridine orange-stained blood smears for microscopy and real-time PCR. Assessment of clearance times and detection of recurrent P. falciparum infections were done for all diagnostic methods.

Results: The median clearance times were 28 (range seven to >42) and seven (two to 14) days for HRP2 and LDH-based RDTs, two (one to seven) and two (one to 14) days for Giemsa and acridine orange-stained blood smear and two (one to 28) days for real-time PCR. RDT specificity against Giemsa-stained blood smear microscopy was 21% for HRP2 on day 14, reaching 87% on day 42, and ≥96% from day 14 to 42 for LDH. There was no significant correlation between parasite density at enrolment and duration of HRP2 positivity (r = 0.13, p = 0.34). Recurrent malaria infections occurred in ten (19%) children. The HRP2 and LDH-based RDTs did not detect eight and two of the recurrent infections, respectively.

Conclusion: The LDH-based RDT was superior to HRP2-based for monitoring of treatment outcome and detection of recurrent infections after ACT in this moderately high transmission setting. The results may have implications for the choice of RDT devices in similar transmission settings for improved malaria case management.

Trial registration: Clinicaltrials.gov, NCT01843764.

Figure 1

Flow of patients through the study.

Figure 2

Median clearance times for the five diagnostic tests. N = number of patients included in the analysis. BS = Giemsa-stained blood smear. AO = acridine orange-stained blood smear. * Last day of follow-up = day 42.

Figure 3

Positivity rates at each sampling point by the five diagnostic tests. HRP2 data represent 43 patients and the remaining diagnostic tests 53 patients. HRP = HRP2 based RDT. LDH = LDH based RDT. BS = Giemsa-stained blood smear. AO = acridine orange-stained blood smear. PCR = real-time PCR.

Figure 4

Correlation between parasite density at enrolment and duration of HRP2 positivity. N = 52, including 43 children without re-infection, two with cleared positivity before re-infection and seven with cleared positivity before being lost to follow-up. Correlation coefficient (r) = 0.13 (p = 0.38).

Figure 5

Cumulative positivity by the diagnostic tests for the ten recurrent Plasmodium falciparum infections detected during follow-up. BS = Giemsa-stained blood smear. AO = acridine orange-stained blood smear.