Performance of a sensitive haemozoin-based malaria diagnostic test validated for vivax malaria diagnosis in Brazilian Amazon

Abstract

Background: Vivax malaria diagnosis remains a challenge in malaria elimination, with current point of care rapid diagnostic tests (RDT) missing many clinically significant infections because of usually lower peripheral parasitaemia. Haemozoin-detecting assays have been suggested as an alternative to immunoassay platforms but to date have not reached successful field deployment. Haemozoin is a paramagnetic crystal by-product of haemoglobin digestion by malaria parasites and is present in the food vacuole of malaria parasite-infected erythrocytes. This study aimed to compare the diagnostic capability of a new haemozoin-detecting platform, the Gazelle™ device with optical microscopy, RDT and PCR in a vivax malaria-endemic region.

Methods: A comparative, double-blind study evaluating symptomatic malaria patients seeking medical care was conducted at an infectious diseases reference hospital in the western Brazilian Amazon. Optical microscopy, PCR, RDT, and Gazelle™ were used to analyse blood samples. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and Kappa values were calculated.

Results: Out of 300 patients, 24 test results were excluded from the final analysis due to protocol violation (6) and inconclusive and/or irretrievable results (18). Gazelle™ sensitivity was 96.1 % (91.3-98.3) and 72.1 % (65.0-78.3) when compared to optical microscopy and PCR, respectively whereas it was 83.9 % and 62.8 % for RDTs. The platform presented specificity of 100 % (97.4-100), and 99.0 % (94.8-99.9) when compared to optical microscopy, and PCR, respectively, which was the same for RDTs. Its correct classification rate was 98.2 % when compared to optical microscopy and 82.3 % for PCR; the test's accuracy when compared to optical microscopy was 98.1 % (96.4-99.7), when compared to RDT was 95.2 % (93.0-97.5), and when compared to PCR was 85.6 % (82.1-89.1). Kappa (95 % CI) values for Gazelle™ were 96.4 (93.2-99.5), 88.2 (82.6-93.8) and 65.3 (57.0-73.6) for optical microscopy, RDT and PCR, respectively.

Conclusions: The Gazelle™ device was shown to have faster, easier, good sensitivity, specificity, and accuracy when compared to microscopy and was superior to RDT, demonstrating to be an alternative for vivax malaria screening particularly in areas where malaria is concomitant with other febrile infections (including dengue fever, zika, chikungunya, Chagas, yellow fever, babesiosis).

Keywords: Diagnostic test; Haemozoin; Magnetic-optical detection; Malaria; Plasmodium vivax.

Fig. 1

The Gazelle™ Device. Battery-powered equipment that can run 200 tests independently. The diagnostic reader can store or upload patient data to a phone or computer for later storage in the Cloud. GPS location, useful for epidemiological studies, can also be saved

Fig. 2

Principle of operation of Gazelle™. The device uses alternating magnetic fields to align haemozoin so that it blocks transmitted light. The light signal detected at the detector is inversely proportional to the amount of haemozoin present in the sample

Fig. 3

Steps involved in diagnosing malaria using the Gazelle™ device

Fig. 4

STARD Flowchart

Fig. 5

ROC analysis: Gazelle™ compared with microscopy and PCR. a With an AUC of 0.9834, Gazelle™ produced results that were comparable to microscopy. b With an AUC of 0.8371, Gazelle™ was less sensitive than PCR but as specific