“A Comparative Evaluation of Conventional Staining Methods and Immunological Techniques for the Diagnosis of Malaria”

Abstract

To compare the conventional staining methods (Leishman stain, JSB stain, field's stain) on peripheral blood smear with rapid immunological methods (Falcivax (HRP2Ag+ pLDH) & SD Bioline (pLDH)) for the diagnosis of malarial parasites and to achieve at a better diagnostic tool for diagnosis of malarial parasites in terms of cost, technical expertise, lab facilities, rapidity, higher sensitivity and specificity. MATERIALS AND METHODS: The present study was conducted in the Microbiology Department of a MGM Medical College & Hospital , Navi Mumbai from July 2009 to June 2010. 339 patients with clinical features s/o Malaria were included in the study. For all the patients in the study group, 1ml of blood was collected by venipuncture aseptically in EDTA bulbs. Thick and thin blood films were prepared on 3 slides one each for Leishman, Fields and JSB stain. All the samples were then subjected to antigen detection using Falcivax (Pf & Pv) and SD Bioline (Pf & Pv) Kits. Test was performed as per kit instruction manual and interpreted accordingly. RESULTS: A total of 339 cases were studied, 238 males and 101 females with age ranges from 15yrs to 72yrs. Of 339 cases, 138 cases were positive for malarial parasites by gold standard viz: Leishman stained thick smear. 68 cases were infected with P.falciparum, 51 with P.vivax and 19 had mixed infection. Falcivax kit showed higher sensitivity and specificity compared to rest of all the rapid methods for detection of P.falciparum. In diagnosing P.falciparum malaria it showed sensitivity of 100% in comparison with gold standard even at low parasitemias. In fact, Falcivax kits also detect falciparum infections even when the parasites are sequestered and not detectable by microscopy. In case of detection of P.vivax, performance of SD bioline and Falcivax kits were similar (96%) and better than conventional staining of thin blood smear examination (92%) by Leishman, JSB and Field's method when compared with gold standard thick smear examination. CONCLUSION: The logistic, economic and technical factors limit rapid access to microscopic confirmation of malaria in many tropical countries including India. So taking into account of all the factors from our study, we recommend Falcivax HRP2 antigen detection as a tool for diagnosis of malaria in future. Although no test can completely replace the conventional method of peripheral blood smear examination, these newer diagnostic tests can be used as supplement to microscopic examination of peripheral blood smear where the diagnosis cannot be made on microscopy alone. Also, rapid immunochromatography tests can be used in times of urgency