Light microscopic detection of Plasmodium falciparum in vitro through Pf histidine rich protein 2 (HRP 2) gold conjugate labeling: Rapid diagnosis of cerebral malaria in humans

Abstract

Plasmodium falciparum (Pf) has been found to be the deadliest of all the known species of the parasite capable of infecting humans; this is because it is capable of causing severe cerebral tissue damage. This study was carried out to demonstrate the parasite in the host blood in vitro through immunogold labeling using antibodies against Plasmodium falciparum histidine rich protein 2 (HRP 2); a major metabolite released during the cause of the parasite infection and feeding in the erythrocyte. 12 known Pf positive samples were obtained from across the six geopolitical zones of Nigeria and were further characterized by Geimsa thick and thin film for parasite identification parasite count expressed as parasites/µl of blood. An average of 400 parasites/µl of blood was obtained in each of the samples used for this study. Pf-HRP 2 antibody was conjugated to freshly prepared colloidal gold of particle size 40 nm. The conjugation process was blocked with bovine serum albumin (BSA) and the conjugate itself preserved by 1% glycerol and 0.01% sodium azide. The parasite count was titrated against the Pf-HRP 2 gold conjugate and was analyzed under the light microscope with a fluorescent filter. Reactivity and specificity of Pf-HRP 2 gold conjugate was found to be highly specific and gave direct identification of the erythrocytes infected with the parasite. A good contrast was also obtained between uninfected erythrocytes, parasite and the infected erythrocytes.

Keywords: Plasmodium falciparum, malaria, fluorescent microscope, HRP 2, antibody, gold conjugates.