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RDT Test antigens: review of advantages and disadvantages
Overview
Several forms of malarial protein may be used to identify malaria based on their expression or structure. For example, the HRP2 protein used to identify Plasmodium falciparum has specific functions for that parasite and is not found in other malarial species (or humans) so has high specificity for that diagnosis. Other proteins are outwardly less specific, with the major examples forming part of metabolic pathways active in both humans and malaria (lactate dehydrogenase and aldolase). However, for these proteins there are clear structural differences between human and parasite forms of these proteins, and in some cases also between the different malarial species. These different structural featues give rise to antigenic epitopses that can be used to identify malarial parasites as a group (pan-malarial antigens) or distinguish different malarial species (species specific antigens).
Malaria-species-specific antigens
These are expressed only by specific malaria species; and can therefore be used to identify these species. Two malaria-specific antigens are widely employed in RDT assays. These are:
(1) Histidine-rich protein 2 (HRP2): An antigen that is specific for P.falciparum - Click for details of HRP2
(2) Detects lactate dehydrogenase epitopes that are specific for either P.falciparum or P.vivax Click for details of PfLDH or PvLDH
Malaria pan-specific antigens used in RDT tests
Other protein antigens are considered to be "pan specific". This means they are found in all malaria species that infect humans and can therefore be used to identify the presence of malaria, although without any species specificity. Again there are two protein antigens that are used for this purpose. These may:
(1) Detect forms of lactate dehydrogenase present on all malaria species (P.panLDH)
(2) Detect atigens specific for the malarial form of the enzyme aldolase that is found in all malarial species
Click for details of pan-malarial aldolase
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