Antigen-based Malaria Rapid Diagnostic Tests

Malaria Antigen Detection Tests are a group of commercially available rapid antigen test-type rapid diagnostic tests that allow rapid diagnosis of malaria in persons unfamiliar with traditional laboratory techniques or in those who do not have such equipment.There are more than 20 such tests on the market (WHO product testing).The first malaria antigen suitable as a target for such tests was the soluble glycolytic enzyme glutamate dehydrogenase.At present, there is no rapid detection method as sensitive as thick blood film, nor as cheap as thick blood film.A major disadvantage of using all current dipstick methods is that the results are largely qualitative. However, in many endemic areas of tropical Africa, quantitative assessment of parasitemia is important because a large proportion of the population would be positive by any qualitative test.Malaria is a curable disease if patients are diagnosed early and treated in time. Antigen-based rapid diagnostic tests (RDTs) have an important role at the periphery of health service capacity, as many rural clinics do not have the capacity to diagnose malaria on-site due to lack of microscopes and trained technicians to evaluate blood smears. Furthermore, laboratory technicians have very limited experience in detecting and identifying malaria parasites in areas where the disease is not endemic.Every year, more and more travelers from temperate regions visit tropical countries, many of whom return with malaria.The RDT test is still seen as a complement to traditional microscopy, but with some improvements it may well replace it. Testing is simple and the procedure can be performed on-site under field conditions.These tests use blood from a fingertip or a vein, take a total of 15-20 minutes to complete and do not require a lab.Detection thresholds for these rapid diagnostic tests are in the range of 100 parasites/µl blood compared to 5 parasites for thick film microscopy. 

Accurate diagnosis is becoming increasingly important given the increasing resistance of P.falciparum and the high cost of chloroquine alternatives.The pGluDH enzyme is not present in host erythrocytes and was recommended as a marker enzyme for Plasmodium species.The malaria marker enzyme assay was adapted for routine use and is now the standard assay in most departments dealing with malaria.Knowing that the presence of pGluDH is indicative of the viability of the parasite a rapid diagnostic test using pGluDH as an antigen will be able to differentiate between living and dead organisms.The complete RDT with pGluDH as antigen has been successfully developed in China and is currently undergoing clinical trials.GluDHs are ubiquitous enzymes that occupy important branch points between carbon and nitrogen metabolism.Both nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate (NADP)-dependent enzymes are present in Plasmodium; NAD-dependent GluDH is relatively unstable and cannot be used for diagnostic purposes.Glutamate dehydrogenase provides a source of oxidizable carbon for energy production and reduces the electron carrier NADH.Glutamate is the major amino donor for other amino acids in subsequent transamination reactions.The multiple roles of glutamate in nitrogen balance make it a gateway between free ammonia and the amino groups of most amino acids.Its crystal structure has been published.GluDH activity in P. vivax, P. ovale, and P. malariae has never been tested, but given the importance of GluDH as a branch point enzyme, each cell must have a high concentration of GluDH. Enzymes with high molecular weight (such as GluDH) are known to have many isozymes, which allow strain differentiation (given the correct monoclonal antibody).The host produced antibodies against the parasitic enzyme, indicating low sequence identity.