Isotopic assays are based on the measurement of the metabolic activity of
P. falciparum and its inhibition under the influence of antimalarial drugs. This technique was developed in 1979 by Desjardins
et al. for the quantitative assessment of antimalarial activity using a semi-automated microdilution technique. The most commonly used radioactive marker is [3H]-labelled hypoxanthine, which is being incorporated in the course of the metabolic activity of the parasite and may be measure in a liquid scintillation counter. This method has a high degree of reproducibility and allows for the screening of a large number of
P. falciparum strains under highly controlled conditions. However it needs well-equipped laboratory facilities, involves the handling of radioactive material, and requires high parasite densities.
FURTHER INFORMATION (not vailable yet)
Drug Resistance
HRP2
The HRP2 assay is a P. falciparum in vitro drug susceptibility assay which allows for a simple assessement of drug sensitivity parameters using commercial ELISA test kits. It uses a novel approach to the measurement of drug sensitivity. The amount of histidine rich protein II produced in the malaria culture is used as a marker for parasite growth and is measured in a simple double-site sandwich ELISA. In a first evaluation it proved to be very sensitive, simple to establish and highly reproducible. It may easily be adapted to be used for a wide range of applications, from epidemiological studies to the screening of new drugs.
The WHO drug sensitivity test is based on the morphological estimation of parasite growth by microscopical assessment of the schizont maturation inhibition caused by antimalarial drugs. The method of continuous culture developed by Trager and Jensen (1976) and its further development into a microculture technique by Rieckmann et al (1978)formed the foundation for these tests, which were later standardised by the WHO. The maturation of P. falciparum in a 24 hour culture is measured by microscopically counting the number of parasites that develop into schizonts (i.e. parasites with three or more chromatins). The WHO assay is economical and simple to perform in the field. However, it is als very labour intensive and subject to individual variability.