Development of a new drug sensitivity test for Plasmodium falciparum applicable in the field

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The spread of drug-resistant Plasmodium falciparum accompanied by the world-wide resurgence of malaria urges the necessity, for the establishment of simplified and standardized method for in vitro drug sensitivity test. Currently drug sensitivity of the parasites has been examined by WHO standard method which requires visual differential counting of parasites by well-trained microscopists. We applied a fluoroassay using ethidium bromide to the test in order to enable objective reading of the results in the first year of the program. Reliable results were obtained in the test, however, the assay requires facilities such as a centrifuge and a fluorescent spectrophotometer that may not be available in the field. As the next step, a DNA hybridization technique was applied to the test using a synthetic oligonucleotide coupled to alkaline phosphatase. The density of the colored spot clearly distinguished development of parasites in culture. The new assay was assessed in Hainan Island, China, under field conditions. The trial demonstrated that, in the in vitro drug sensitivity test, the DNA hybridization technique could yield results parallel to those obtained by microscopical examination of blood smears. All procedures were carried out in an ordinary hospital laboratory on Hainan Island. Thus we consider that the new drug sensitivity test using a non-radioactive DNA probe is applicable to use in the field. We are developing some appropriate kits for the test and are expecting to be able to supply them to malaria endemic areas in the near future.