Tests for Drug Resistance

CDC recommends that all cases of malaria diagnosed in the United States should be evaluated for drug resistance. Specimens from all cases diagnosed in the United States should be sent to the CDC Malaria Laboratory for this testing.

All specimens submitted for drug resistance testing will first undergo molecular testing by polymerase chain reaction (PCR) for species confirmation. Depending on the species, the age of the specimen, and the previous receipt of antimalaria medicines, different testing methods may be employed to assess for the presence of drug resistance. Laboratory methods for testing for malaria drug resistance include in vitro tests, molecular characterization, determination of drug levels, and animal models.

In vitro tests: In these tests, blood samples from malaria patients are cultured and if found to be viable, the malaria parasites are exposed to different concentrations of antimalarial drugs in the laboratory. Culturing malaria parasites will be attempted only for pre-treatment specimens that arrive within 72 hours of collection.

Molecular characterization: For some drugs (chloroquine, SP and similar drugs, atovaquone), molecular markers have been identified that confer resistance. Molecular techniques, such as PCR or gene sequencing. can identify these markers in blood taken from malaria-infected patients.

Drug levels:  When individuals who are presumably taking malaria prophylaxis develop malaria, blood samples can be collected and analyzed for the presence of the drug. The drug is extracted from the blood and the concentration is determined by high-performance liquid chromatographic methods. Determining the drug level in the blood can help distinguish between drug non-adherence and drug resistance.

For a general overview of drug resistance and methods for testing for drug resistance in malaria:
Drug Resistance In Malaria [PDF, 350 KB, 32 pages] (WHO, 2001)

For a detailed description of the in vivo methods:
Assessment And Monitoring of Antimalarial Drug Efficacy for The Treatment of Uncomplicated Falciparum Malaria [PDF, 471 KB, 68 pages] (WHO, 2003)