Plasmodium falciparum: detection of polymorphisms in the dihydrofolate reductase and dihydropteroate synthetase genes by PCR and restriction digestion.

With the spread of resistance to chloroquine, the combination of sulphadoxine and pyrimethamine is growing in importance for the treatment of infection with the malaria parasite Plasmodium falciparum. Mutations in the dhfr gene of P. falciparum have been associated with resistance to pyrimethamine. Recently, several polymorphisms have been identified in the P. falciparum dhps gene which may correlate with sulphadoxine-resistance. Simple and rapid tests have been developed to detect these polymorphisms, using PCR followed by restriction digestion. These tests can accurately identify all the polymorphisms described to date at codons 16, 51, 59, 108, and 164 in the dhfr gene and those at codons 436, 437, 540, 581, and 613 in the dhps gene. A nested system has been developed which allows the accurate detection of these polymorphisms in samples of fingerprick blood collected on glass fiber membranes and filter papers, some with very low parasitaemias.