PCR TYPING OF FIELD ISOLATES OF PLASMODIUM-FALCIPARUM

We report on an analysis of the constraints of PCR typing of field Pla smodium falciparum isolates by using a few highly polymorphic markers, MSA-1, MSA-2, TRAP, and CS. We show that the reactions are specific f or the P. falciparum species. The detection threshold (minimum number of parasites required to detect a visible band by ethidium bromide) di ffered from one marker to the other and, within one locus, from one pr imer combination to the other. Importantly, the various MSA-1 and MSA- 2 reference alleles were amplified with the same efficiency. Amplifica tion from reconstituted allele mixtures indicated that at certain alle le ratios, the most abundant allele interfered with the amplification of the less abundant one. An analysis of nine isolates collected from patients with acute malaria in Dielmo, Senegal, during a transmission season when the inoculation rate was one infective bite every second n ight is presented and discussed. All samples contained more than one p arasite type. A significant polymorphism was observed for the four mar kers. Novel TaqI restriction fragment length polymorphisms were found for the TRAP gene, and TRAP gene typing alone allowed a distinction be tween the various isolates. MSA-1 and MSA-2 gave multiple band pattern s specific for each sample.