Copyright©1991byThe AmericanSocietyofTropicalMedicineandHygiene COEXISTENCE OF GP195 ALLELES OF PLASMODIUM FALCIPARUM IN A SMALL

Abstract. Dimorphic variations in the genotype of the precursor to Plasmodium fal ciparummajor merozoitesurfaceantigensorgpl9s,among wildisolatesina smallmalaria parasite population were examined using Southern blot hybridization techniques. Hybrid ization, with DNA fragment probes and oligonucleotide probes derived from variable blocks of known gpl95 alleles against 18 wild isolates from Mae Sod district in Thailand, revealed the existence of seven gpl95 alleles, two of which were newly identified in this study. In four out of 17 patients, two different alleles coexisted in the circulation. It was furthermore noted that the seven alleles did not occur at the same frequency, but rather several alleles predominated in the population of P. fakiparum in this small malaria field. The precursor ofPlasmodiumfakiparum ma jor merozoite surface antigens (MSA-1), orgpl95, is one of the potential candidates for asexual blood-stage malaria vaccine. ' It is synthesized during schizogony and is proteolytically pro cessed into several products of a lower molecula