SEQUENCE VARIATION IN THE SMALL-SUBUNIT RIBOSOMAL-RNA GENE OF PLASMODIUM-MALARIAE AND PREVALENCE OF ISOLATES WITH THE VARIANT SEQUENCE IN SICHUAN, CHINA

By two PCR-based diagnostic methods, Plasmodium malariae infections ha ve been rediscovered at two foci in the Sichuan province of China, a r egion where no cases of P. malariae have been officially reported for the last 2 decades. In addition, a variant form of P. malariae which h as a deletion of 19 bp and seven substitutions of base pairs in the ta rget sequence of the small-subunit (SSU) rRNA gene was detected with h igh frequency. Alignment analysis of Plasmodium sp. SSU rRNA gene sequ ences revealed that the 5' region of the variant sequence is identical to that of P. vivax or P. knowlesi and its 3' region is identical to that of P. malariae. The same sequence variations were also found in P . malariae isolates collected along the Thai-Myanmar border, suggestin g a wide distribution of this variant form from southern China to Sout heast Asia.