Chloroquine-resistant isolates of Plasmodium falciparum with alternative CG2 omega repeat length polymorphisms

A particular polymorphism in the cg2 gene has previously been linked to chloroquine resistance in reference isolates of Plasmodium falciparum. To assess the association of this polymorphism with chloroquine resistance in field specimens of P. falciparum, we analyzed the omega repeat region of the cg2 gene in 47 isolates of P. falciparum collected in the Ingwavuma District of northern KwaZulu-Natal, South Africa. Polymerase chain reaction (PCR) primers, which were designed to amplify the region of DNA surrounding the omega repeat, were used to obtain omega repeat PCR products from the field isolates. The PCR product for each isolate varied in length, depending on the number of cg2 omega repeats for that isolate. We found that several in vivo and in vitro chloroquine-resistant isolates of P. falciparum did not have the expected 16 omega repeats. These results suggest that the link between the cg2 polymorphism and chloroquine resistance identified previously may not apply in all malarious areas.