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 chl oroquine resistance in reference isolates of Plasmodium falciparum. To asse ss the association of this polymorphism with chloroquine resistance in fiel d specimens of P. falciparum, we analyzed the omega repeat region of the cg 2 gene in 47 isolates of P. falciparum collected in the Ingwavuma District of northern KwaZulu-Natal, South Africa. Polymerase chain reaction (PCR) pr imers, which were designed to amplify the region of DNA surrounding the ome ga repeat, were used to obtain omega repeat PCR products from the field iso lates. 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 n ot apply in all malarious areas.