Decreased prevalence of the Plasmodium falciparum chloroquine resistance transporter 76T marker associated with cessation of chloroquine use against P. falciparum malaria in Hainan, People's Republic of China.

The use of chloroquine treatment for Plasmodium falciparum malaria was abandoned in China in 1979 because of widespread drug resistance. Subsequent studies found decreases in the prevalence of chloroquine-resistant strains. To evaluate these decreases and assess the current status of chloroquine sensitivity in Hainan, China, we determined the prevalence of the P. falciparum chloroquine resistance transporter (PfCRT) 76T marker in the DNA of blood samples collected from 1978 to 2001. Results showed the presence of PfCRT 76T in 101 of 112 samples (90%) from 1978 to 1981, 30 of 43 samples (70%) from 1986, 22 of 34 samples (65%) from 1997 to 1998, and 37 of 68 samples (54%) from 2001. The prevalence of PfCRT 76T thus progressively decreased after chloroquine was discontinued as a treatment for P. falciparum malaria (chi(2) = 5.2, P < 0.022 [1978-1981 versus 1986]; chi(2) = 7.4, P < 0.006 [1978-1981 versus 1997-1998]; and chi(2) = 28.8, P < 0.0001 [1978-1981 versus 2001]). Reduced prevalence of the PfCRT 76T marker is consistent with greater rates of chloroquine sensitivity from in vitro drug assays of blood samples in 1997 and 2001. Monitoring for continued decreases will provide valuable information for future drug-use policies in China.