Plasmodium vivax resistance to chloroquine in Dawei, southern Myanmar

The objective was to assess the efficacy of chloroquine in the treatment of Plasmodium vivax malaria in Dawei District southern Myanmar. Enrolled patients at Sonsinphya clinic greater than 6 months of age were assessed clinically and parasitologically every week for 28 days. To differentiate new infections from recrudescence we genotyped pre- and post-treatment parasitaemia. Blood chloroquine was measured to confirm resistant strains. Between December 2002 and April 2003 2661 patients were screened of whom 252 were included and 235 analysed. Thirty-four per cent (95% CI: 28.1-40.6) of patients had recurrent parasitaemia and were considered treatment failures. 59.4% of these recurrences were with a different parasite strain. Two (0.8%) patients with recurrences on day 14 had chloroquine concentrations above the threshold of 100 ng/ml and were considered infected with chloroquine resistant parasites. 21% of failures occurred during the first 3 weeks of follow-up: early recurrence and median levels of blood chloroquine comparable to those of controls suggested P. vivax resistance. Plasmodium vivax resistance to chloroquine seems to be emerging in Dawei near the Thai-Burmese border. While chloroquine remains the first-line drug for P. vivax infections in this area of Myanmar regular monitoring is needed to detect further development of parasite resistance. (authors)