Therapeutic responses of Plasmodium vivax and P. falciparum to chloroquine, in an area of western India where P. vivax predominates.

In 2003-2005, following an increase in the local incidence of human malaria, the therapeutic efficacy of chloroquine (CQ) in the treatment of Plasmodium vivax and P. falciparum malaria was evaluated in the Anand district of Gujarat state, in western India. After oral administration of CQ, clinical and parasitological responses were measured over a follow-up period of 28 days, following the standard protocol of the World Health Organization. Most of the recurrent infections were checked, by genotyping, to see whether they were the result of treatment failure or re-infection during the follow-up. At the primary health centre (PHC) in Deva, all 57 P. vivax cases included in the study responded to CQ within 3 days. At the Pansora PHC, however, only 59 [90.8%, with a 95% confidence interval (CI) of 83.7%-97.8%] of the 65 P. vivax cases appeared to respond completely, recurrent infections being observed in the other six cases (9.2%; CI=2.2%-16.3%). Of the four recurrent infections checked by genotyping, however, only two appeared to be the result of true treatment failure. Twenty-seven (81.8%; CI=67.2%-94.4%) of the 33 P. falciparum cases who were enrolled in the study, all from Pansora PHC also showed apparent treatment failure, with one early failure, 17 late clinical failures and nine late parasitological failures. All 23 P. falciparum cases that showed apparent treatment failure and were investigated by genotyping appeared to be true cases of failure, none showing any evidence of re-infection during follow-up. The mean parasite-clearance times for those infected with P. falciparum, both those considered CQ-sensitive and the treatment failures, exceeded 2 days. These results indicate the presence of CQ-resistant P. vivax and P. falciparum in Anand district. The high frequency of CQ failure against P. falciparum observed in this study led to a change in the drug policy at the Pansora PHC, with artemisinin-based combination therapy now being used for the first-line treatment of P. falciparum malaria. Chloroquine remains the recommended first-line treatment for P. vivax infections in the area but the treatment failure seen in at least two P. vivax cases indicates a need for further monitoring of the therapeutic efficacy of CQ against such infections, in central Gujarat and elsewhere.