• Assessing the Asymptomatic Reservoir and Dihydroartemisinin-Piperaquine Effectiveness in a Low Transmission Setting Threatened by Artemisinin Resistant Plasmodium Falciparum

      Falq, G; Van Den Bergh, R; De Smet, M; Etienne, W; Nguon, C; Rekol, H; Imwong, M; Dondorp, A; Kindermans, JM (BioMed Central, 2016-09-01)
      In Cambodia, elimination of artemisinin resistance through direct elimination of the Plasmodium falciparum parasite may be the only strategy. Prevalence and incidence at district and village levels were assessed in Chey Saen district, Preah Vihear province, North of Cambodia. Molecular and clinical indicators for artemisinin resistance were documented.
    • Optimal Health and Disease Management Using Spatial Uncertainty: A Geographic Characterization of Emergent Artemisinin-Resistant Plasmodium Falciparum Distributions in Southeast Asia

      Grist, EPM; Flegg, JA; Humphreys, G; Mas, IS; Anderson, TJC; Ashley, EA; Day, NPJ; Dhorda, M; Dondorp, AM; Faiz, MA; Gething, PW; Hien, TT; Hlaing, TM; Imwong, M; Kindermans, JM; Maude, RJ; Mayxay, M; McDew-White, M; Menard, D; Nair, S; Nosten, F; Newton, PN; Price, RN; Pukrittayakamee, S; Takala-Harrison, S; Smithuis, F; Nguyen, NT; Tun, KM; White, NJ; Witkowski, B; Woodrow, CJ; Fairhurst, RM; Sibley, CH; Guerin, PJ (BioMed Central, 2016-10-24)
      Artemisinin-resistant Plasmodium falciparum malaria parasites are now present across much of mainland Southeast Asia, where ongoing surveys are measuring and mapping their spatial distribution. These efforts require substantial resources. Here we propose a generic 'smart surveillance' methodology to identify optimal candidate sites for future sampling and thus map the distribution of artemisinin resistance most efficiently.
    • Plasmodium vivax resistance to chloroquine in Dawei, southern Myanmar.

      Guthmann, J P; Pittet, A; Lesage, A; Imwong, M; Lindegardh, N; Min Lwin, M; Zaw, T; Annerberg, A; de Radiguès, X; Nosten, F; Epicentre, Paris, France. (Wiley-Blackwell, 2008-01)
      OBJECTIVE: To assess the efficacy of chloroquine in the treatment of Plasmodium vivax malaria in in Dawei District, southern Myanmar. METHODS: Enrolled patients at Sonsinphya clinic >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. RESULTS: 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. CONCLUSIONS: 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.
    • Relapses of Plasmodium vivax infection usually result from activation of heterologous hypnozoites.

      Imwong, M; Snounou, G; Pukrittayakamee, S; Tanomsing, N; Kim, J R; Nandy, A; Guthmann, J P; Nosten, F; Carlton, J; Looareesuwan, S; Nair, S; Sudimack, D; Day, N P J; Anderson, T J C; White, N J; Department of Clinical Tropical Medicine, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand. (Infectious Diseases Society of America and University of Chicago Press, 2007-04-01)
      BACKGROUND: Relapses originating from hypnozoites are characteristic of Plasmodium vivax infections. Thus, reappearance of parasitemia after treatment can result from relapse, recrudescence, or reinfection. It has been assumed that parasites causing relapse would be a subset of the parasites that caused the primary infection. METHODS: Paired samples were collected before initiation of antimalarial treatment and at recurrence of parasitemia from 149 patients with vivax malaria in Thailand (n=36), where reinfection could be excluded, and during field studies in Myanmar (n=75) and India (n=38). RESULTS: Combined genetic data from 2 genotyping approaches showed that novel P. vivax populations were present in the majority of patients with recurrent infection (107 [72%] of 149 patients overall [78% of patients in Thailand, 75% of patients in Myanmar {Burma}, and 63% of patients in India]). In 61% of the Thai and Burmese patients and in 55% of the Indian patients, the recurrent infections contained none of the parasite genotypes that caused the acute infection. CONCLUSIONS: The P. vivax populations emerging from hypnozoites commonly differ from the populations that caused the acute episode. Activation of heterologous hypnozoite populations is the most common cause of first relapse in patients with vivax malaria.