Characterization of Plasmodium falciparum isolated from the Amazon region of Brazil: evidence for quinine resistance.

Abstract

The prevalence and severity of drug-resistant malaria is emerging rapidly in the Amazon basin of Brazil. In support of clinical trials using the new antimalarial drug combination of atovaquone and proguanil, we performed in vitro drug sensitivities, molecular characterization of parasite populations using the circumsporozoite protein, merozoite surface antigen-1 (MSA-1), and MSA-2 markers, and an analysis of the Plasmodium falciparum multidrug resistance (pfmdr1) gene sequence and copy number in 26 isolates of P. falciparum obtained in a gold-mining endemic area in Peixoto de Azevedo, Mato Grosso State. All 26 isolates were found to be resistant to chloroquine (50% inhibitory concentration [IC 50 ] ϭ 100-620 nM) and sensitive to mefloquine (IC 50 Ͻ 23 nM) and halofantrine (IC 50 Ͻ 6 nM). The isolates also show reduced susceptibility to quinine (IC 50 ϭ 48-280 nM). Sequence analysis of the pfmdr1 gene revealed Asn, Phe, Cys, Asp, and Tyr in positions 86, 184, 1034, 1042, and 1246, respectively. These point mutations were similar to that previously described in other Brazilian isolates. Southern blot analysis revealed no amplification of the pfmdr1 gene. These results suggest that three different mechanisms for drug resistance exist for chloroquine, mefloquine, and quinine.

Antimalarial drug susceptibility testing of Plasmodium falciparum in Brazil using a radioisotope method

“…In order to avoid such a impairment, resistance monitoring is of uppermost importance, at best by in vivo and in vitro methods. The present study confirmed the high level of resistance to chloroquine previously demonstrated in other areas of the Amazon basin (Boulos et al 1986, Alecrim 1986, Di Santi et al 1988, Zalis et al 1998. Regarding quinine, besides the low true-resistance percentage observed (3.3%), IC 50s to the tested samples were as high as those observed in other areas of the world with decreased susceptibility (Webster et al 1985), suggesting that the usefulness of the drug will not last for a long time.…”

“…Malaria prevalence in Brazil has increased three times during the past and quinine in those studies were too low, leading to overestimation of the resistance percentages (Alecrim 1986, Di Santi et al 1988) When adequate "cut off" limits are employed, taking together in vivo and in vitro data, parasite resistance has been observed at levels greater than 70% to chloroquine, greater than 60% to sulfadoxine-pyrimethamine, lower than 20% to quinine and almost none to mefloquine (Boulos et al 1986, Alecrim 1986, Di Santi et al 1988, Kremsner et al 1989, Souza 1992, Couto et al 1993. As in vitro evaluations of P. falciparum sensitivity have not been performed since the 80's (Di Santi et al 1988, Kremsner et al 1989, and considering that radioisotopic methods had not been used, except in one occasion (Zalis et al 1998), we decided to verify the patterns of resistance in a typical endemic area of the Brazilian Amazon region.…”

Polimorfismos del gen pfmdr1 en muestras clínicas de Plasmodium falciparum y su relación con la respuesta terapéutica a antipalúdicos y paludismo grave en Colombia

“…Con respecto a la frecuencia del alelo silvestre Asn 86, mediante este estudio se confirma su presencia en el 100% de las muestras de los municipios de Tumaco, Zaragoza y El Bagre. La alta frecuencia de este alelo silvestre coincide con los estudios realizados en la Amazonia peruana (34) y la brasilera (18,33), muestras resistentes in vitro a cloroquina y sensibles a mefloquina.…”

“…Esta última mutación también se describió en muestras resistentes a la cloroquina en Brasil (18), pero no se encontró en muestras resistentes a la cloroquina de Asia y África (16,19).…”

pfmdr1 mutations associated with chloroquine resistance incur a fitness cost in Plasmodium falciparum

“…In isolates from most areas of the world where falciparum malaria is endemic, there is typically a positive correlation between mutations in either or both these genes, and in vitro CQ resistance (Foote et al ., 1990;Zalis et al ., 1998;Duraisingh et al ., 2000a;Babiker et al ., 2001;Durand et al ., 2001;Vieira et al ., 2001;Chen et al ., 2003;Lim et al ., 2003;Pickard et al ., 2003). However, with the identification of at least four different foci of emergence of CQ resistance (Wootton et al ., 2002), the genetic basis of resistance to CQ may well vary in different geographical regions, albeit with strong tendencies for convergence at the pfmdr1 and pfcrt loci.…”