Resistance to Antimalarials in Southeast Asia and Genetic Polymorphisms in pfmdr1

Abstract

Resistance to antimalarial drugs is a public health problem worldwide. Molecular markers for drugresistant malaria, such as pfcrt and pfmdr1 polymorphisms, could serve as useful surveillance tools. To evaluate this possibility, sequence polymorphisms in pfcrt (position 76) and pfmdr1 (positions 86, 184, 1034, 1042, and 1246) and in vitro drug sensitivities were measured for 65 Plasmodium falciparum isolates from Thailand, Myanmar, Vietnam, and Bangladesh. The pfcrt Thr76 polymorphism was present in 97% of samples, consistent with observations that chloroquine resistance is well established in this region. Polymorphisms in pfmdr1 clustered into four specific patterns: the wild type (category I), a Tyr86 polymorphism only (category II), a Phe184 polymorphism only (category III), and Phe184 in combination with Cys1034 and/or Asp1042 (category IV). Isolates in categories I and III were more sensitive to chloroquine and more resistant to mefloquine, artesunate, and artemisinin than isolates in categories II and IV (P < 0.01). Mefloquine resistance was significantly more common in category I and III isolates than in category II and IV isolates, with a prevalence ratio of 14.95 (95% confidence interval, 3.88 to 57.56). These categories identified mefloquine resistance with a sensitivity and a specificity of 94 and 91%, respectively. The pfmdr1 gene copy number was measured by real-time PCR as a ratio of the amount of pfmdr1 DNA to the amount of lactate dehydrogenase (ldh) DNA. Eight samples had pfmdr1 DNA/ldh DNA ratios >3. The isolates in all 8 samples fell into categories I and III and were significantly more resistant to mefloquine, quinine, artemisinin, and artesunate and more sensitive to chloroquine than the isolates in the 57 samples with <3 copies of the gene (P < 0.001). Thus, measurement of pfmdr1 mutations and gene copy number may be useful for surveillance of mefloquine-resistant malaria in Southeast Asia.

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

“…La mutación 86 Tir en pfmdr1 asociada con resistencia a la cloroquina, también puede incrementar la sensibilidad a mefloquina y halofantrina (15), mientras que la presencia del alelo silvestre Asn 86 se ha correlacionado con resistencia a la mefloquina (16,17).…”

“…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.…”

Pfmdr1 gene polymorphism of Plasmodium falciparum isolates from asymptomatic individuals of Dienga, southeastern Gabon

“…However, these successes are threatened by the emergence of parasite resistance against artemisinin [9][10][11]. Moreover, this resistance was firmly established in Cambodia, Thailand, Vietnam and Burma and its possible spread over the rest of South-east Asia has been documented [12,13]. On the other hand, the therapeutic failures of ACTs could be associated with single nucleotide polymorphism (SNP) in P. falciparum multidrug resistance gene-1 (Pfmdr1) [14,13], as well as with K13 propeller [15,16].…”