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Antimicrobial Agents and Chemotherapy, February 2005, p. 733-740, Vol. 49, No. 2
0066-4804/05/$08.00+0 doi:10.1128/AAC.49.2.733-740.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Peter A. Zimmerman,3,4
John C. Reeder,4
J. Kevin Baird,2 and
Carol Hopkins Sibley1*
Department of Genome Sciences, University of Washington, Seattle, Washington,1 The Center for Global Health and Diseases, Case Western Reserve University, Cleveland, Ohio,3 Parasitic Diseases Program, United States Naval Medical Research Unit 2, Jakarta, Indonesia,2 Papua New Guinea Institute of Medical Research, Goroka, Papua New Guinea4
Received 3 August 2004/ Returned for modification 16 September 2004/ Accepted 29 September 2004
In plasmodia, the dihydrofolate reductase (DHFR) enzyme is the target of the pyrimethamine component of sulfadoxine-pyrimethamine (S/P). Plasmodium vivax infections are not treated intentionally with antifolates. However, outside Africa, coinfections with Plasmodium falciparum and P. vivax are common, and P. vivax infections are often exposed to S/P. Cloning of the P. vivax dhfr gene has allowed molecular comparisons of dhfr alleles from different regions. Examination of the dhfr locus from a few locations has identified a very diverse set of alleles and showed that mutant alleles of the vivax dhfr gene are prevalent in Southeast Asia where S/P has been used extensively. We have surveyed patient isolates from six locations in Indonesia and two locations in Papua New Guinea. We sequenced P. vivax dhfr alleles from 114 patient samples and identified 24 different alleles that differed from the wild type by synonymous and nonsynonymous point mutations, insertions, or deletions. Most importantly, five alleles that carried four or more nonsynonymous mutations were identified. Only one of these highly mutant alleles had been previously observed, and all carried the 57L and 117T mutations. P. vivax cannot be cultured continuously, so we used a yeast assay system to determine in vitro sensitivity to pyrimethamine for a subset of the alleles. Alleles with four nonsynonymous mutations conferred very high levels of resistance to pyrimethamine. This study expands significantly the total number of novel dhfr alleles now identified from P. vivax and provides a foundation for understanding how antifolate resistance arises and spreads in natural P. vivax populations.
Present address: Navy Disease Vector Ecology and Control Center, Silverdale, WA 98315-0304.
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