Indigenous evolution of Plasmodium falciparum pyrimethamine resistance multiple times in Africa.
OBJECTIVE
Resistance to pyrimethamine in Plasmodium falciparum is conferred by mutations in the gene encoding dihydrofolate reductase (DHFR). It is known that DHFR double mutants have evolved independently in multiple geographic areas, whereas the triple mutant prevalent in Africa appears to have originated in south-east Asia. In this study, we investigated whether other triple mutants may have evolved independently in Africa.


METHODS
We determined the DHFR genotypes and haplotypes of five microsatellite loci flanking the DHFR locus between 4.49 kb upstream and 1.48 kb downstream of 159 isolates collected from three African countries (Republic of Congo, Ghana and Kenya).


RESULTS
The CIRNI type of DHFR triple mutant (with mutations underlined at amino acid positions 51, 59 and 108) was predominant in the Republic of Congo (82%) and Ghana (81%) and was the second most prevalent in Kenya (27%), where the CICNI type of DHFR double mutant was dominant. Three distinct microsatellite haplotypes were identified in the DHFR triple mutant. One haplotype was identical to that originating in south-east Asia. The other two haplotypes occurred in Ghana and Kenya, which were unique, previously undescribed and identical to those of the two DHFR double mutants found in the same locations.


CONCLUSIONS
This study presents strong evidence for the unique, multiple independent evolution of pyrimethamine resistance in Africa. Indigenous evolution of the triple mutant from the double mutant appears to have occurred in a step-wise manner in Kenya and Ghana or in nearby countries in east and west Africa.
Mita
Toshihiro
T
Department of International Affairs and Tropical Medicine, Tokyo Women's Medical University, 9-1 Kawada-cho, Shinjuku-ku, Tokyo 162-8666, Japan. hiro-tm@research.twmu.ac.jp
Tanabe
Kazuyuki
K
Takahashi
Nobuyuki
N
Culleton
Richard
R
Ndounga
Mathieu
M
Dzodzomenyo
Mawuli
M
Akhwale
Willis S
WS
Kaneko
Akira
A
Kobayakawa
Takatoshi
T
D019943:Amino Acid Substitution; D000818:Animals; D000962:Antimalarials / Q000494:pharmacology*; D003223:Congo; D016172:DNA Fingerprinting; D016054:DNA, Protozoan / Q000235:genetics; D004351:Drug Resistance; D005838:Genotype; D005869:Ghana; D006801:Humans; D007630:Kenya; D016778:Malaria, Falciparum / Q000469:parasitology*; D018895:Microsatellite Repeats; D020125:Mutation, Missense; D010963:Plasmodium falciparum / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D015800:Protozoan Proteins / Q000235:genetics; D011739:Pyrimethamine / Q000494:pharmacology*; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics
D000962:Antimalarials; D016054:DNA, Protozoan; D015800:Protozoan Proteins; D013762:Tetrahydrofolate Dehydrogenase; D011739:Pyrimethamine