• Drug resistance in Plasmodium falciparum from the Chittagong Hill Tracts, Bangladesh.

      van den Broek, I; van der Wardt, S; Talukder, L; Chakma, S; Brockman, A; Nair, S; Anderson, T C; Médecins sans Frontières-Holland, Gulshan, Dhaka, Bangladesh. ingrid.van.den.braek@london.msf.org (Wiley-Blackwell, 2004-06)
      OBJECTIVE: To assess the efficacy of antimalarial treatment and molecular markers of Plasmodium falciparum resistance in the Chittagong Hill Tracts of Bangladesh. METHODS: A total of 203 patients infected with P. falciparum were treated with quinine 3 days plus sulphadoxine/pyrimethamine (SP) combination therapy, and followed up during a 4-week period. Blood samples collected before treatment were genotyped for parasite mutations related to chloroquine (pfcrt and pfmdr1 genes) or SP resistance (dhfr and dhps). RESULTS: Of 186 patients who completed follow-up, 32 patients (17.2%) failed to clear parasitaemia or became positive again within 28 days after treatment. Recurring parasitaemia was related to age (chi(2) = 4.8, P < 0.05) and parasite rates on admission (t = 3.1, P < 0.01). PCR analysis showed that some of these cases were novel infections. The adjusted recrudescence rate was 12.9% (95% CI 8.1-17.7) overall, and 16.6% (95% CI 3.5-29.7), 15.5% (95% CI 8.3-22.7) and 6.9% (95% CI 0.4-13.4) in three age groups (<5 years, 5-14, > or =15). The majority of infections carried mutations associated with chloroquine resistance: 94% at pfcrt and 70% at pfmdr. Sp-resistant genotypes were also frequent: 99% and 73% of parasites carried two or more mutations at dhfr and dhps, respectively. The frequency of alleles at dhfr, dhps and pfmdr was similar in cases that were successfully treated and those that recrudesced. CONCLUSIONS: The clinical trial showed that quinine 3-days combined to SP is still relatively effective in the Chittagong Hill Tracts. However, if this regimen is continued to be widely used, further development of SP resistance and reduced quinine sensitivity are to be expected. The genotyping results suggest that neither chloroquine nor SP can be considered a reliable treatment for P. falciparum malaria any longer in this area of Bangladesh.
    • Malaria in the Nuba Mountains of Sudan: baseline genotypic resistance and efficacy of the artesunate plus sulfadoxine-pyrimethamine and artesunate plus amodiaquine combinations.

      Hamour, S; Melaku, Y; Keus, K; Wambugu, J; Atkin, S; Montgomery, J; Ford, N; Hook, C; Checchi, F; Médecins Sans Frontières, Plantage Middenlaan 14, 1018 DD Amsterdam, The Netherlands. (Elsevier, 2005-07)
      Both northern and southern Sudan are deploying artemisinin-based combinations against uncomplicated Plasmodium falciparum malaria (artesunate+sulfadoxine-pyrimethamine [AS+SP] in the north, artesunate+amodiaquine [AS+AQ] in the south). In 2003, we tested the efficacy of 3 day AS+SP and AS+AQ regimens in vivo in the isolated, seasonally endemic Nuba Mountains region (the first study of AS combinations in southern Sudan). We also analysed pre-treatment blood samples for mutations at the P. falciparum chloroquine transporter (Pfcrt) gene (associated with CQ resistance), and at the dihydrofolate reductase (Dhfr) gene (associated with pyrimethamine resistance). Among 161 randomized children under 5 years, PCR-corrected cure rates after 28 days were 91.2% (52/57, 95% CI 80.7-97.1) for AS+SP and 92.7% (51/55, 95% CI 82.4-98.0) for AS+AQ, with equally rapid parasite and fever clearance. The Pfcrt K76T mutation occurred in 90.0% (144/160) of infections, suggesting CQ would work poorly in this region. Overall, 82.5% (132/160) carried mutations at Dhfr (N51I, C59R or S108N, but not I164L), but triple mutants (more predictive of in vivo SP failure) were rare (3.1%). CQ use should be rapidly discontinued in this region. SP resistance may propagate rapidly, and AS+AQ is likely to be a better long-term option, provided AQ use is limited to the combination.
    • Selection strength and hitchhiking around two anti-malarial resistance genes.

      Nash, D; Nair, S; Mayxay, M; Newton, P N; Guthmann, J P; Nosten, F; Anderson, T J C; Southwest Foundation for Biomedical Research (SFBR), San Antonio, TX 78245, USA. (2005-06-07)
      Neutral mutations may hitchhike to high frequency when they are situated close to sites under positive selection, generating local reductions in genetic diversity. This process is thought to be an important determinant of levels of genomic variation in natural populations. The size of genome regions affected by genetic hitchhiking is expected to be dependent on the strength of selection, but there is little empirical data supporting this prediction. Here, we compare microsatellite variation around two drug resistance genes (chloroquine resistance transporter (pfcrt), chromosome 7, and dihydrofolate reductase (dhfr), chromosome 4) in malaria parasite populations exposed to strong (Thailand) or weak selection (Laos) by anti-malarial drugs. In each population, we examined the point mutations underlying resistance and length variation at 22 (chromosome 4) or 25 (chromosome 7) microsatellite markers across these chromosomes. All parasites from Thailand carried the K76T mutation in pfcrt conferring resistance to chloroquine (CQ) and 2-4 mutations in dhfr conferring resistance to pyrimethamine. By contrast, we found both wild-type and resistant alleles at both genes in Laos. There were dramatic differences in the extent of hitchhiking in the two countries. The size of genome regions affected was smaller in Laos than in Thailand. We observed significant reduction in variation relative to sensitive parasites for 34-64 kb (2-4 cM) in Laos on chromosome 4, compared with 98-137 kb (6-8 cM) in Thailand. Similarly, on chromosome 7, we observed reduced variation for 34-69 kb (2-4 cM) around pfcrt in Laos, but for 195-268 kb (11-16 cM) in Thailand. Reduction in genetic variation was also less extreme in Laos than in Thailand. Most loci were monomorphic in a 12 kb region surrounding both genes on resistant chromosomes from Thailand, whereas in Laos, even loci immediately proximal to selective sites showed some variation on resistant chromosomes. Finally, linkage disequilibrium (LD) decayed more rapidly around resistant pfcrt and dhfr alleles from Laos than from Thailand. These results demonstrate that different realizations of the same selective sweeps may vary considerably in size and shape, in a manner broadly consistent with selection history. From a practical perspective, genomic regions containing resistance genes may be most effectively located by genome-wide association in populations exposed to strong drug selection. However, the lower levels of LD surrounding resistance alleles in populations under weak selection may simplify identification of functional mutations.
    • Short Report: Association Between Chloroquine and Amodiaquine Resistance and Allelic Variation in the Plasmodium Falciparum Multiple Drug Resistance 1 Gene and the Chloroquine Resistance Transporter Gene in Isolates from the Upper Nile in Southern Sudan.

      Ochong, E; van den Broek, I; Keus, K; Nzila, A; Kenya Medical Research Institute, Wellcome Trust Collaborative Program, Médecins sans Frontières-Holland, South Sudan Section, Nairobi, Kenya. (Published by: American Society of Tropical Medicine and Hygiene, 2003-08)
      Amodiaquine, a 4-aminoquinoline compound, is being considered as an alternative to chloroquine and pyrimethamine/sulfadoxine where resistance in Plasmodium falciparum to both drugs has been selected. Although amodiaquine is more potent than chloroquine, its effectiveness is reduced in areas where chloroquine resistance is high. We report an association of the P. falciparum chloroquine resistance transporter (pfcrt) gene and the P. falciparum multiple drug resistance 1 (pfmdr1) gene, two chloroquine resistance markers, with chloroquine and amodiaquine efficacy in vivo in southern Sudan. The data show that the allele of the pfcrt gene with a lysine to threonine change at codon 76 is strongly associated with both chloroquine and amodiaquine resistance. No such association was observed with the pfmdr1 gene.