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Background: Artemisinin resistance in Plasmodium falciparum malaria has emerged in Western Cambodia. This is a major threat to global plans to control and eliminate malaria as the artemisinins are a key component of antimalarial treatment throughout the world. To identify key features associated with the delayed parasite clearance phenotype, we employed DNA microarrays to profile the physiological gene expression pattern of the resistant isolates., Results: In the ring and trophozoite stages, we observed reduced expression of many basic metabolic and cellular pathways which suggests a slower growth and maturation of these parasites during the first half of the asexual intraerythrocytic developmental cycle (IDC). In the schizont stage, there is an increased expression of essentially all functionalities associated with protein metabolism which indicates the prolonged and thus increased capacity of protein synthesis during the second half of the resistant parasite IDC. This modulation of the P. falciparum intraerythrocytic transcriptome may result from differential expression of regulatory proteins such as transcription factors or chromatin remodeling associated proteins. In addition, there is a unique and uniform copy number variation pattern in the Cambodian parasites which may represent an underlying genetic background that contributes to the resistance phenotype., Conclusions: The decreased metabolic activities in the ring stages are consistent with previous suggestions of higher resilience of the early developmental stages to artemisinin. Moreover, the increased capacity of protein synthesis and protein turnover in the schizont stage may contribute to artemisinin resistance by counteracting the protein damage caused by the oxidative stress and/or protein alkylation effect of this drug. This study reports the first global transcriptional survey of artemisinin resistant parasites and provides insight to the complexities of the molecular basis of pathogens with drug resistance phenotypes in vivo.

Summary: We monitored post-treatment Plasmodium falciparum among patients treated with chloroquine (CQ) and sulfadoxine–pyrimethamine (SP; Fansidar®) in a village in eastern Sudan. Parasites were examined on day 0 (pre-treatment), day 7, day 14 and day 21 (post-treatment) during the transmission season. A further sample was taken 2 months later (day 80) at the start of the dry season. Asexual forms and gametocytes were detected by microscopy, and reverse transcriptase polymerase chain reaction (RT-PCR) was used to detect expression of gametocyte-specific proteins pfs25 and pfg377. Gametocyte carriage, as revealed by microscopy, increased significantly following CQ and SP treatment, reaching a maximum between days 7 and 14. When measured by RT-PCR, however, there was no significant difference in gametocyte rate between day 0 and days 7 or 14. RT-PCR gametocyte rates dropped dramatically by day 80 post treatment but were still 33% and 8% in the CQ- and SP-treated group at this time. Alleles associated with drug resistance of P. falciparum to chloroquine (the chloroquine resistance transporter, pfcrt, and multidrug resistance, pfmdr1) and to pyrimethamine (dihydrofolate reductase, dhfr) were seen at a high frequency at the beginning of treatment and increased further through time following both drug treatments. Infections with drug-resistant parasites tended to have higher gametocyte prevalence than drug-sensitive infections. [Copyright &y& Elsevier]