Malaria News |
Rapid Detection of Lactate Dehydrogenase and Genotyping of Plasmodium falciparum in Saliva of Children with Acute Uncomplicated Malaria 
The diagnosis of malaria in biological fluids other than blood using non-invasive, rapid diagnostic techniques provides a valuable approach in case management and epidemiological studies of malaria. Rapid detection of Plasmodium falciparum lactate dehydrogenase (pLDH) in saliva samples from 130 of 144 children with microscopically confirmed P. falciparum infection was evaluated using Optimal-IT dipsticks. Genotyping of parasites was also performed in saliva and blood samples from a cohort of patients by polymerase chain reaction (PCR). The sensitivity of the dipstick in whole-blood, whole-saliva, or supernatant of spun saliva samples was 97.2%, 77.9%, and 48.4%, respectively. The sensitivity of the dipstick in whole-saliva samples was significantly higher than in supernatant of spun saliva samples (P < 0.0005). Mutant T76 allele was detectable in 60% and 57% of blood and saliva samples, respectively. This finding shows rapid detection of pLDH in patient saliva.
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Evaluation of Recurrent Parasitemia after Artemether-Lumefantrine Treatment for Uncomplicated Malaria in Children in Western Kenya
From April 2005 to April 2006, a phase 2 malaria vaccine trial in Kenya enrolled 400 children aged 12-47 months. Each received mixed supervised and unsupervised artemether-lumefantrine for uncomplicated malaria, using a standard six-dose regimen, by weight. Children were followed for detection of parasitemia and clinical malaria. A median of two negative malaria blood films occurred during every recurrent parasitemia (RP) episode, suggesting reinfection over late recrudescence. Median time to RP after starting artemether-lumefantrine was 37 days (36-38). Of 2,020 evaluable artemether-lumefantrine treatments, there were no RPs in 99% by day 14, 71% by day 28, and 41% by day 42. By World Health Organization standards, 71% of treatment courses had adequate responses. Although recrudescence in some cannot be ruled out, our cohort had a shorter median time to RP compared with other artemether-lumefantrine treatment studies. This underscores patient counseling on completing all treatment doses for optimal protection from RP.
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Mutations in the Antifolate-Resistance-Associated Genes Dihydrofolate Reductase and Dihydropteroate Synthase in Plasmodium vivax Isolates from Malaria-Endemic Countries
Parasite dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) are known target enzymes of antifolate drugs used for the treatment and prophylaxis of persons with malaria. We sequenced the Plasmodium vivax dihydrofolate reductase (pvdhfr) and dihydropteroate synthase (pvdhps) genes to examine the prevalence and extent of point mutations in isolates from malaria-endemic countries. Double mutations (S58R and S117N) or quadruple mutations (F57L/I, S58R, T61M, and S117T) in the pvdhfr gene were found in isolates from Thailand (96.4%) and Myanmar (71.4%), but in only one isolate (1.0%) from Korea, where sulfadoxine-pyrimethamine has never been used. The pvdhfr point mutations correlated strongly with the pvdhps point mutations and ranged from single to triple mutations (S382A, A383G, and A553G), among isolates from Thailand, Myanmar, and Korea. These findings suggests that the prevalence of mutations in pvdhfr and pvdhps in P. vivax isolates from different malaria-endemic countries is associated with selection pressure imposed by sulfadoxine-pyrimethamine.
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Malaria Incidence and Prevalence Among Children Living in a Peri-Urban Area on the Coast of Benin, West Africa: A Longitudinal Study
Clinical malaria incidence was determined over 18 months in a cohort of 553 children living in a peri-urban area near Cotonou. Three cross-sectional surveys were also carried out. Malaria incidence showed a marked seasonal distribution with two peaks: the first corresponding to the long rainy season, and the second corresponding to the overflowing of Lake Nokoue. The overall Plasmodium falciparum incidence rate was estimated at 84/1,000 person-months, and its prevalence was estimated at over 40% in the two first surveys and 68.9% in the third survey. Multivariate analysis showed that girls and people living in closed houses had a lower risk of clinical malaria. Bed net use was associated with a lower risk of malaria infection. Conversely, children of families owing a pirogue were at higher risk of clinical malaria. Considering the high pyrethroids resistance, indoor residual spraying with either a carbamate or an organophospate insecticide may have a major impact on the malaria burden.
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Scaling Up Malaria Control in Zambia: Progress and Impact 2005-'2008
Zambia national survey, administrative, health facility, and special study data were used to assess progress and impact in national malaria control between 2000 and 2008. Zambia malaria financial support expanded from US$9 million in 2003 to US$ ~40 million in 2008. High malaria prevention coverage was achieved and extended to poor and rural areas. Increasing coverage was consistent in time and location with reductions in child (age 6-'59 months) parasitemia and severe anemia (53% and 68% reductions, respectively, from 2006 to 2008) and with lower post-neonatal infant and 1-'4 years of age child mortality (38% and 36% reductions between 2001/2 and 2007 survey estimates). Zambia has dramatically reduced malaria transmission, disease, and child mortality burden through rapid national scale-up of effective interventions. Sustained progress toward malaria elimination will require maintaining high prevention coverage and further reducing transmission by actively searching for and treating infected people who harbor malaria parasites.
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An Exposure-Free Tool for Monitoring Adult Malaria Mosquito Populations
Catches of Anopheles gambiae and An. arabiensis with the Ifakara Tent Trap-model B (ITT-B) correlate better with human landing catches than any other method but fail to reduce the proportion of blood-fed mosquito caught, which indicates that users are exposed to bites during collection. An improved C model (ITT-C) was developed and evaluated by comparing with ITT-B in semi-field and full-field conditions in southern Tanzania. The sensitivity of the ITT-C was approximately two times that of the ITT-B: relative rate (95% confidence interval) = 1.92 (1.52-2.42), 1.90 (1.48-2.43), and 2.30 (1.54-3.30) for field populations of An. arabiensis, Culex spp., and Mansonia spp., respectively. The ITT-C caught 73% less blood-fed An. arabiensis than the ITT-B in open field experiments and none in semi-field experiments, which confirmed that the C design is a safe trapping method. Validation of ITT-C by comparison with human landing catches and parasitologic measures of human infection status may be necessary to confirm that this design produces consistent and epidemiologically meaningful results.
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A Comparison of Methods to Detect and Quantify the Markers of Antimalarial Drug Resistance
We compare, contrast, and evaluate methods to quantify genetic markers of antimalarial drug resistance. Frequency estimates should be reported along with crude prevalence. There are four main potential methods to estimate frequencies in blood samples: simple counting of single nucleotide polymorphisms (SNPs) and haplotypes in samples with multiplicity of infection (MOI) = 1; SNP counting in samples with MOI <= 2; SNP and haplotypes counting in samples with unambiguous genotypes; statistical inference using SNP and MOI data from all samples. Large differences between the methods became apparent when analyzing field data with high MOI. Simple counting dramatically reduced sample size and estimate precision, and we show that analysis of unambiguous samples is biased, leaving maximum likelihood or similar statistical inference as the only practical option. It is essential to account for genotyping missing minor clones; ignoring this phenomenon resulted in a 2-fold underestimation of SNPs and haplotypes present at low frequencies.
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An Outbreak of Plasmodium falciparum Malaria in U.S. Marines Deployed to Liberia
In 2003, 44 U.S. Marines were evacuated from Liberia with either confirmed or presumed Plasmodium falciparum malaria. An outbreak investigation showed that only 19 (45%) used insect repellent, 5 (12%) used permethrin-treated clothing, and none used bed netting. Adherence with weekly mefloquine (MQ) was reported by 23 (55%). However, only 4 (10%) had serum MQ levels high enough to correlate with protection (> 794 ng/mL), and 9 (22%) had evidence of steady-state kinetics (MQ carboxy metabolite/MQ > 3.79). Tablets collected from Marines met USP identity and dissolution specifications for MQ. Testing failed to identify P. falciparum isolates with MQ resistance. This outbreak resulted from under use of personal protective measures and inadequate adherence with chemophrophylaxis. It is essential that all international travelers make malaria prevention measures a priority, especially when embarking to regions of the world with high transmission intensity such as west Africa.
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