45 research outputs found
Diversity of Plasmodium falciparuin infections within a trial of intermittent preventive treatment in Ghanian children.
No full textDiversity and dynamics of Plasmodium falciparum malaria
No full textThe epidemiology of genetic diversity of malaria parasites in relation to clinical parameters, acquisition of immunity and malaria transmission has implications for the development and evaluation of control measures such as vaccines and drugs. The diversity and dynamics of Plasmodium falciparum infections were therefore studied with a polymerase chain reaction (PCR)-based genotyping method targeting three highly polymorphic genes coding for potential vaccine candidate antigens: the two merozoite surface proteins msp1 block 2 and msp2 and the glutamine rich protein (glurp). The methodology was evaluated with regards to sampling and storage of blood samples as well as reproducibility and comparability between different laboratories.P. falciparum infections were found to be highly dynamic in asymptomatic children in a holoendemic area in Tanzania. Fluctuations of parasite densities and detection of different genotypes on consecutive days, many appearing only every 48 hours, suggested highly synchronised sequestration of parasite populations in asymptomatic infection. Parasites detected in an single blood sample thus only partly represent the total parasite population in an individual. In contrast, no synchronicity was observed in symptomatic infections during treatment in non-immune travellers, suggesting that P. falciparum populations are asynchronous in the early phase of infection.In a cohort of children followed for four years, parasite prevalence and genetic diversity varied substantially between the children but showed a high degree of consistency within the individual child. A reverse correlation was found between both parasite prevalence and multiplicity and the number of clinical episodes, suggesting that asymptomatic, especially multiclonal, P falciparum infections protect against clinical disease. Malaria infections in travellers returning from malaria endemic areas were found to be composed of several P. falciparum genotypes despite short term travel, suggesting that single mosquito inoculations transmit multiple clones. P. falciparum infections are highly genetically diverse and dynamic. The diversity may be of protective value for the human host and needs to be considered in relation to malaria prevention and treatment.List of scientific papersI. Färnert A, Arez AP, Babiker HA, Beck HP, Benito A, Bjorkman A, Bruce MC, Conway D, Day KP, Henning L, Mercereau-Puijalon O, Ranford-Cartwright LC, Rubio JM, Snounou G, Walliker D, Zwetyenga J, do Rosário VE (2000). Genotyping of Plasmodium falciparum infections by PCR: a comparative multicentre study. [Submitted]II. Farnert A, Arez AP, Correia AT, Bjorkman A, Snounou G, do Rosario V. (1999). Sampling and storage of blood and the detection of malaria parasites by polymerase chain reaction. Trans R Soc Trop Med Hyg. 93(1):50-3. https://pubmed.ncbi.nlm.nih.gov/10492790III. Farnert A, Snounou G, Rooth I, Bjorkman A. (1997). Daily dynamics of Plasmodium falciparum subpopulations in asymptomatic children in a holoendemic area. Am J Trop Med Hyg. 56(5):538-47. https://pubmed.ncbi.nlm.nih.gov/9180605IV. Farnert A, Bjorkman A (2000). Asynchronous parasite populations in clinical Plasmodium falciparum infections. [Manuscript]V. Farnert A, Rooth I, Svensson, Snounou G, Bjorkman A (1999). Complexity of Plasmodium falciparum infections is consistent over time and protects against clinical disease in Tanzanian children. J Infect Dis. 179(4):989-95. https://pubmed.ncbi.nlm.nih.gov/10068596VI. Farnert A, Rooth I, Svensson A, Snounou G, Bjorkman A (2000). Multiple Plasmodium falciparum infections in travellers and selection of antifolate mutations after proguanil prophylaxis. [Submitted]</p
Optimization and validation of multi-coloured capillary electrophoresis for genotyping of Plasmodium falciparum merozoite surface proteins (msp1 and 2).
No full textBACKGROUND: Genotyping of Plasmodium falciparum based on PCR amplification of the polymorphic genes encoding the merozoite surface proteins 1 and 2 (msp1 and msp2) is well established in the field of malaria research to determine the number and types of concurrent clones in an infection. Genotyping is regarded essential in anti-malarial drug trials to define treatment outcome, by distinguishing recrudescent parasites from new infections. Because of the limitations in specificity and resolution of gel electrophoresis used for fragment analysis in most genotyping assays it became necessary to improve the methodology. An alternative technique for fragment analysis is capillary electrophoresis (CE) performed using automated DNA sequencers. Here, one of the most widely-used protocols for genotyping of P. falciparum msp1 and msp2 has been adapted to the CE technique. The protocol and optimization process as well as the potentials and limitations of the technique in molecular epidemiology studies and anti-malarial drug trials are reported. METHODS: The original genotyping assay was adapted by fluorescent labeling of the msp1 and msp2 allelic type specific primers in the nested PCR and analysis of the final PCR products in a DNA sequencer. A substantial optimization of the fluorescent assay was performed. The CE method was validated using known mixtures of laboratory lines and field samples from Ghana and Tanzania, and compared to the original PCR assay with gel electrophoresis. RESULTS: The CE-based method showed high precision and reproducibility in determining fragment size (< 1 bp). More genotypes were detected in mixtures of laboratory lines and blood samples from malaria infected children, compared to gel electrophoresis. The capacity to distinguish recrudescent parasites from new infections in an anti-malarial drug trial was similar by both methods, resulting in the same outcome classification, however with more precise determination by CE. CONCLUSION: The improved resolution and reproducibility of CE in fragment sizing allows for comparison of alleles between separate runs and determination of allele frequencies in a population. The more detailed characterization of individual msp1 and msp2 genotypes may contribute to improved assessments in anti-malarial drug trials and to a further understanding of the molecular epidemiology of these polymorphic P. falciparum antigens
Daily Dynamics of Plasmodium falciparum Subpopulations in Asymptomatic Children in a Holoendemic Area
No full textPopulation Pharmacokinetics and Pharmacodynamics of Artemether and Lumefantrine During Combination Treatment in Children with Uncomplicated Falciparum Malaria in Tanzania.
No full textThe combination of artemether (ARM) and lumefantrine is currently the first-line treatment of uncomplicated falciparum malaria in mainland Tanzania. While the exposure to lumefantrine has been associated with the probability of adequate clinical and parasitological cure, increasing exposure to artemether and the active metabolite dihydroartemisinin (DHA) has been shown to decrease the parasite clearance time. The aim of this analysis was to describe the pharmacokinetics and pharmacodynamics of artemether, dihydroartemisinin, and lumefantrine in African children with uncomplicated malaria. In addition to drug concentrations and parasitemias from 50 Tanzanian children with falciparum malaria, peripheral parasite densities from 11 asymptomatic children were included in the model of the parasite dynamics. The population pharmacokinetics and pharmacodynamics of artemether, dihydroartemisinin, and lumefantrine were modeled in NONMEM. The distribution of artemether was described by a two-compartment model with a rapid absorption and elimination through metabolism to dihydroartemisinin. Dihydroartemisinin concentrations were adequately illustrated by a one-compartment model. The pharmacokinetics of artemether was time dependent, with typical oral clearance increasing from 2.6 liters/h/kg on day 1 to 10 liters/h/kg on day 3. The pharmacokinetics of lumefantrine was sufficiently described by a one-compartment model with an absorption lag time. The typical value of oral clearance was estimated to 77 ml/h/kg. The proposed semimechanistic model of parasite dynamics, while a rough approximation of the complex interplay between malaria parasite and the human host, adequately described the early effect of ARM and DHA concentrations on the parasite density in malaria patients. However, the poor precision in some parameters illustrates the need for further data to support and refine this model
Swedish traveller with <it>Plasmodium knowlesi </it>malaria after visiting Malaysian Borneo
No full textAbstract Plasmodium knowlesi is typically found in nature in macaques and has recently been recognized as the fifth species of Plasmodium causing malaria in human populations in south-east Asia. A case of knowlesi malaria is described in a Swedish man, who became ill after returning from a short visit to Malaysian Borneo in October 2006. His P. knowlesi infection was not detected using a rapid diagnostic test for malaria, but was confirmed by PCR and molecular characterization. He responded rapidly to treatment with mefloquine. Evaluation of rapid diagnostic kits with further samples from knowlesi malaria patients are necessary, since early identification and appropriate anti-malarial treatment of suspected cases are essential due to the rapid growth and potentially life-threatening nature of P. knowlesi. Physicians should be aware that knowlesi infection is an important differential diagnosis in febrile travellers, with a recent travel history to forested areas in south-east Asia, including short-term travellers who tested negative with rapid diagnostic tests.</p
Biomarkers of cellular aging during a controlled human malaria infection
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237639.pdf (Publisher’s version ) (Open Access
Molecular genotyping in a malaria treatment trial in Uganda - unexpected high rate of new infections within 2 weeks after treatment.
No full textPolymerase chain reaction (PCR) genotyping of malaria parasites in drug efficacy trials helps differentiate reinfections from recrudescences. A combination therapy trial of one (n = 115) or three (n = 117) days artesunate (1AS, 3AS 4 mg/kg/day) plus sulphadoxine-pyrimethamine (SP) vs. SP alone (n = 153) was conducted in Mbarara, a mesoendemic area of western Uganda. All paired recurrent Plasmodium falciparum parasitaemias on days 7, 14, 21 and 28 post-treatment were genotyped by PCR amplification and analysis of glutamate-rich protein (glurp) and merozoite surface proteins (msp) 1 and 2 genes to distinguish recrudescent from new infections. A total of 156 (1AS = 61, 3AS = 35, SP alone = 60) of 199 paired recurrent samples were successfully analysed and were resolved as 79 recrudescences (1AS = 32, 3AS = 8, SP = 39) and 77 as new infections (1AS = 29, 3AS = 27, SP = 21). The ratios of proportions of new to recrudescent infections were 0.2, 0.9, 1.4 and 1.9 on days 7, 14, 21 and 28, respectively (P < 0.001, chi(2) test for linear trend). Unexpected high new infection rates were observed early in follow-up on days 7 [5/26 (19.2%)] and 14 [24/51 (47.1%)]. These results impact significantly on resistance monitoring and point to the value of genotyping all recurrent infections in antimalarial trials
