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Extensive dynamics of Plasmodium falciparum densities, stages and genotyping profiles
Background:
Individuals living in areas of high malaria transmission often have different Plasmodium falciparum clones detected in the peripheral blood over time. The aim of this study was to assess the dynamics of asymptomatic P. falciparum infections in a few hours intervals.
Methods:
Capillary blood samples were collected 6-hourly during 5 days from asymptomatic children in a highly endemic area in Tanzania. Parasite densities and maturation stages were investigated by light microscopy. Types and number of clones were analysed by PCR based genotyping of the polymorphic merozoite surface proteins 1 and 2 genes.
Results:
Parasite densities and maturation stages fluctuated 48 hourly with a gradual shift into more mature forms. Various genotyping patterns were observed in repeated samples over five days with only few samples with identical profiles. Up to six alleles differed in samples collected 6 hours apart in the same individual.
Conclusion:
This detailed assessment highlights the extensive within-host dynamics of P. falciparum populations and the limitations of single blood samples to determine parasite densities, stages and genotyping profiles in a malaria infected individual.
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Mutations in the Plasmodium falciparum cytochrome b gene are associated with delayed parasite recrudescence in malaria patients treated with atovaquone-proguanill
Background:
Fixed-dose combination antimalarial drugs have played an increasingly important role in the treatment and chemoprophylaxis of falciparum malaria since the worldwide failure of monotherapy with chloroquine. Atovaquone-proguanil is one such combination drug used both for prophylaxis in travellers, and for treatment of acute malaria cases in European hospitals and clinics.
Methods:
A series of seven atovaquone-proguanil treatment failures and three prophylaxis breakthroughs from four UK hospitals from 2004-2008 were analysed for evidence of mutations in the pfcyt-b gene, previously found to be associated with failure of the atovaquone component.
Results:
Parasites carrying pfcyt-b mutations were found in five falciparum malaria patients with recrudescent parasitaemia occurring weeks after apparently successful treatment of a primary infection with atovaquone-proguanil. Four of these cases carried parasites with the Tyr268Cys mutation in pfcyt-b, previously reported in two French patients with malaria. In contrast, mutations in pfcyt-b were not found in three patients treated with atovaquone-proguanil who exhibited delayed clearance of the primary infection, nor in two returning travellers with malaria who had used the combination for prophylaxis. Using current and previously published data, mean time to recrudescence of parasites carrying pfcytb codon 268 mutations was estimated as 28.0 days after treatment (95% C.I. 23.0 - 33.0 days), whereas treatment failures without codon 268 mutations received rescue treatment an average of 4.71 days after initial AP treatment (95% C.I. 1.76 - 7.67 days).
Conclusions:
Genetically-determined parasite resistance to atovaquone is associated with delayed recrudescence of resistant parasites three weeks or more after initial clearance of parasitaemia by atovaquone/proguanil therapy. The 268-Cys allele of pfcyt-b may have been overlooked in previous studies of atovaquone-proguanil treatment failure as it is not detected by current RFLP methods.
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Dispensary level pilot implementation of rapid diagnostic tests: an evaluation of RDT acceptance and usage by providers and patients - Tanzania, 2005
Background:
Malaria rapid diagnostic tests (RDTs) may assist in diagnosis, improve prescribing practices and reduce potential drug resistance development. Without understanding operational issues or acceptance and usage by providers and patients, the costs of these tests may not be justified.
Objectives
To evaluate the impact of RDTs on prescribing behaviours, assess prescribers' and patients' perceptions, and identify operational issues during implementation.
Methods:
Baseline data were collected at six Tanzanian public dispensaries. RDTs were implemented for eight weeks and data collected on frequency of RDT use, results, malaria diagnoses and the prescription of antimalarials. Patients referred for RDTs completed a standardised exit interview. Qualitative methods assessed attitudes toward and satisfaction with RDTs, perceptions about the test and operational issues related to implementation.
Results:
Of 595 patients at baseline, 200 (33%) were diagnosed clinically with malaria but had a negative RDT. Among the 2519 RDTs performed during implementation, 289 (11.5%) had a negative result and antimalarials prescribed. The proportion of "over-prescriptions" at baseline was 54.8% (198/365). At weeks four and eight this decreased to 16.1% (27/168) and 16.4% (42/256) respectively.
A total of 355 patient or parent/caregiver and 21 prescriber individual interviews and 12 focus group discussions (FGDs) were conducted. Patients, caregivers and providers trusted RDT results, agreed that use of RDTs was feasible at dispensary level, and perceived that RDTs improved clinical diagnosis. Negative concerns included community suspicion and fear that RDTs were HIV tests, the need for additional supervision in interpreting the results, and increased work loads without added compensation.
Conclusions:
Overprescriptions decreased over the study period. There was a high degree of patient/caregiver and provider acceptance and satisfaction with RDTs. Implementation should include community education, sufficient levels of training and supervision and consideration of the need for additional staff.
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Alterations on peripheral B cell subsets following an acute uncomplicated clinical malaria infection in children
Background:
The effects of Plasmodium falciparum on B-cell homeostasis have not been well characterized. This study investigated whether an episode of acute malaria in young children results in changes in the peripheral B cell phenotype.
Methods:
Using flow-cytofluorimetric analysis, the B cell phenotypes found in the peripheral blood of children aged 2-5 years were characterized during an episode of acute uncomplicated clinical malaria and four weeks post-recovery and in healthy age-matched controls.
Results:
There was a significant decrease in CD19+ B lymphocytes during acute malaria. Characterization of the CD19+ B cell subsets in the peripheral blood based on expression of IgD and CD38 revealed a significant decrease in the numbers of naive CD38-IgD+ B cells while there was an increase in CD38+IgD- memory B cells during acute malaria. Further analysis of the peripheral B cell phenotype also identified an expansion of transitional CD10+CD19+ B cells in children following an episode of acute malaria with up to 25% of total CD19+ B cell pool residing in this subset.
Conclusion:
Children experiencing an episode of acute uncomplicated clinical malaria experienced profound disturbances in B cell homeostasis.
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A randomized trial to monitor the efficacy and effectiveness by QT-NASBA of artemether-lumefantrine versus dihydroartemisinin-piperaquine for treatment and transmission control of uncomplicated Plasmodium falciparum malaria in western Kenya
Background:
Many countries have implemented artemisinin-based combination therapy (ACT) for the first-line treatment of malaria. Although many studies have been performed on efficacy and tolerability of the combination arthemeter-lumefantrine (AL) or dihydroartemisinin-piperaquine (DP), less is known of the effect of these drugs on gametocyte development, which is an important issue in malaria control.
Methods and results
In this two-arm randomized controlled trial, 146 children were treated with either AL or DP. Both groups received directly observed therapy and were followed for 28 days after treatment. Blood samples were analysed with microscopy and NASBA. In comparison with microscopy NASBA detected much more gametocyte positive individuals. Moreover, NASBA showed a significant difference in gametocyte clearance in favour of AL compared to DP. The decline of parasitaemia was slower and persistence or development of gametocytes was significantly higher and longer at day 3, 7 and 14 in the DP group but after 28 days no difference could be observed between both treatment arms.
Conclusions:
Although practical considerations could favour the use of one drug over another, the effect on gametocytogenesis should also be taken into account and studied further using molecular tools like NASBA. This also applies when a new drug is introduced.
Trial registration
Current controlled trials ISRCTN36463274
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Prevalence of pfmdr1, pfcrt, pfdhfr and pfdhps mutations associated with drug resistance, in Luanda, Angola
Background:
Malaria is the infectious disease causing the highest morbidity and mortality in Angola and due to widespread chloroquine (CQ) resistance, the country has recently changed its first-line treatment recommendations for uncomplicated malaria, from CQ to artemisinin combination therapies (ACT) in adults, and sulphadoxine/pyrimethamine (S/P) in pregnant women. Loss of SP sensitivity is, however, progressing rapidly in Africa and, in this study, were investigated a number of molecular markers associated to CQ and S/P.
Methods:
Blood samples were collected from 245 children with uncomplicated malaria, admitted at the Pediatric Hospital Dr. David Bernardino (HPDB), Angola, and the occurrence of mutations in Plasmodium falciparum was investigated in the pfmdr1 (N86Y) and pfcrt (K76T) genes, associated with CQ resistance, as well as in pfdhfr (C59R) and pfdhps (K540E), conferring SP resistance.
Results:
The frequencies of pfmdr1 mutations in codon 86 were 28.6% N, 61.3% Y and 10.1% mixed infections (NY). The frequency of pfcrt mutations in codon 76 were 93.9% K, 5.7% T and 0.4% mixed infections (KT). For pfdhfr the results were in codon 59, 60.6% C, 20.6% R and 18.8% mixed infections (CR). Concerning pfdhps, 6.3% of the isolates were bearers of the mutation 540E and 5.4% mixed infections (K540E).
Conclusions:
The results of this epidemiologic study showed high presence of CQ resistance markers while for SP a much lower prevalence was detected for the markers under study.
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Declining incidence of malaria imported into the UK from West Africa
Background:
Two thirds of all falciparum malaria cases reported in the United Kingdom (UK) are acquired in West Africa (WA). To ensure recommendations and guidelines for malaria prophylaxis in travellers to West Africa correlate to the risk of infection, a study was undertaken to examine recent trends and predict future patterns of imported malaria acquired by UK residents visiting West Africa and West African visitors to the UK between 1993 and 2006.
Methods and Results
Using passenger numbers and malaria surveillance reports, the data revealed a 2.3-fold increase in travel to West Africa with a five-fold increase in travelers visiting friends and relatives (VFR). Malaria incidence fell through the study period, the greatest decline noted in VFR with a fall from 196 cases/1,000 person-years to 52 cases/1,000 person-years, 9.8% per year p<0.0001. The risk for travellers from the UK visiting for other reasons declined 2.7 fold, at an annual decrease of 7.0%, with the incidence in West African visitors to the UK falling by 2.3 fold, a rate of 7.9% annually.DiscussionThe reduction in incidence among all three groups of travellers may be explained by several factors; changing chemoprophylaxis usage and / or increased travel in urban areas where malaria risk has declined over the past decade, or widespread reduction in malaria transmission in West Africa.
Conclusion:
With the reduction in malaria incidence seen in both visitors to and from West Africa, the most rational explanation for these findings is a fall in malaria transmission in West Africa, which may require a change in prophylaxis policy for UK travelers over the next 5-10 years.
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Implementation of Intermittent Preventive Treatment in pregnancy with sulphadoxine/pyrimethamine (IPTp-SP) at a district health centre in rural Senegal
Background:
Intermittent preventive treatment with sulphadoxine-pyrimethamine (SP) is recommended for reducing the risk of malaria in pregnancy and its consequences on mothers and babies (IPTp-SP). Indicators of implementation and effects of IPTp-SP were collected in a rural clinic in Southern Senegal.
Methods:
Women seen routinely at the antenatal clinic (ANC) of a rural dispensary during 2000-2007. Deployment of IPTp-SP started in January 2004. Inspection of antenatal and outpatient clinic registries of the corresponding period.
Results:
Between 1st January 2000 and 30th April 2007, 1,781 women of all gravitidities and parities attended the ANC with 965 deliveries (606 and 398 respectively since 1st January 2004, when IPTp-SP was started.) 69% of women were seen >3 times; 95% received at least one dose and 70% two doses of SP (from 61% in 2004 to 86% in 2007). The first visit, first and second dose of SP occurred at a median week 20, 22 and 31. The probability of receiving two doses was >80% with >3 antenatal visits and a first dose of SP by week 20.
The prevalence of maternal malaria was low and similar pre- (0.7%) and during IPTp (0.8%). Effects on of low birth weight (LBW, <2.5kg) were non-statistically significant. The prevalence of LBW was 10.8% pre- and 7.7% during IPTp deployment (29% risk reduction, p=0.12).
Unfavourable pregnancy outcomes numbered 72 (7.5% of pregnancies with known outcome), including 30 abortions and 42 later deaths (late foetal deaths, stillbirth, peri-natal) of which 13 with one or more malformations (1.35% of all recorded deliveries).
Conclusions:
The implementation of IPTp-SP was high. Early attendance to ANC favours completion of IPTp-SP. The record keeping system in place is amenable to data extraction and linkage. A model was developed that predicts optimal compliance to two SP doses, and could be tested in other settings. Maternal malaria was infrequent and unaffected by IPTp-SP. The risk of LBW was lower during IPT implementation but the difference was non-significant and could have other explanations.
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Auditory assessment of patients with acute uncomplicated Plasmodium falciparum malaria treated with three-day mefloquine-artesunate on the north-western border of Thailand
Background:
The use of artemisinin derivatives has increased exponentially with the deployment of artemisinin combination therapy (ACT) in all malarious areas. They are highly effective and are considered safe, but in animal studies artemisinin derivatives produce neurotoxicity targeting mainly the auditory and vestibular pathways. The debate remains as to whether artemisinin derivatives induce similar toxicity in humans.
Methods:
This prospective study assessed the effects on auditory function of a standard 3-day oral dose of artesunate (4 mg/kg/day) combined with mefloquine (25 mg/kg) in patients with acute uncomplicated falciparum malaria treated at the Shoklo Malaria Research Unit, on the Thai-Burmese border. A complete auditory evaluation with tympanometry, audiometry and auditory brainstem responses (ABR) was performed before the first dose and seven days after initiation of the antimalarial treatment.
Results:
Complete auditory tests at day 0 (D0) and day 7 (D7) were obtained for 93 patients. Hearing loss (threshold > 25 dB) on admission was common (57%) and associated with age only. No patient had a threshold change exceeding 10 dB between D0 and D7 at any tested frequency. No patient showed a shift in Wave III peak latency of more than 0.30 msec between baseline and D7.
Conclusions:
Neither audiometric or the ABR tests showed clinical evidence of auditory toxicity seven days after receiving oral artesunate and mefloquine.
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Overuse of artemisinin-combination therapy in Mto wa Mbu (river of mosquitoes), an area misinterpreted as high endemic for malaria
Background:
Adequate malaria diagnosis and treatment remain major difficulties in rural sub-Saharan Africa. These issues deserve renewed attention in the light of first-line treatment with expensive artemisinin-combination therapy (ACT) and changing patterns of transmission intensity. This study describes diagnostic and treatment practices in Mto wa Mbu, an area that used to be hyperendemic for malaria, but where no recent assessments of transmission intensity have been conducted.
Methods:
Retrospective and prospective data were collected from the two major village health clinics. The diagnosis in prospectively collected data was confirmed by microscopy. The level of transmission intensity was determined by entomological assessment and by estimating sero-conversion rates using anti-malarial antibody responses.
Results:
Malaria transmission intensity by serological assessment was equivalent to < 1 infectious bites per person per year. Despite low transmission intensity, >40% of outpatients attending the clinics in 2006-2007 were diagnosed with malaria. Prospective data demonstrated a very high overdiagnosis of malaria. Microscopy was unreliable with <1% of slides regarded as malaria parasite-positive by clinic microscopists being confirmed by trained research microscopists. In addition, many 'slide negatives' received anti-malarial treatment. As a result, 99.6% (248/249) of the individuals who were treated with ACT were in fact free of malaria parasites.
Conclusions:
Transmission intensity has dropped considerably in the area of Mto wa Mbu. Despite this, most fevers are still regarded and treated as malaria, thereby ignoring true causes of febrile illness and over-prescribing ACT. The discrepancy between the perceived and actual level of transmission intensity may be present in many areas in sub-Saharan Africa and calls for greater efforts in defining levels of transmission on a local scale to help rational drug-prescribing behaviour.
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