Malaria Journal - Latest articles

Atelier paludisme: an international malaria training course held in Madagascar

2008-05-09

The Atelier Paludisme (Malaria Workshop) is an international training course organized by the Institut Pasteur de Madagascar, which has been held annually for the past five years. The course was designed for both young and experienced researchers, as well as for healthcare professionals, mostly from malaria-endemic countries. Its objective is to provide participants with a broad knowledge of all features of malaria, to improve their skills in project management, to break geographical isolation by using the Internet as a source of documentary information. This six-week course makes use of concepts of andragogy and problem-based learning, i.e. a relationship between participants and tutors, which promotes a process of exchange rather than the simple transmission of knowledge, where participants have to search actively for information. This approach to training, combined with the wide background and experience of those involved, creates positive dynamics and enables participants to acquire new skills, develop their critical and analytical abilities. This paper describes the course and the lessons learned from its evaluation.

Timing of intermittent preventive treatment for malaria during pregnancy and the implications of current policy on early uptake in north-east Tanzania

Katherine Anders, Tanya Marchant, Pili Chambo, Pasiens Mapunda and Hugh Reyburn — 2008-05-09

Background: Intermittent preventive treatment (IPTp) is efficacious in reducing the adverse outcomes associated with pregnancy-associated malaria, however uptake of the recommended two doses is low in Tanzania, and little is known of the timepoint during pregnancy at which it is delivered. This study investigated the timing of delivery of IPTp to pregnant women attending antenatal clinics (ANC), and the potential determinants of timely uptake. Methods: Structured interviews were conducted with staff and pregnant women at antenatal clinics in northeast Tanzania, and antenatal consultations were observed. Facility-based and individual factors were analysed for any correlation with timing of IPTp uptake. Results: Almost half the women interviewed first attended ANC during or before the fourth month of gestation, however 86% of these early attendees did not receive IPTp on their first visit. The timing of IPTp delivery complied closely with the national guidelines which stipulate giving the first dose at 20-24 weeks gestation. Uptake of at least one dose of IPTp among women who had reached this gestation age was 67%, although this varied considerably between clinics. At one facility, IPTp was not delivered because SP was out of stock. Conclusions: Early uptake of IPTp was found to be hampered by factors external to health worker performance or women's individual preferences. These include insufficient drug stocks and an apparent lack of information to health workers on the reasoning for continued use of SP for IPTp when it has been replaced as a first-line treatment. In addition, an unexpectedly high proportion of women attend antenatal clinics before 20 weeks of pregnancy. While current policy denies the use of IPTp at this time, there is emerging, but incomplete, evidence that malaria in early pregnancy may contribute considerably to the burden of pregnancy-related malaria. Current policy may thus result in a missed opportunity for maximizing the benefit of this intervention, and efforts to encourage earlier attendance at ANC alone are unlikely to improve uptake of IPTp. More evidence is needed to weigh the benefits of early IPTp use against theoretical risks of antifolate drugs in early pregnancy.

Heterogeneous distribution of Plasmodium falciparum drug resistance haplotypes in subsets of the host population

2008-05-06

Background: The emergence of drug resistance is a major problem in malaria control. For mathematical modelling of the transmission and spread of drug resistance the determinant parameters need to be identified and measured. The underlying hypothesis is that mutations associated with drug resistance incur fitness costs to the parasite in absence of drug pressure. The distribution of drug resistance haplotypes in different subsets of the host population was investigated. In particular newly acquired haplotypes after radical cure were characterized and compared to haplotypes from persistent infections. Methods: Mutations associated with antimalarial drug resistance were analysed in parasites from children, adults, and new infections occurring after treatment. Twenty-five known single nucleotide polymorphisms from four Plasmodium falciparum genes associated with drug resistance were genotyped by DNA chip technology. Results: Haplotypes were found to differ between subsets of the host population. A seven-fold mutated haplotype was significantly reduced in adults compared to children and new infections, whereas parasites harbouring fewer mutations were more frequent in adults. Conclusion: The reduced frequency of highly mutated parasites in chronic infections in adults is likely a result of fitness costs of drug resistance that increases with number of mutations and is responsible for reduced survival of mutant parasites.

Temporal correlation between malaria and rainfall in Sri Lanka

2008-05-06

Background: Rainfall data have potential use for malaria prediction. However, the relationship between rainfall and the number of malaria cases is indirect and complex. Methods: The statistical relationships between monthly malaria case count data series and monthly mean rainfall series (extracted from interpolated station data) over the period 1972 - 2005 in districts in Sri Lanka was explored in four analyses: cross-correlation; cross-correlation with pre-whitening; inter-annual; and seasonal inter-annual regression. Results: For most districts, strong positive correlations were found for malaria time series lagging zero to three months behind rainfall, and negative correlations were found for malaria time series lagging four to nine months behind rainfall. However, analysis with pre-whitening showed that most of these correlations were spurious. Only for a few districts, weak positive (at lags zero and one) or weak negative (at lags two to six) correlations were found in pre-whitened series. Inter-annual analysis showed strong negative correlations between malaria and rainfall for a group of districts in the centre-west of the country. Seasonal inter-annual analysis showed that the effect of rainfall on malaria varied according to the season and geography. Conclusions: Seasonally varying effects of rainfall on malaria case counts may explain weak overall cross-correlations found in pre-whitened series, and should be taken into account in malaria predictive models making use of rainfall as a covariate.

Models for short term malaria prediction in Sri Lanka

2008-05-06

Background: Malaria in Sri Lanka is unstable and fluctuates in intensity both spatially and temporally. Although the case counts are dwindling at present, given the past history of resurgence of outbreaks despite effective control measures, the control programmes have to stay prepared. The availability of long time series of monitored/diagnosed malaria cases allows for the study of forecasting models, with an aim to developing a forecasting system which could assist in the efficient allocation of resources for malaria control. Methods: Exponentially weighted moving average models, autoregressive integrated moving average (ARIMA) models with seasonal components, and seasonal multiplicative autoregressive integrated moving average (SARIMA) models were compared on monthly time series of district malaria cases for their ability to predict the number of malaria cases one to four months ahead. The addition of covariates such as the number of malaria cases in neighbouring districts or rainfall were assessed for their ability to improve prediction of selected (seasonal) ARIMA models. Results: The best model for forecasting and the forecasting error varied strongly among districts. The addition of rainfall as a covariate improved prediction of selected (seasonal) ARIMA models modestly, in some districts but worsened prediction in other districts. Improvement by adding rainfall was more frequent at larger forecasting horizons. Conclusions: Heterogeneity of patterns of malaria in Sri Lanka requires regionally specific prediction models. Prediction error was large at a minimum of 22% (for one of the districts) for one month ahead predictions. The modest improvement made in short term prediction by adding rainfall as a covariate to these prediction models may not be sufficient to merit investing in a forecasting system for which rainfall data are routinely processed.

Impact of community-based presumptive chloroquine treatment of fever cases on malaria morbidity and mortality in a tribal area in Orissa State, India

Lalit K Das, Purushothaman Jambulingam and Candasamy Sadanandane — 2008-05-05

Background: In the Global Strategy for Malaria Control, one of the basic elements is early detection and prompt treatment of malaria cases, especially in areas where health care facilities are inadequate. Establishing or reviving the existing drug distribution centers (DDC) at the peripheral levels of health care can achieve this. The DDCs should be operationally feasible, acceptable by community and technical efficient, particularly in remote hard-core malaria endemic areas. Methods: Volunteers from villages were selected for distribution of chloroquine and the selection was made either by villagers or head of the village. The services of the volunteers were absolutely free and voluntary in nature. Chloroquine was provided free of charge to all fever cases. The impact was evaluated based on the changes observed in fever days, fever incidence, parasite incidence and parasite prevalence (proportion of persons harbouring malaria parasite) in the community. Comparisons were made between 1st, 2nd and 3rd year of operation in the experimental villages and between the experimental and check areas. Results: A total of 411 village volunteers in 378 villages in the experimental community health center with a population of 125,439 treated 88,575 fever cases with a mean annual incidence of 331.8 cases per 1,000 population during the three-year study period. The average morbid days due to fever (AFD) was reduced to 1.6 +0.1 from 5.9+2.1 in the experimental villages while it remained at 5.0 + 1.0 in the check villages. There was a significant reduction, (p<0.05) in Annual Fever Incidence (AFI) in the experimental hilltop and foothill villages in comparison to check villages. The change in Annual Parasite Incidence (API) was, however, not statistically significant (p>0.05). In plain villages that were low endemic, the reductions in AFI and API in experimental villages were statistically significant (p<0.05). There was significant reduction in the parasite prevalence in high endemic villages of the experimental area both during 2nd and 3rd year when compared with the check area (p<0.05) but no such reduction was observed in low endemic areas (p>0.0.5). Mortality due to malaria declined by 75% in the experimental villages in the adult age group whereas there was an increasing trend in check villages. Conclusion: The study demonstrated that a passive chloroquine distribution system operated by village volunteers in tribal areas is feasible and effective in reducing malaria-related morbidity and mortality.

Distribution of knock-down resistance mutations in Anopheles gambiae molecular forms in west and west-central Africa

2008-04-29

Background: Knock-down resistance (kdr) to DDT and pyrethroids in the major Afrotropical vector species, Anopheles gambiae sensu stricto, is associated with two alternative point mutations at amino acid position 1014 of the voltage-gated sodium channel gene, resulting in either a leucine-phenylalanine (L1014F), or a leucine-serine (L1014S) substitution. In An. gambiae S-form populations, the former mutation appears to be widespread in west Africa and has been recently reported from Uganda, while the latter, originally recorded in Kenya, has been recently found in Gabon, Cameroon and Equatorial Guinea. In M-form populations surveyed to date, only the L1014F mutation has been found, although less widespread and at lower frequencies than in sympatric S-form populations. Methods: Anopheles gambiae M- and S-form specimens from 19 sites from 11 west and west-central African countries were identified to molecular form and genotyped at the kdr locus either by Hot Oligonucleotide Ligation Assay (HOLA) or allele-specific PCR (AS-PCR). Results: The kdr genotype was determined for about 1,000 An. gambiae specimens. The L1014F allele was found at frequencies ranging from 6% to 100% in all S-form samples (N=628), with the exception of two samples from Angola, where it was absent, and coexisted with the L1014S allele in samples from Cameroon, Gabon and north-western Angola. The L1014F allele was present in M-form samples (N=354) from Benin, Nigeria, and Cameroon, where both M- and S-forms were sympatric. Conclusions: The results represent the most comprehensive effort to analyse the overall distribution of the L1014F and L1014S mutations in An. gambiae molecular forms, and will serve as baseline data for monitoring of this resistance mechanism. The overall picture shows that the emergence and spread of kdr alleles in An. gambiae is a dynamic process and that there is marked intra- and inter-form heterogeneity in resistance allele frequencies. Further studies are needed to determine: i) the importance of selection pressure exerted by both agricultural and public health use of pyrethroid insecticides, ii) the phenotypic effects of the two mutations, particularly when they co-occur; and iii) the epidemiological importance of kdr for both pyrethroid- and DDT-based malaria control operations, particularly if/when the two insecticides are to be used in concert.

Cost-effectiveness analysis of insecticide-treated net distribution as part of the Togo Integrated Child Health Campaign

2008-04-29

Background: To evaluate the cost-effectiveness of the first nationwide delivery of long-lasting insecticide-treated nets (LLITNs) as part of the 2004 measles vaccination campaign in Togo to all children between nine months and five years. Methods: An incremental approach was used to calculate the economic costs and effects from a provider perspective. Effectiveness was estimated in terms of malaria cases averted, deaths averted and Disability-Adjusted Life Years (DALYs) averted. Malaria cases were modelled using regional estimates. Programme and treatment costs were derived through reviews of financial records and interviews with key stakeholders. Uncertain variables were subjected to a univariate sensitivity analysis. Results: Assuming equal attribution of shared costs between the LLITN distribution and the measles vaccination, the net costs per LLITN distributed were 4.41 USD when saved treatment costs were taken into account. Assuming a constant utilization of LLITNs by the target group over three years, 1.2 million cases could be prevented at a net cost per case averted of 3.26 USD. The net costs were 635 USD per death averted and 16.39 USD per DALY averted, respectively. Conclusions: The costs per case, death and DALY averted are well within commonly agreed benchmarks set by other malaria prevention studies. Varying transmission levels are shown to have a significant impact on cost-effectiveness ratios. Results also suggests that substantial efficiency gains may be derived from the joint delivery of vaccination campaigns and malaria interventions.

Multiple origins of resistance-conferring mutations in Plasmodium vivax dihydrofolate reductase

2008-04-28

Background: In order to maximize the useful therapeutic life of antimalarial drugs, it is crucial to understand the mechanisms by which parasites resistant to antimalarial drugs are selected and spread in natural populations. Recent work has demonstrated that pyrimethamine-resistance conferring mutations in Plasmodium falciparum dihydrofolate reductase (dhfr) have arisen rarely de novo, but spread widely in Asia and Africa. The origin and spread of mutations in Plasmodium vivax dhfr were assessed by constructing haplotypes based on sequencing dhfr and its flanking regions. Methods: The P. vivax dhfr coding region, 792 bp upstream and 683 bp downstream were amplified and sequenced from 137 contemporary patient isolates from Colombia, India, Indonesia, Papua New Guinea, Sri Lanka, Thailand, and Vanuatu. A repeat motif located 2.6kb upstream of dhfr was also sequenced from 75 of 137 patient isolates, and mutational relationships among the haplotypes were visualized using the programme Network. Results: Synonymous and non-synonymous single nucleotide polymorphisms (SNPs) within the dhfr coding region were identified, as was the well-documented in-frame insertion/deletion (indel). SNPs were also identified upstream and downstream of dhfr, with an indel and a highly polymorphic repeat region identified upstream of dhfr. The regions flanking dhfr were highly variable. The double mutant (58R/117N) dhfr allele has evolved from several origins, because the 58R is encoded by at least 3 different codons. The triple (58R/61M/117T) and quadruple (57L/61M/117T/173F, 57I/58R/61M/117T and 57L/58R/61M/117T) mutant alleles had at least three independent origins in Thailand, Indonesia, and Papua New Guinea/Vanuatu. Conclusions: It was found that the P. vivax dhfr coding region and its flanking intergenic regions are highly polymorphic and that mutations in P. vivax dhfr that confer antifolate resistance have arisen several times in the Asian region. This contrasts sharply with the selective sweep of rare antifolate resistant alleles observed in the P. falciparum populations in Asia and Africa. The finding of multiple origins of resistance-conferring mutations has important implications for drug policy.

Determination of nitric oxide metabolites, nitrate and nitrite, in Anopheles culicifacies mosquito midgut and haemolymph by anion exchange high-performance liquid chromatography: plausible mechanism of refractoriness

Arun Sharma, Kamaraju Raghavendra, Tridibesh Adak and Aditya P Dash — 2008-04-28

Background: The diverse physiological and pathological role of nitric oxide in innate immune defenses against many intra and extracellular pathogens, have led to the development of various methods for determining nitric oxide (NO) synthesis. NO metabolites, nitrite (NO2-) and nitrate (NO3-) are produced by the action of an inducible Anopheles culicifacies NO synthase (AcNOS) in mosquito mid-guts and may be central to anti-parasitic arsenal of these mosquitoes. MethodWhile exploring a plausible mechanism of refractoriness based on nitric oxide synthase physiology among the sibling species of An. culicifacies, a sensitive, specific and cost effective high performance liquid chromatography (HPLC) method was developed, which is not influenced by the presence of biogenic amines, for the determination of NO2- and NO3- from mosquito mid-guts and haemolymph. Results: This method is based on extraction, efficiency, assay reproducibility and contaminant minimization. It entails de-proteinization by centrifugal ultra filtration through ultracel 3K filter and analysis by high performance anion exchange liquid chromatography (Sphereclone, 5u SAX column) with UV detection at 214 nm. The lower detection limit of the assay procedure is 50 pmoles in all midgut and haemolymph samples. Retention times for NO2- and NO3- in standards and in mid-gut samples were 3.42 and 4.53 min. respectively. Assay linearity for standards ranged between 50 nM and 1 mM. Recoveries of NO2- and NO3- from spiked samples (1-100 uM) and from the extracted standards (1-100 uM) were calculated to be 100%. Intra-assay and inter assay variations and relative standard deviations (RSDs) for NO2- and NO3- in spiked and un-spiked midgut samples were 5.7% or less. Increased levels NO2- and NO3- in midguts and haemolymph of An. culicifacies sibling species B in comparison to species A reflect towards a mechanism of refractoriness based on AcNOS physiology. Conclusion: HPLC is a sensitive and accurate technique for identification and quantifying pmole levels of NO metabolites in mosquito midguts and haemolymph samples that can be useful for clinical investigations of NO biochemistry, physiology and pharmacology in various biological samples.

Evaluation of FRET real-time PCR assay for rapid detection and differentiation of Plasmodium species in returning travellers and migrants

2008-04-28

Background: A simple real-time PCR assay using one set of primer and probe for rapid, sensitive and quantitative detection of Plasmodium species, with simultaneous differentiation of Plasmodium falciparum from the three other Plasmodium species (Plasmodium vivax, Plasmodium ovale and Plasmodium malariae) in febrile returning travellers and migrants was developed and evaluated. Methods: Consensus primers were used to amplify a species-specific region of the multicopy 18S rRNA gene, and fluorescence resonance energy transfer hybridization probes were used for detection in a LightCycler platform (Roche). The anchor probe sequence was designed to be perfect matches to the 18S rRNA gene of the fourth Plasmodium species, while the acceptor probe sequence was designed for P. falciparum over a region containing one mismatched, which allowed differentiation of the three other Plasmodium species. The performance characteristics of the real-time PCR assay were compared with those of conventional PCR and microscopy-based diagnosis from 119 individuals with a suspected clinical diagnostic of imported malaria. Results: Blood samples with parasite densities less than 0.01% were all detected, and analytical sensitivity was 0.5 parasite per PCR reaction. The melt curve means Tms (standard deviation) in clinical isolates were 60.5degreesC (0.6degreesC) for P. falciparum infection and 64.6degreesC (1.8degreesC) for non-P. falciparum species. These Tms values of the P. falciparum or non-P. falciparum species did not vary with the geographic origin of the parasite. The real-time PCR results correlated with conventional PCR using both genus-specific (Kappa coefficient: 0.95, 95% confidence interval: 0.9 - 1) or P. falciparum-specific (0.91, 0.8 - 1) primers, or with the microscopy results (0.70, 0.6 - 0.8). The real-time assay was 100% sensitive and specific for differentiation of P. falciparum to non-P. falciparum species, compared with conventional PCR or microscopy. The real-time PCR assay can also detect individuals with mixed infections (P. falciparum and non-P. falciparum sp.) in the same sample. Conclusion: This real-time PCR assay with melting curve analysis is rapid, and specific for the detection and differentiation of P. falciparum to other Plasmodium species. The suitability for routine use of this assay in clinical diagnostic laboratories is discussed.

Evaluation of an operational malaria outbreak identification and response system in Mpumalanga Province, South Africa

2008-04-27

Background and objective To evaluate the performance of a novel malaria outbreak identification system in the epidemic prone rural area of Mpumalanga Province, South Africa, for timely identification of malaria outbreaks and guiding integrated public health responses. Methods: Using five years of historical notification data, two binomial thresholds were determined for each primary health care facility in the highest malaria risk area of Mpumalanga province. Whenever the thresholds were exceeded at health facility level (tier 1), primary health care staff notified the malaria control programme, which then confirmed adequate stocks of malaria treatment to manage potential increased cases. The cases were followed up at household level to verify the likely source of infection. The binomial thresholds were reviewed at village/town level (tier 2) to determine whether additional response measures were required. In addition, an automated electronic outbreak identification system at town/village level (tier 2) was integrated into the case notification database (tier 3) to ensure that unexpected increases in case notification were not missed. The performance of these binomial outbreak thresholds was evaluated against other currently recommended thresholds using retrospective data. The acceptability of the system at primary health care level was evaluated through structured interviews with health facility staff. Results: Eighty four percent of health facilities reported outbreaks within 24 hours (n=95), 92% (n=104) within 48 hours and 100% (n=113) within 72 hours. Appropriate response to all malaria outbreaks (n=113, tier 1, n=46, tier 2) were achieved within 24 hours. The system was positively viewed by all health facility staff. When compared to other epidemiological systems for a specified 12 month outbreak season (June 2003 to July 2004) the binomial exact thresholds produced one false weekly outbreak, the C-sum 12 weekly outbreaks and the mean + 2 SD nine false weekly outbreaks. Exceeding the binomial level 1 threshold triggered an alert four weeks prior to an outbreak, but exceeding the binomial level 2 threshold identified an outbreak as it occurred. Conclusion: The malaria outbreak surveillance system using binomial thresholds achieved its primary goal of identifying outbreaks early facilitating appropriate local public health responses aimed at averting a possible large-scale epidemic in a low, and unstable, malaria transmission setting.