Predictors of chloroquine treatment failure in children and adults with falciparum malaria in Kampala, Uganda

The extent of chloroquine underdosing in adult patients with malaria by Plasmodium vivax from an endemic area of the Brazilian Amazon basin

OBJECTIVES

To evaluate the extent of chloroquine underdosing and to measure the concentrations of chloroquine and desethylchloroquine in adult patients with P. vivax malaria in the Brazilian Amazon basin.

METHODS

Prospective study of cases in male adult patients with malaria by Plasmodium vivax treated with a total dose of 1500 mg chloroquine over three days and a short course of primaquine. Patients were weighed at admission, and the dose per mg/kg was determined. Blood samples were collected at 24 and 168 h after enrolment, and the concentrations of chloroquine and desethylchloroquine were measured in plasma by high-performance liquid chromatography with fluorescence detection.

RESULTS

Of 61 patients were included in the study, and 60% received a total dose of chloroquine below 25 mg/kg. Plasma chloroquine concentrations ranged from 90 to 184 ng/ml and from 175 to 827 ng/ml at 24 and 168 hours. For desethylchloroquine, the values ranged from 32 to 144 ng/ml and from 90 to 440 ng/ml at 24 and 168 h. There were no significant correlations between the plasma levels of chloroquine and the doses administered (mg/kg) at 24 and 196 h. Similar results were found for desethylchloroquine.

CONCLUSION

There is widespread suboptimal dosing of chloroquine that is probably due to the dosing regimen based on patient age, which reduces the drug exposure with a possible influence on parasite clearance.

Signatures of divergent anti-malarial treatment responses in peripheral blood from adults and young children in Malawi

BACKGROUND

Heterogeneity in the immune response to parasite infection is mediated in part by differences in host genetics, gender, and age group. In infants and young children, ongoing immunological maturation often results in increased susceptibility to infection and variable responses to drug treatment, increasing the risk of complications. Even though significant age-associated effects on host cytokine responses to Plasmodium falciparum infection have been identified, age-associated effects on uncomplicated malaria infection and anti-malarial treatment remain poorly understood.

METHODS

In samples of whole blood from a cohort of naturally infected malaria-positive individuals with non-severe falciparum malaria in Malawi (n = 63 total; 34 infants and young children < 2 years old, 29 adults > 18 years old), blood cytokine levels and monocyte and dendritic cell frequencies were assessed at two timepoints: acute infection, and 4 weeks post anti-malarial treatment. The effects of age group, gender, and timepoint were modeled, and the role of these factors on infection and treatment outcomes was evaluated.

RESULTS

Regardless of treatment timepoint, in this population age was significantly associated with overall blood haemoglobin, which was higher in adults, and plasma nitric oxide metabolites, IL-10, and TNF levels, which were higher in young children. There was a significant effect of age on the haemoglobin treatment response, whereby after treatment, levels increased in young children and decreased in adults. Furthermore, there were significant age-associated effects on treatment response for overall parasite load, IFN-γ, and IL-12(p40), and these effects were gender-dependent. Significant age effects on the overall levels and treatment response of myeloid dendritic cell frequencies were observed. In addition, within each age group, results showed continuous age effects on gametocyte levels (Pfs16), TNF, and nitric oxide metabolites.

CONCLUSIONS

In a clinical study of young children and adults experiencing natural falciparum malaria infection and receiving anti-malarial treatment, age-associated signatures of infection and treatment responses in peripheral blood were identified. This study describes host markers that may indicate, and potentially contribute to, differential post-treatment outcomes for malaria in young children versus adults.

Changing Antimalarial Drug Sensitivities in Uganda

Dihydroartemisinin-piperaquine (DP) has demonstrated excellent efficacy for the treatment and prevention of malaria in Uganda. However, resistance to both components of this regimen has emerged in Southeast Asia. The efficacy of artemether-lumefantrine, the first-line regimen to treat malaria in Uganda, has also been excellent, but continued pressure may select for parasites with decreased sensitivity to lumefantrine. To gain insight into current drug sensitivity patterns, ex vivo sensitivities were assessed and genotypes previously associated with altered drug sensitivity were characterized for 58 isolates collected in Tororo, Uganda, from subjects presenting in 2016 with malaria from the community or as part of a clinical trial comparing DP chemoprevention regimens. Compared to community isolates, those from trial subjects had lower sensitivities to the aminoquinolines chloroquine, monodesethyl amodiaquine, and piperaquine and greater sensitivities to lumefantrine and mefloquine, an observation consistent with DP selection pressure. Compared to results for isolates from 2010 to 2013, the sensitivities of 2016 community isolates to chloroquine, amodiaquine, and piperaquine improved (geometric mean 50% inhibitory concentrations [IC₅₀] = 248, 76.9, and 19.1 nM in 2010 to 2013 and 33.4, 14.9, and 7.5 nM in 2016, respectively [P < 0.001 for all comparisons]), the sensitivity to lumefantrine decreased (IC₅₀ = 3.0 nM in 2010 to 2013 and 5.4 nM in 2016 [P < 0.001]), and the sensitivity to dihydroartemisinin was unchanged (IC₅₀ = 1.4 nM). These changes were accompanied by decreased prevalence of transporter mutations associated with aminoquinoline resistance and low prevalence of polymorphisms recently associated with resistance to artemisinins or piperaquine. Antimalarial drug sensitivities are changing in Uganda, but novel genotypes associated with DP treatment failure in Asia are not prevalent.

Malaria in Uganda: challenges to control on the long road to elimination: I. Epidemiology and current control efforts

Malaria remains one of the leading health problems of the developing world, and Uganda bears a particularly large burden from the disease. Our understanding is limited by a lack of reliable data, but it is clear that the prevalence of malaria infection, incidence of disease, and mortality from severe malaria all remain very high. Uganda has made progress in implementing key malaria control measures, in particular distribution of insecticide-impregnated bednets, indoor residual spraying of insecticides, utilization of artemisinin-based combination therapy to treat uncomplicated malaria, and provision of intermittent preventive therapy for pregnant women. However, despite enthusiasm regarding the potential for the elimination of malaria in other areas, there is no convincing evidence that the burden of malaria has decreased in Uganda in recent years. Major challenges to malaria control in Uganda include very high malaria transmission intensity, inadequate health care resources, a weak health system, inadequate understanding of malaria epidemiology and the impact of control interventions, increasing resistance of parasites to drugs and of mosquitoes to insecticides, inappropriate case management, inadequate utilization of drugs to prevent malaria, and inadequate epidemic preparedness and response. Despite these challenges, prospects for the control of malaria have improved, and with attention to underlying challenges, progress toward the control of malaria in Uganda can be expected.

Host candidate gene polymorphisms and clearance of drug-resistant Plasmodium falciparum parasites

Background

Resistance to anti-malarial drugs is a widespread problem for control programmes for this devastating disease. Molecular tests are available for many anti-malarial drugs and are useful tools for the surveillance of drug resistance. However, the correlation of treatment outcome and molecular tests with particular parasite markers is not perfect, due in part to individuals who are able to clear genotypically drug-resistant parasites. This study aimed to identify molecular markers in the human genome that correlate with the clearance of malaria parasites after drug treatment, despite the drug resistance profile of the protozoan as predicted by molecular approaches.

Methods

3721 samples from five African countries, which were known to contain genotypically drug resistant parasites, were analysed. These parasites were collected from patients who subsequently failed to clear their infection following drug treatment, as expected, but also from patients who successfully cleared their infections with drug-resistant parasites. 67 human polymorphisms (SNPs) on 17 chromosomes were analysed using Sequenom's mass spectrometry iPLEX gold platform, to identify regions of the human genome, which contribute to enhanced clearance of drug resistant parasites.

Results

An analysis of all data from the five countries revealed significant associations between the phenotype of ability to clear drug-resistant Plasmodium falciparum infection and human immune response loci common to all populations. Overall, three SNPs showed a significant association with clearance of drug-resistant parasites with odds ratios of 0.76 for SNP rs2706384 (95% CI 0.71-0.92, P = 0.005), 0.66 for SNP rs1805015 (95% CI 0.45-0.97, P = 0.03), and 0.67 for SNP rs1128127 (95% CI 0.45-0.99, P = 0.05), after adjustment for possible confounding factors. The first two SNPs (rs2706384 and rs1805015) are within loci involved in pro-inflammatory (interferon-gamma) and anti-inflammatory (IL-4) cytokine responses. The third locus encodes a protein involved in the degradation of misfolded proteins within the endoplasmic reticulum, and its role, if any, in the clearance phenotype is unclear.

Conclusions

The study showed significant association of three loci in the human genome with the ability of parasite to clear drug-resistant P. falciparum in samples taken from five countries distributed across sub-Saharan Africa. Both SNP rs2706384 and SNP1805015 have previously been reported to be associated with risk of malaria infection in African populations. The loci are involved in the Th1/Th2 balance, and the association of SNPs within these genes suggests a key role for antibody in the clearance of drug-resistant parasites. It is possible that patients able to clear drug-resistant infections have an enhanced ability to control parasite growth.

Molecular markers of anti-malarial drug resistance in Lahj Governorate, Yemen: baseline data and implications

Background

This is an investigation of anti-malarial molecular markers coupled with a therapeutic efficacy test of chloroquine (CQ) against falciparum malaria in an area of unstable malaria in Lahj Governorate, Yemen. The study was aimed at assessment of therapeutic response to CQ and elucidation of baseline information on molecular markers for Plasmodium falciparum resistance against CQ and sulphadoxine/pyrimethamine (SP).

Methods

Between 2002 and 2003 the field test was conducted according to the standard WHO protocol to evaluate the therapeutic efficacy of CQ in 124 patients with falciparum malaria in an endemic area in Lahj Governorate in Yemen. Blood samples collected during this study were analysed for P. falciparum chloroquine resistance transporter gene (pfcrt)-76 polymorphisms, mutation pfcrt-S163R and the antifolate resistance-associated mutations dihydrofolate reductase (dhfr)-C59R and dihydropteroate synthase (dhps)-K540E. Direct DNA sequencing of the pfcrt gene from three representative field samples was carried out after DNA amplification of the 13 exons of the pfcrt gene.

Results

Treatment failure was detected in 61% of the 122 cases that completed the 14-day follow-up. The prevalence of mutant pfcrt T76 was 98% in 112 amplified pre-treatment samples. The presence of pfcrt T76 was poorly predictive of in vivo CQ resistance (PPV = 61.8%, 95% CI = 52.7-70.9). The prevalence of dhfr Arg-59 mutation in 99 amplified samples was 5%, while the dhps Glu-540 was not detected in any of 119 amplified samples. Sequencing the pfcrt gene confirmed that Yemeni CQ resistant P. falciparum carry the old world (Asian and African) CQ resistant haplotype CVIETSESI at positions 72,73,74,75,76,220,271, 326 and 371.

Conclusion

This is the first study to report baseline information on the characteristics and implications of anti-malarial drug resistance markers in Yemen. It is also the first report of the haplotype associated with CQR P. falciparum parasites from Yemen. Mutant pfcrtT76 is highly prevalent but it is a poor predictor of treatment failure in the study population. The prevalence of mutation dhfrArg59 is suggestive of emerging resistance to SP, which is currently a component of the recommended combination treatment of falciparum malaria in Yemen. More studies on these markers are recommended for surveillance of resistance in the study area.

Patterns of chloroquine use and resistance in sub-Saharan Africa: a systematic review of household survey and molecular data

BACKGROUND

As a result of widespread chloroquine and sulphadoxine-pyrimethamine (SP) resistance, 90% of sub-Saharan African countries had adopted policies of artemisinin-based combination therapy (ACT) for treatment of uncomplicated malaria by 2007. In Malawi, cessation of chloroquine use was followed by the re-emergence of chloroquine-susceptible malaria. It was expected that introduction of ACT would lead to a return in chloroquine susceptibility throughout Africa, but this has not yet widely occurred. This observation suggests that there is continuing use of ineffective anti-malarials in Africa and that persistent chloroquine-resistant malaria is due to ongoing drug pressure despite national policy changes.

METHODS

To estimate drug use on a national level, 2006-2007 Demographic Health Survey and Multiple Indicator Cluster Survey data from 21 African countries were analysed. Resistance data were compiled by systematic review of the published literature on the prevalence of the Plasmodium falciparum chloroquine resistance transporter polymorphism at codon 76, which causes chloroquine resistance.

RESULTS

Chloroquine was the most common anti-malarial used according to surveys from 14 of 21 countries analysed, predominantly in West Africa. SP was most commonly reported in two of 21 countries. Among eight countries with longitudinal molecular resistance data, the four countries where the highest proportion of children treated for fever received chloroquine (Uganda, Burkina Faso, Guinea Bissau, and Mali) also showed no significant declines in the prevalence of chloroquine-resistant infections. The three countries with low or decreasing chloroquine use among children who reported fever treatment (Malawi, Kenya, and Tanzania) had statistically significant declines in the prevalence of chloroquine resistance.

CONCLUSIONS

This study demonstrates that in 2006-2007, chloroquine and SP continued to be used at high rates in many African countries. In countries reporting sustained chloroquine use, chloroquine-resistant malaria persists. In contrast, a low level of estimated chloroquine use is associated with a declining prevalence of chloroquine resistance.

Epidemiology and infectivity of Plasmodium falciparum and Plasmodium vivax gametocytes in relation to malaria control and elimination

Malaria remains a major cause of morbidity and mortality in the tropics, with Plasmodium falciparum responsible for the majority of the disease burden and P. vivax being the geographically most widely distributed cause of malaria. Gametocytes are the sexual-stage parasites that infect Anopheles mosquitoes and mediate the onward transmission of the disease. Gametocytes are poorly studied despite this crucial role, but with a recent resurgence of interest in malaria elimination, the study of gametocytes is in vogue. This review highlights the current state of knowledge with regard to the development and longevity of P. falciparum and P. vivax gametocytes in the human host and the factors influencing their distribution within endemic populations. The evidence for immune responses, antimalarial drugs, and drug resistance influencing infectiousness to mosquitoes is reviewed. We discuss how the application of molecular techniques has led to the identification of submicroscopic gametocyte carriage and to a reassessment of the human infectious reservoir. These components are drawn together to show how control measures that aim to reduce malaria transmission, such as mass drug administration and a transmission-blocking vaccine, might better be deployed.

Resistance-mediating polymorphisms of Plasmodium falciparum among isolates from children with severe malaria in kumasi, ghana

BACKGROUND

Antimalarial drug resistance has been a major contributor to the failure of the battle against malaria in many developing countries. The P. falciparum genes, pfcrt and pfmdr-1, have been implicated in chloroquine resistance. The objective of this study was to determine the presence of mutant alleles of these chloroquine resistance genes among isolates of P. falciparum from children presenting with severe malaria in Ghana.

METHODS

Venous blood samples were taken from patients, and plasma chloroquine levels measured. P. falciparum chromosomal DNA was isolated from the blood samples, and subjected to PCR, restriction digestion and sequencing. Resulting data were analysed using the STATA statistical software.

RESULTS

Of 140 children recruited into the study, 109 (77.9%) had detectable pre-treatment chloroquine levels. PCR and restriction digestion analysis of the pfcrt gene indicated that 124 (88.6%) had the mutant T76 gene, and that this correlated with higher chloroquine levels. Sequence analysis of these showed consistent genetic sequences for chloroquine resistant and sensitive parasites with respect to Pfcrt codons 72 through 76.The Pfcrt T76 mutation was found in 88.4% of isolates having the Pfmdr-1Y86 mutation. The Pfmdr-1 Y86 mutation was found in 67.6% of isolates having the Pfcrt T76 mutation.

CONCLUSION

The study affirms Pfcrt as a better chloroquine resistance marker. Both mutations are independently selected by chloroquine levels and that one mutation (Y86) might modify/increase the effect of the other (T76). This study also depicts the much-overlooked antimalarial drug resistance situation in the area and emphasizes the need for a proper treatment strategy.

Host immunity as a determinant of treatment outcome in Plasmodium falciparum malaria

Host immunity is an important but poorly understood determinant of antimalarial efficacy, influencing the outcome of prevention and treatment trials. Variations in host immunity might explain why factors such as host genetics, age, pregnancy, infection with HIV, parasite density, and malaria transmission intensity, can raise or lower apparent cure rates. Recently, attempts have been made to characterise immunological correlates of treatment outcome in Plasmodium falciparum malaria, but not yet for Plasmodium vivax. A better understanding of such correlates might improve trials of antimalarial drugs and provide leads for vaccine development. Greater understanding of the relation between host immunity and treatment outcome is crucial to making informed choices about the use of safe but partly effective drugs for malaria prevention in children and pregnant women. With increasing malaria control efforts worldwide, declining population immunity might alter drug response profiles. Improved methods for assessing antimalarial immunity will strengthen malaria control efforts.

In vitro sensitivities of Plasmodium falciparum to different antimalarial drugs in Uganda

The control of malaria is challenged by resistance of Plasmodium falciparum to multiple drugs. New combination regimens are now advocated for the treatment of uncomplicated falciparum malaria, but the extent of resistance to newer agents is incompletely understood. We measured the in vitro sensitivity of P. falciparum parasites cultured from children enrolled in a drug efficacy trial in Kampala, Uganda, from 2006 to 2008. Sensitivities were measured by comparing levels of histidine-rich protein-2 in parasites incubated with different concentrations of drugs with those in untreated controls. The cultured parasites exhibited a wide range of sensitivities to chloroquine (CQ); monodesethylamodiaquine (MDAQ), the major active metabolite of amodiaquine; and quinine (QN). Mean 50% inhibitory concentration (IC(50)) results were above standard cutoffs for resistance for CQ and MDAQ. Parasites were generally sensitive to dihydroartemisinin (DHA), lumefantrine (LM), and piperaquine (PQ). For CQ, MDAQ, and QN but not the other drugs, activities against individual strains were highly correlated. We also assessed known resistance-mediating polymorphisms in two putative transporters, pfcrt and pfmdr1. When parasites that were least and most sensitive to each drug were compared, the pfmdr1 86Y mutation was significantly more common in parasites that were most resistant to CQ and MDAQ, and the pfmdr1 D1246Y mutation was significantly more common in parasites that were most resistant to MDAQ and QN. In summary, we demonstrated in parasites from Kampala a range of sensitivities to older drugs; correlation of sensitivities to CQ, MDAQ, and QN; and good activity against nearly all strains for DHA, LM, and PQ.

Efficacy of oral single dose therapy with artemisinin-naphthoquine phosphate in uncomplicated falciparum malaria

All artemisinin-based combination therapies (ACTs), recommended by the World Health Organization, are 3-day regimens. A considerable level of non-compliance on ACTs has been reported from some countries. The study aimed to assess the therapeutic efficacy of single dose treatment with new generation ACT containing artemisinin plus naphthoquine. An oral single dose of eight tablets (400 mg of naphthoquine+1000 mg artemisinin) of the combination drug was administered to adult uncomplicated falciparum malaria patients. Observations of fever, parasite clearance and reappearance, and other clinical manifestations were made on Days 0, 1, 2, 3, 7, 14, 21 and 28. Fifty-three adult falciparum positive cases, with fever or history of fever within the previous 24 h, were included in the final evaluation of the study. Mean fever clearance time, parasite clearance time were 18.2+/-8.6 h and 34.6+/-14.3 h, respectively. Adequate clinical and parasitological response was achieved in 52 cases, the rate being 98.1% (95% CI, 91.1-99.9). One patient was classified as late parasitological failure because of the reappearance of falciparum parasite on Day 14. The drug was well tolerated and no adverse reactions were detected in the patients. Since it is a single dose therapy, health workers can administer the drug as directly observed treatment.

Efficacy of sulphadoxine-pyrimethamine with or without artesunate for the treatment of uncomplicated Plasmodium falciparum malaria in southern Mozambique: a randomized controlled trial

BACKGROUND

An artemisinin-based combination therapy, artesunate (AS) plus sulphadoxine-pyrimethamine (SP), was compared to SP monotherapy to provide evidence of further treatment options in southern Mozambique.

METHODS

Between 2003 and 2005, 411 patients over one year and 10 kg with uncomplicated Plasmodium falciparum malaria were randomly allocated SP (25/1.25 mg per kg day 0) or AS/SP (as above plus 4 mg/kg artesunate days 0, 1 and 2). Allocation was concealed, but treatment was open-label except to microscopists. The primary objective was the relative risk of treatment failure, which was assessed using World Health Organization response definitions modified to a 42-day follow-up.

RESULTS

Of the 411 subjects enrolled, 359 (87.3%) completed the follow up period (SP n = 175, AS/SP n = 184). A survival analysis including 408 subjects showed that the polymerase chain reaction-adjusted cure rates were 90.4% (95% confidence interval [CI] 84.9%-93.9%) and 98.0% (95% CI 94.8%-99.3%) for SP and AS/SP respectively. Multivariable analysis showed that treatment with AS/SP decreased the relative hazard of treatment failure by 80% compared to SP (hazard ratio [HR] 0.2; 95% CI 0.1-0.6) and age over seven years decreased the relative hazard of failure by 70% (HR 0.3; 95% CI 0.1-0.9), when compared to younger age. However, having a quintuple dhfr/dhps mutation increased the relative hazard of failure compared to fewer mutations (HR 3.2; 95% CI 1.3-7.5) and baseline axillary temperature increased the relative hazard of failure by 50% for each degree C increase (HR 1.5; 95% CI 1.1-2.2).

CONCLUSION

While both treatments were efficacious, AS plus SP significantly decreased the relative hazard of treatment failure compared to SP monotherapy Artesunate plus sulphadoxine-pyrimethamine, but not sulphadoxine-pyrimethamine monotherapy, met the current WHO criteria of >95% efficacy for policy implementation.

TRIAL REGISTRATION

NCT00203736 and NCT00203814.

Decreasing efficacy of antimalarial combination therapy in Uganda is explained by decreasing host immunity rather than increasing drug resistance

BACKGROUND

Improved control efforts are reducing the burden of malaria in Africa but may result in decreased antimalarial immunity.

METHODS

A cohort of 129 children aged 1-10 years in Kampala, Uganda, were treated with amodiaquine plus sulfadoxine-pyrimethamine for 396 episodes of uncomplicated malaria over a 29-month period as part of a longitudinal clinical trial.

RESULTS

The risk of treatment failure increased over the course of the study from 5% to 21% (hazard ratio [HR], 2.4 per year [95% confidence interval {CI}, 1.3-4.3]). Parasite genetic polymorphisms were associated with an increased risk of failure, but their prevalence did not change over time. Three markers of antimalarial immunity were associated with a decreased risk of treatment failure: increased age (HR, 0.5 per 5-year increase [95% CI, 0.2-1.2]), living in an area of higher malaria incidence (HR, 0.26 [95% CI, 0.11-0.64]), and recent asymptomatic parasitemia (HR, 0.06 [95% CI, 0.01-0.36]). In multivariate analysis, adjustment for recent asymptomatic parasitemia, but not parasite polymorphisms, removed the association between calendar time and the risk of treatment failure (HR, 1.5 per year [95% CI, 0.7-3.4]), suggesting that worsening treatment efficacy was best explained by decreasing host immunity.

CONCLUSION

Declining immunity in our study population appeared to be the primary factor underlying decreased efficacy of amodiaquine plus sulfadoxine-pyrimethamine. With improved malaria-control efforts, decreasing immunity may unmask resistance to partially efficacious drugs.

Spread of anti-malarial drug resistance: mathematical model with implications for ACT drug policies

BACKGROUND

Most malaria-endemic countries are implementing a change in anti-malarial drug policy to artemisinin-based combination therapy (ACT). The impact of different drug choices and implementation strategies is uncertain. Data from many epidemiological studies in different levels of malaria endemicity and in areas with the highest prevalence of drug resistance like borders of Thailand are certainly valuable. Formulating an appropriate dynamic data-driven model is a powerful predictive tool for exploring the impact of these strategies quantitatively.

METHODS

A comprehensive model was constructed incorporating important epidemiological and biological factors of human, mosquito, parasite and treatment. The iterative process of developing the model, identifying data needed, and parameterization has been taken to strongly link the model to the empirical evidence. The model provides quantitative measures of outcomes, such as malaria prevalence/incidence and treatment failure, and illustrates the spread of resistance in low and high transmission settings. The model was used to evaluate different anti-malarial policy options focusing on ACT deployment.

RESULTS

The model predicts robustly that in low transmission settings drug resistance spreads faster than in high transmission settings, and treatment failure is the main force driving the spread of drug resistance. In low transmission settings, ACT slows the spread of drug resistance to a partner drug, especially at high coverage rates. This effect decreases exponentially with increasing delay in deploying the ACT and decreasing rates of coverage. In the high transmission settings, however, drug resistance is driven by the proportion of the human population with a residual drug level, which gives resistant parasites some survival advantage. The spread of drug resistance could be slowed down by controlling presumptive drug use and avoiding the use of combination therapies containing drugs with mismatched half-lives, together with reducing malaria transmission through vector control measures.

CONCLUSION

This paper has demonstrated the use of a comprehensive mathematical model to describe malaria transmission and the spread of drug resistance. The model is strongly linked to the empirical evidence obtained from extensive data available from various sources. This model can be a useful tool to inform the design of treatment policies, particularly at a time when ACT has been endorsed by WHO as first-line treatment for falciparum malaria worldwide.

Effects of Plasmodium falciparum parasite population size and patient age on early and late parasitological outcomes of antimalarial treatment in children

The design and interpretation of trials assessing the chemotherapeutic effects of antimalarial drugs depend on our understanding of how different selection criteria affect treatment outcomes. In this study, we analyzed the effects of baseline parameters on the initial parasite elimination rate and the risk of subsequent recrudescence as a marker for incompletely eliminated asexual blood-stage parasites in pediatric patients with uncomplicated Plasmodium falciparum infection treated with amodiaquine in a high-transmission area. We found that (i) parasite population size and patient age independently determine early and late parasitological treatment outcome measurements; (ii) the rate of recrudescence is higher in patients 1 to 3 years of age than in patients aged <1 or >3 years; (iii) patients aged >5 years with parasite densities between 2,000 and 10,000/microl have a lower recrudescence rate (13%; 95% confidence interval [CI], 8% to 21%) than patients aged <5 years with parasite densities of >10,000/microl (40%; 95% CI, 30% to 50%); and (iv) the sensitivity of detecting recrudescences outside this high-risk group, i.e., in patients of >5 years of age or with parasite densities of <10,000/microl, is as low as 27% or 22%, respectively. In conclusion, these findings highlight the need to use adequate selection criteria and to report parasitological outcome results adjusted for the readily available determinants of chemotherapeutic failure, i.e., patient age and baseline parasitemia. The thresholds may vary by transmission intensity and drug regimen. A better understanding of the limitations of antimalarial regimens in high-risk subgroups of patients has important implications for setting policy recommendations.

Discordant patterns of genetic variation at two chloroquine resistance loci in worldwide populations of the malaria parasite Plasmodium falciparum

Mutations in the chloroquine resistance (CQR) transporter gene of Plasmodium falciparum (Pfcrt; chromosome 7) play a key role in CQR, while mutations in the multidrug resistance gene (Pfmdr1; chromosome 5) play a significant role in the parasite's resistance to a variety of antimalarials and also modulate CQR. To compare patterns of genetic variation at Pfcrt and Pfmdr1 loci, we investigated 460 blood samples from P. falciparum-infected patients from four Asian, three African, and three South American countries, analyzing microsatellite (MS) loci flanking Pfcrt (five loci [approximately 40 kb]) and Pfmdr1 (either two loci [approximately 5 kb] or four loci [approximately 10 kb]). CQR Pfmdr1 allele-associated MS haplotypes showed considerably higher genetic diversity and higher levels of subdivision than CQR Pfcrt allele-associated MS haplotypes in both Asian and African parasite populations. However, both Pfcrt and Pfmdr1 MS haplotypes showed similar levels of low diversity in South American parasite populations. Median-joining network analyses showed that the Pfcrt MS haplotypes correlated well with geography and CQR Pfcrt alleles, whereas there was no distinct Pfmdr1 MS haplotype that correlated with geography and/or CQR Pfmdr1 alleles. Furthermore, multiple independent origins of CQR Pfmdr1 alleles in Asia and Africa were inferred. These results suggest that variation at Pfcrt and Pfmdr1 loci in both Asian and African parasite populations is generated and/or maintained via substantially different mechanisms. Since Pfmdr1 mutations may be associated with resistance to artemisinin combination therapies that are replacing CQ, particularly in Africa, it is important to determine if, and how, the genetic characteristics of this locus change over time.

Inpatient mortality in children with clinically diagnosed malaria as compared with microscopically confirmed malaria

BACKGROUND

Inpatient treatment for malaria without microscopic confirmation of the diagnosis occurs commonly in sub-Saharan Africa. Differences in mortality in children who are tested by microscopy for Plasmodium falciparum infection as compared with those not tested are not well characterized.

METHODS

A retrospective chart review was conducted of all children up to 15 years of age admitted to Mulago Hospital, Kampala, Uganda from January 2002 to July 2005, with a diagnosis of malaria and analyzed according to microscopy testing for P. falciparum.

RESULTS

A total of 23,342 children were treated for malaria during the study period, 991 (4.2%) of whom died. Severe malarial anemia in 7827 (33.5%) and cerebral malaria in 1912 (8.2%) were the 2 common causes of malaria-related admissions. Children who did not receive microscopy testing had a higher case fatality rate than those with a positive blood smear (7.5% versus 3.2%, P < 0.001). After adjustment for age, malaria complications, and comorbid conditions, children who did not have microscopy performed or had a negative blood smear had a higher risk of death than those with a positive blood smear [odds ratio (OR): 3.49, 95% confidence interval (CI): 2.88-4.22, P < 0.001; and OR: 1.59, 95% CI: 1.29-1.96, P < 0.001, respectively].

CONCLUSIONS

Diagnosis of malaria in the absence of microscopic confirmation is associated with significantly increased mortality in hospitalized Ugandan children. Inpatient diagnosis of malaria should be supported by microscopic or rapid diagnostic test confirmation.

Effect of HIV-1 infection on malaria treatment outcome in Ugandan patients

BACKGROUND

Malaria and HIV-1 infection cause significant morbidity and mortality in sub-Saharan Africa. HIV-1 increases risk for malaria with the risk increasing as immunity declines. The effect of HIV-1 infection on antimalarial treatment outcome is still inconclusive.

OBJECTIVE

To compare antimalarial treatment outcome among HIV-1 positive and negative patients with acute uncomplicated falciparum malaria treated with chloroquine plus sulfadoxine-pyrimethamine (CQ+SP).

METHODS

Ninety eight HIV-1 positive patients aged 18 months or older with acute uncomplicated falciparum malaria were treated with CQ+SP and followed for 28 days to monitor outcome. Treatment outcome of HIV-1 positive patients was compared to that of 193 HIV-1 negative historical controls. The primary study outcome for both groups was treatment failure.

RESULTS

HIV-1 positive patients older than 5 years of age were less likely to have treatment failure compared to HIV-1 negative patients in the same age group (RR 0.59 95% CI 0.4-0.8, p < 0.001) and HIV-1 positive patients on routine cotrimoxazole prophylaxis were less likely to have treatment failure following CQ+SP treatment compared to HIV negative patients (RR 0.6 95% CI 0.43-0.92, p = 0.006). There was no difference in treatment outcome according to HIV-1 status for children younger than 5 years of age.

CONCLUSIONS

Adherence to cotrimoxazole prophylaxis should be reinforced in HIV positive patients and it should be reassessed if these patients present with acute episodes of malaria.

Dynamics of immune response and drug resistance in malaria infection

Background

Malaria parasites that concurrently infect a host compete on the basis of their intrinsic growth rates and by stimulating cross-reactive immune responses that inhibit each others' growth. If the phenotypes also show different drug sensitivities ('sensitive' vs. 'resistant' strains), drug treatment can change their joint dynamics and the long-term outcome of the infection: most obviously, persistent drug pressure can permit the more resistant, but otherwise competitively-inferior, strains to dominate.

Methods

Here a mathematical model is developed to analyse how these and more subtle effects of antimalarial drug use are modulated by immune response, repeated re-inoculation of parasites, drug pharmacokinetic parameters, dose and treatment frequency.

Results

The model quantifies possible effects of single and multiple (periodic) treatment on the outcome of parasite competition. In the absence of further inoculation, the dosage and/or treatment frequency required for complete clearance can be estimated. With persistent superinfection, time-average parasite densities can be derived in terms of the basic immune-regulating parameters, the drug efficacy and treatment regimen.

Conclusion

The functional relations in the model are applicable to a wide range of conditions and transmission environments, allowing predictions to be made on both the individual and the community levels, and, in particular, transitions from drug-sensitive to drug-resistant parasite dominance to be projected on both levels.

Predictors of the failure of treatment with pyrimethamine-sulfadoxine in children with uncomplicated falciparum malaria

The prevalence of pyrimethamine-sulfadoxine (PS)-resistant Plasmodium falciparum malaria has been increasing in sub-Saharan Africa or other parts of the world in the last one or two decades. The factors that identify children at risk of treatment failure after being given PS were evaluated in 291 children with acute, symptomatic, uncomplicated, P. falciparum malaria. The children took part in four antimalarial drug trials between July 1996 and July 2004 in a hyperendemic area of southwestern Nigeria. Following treatment, 64 (22%) of 291 children failed treatment by day 7 or 14. In a multivariate analysis, an age < or = 1.5 years (AOR=2.9, 95% CI 1.3-6.4, P = 0.009) and presence of fever (AOR = 3.3, 95% CI 1.28-7.14, P = 0.01) were independent predictors of the failure of treatment with PS at presentation. Following treatment, delay in parasite clearance >3 days (AOR = 2.56, CI 1.19-5.56, P = 0.016) was an independent predictor of the failure of treatment with PS. In addition, compared with the children who had no fever then, children with fever three or more days after starting treatment were more likely to be treatment failures. These findings may have implications for malaria control efforts in some sub-Saharan African countries where treatment of malaria disease depends almost entirely on PS monotherapy, and for programmes employing PS or PS-based combination therapy.

Chloroquine-treatment failure in northern Ghana: roles of pfcrt T76 and pfmdr1 Y86

Although chloroquine (CQ) monotherapy is now generally inadequate for the treatment of Plasmodium falciparum malaria in northern Ghana--recently, 58% of 225 children failed treatment by day 14--use of the drug continues because of its low cost and wide availability. The risk factors associated with CQ-treatment failure in this region of Africa, including the T76 mutation in the chloroquine resistance transporter (pfcrt) gene and the Y86 mutation in the multidrug resistance (pfmdr1) gene of P. falciparum, have now been investigated, and genotype-failure indices (GFI) have been calculated. Treatment failure was found to be associated with young age, poor nutritional status, pfcrt T76 and pfmdr1 Y86, and early treatment failure (ETF) was also associated with high parasitaemia. The presence and concentration of 'residual' CQ in the blood of patients immediately before they were treated with CQ for the present study appeared to have no effect on outcome. Presence at recruitment of pfcrt T76 or pfmdr1 Y86 or both mutations increased the risk of treatment failure by 3.2-, 2.4- and 4.5-fold, and the risk of ETF by 9.8-, 2.7- and 10.2-fold, respectively. The pfcrt T76 GFI for clinical and all treatment failures were 2.8 and 1.4, respectively. These indices were relatively low in the younger children, those with malnutrition, and those with high parasitaemias when treated. Residual CQ did not affect the GFI substantially. Both pfcrt T76 and, to a lesser extent, pfmdr1 Y86 would be useful tools for the surveillance of CQ resistance in northern Ghana. In the current transition phase to alternative first-line treatment for P. falciparum malaria, it should be possible to provide estimates of the level of CQ resistance by monitoring the prevalences of these mutations.

Predictors of the failure of treatment with chloroquine in children with acute, uncomplicated, Plasmodium falciparum malaria, in an area with high and increasing incidences of chloroquine resistance

Resistance to chloroquine (CQ) in Plasmodium falciparum has reached unacceptably high levels in many endemic countries. The pre-treatment factors that identify the children who are at risk of treatment failure after being given CQ were evaluated in 385 children with acute, uncomplicated, Plasmodium falciparum malaria. These children each took part in one of six antimalarial drug trials conducted, between July 1996 and July 2004, in a hyper-endemic area of south-western Nigeria. Following treatment with CQ, 149 (39%) of the children failed treatment by day 7 or 14. In a multivariate analysis, an age of < or =7 years [giving an adjusted odds ratio (AOR) of 2.17, with a 95% confidence interval (CI) of 1.19-3.85; P = 0.01], an asexual parasitaemia of > or =100,000/microl (AOR = 2.17; CI = 1.08-4.35; P = 0.03), the presence of gametocytaemia (AOR = 2.08; CI = 1.14-3.85; P = 0.02) and enrolment >4 years after commencement of the study (i.e. after 2000; AOR = 2.13; CI = 1.3-4.0; P = 0.003) were found to be independent predictors at presentation of the subsequent failure of treatment with CQ. Compared with the other children, those who failed to clear their parasitaemias within 3 days and those who still had fever 1-2 days after commencing treatment were more likely to be treatment failures. Together, these findings may have implications for malaria-control efforts in all areas of sub-Saharan Africa where treatment of malaria depends almost entirely on antimalarial monotherapy.

Predictors of the failure of treatment with chloroquine plus chlorpheniramine, in children with acute, uncomplicated, Plasmodium falciparum malaria

Resistance to chloroquine in Plasmodium falciparum can be reversed, both in vitro and in vivo, by chlorpheniramine, a histamine H(1) receptor antagonist. This reversal raises the possibility of using chlorpheniramine to prolong the clinical usefulness of chloroquine in resource-poor communities. The factors that identify children at risk of treatment failure after being given chloroquine plus chlorpheniramine have now been evaluated in 281 children with uncomplicated, P. falciparum malaria. The children, who had taken part in six trials of antimalarial drugs between February 1996 and September 1999, in a hyper-endemic area of south-western Nigeria, were enrolled prospectively for the present study. Following treatment with chloroquine plus chlorpheniramine, 13 (5%) of the children failed treatment by day 7 or 14. In a multivariate analysis, an age of < or =3 years (adjusted odds ratio = 11.1; 95% confidence interval = 2.2-55.3; P = 0.003) and a parasitaemia that took >3 days to clear (adjusted odds ratio=7.9; 95% confidence interval = 1.3-49.4; P = 0.027) were found to be independent predictors of treatment failure. In addition, compared with the children who had a lower axillary temperature then, the children who had an axillary temperature of > or =38 degrees C 2 days after commencing treatment were significantly more likely to be treatment failures. In resource-poor communities using chloroquine plus chlorpheniramine, the easily identifiable predictors of treatment failure might be used to identify children requiring alternative antimalarial drugs.

Polymorphisms in Plasmodium falciparum dhfr and dhps genes and age related in vivo sulfadoxine-pyrimethamine resistance in malaria-infected patients from Nigeria

Mutations in Plasmodium falciparum dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) genes have been used as means to predict treatment failure to sulfadoxine-pyrimethamine (SP) and for monitoring/surveillance of resistance to the drug in many areas where malaria is endemic. However, patients responses to treatment are significantly dependent on factors like host immunity profile of treated patients. In order to investigate the relationship between molecular markers of SP resistance, host immunity and clinical outcome, the association between pre-treatment dhfr and dhps genotypes, age and treatment outcomes was evaluated in 109 children treated with SP for acute uncomplicated malaria in Ibadan, Nigeria. Seventy-three percent of the children were cured with the drug, while 27% failed treatment after 28 days of follow-up. All children infected with parasites harboring less than two dhfr/dhps mutations were cured with SP. The dhfr triple (Asn-108/Ile-51/Arg-59) mutants or the dhps double mutants (Gly-437/Glu-540) were independently associated with SP treatment failure in children aged less than 5 years, but not in older children. The dhfr and dhps quintuple mutant (dhfr triple mutant+dhps double mutant) was the genotype most strongly associated with SP treatment failure (OR=24.72, 95%CI=8.24-74.15) in both younger and older children.

Combination treatments for uncomplicated falciparum malaria in Kampala, Uganda: randomised clinical trial

BACKGROUND

Plasmodium falciparum resistance has rendered chloroquine monotherapy ineffective in much of Africa, but data on alternative regimens are limited. We compared chloroquine+sulfadoxine-pyrimethamine, amodiaquine+sulfadoxine-pyrimethamine, and amodiaquine+artesunate for treatment of uncomplicated malaria in Kampala, Uganda.

METHODS

Of 1017 consecutive patients aged 6 months to 10 years with uncomplicated malaria who were screened, 418 were randomised to receive: chloroquine (25 mg/kg over 3 days) and sulfadoxine-pyrimethamine (25 mg/kg sulfadoxine, 1.25 mg/kg pyrimethamine, single dose); amodiaquine (25 mg/kg over 3 days) and sulfadoxine-pyrimethamine; or amodiaquine and artesunate (4 mg/kg daily for 3 days). Primary efficacy outcomes were 28-day clinical failure risks, adjusted and unadjusted by genotyping to distinguish new infection and recrudescence. The primary safety endpoint was incidence of serious adverse events during follow-up. Analysis was intention to treat and per protocol.

FINDINGS

18 patients were excluded before enrollment. Of those enrolled, 384 of 400 (96%) were assigned an efficacy outcome and 396 (99%) were assessed for safety. Risk of 28-day clinical treatment failure was significantly higher with chloroquine+sulfadoxine-pyrimethamine (44/125 [35%]) than with amodiaquine+sulfadoxine-pyrimethamine (12/129 [9%]; risk difference 26% [95% CI 16-36]; p<0.0001) or amodiaquine+artesunate (3/130 [2%]; 33% [24-42]; p<0.0001). The greater risk of clinical treatment failure with amodiaquine+sulfadoxine-pyrimethamine was balanced by a lower risk of new infection, resulting in a similar need for retreatment over 28 days for amodiaquine+sulfadoxine-pyrimethamine (17/129 [13%]) and amodiaquine+artesunate (16/130 [12%]; p=0.854). Serious adverse events were uncommon with all regimens.

INTERPRETATION

Risk of treatment failure with chloroquine+sulfadoxine-pyrimethamine was unacceptably high. Combinations of amodiaquine and sulfadoxine-pyrimethamine or artesunate were significantly more efficacious, and each regimen could be an appropriate alternative for treatment of uncomplicated malaria in Africa.

Age, temperature, and parasitaemia predict chloroquine treatment failure and anaemia in children with uncomplicated Plasmodium falciparum malaria

The prevalence of chloroquine-resistant Plasmodium falciparum malaria has been increasing in sub-Saharan Africa and parts of South America over the last 2 decades, and has been associated with increased anaemia-associated morbidity and higher mortality rates. Prospectively collected clinical and parasitological data from a multicentre study of 788 children aged 6-59 months with uncomplicated P. falciparum malaria were analysed in order to identify risk factors for chloroquine treatment failure and to assess its impact on anaemia after therapy. The proportion of chloroquine treatment failures (combined early and late treatment failures) was higher in the central-eastern African countries (Tanzania, 53%; Uganda, 80%; Zambia, 57%) and Ecuador (54%) than in Ghana (36%). Using logistic regression, predictors of early treatment failure included younger age, higher baseline temperature, and greater levels of parasitaemia. We conclude that younger age, higher initial temperature, and higher baseline parasitaemia predict early treatment failure and a higher probability of worsening anaemia between admission and days 7 or 14 post-treatment.

Relationship between age, molecular markers, and response to sulphadoxine-pyrimethamine treatment in Kampala, Uganda

Sulphadoxine/pyrimethamine (SP) has become the first-line treatment of uncomplicated malaria in a number of African countries. Molecular surveillance of resistance-mediating mutations in Plasmodium falciparum dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) has been proposed as a means of predicting SP treatment outcomes, but optimal methods of surveillance in different populations have not been well established. To investigate the relationship between molecular markers of SP resistance, host immunity, and response to therapy, we evaluated the association between the presence of five key dhfr and dhps mutations at enrollment and clinical outcome in children and adults treated with SP for uncomplicated malaria in Kampala, Uganda. Clinical treatment failure was 11% at 14 days, increasing to 30% at 28 days, after excluding new infections. Outcomes varied markedly based on the number of dhfr and dhps mutations and on the age of treated subjects. All infections with less than two dhfr/dhps mutations were successfully treated. Treatment failure associated with any two, three, or four dhfr/dhps mutations occurred in nine of 24 (38%) children up to 5 years, but not in older patients (0/20). In the presence of all five mutations, treatment failure occurred equally in children aged 5 years or younger [7/16 (44%)] and in older patients [8/16 (50%)]. Our results showed that age, a surrogate marker of antimalarial immunity, had a major impact on the relationship between polymorphisms in SP target enzymes and treatment outcomes. The use of molecular markers of SP resistance to predict treatment failure rates should take age into account.

Antimicrobial resistance: is it really that bad?

Antimicrobial resistance has been the subject of this and numerous other special issues of pediatric and infectious disease journals during the past several years. Pediatricians may be forgiven for expressing skepticism occasionally about dour scenarios predicting the advent of untreatable infections or a return to the preantibiotic era. Certainly, some benefits may accrue to pharmaceutical companies, academic and public health experts, and managed care systems from promoting concern about antimicrobial resistance. In fact, the response to the spread of resistance has been forceful, and in some cases successful, with reductions achieved in unnecessary prescribing, treatment regimens modified, and some new antimicrobial agents made available during the past several years. The problem, however, remains substantial, as several clear examples of dangerous and nearly untreatable multiply resistant organisms exist and the costs associated with treating resistant organisms continue to skyrocket. In many instances in the developing world, antimicrobial resistance can mean that a formerly treatable infection has become untreatable, and for pediatricians in the United States, resistance has, at the least, complicated therapy and limited options in everyday practice.

History, dynamics, and public health importance of malaria parasite resistance

Despite considerable efforts, malaria is still one of the most devastating infectious diseases in the tropics. The rapid spread of antimalarial drug resistance currently compounds this grim picture. In this paper, we review the history of antimalarial drug resistance and the methods for monitoring it and assess the current magnitude and burden of parasite resistance to two commonly used drugs: chloroquine and sulfadoxine-pyrimethamine. Furthermore, we review the factors involved in the emergence and spread of drug resistance and highlight its public health importance. Finally, we discuss ways of dealing with such a problem by using combination therapy and suggest some of the research themes needing urgent answers.

The efficacy of chloroquine, sulfadoxine-pyrimethamine and a combination of both for the treatment of uncomplicated Plasmodium falciparum malaria in an area of low transmission in western Uganda

We conducted an efficacy study of chloroquine (CQ), sulfadoxine-pyrimethamine (SP) and a combination of both (SP+CQ) for the treatment of uncomplicated malaria in an area of low transmission with low drug pressure. On day 3, fever clearance was 97.4% (95% CI, 86.8-99.9), 100% (95% CI, 87.2-100) and 96.6% (95% CI, 82.2-99.9) in the CQ, SP and SP+CQ groups, respectively, (P=0.65). On day 14, clinical success was 92.5% (95% CI, 79.6-98.4), 100% (95% CI, 87.2-100) and 100% (95% CI, 88.1-100) in the CQ, SP and CQ+SP groups, respectively. Clinical failure was seen in 7.5% with 5% (95% CI, 0.61-16.9) early treatment failure and 2.5% (95% CI, 0.06-13.2) late treatment failure of cases in the CQ group and 0% in the SP and SP+CQ groups. Parasitological resistance was observed at RI level in 10% (95% CI, 2.8-23.7), 18.5% (95% CI, 6.3-38.1) and 6.9% (95% CI, 0.85-22.8) for the CQ, SP and SP+CQ, respectively (P=0.37). There was no age-dependent difference in clinical failure or parasitological resistance in any of the treatment groups and prior CQ use within the last 2 weeks did not affect CQ treatment outcome. The findings of this study suggest that CQ is still effective for the treatment of uncomplicated malaria in this area of low transmission and SP. However, combination therapy of SP+CQ is recommended to delay the development SP resistance, and regular surveillance for emerging CQ and SP resistance is needed to plan for alternative antimalarial drug regimens.

Prevalence of the K76T mutation in the pfcrt gene of Plasmodium falciparum among chloroquine responders in India

Chloroquine-resistant Plasmodium falciparum needs to be monitored in the field for effective malaria control strategies. A point mutation K76T in the P. falciparum chloroquine resistance transporter (Pfcrt) protein has recently been proposed as a molecular marker for the faster detection of chloroquine-resistant falciparum malaria in field. We describe here the evaluation of this marker in Indian P. falciparum isolates. A total of 274 Indian P. falciparum isolates were analyzed for the K76T mutation. This mutation was detected in all the clinical isolates obtained from the in vivo chloroquine non-responders. But majority of the clinical isolates from chloroquine responders (71 of 74 patients, i.e. 96%) also harbored this mutation. The K76T mutation was indeed highly prevalent (91%) among 213 clinical isolates. There was a significant association between K76T mutation and the in vitro chloroquine response (P<0.05) but six isolates showed discordant results. In conclusion, the K76T mutation fails to differentiate majority of the chloroquine responders from that of the non-responders and thus will be of limited use in the field in India.

Sulfadoxine/pyrimethamine alone or with amodiaquine or artesunate for treatment of uncomplicated malaria: a longitudinal randomised trial

BACKGROUND

New antimalarial treatments are urgently needed in sub-Saharan Africa. Improved therapies should decrease failure rates in the short term, but their effect on incidence of subsequent episodes of malaria is little studied. We aimed to compare the short-term and long-term effectiveness of three antimalarial regimens in children from Kampala, Uganda.

METHODS

We randomly allocated healthy children aged 6 months to 5 years to receive 25 mg/kg sulfadoxine and 1.25 mg/kg pyrimethamine plus either placebo, 25 mg/kg amodiaquine, or 12 mg/kg artesunate. Participants were followed up for 1 year and received the same preassigned treatment for every new episode of uncomplicated malaria diagnosed during follow-up. Recrudescent and new infections were distinguished by comparison of polymorphisms in merozoite surface protein 2 (MSP2). Our primary endpoint was the total number of treatments for malaria per time at risk. Analyses were done per protocol.

FINDINGS

183 (61%) of 316 participants were diagnosed with at least one episode of uncomplicated malaria. A total of 577 episodes of uncomplicated Plasmodium falciparum malaria were treated with study drugs; all regimens were safe and well tolerated. Clinical treatment failure after 14 days was significantly more frequent in the sulfadoxine/pyrimethamine group (38 of 215, 18%) compared with either the sulfadoxine/pyrimethamine plus amodiaquine group (two of 164, 1%; p<0.0001) or sulfadoxine/pyrimethamine plus artesunate group (one of 198, 1%; p<0.0001). After 28 and 42 days, patients in the sulfadoxine/pyrimethamine plus amodiaquine group were significantly less likely to develop malaria than were those in the other groups. Overall, sulfadoxine/pyrimethamine plus amodiaquine reduced the rate of subsequent treatments for malaria by 54% (95% CI 36-66, p<0.0001) compared with sulfadoxine/ pyrimethamine alone and by 37% (12-54, p=0.007) compared with sulfadoxine/pyrimethamine plus artesunate.

INTERPRETATION

Sulfadoxine/pyrimethamine plus amodiaquine could be used as an inexpensive regimen to decrease the rate of subsequent episodes of malaria.

Increasing antimalarial drug resistance in Uganda and revision of the national drug policy

Chloroquine (CQ) resistance was first documented in Uganda in 1988. Subsequent surveillance of antimalarial drug resistance, conducted by the Ugandan Ministry of Health and several research organizations, suggests that resistance to CQ is now widespread, reaching critical levels in many areas of the country. In June 2000, the Ministry of Health held a National Consensus Meeting to evaluate the available drug efficacy data and review the national antimalarial drug policy. After extensive debate, the combination of CQ + sulfadoxine-pyrimethamine (SP) was chosen to replace CQ as the first-line treatment of uncomplicated malaria as an interim policy. This review evaluates the in vivo drug efficacy studies conducted in Uganda since 1988 and issues confronted in revision of the drug policy. The Ugandan experience illustrates the challenges faced by sub-Saharan African countries confronted with rising CQ resistance but limited data on potential alternative options. The choice of CQ + SP as a provisional policy in the absence of prerequisite efficacy, safety and cost-effectiveness data reflects the urgency of the malaria treatment problem, and growing pressure to adopt combination therapies. Surveillance of CQ + SP treatment efficacy, collection of additional data on alternative regimens and active consensus building among key partners in the malaria community will be necessary to develop a rational long-term antimalarial treatment policy in Uganda.

Efficacy of chloroquine in the treatment of uncomplicated, Plasmodium falciparum malaria in northern Ghana

Chloroquine (CQ) resistance in Plasmodium falciparum contributes to growing malaria-attributable morbidity and mortality in sub-Saharan Africa. However, the extent and degree of such resistance vary considerably between endemic areas. Data on CQ resistance in northern Ghana are almost entirely lacking. The therapeutic efficacy of CQ in uncomplicated malaria was therefore assessed, in a standard, 14-day protocol, in 225 children aged <5 years in Tamale, in the Northern region of Ghana. Early treatment failure (ETF) was observed in 11% of the children and late treatment failure in 18%. High initial parasite density and young age were independent predictors for ETF. Resistant parasitological responses (RI-RIII) were seen in 57% of the cases that could be classified. More than half of these responses occurred in children fulfilling the criteria for adequate clinical response (ACR), indicating a considerable lack of agreement between parasitological and clinical outcome. During the follow-up period, haemoglobin levels increased by approximately 1g/dl not only in patients with ACR but also in those who experienced clinical failure more than 1 week post-treatment. As CQ-treatment failure occurred in >25% of the children and more than half of the parasitological responses indicated resistance, current recommendations for the treatment of uncomplicated malaria in young children in northern Ghana have to be reconsidered.

Amodiaquine, sulfadoxine/pyrimethamine, and combination therapy for treatment of uncomplicated falciparum malaria in Kampala, Uganda: a randomised trial

BACKGROUND

Increasing Plasmodium falciparum resistance to chloroquine in sub-Saharan Africa necessitates use of alternative antimalarial agents. Affordable alternative treatments include sulfadoxine/pyrimethamine and amodiaquine. Combination of antimalarial agents can increase therapeutic efficacy and delay emergence of drug resistance. We compared the efficacy of sulfadoxine/pyrimethamine, amodiaquine, and an amodiaquine/sulfadoxine/pyrimethamine combination for treatment of uncomplicated malaria in a region of high chloroquine resistance.

METHODS

Patients with symptoms of uncomplicated falciparum malaria and confirmed disease in Kampala, Uganda, were randomly assigned to receive sulfadoxine/pyrimethamine (25 mg/kg sulfadoxine, and 1.25 mg/kg pyrimethamine) plus placebo; amodiaquine (25 mg/kg) plus placebo; or amodiaquine plus sulfadoxine/pyrimethamine. Patients were followed up for 14 days, and clinical and parasitological outcomes were assessed.

FINDINGS

90% (400/445) of patients enrolled in the study successfully completed 14 days of follow-up. Treatment failure based on clinical criteria occurred in 13 of 131 (10%) patients on sulfadoxine/ pyrimethamine, nine of 131 (7%) on amodiaquine, and four of 138 (3%) on amodiaquine/sulfadoxine/pyrimethamine. Based on parasitological criteria, treatment failed in 26%, 16%, and 10% of these patients, respectively. Amodiaquine/sulfadoxine/pyrimethamine was significantly more effective than sulfadoxine/pyrimethamine alone in children aged younger than 5 years (clinical failure in 3.5% vs 13.9%, respectively, risk difference 10.4% [95% CI, 1.6-19.3] p=0.021; parasitological failure in 12.8% vs 26.4%, risk difference 13.6% [1.2-26.0] p=0.041).

INTERPRETATION

Sulfadoxine/pyrimethamine, amodiaquine, and amodiaquine/sulfadoxine/pyrimethamine were all effective for treatment of uncomplicated falciparum malaria in Uganda. The amodiaquine/sulfadoxine/pyrimethamine combination was the most effective, and could be the optimum low-cost alternative to chloroquine in Africa.

The comparative efficacy of chloroquine and sulfadoxine-pyrimethamine for the treatment of uncomplicated falciparum malaria in Kampala, Uganda

Chloroquine (CQ) remains the first-line treatment for uncomplicated malaria in much of Africa despite the growing problem of resistance to this drug. Sulfadoxine-pyrimethamine (SP) is often used after CQ treatment failure and has replaced CQ as the first-line treatment in parts of Africa. To compare the efficacy of these 2 regimens, we evaluated, in March-August 1999, clinical and parasitological responses over 28 days in 214 children and adults from Kampala, Uganda, with uncomplicated falciparum malaria. Compared to SP, significantly more patients treated with CQ developed early or late clinical failure (54% vs 11%, P < 0.001) and parasitological failure (72% vs 30%, P < 0.001) during 14 days of follow-up. The risk of treatment failure occurring after day 14 was similar between the 2 treatment groups. Among those treated with CQ, children aged < 5 years were at higher risk of clinical failure than older individuals (76% vs 28%, P < 0.001), an association not seen with SP (11% vs 10%, P = 0.91). Although early parasite clearance was significantly better in the SP group (P = 0.001), fever clearance at day 3 was the same (CQ 85%, SP 86%). These and other recent findings suggest that consideration be given to replacing CQ as the first-line therapy for uncomplicated malaria in Uganda, particularly in young children.