Dr Julie Makani
|Research Area:||Global Health|
|Technology Exchange:||Medical statistics|
|Scientific Themes:||Tropical Medicine & Global Health and Genetics & Genomics|
|Keywords:||Sickle Cell Disease, Genetics, Haematology and Malaria|
Sickle Cell Disease (SCD), is the single most important genetic cause of childhood mortality world-wide. Although SCD is essentially an African problem, where over 90% of affected individuals are born, virtually no systematic studies have been conducted and there are limited data on even the most basic issues, such as the common complications and the current mortality. The research group has established a systematic framework for prospective studies in Tanzania and they have recruited an active cohort of 1,600 SCD patients, which is one of the largest in Africa. The aim is to describe the clinical spectrum of SCD in E Africa by defining the major causes of morbidity and mortality, in order to determine the most appropriate interventions to be introduced in Africa. This study will also allow better understanding of the molecular, genetic and environmental mechanisms determining disease course and severity in Africa.
Due to its molecular basis, SCD presents great opportunities for integrating clinical, epidemiological, patho-physiological and genetic research. However, the fundamental problems limiting health care, training and research in Africa include lack of infrastructure and low critical mass of scientists and health care professionals. This has led to collaboration to support training programmes in Haematology and Blood transfusion in Tanzania with the intention of developing sustainable human resource capacity (pre-service and continuing professional training) in order to get adequate well-trained, knowledgeable people, with their own scientific and clinical capabilities to participate and contribute to sustainable health care solutions.
Julie is a Clinical Research Fellow in the Nuffield Department of Medicine and is based in the Department of Haematology and Blood Transfusion at Muhimbili University of Health and Allied Sciences (www.muchs.ac.tz) which is the main clinical, academic and research centre in Tanzania.
|Dr Sharon Cox||London School of Hygiene & Tropical Medicine||United Kingdom|
|Prof Charles Newton||Tropical Medicine||University of Oxford||United Kingdom|
|Prof Fenella Kirkham FRCP||Institute of Child Health, University College London||United Kingdom|
|Prof Swee Lay Thein||Guys, Kings and St Thomas School of Medicine||United Kingdom|
|Prof Ephata Kaaya||Muhimbili University of Health and Allied Sciences||Tanzania|
|Prof David Roberts (RDM)||Nuffield Division of Clinical Laboratory Sciences||University of Oxford||United Kingdom|
|Dr Jeffrey Barrett||Wellcome Trust Sanger Institute||United Kingdom|
|Dr Ines Barroso||Wellcome Trust Sanger Institute||United Kingdom|
|Prof Bob W Snow||Tropical Medicine||University of Oxford||United Kingdom|
|Prof Andrew Prentice||London School of Hygiene and Tropical Medicine||United Kingdom|
|Khadija Malima||KEMRI Wellcome Programme / University of Oxford||Kenya|
|Prof Simon Hay||Zoology||University of Oxford||Kenya|
|Bernard Davies||University College London||United Kingdom|
BMJ, 348 (mar10 11), pp. g1765. | Read more2014. Management of sickle cell disease in the community.
BACKGROUND: Fetal hemoglobin (HbF) is an important modulator of sickle cell disease (SCD). HbF has previously been shown to be affected by variants at three loci on chromosomes 2, 6 and 11, but it is likely that additional loci remain to be discovered. METHODS AND FINDINGS: We conducted a genome-wide association study (GWAS) in 1,213 SCA (HbSS/HbSβ0) patients in Tanzania. Genotyping was done with Illumina Omni2.5 array and imputation using 1000 Genomes Phase I release data. Association with HbF was analysed using a linear mixed model to control for complex population structure within our study. We successfully replicated known associations for HbF near BCL11A and the HBS1L-MYB intergenic polymorphisms (HMIP), including multiple independent effects near BCL11A, consistent with previous reports. We observed eight additional associations with P<10(-6). These associations could not be replicated in a SCA population in the UK. CONCLUSIONS: This is the largest GWAS study in SCA in Africa. We have confirmed known associations and identified new genetic associations with HbF that require further replication in SCA populations in Africa. Hide abstract
Haematologica, 99 (1), pp. e1-e4. | Read more2014. Tricuspid regurgitant jet velocity and hospitalization in Tanzanian children with sickle cell anemia.
Sickle cell disease (SCD) is one of the most common genetic causes of illness and death in the world. This is a review of SCD in Africa, which bears the highest burden of disease. The first section provides an introduction to the molecular basis of SCD and the pathophysiological mechanism of selected clinical events. The second section discusses the epidemiology of the disease (prevalence, morbidity, and mortality), at global level and within Africa. The third section discusses the laboratory diagnosis and management of SCD, emphasizing strategies that been have proven to be effective in areas with limited resources. Throughout the review, specific activities that require evidence to guide healthcare in Africa, as well as strategic areas for further research, will be highlighted. Hide abstract
In Tanzania, there is paucity of data for monitoring laboratory medicine including haematology. This therefore calls for audits of practices in haematology and blood transfusion in order to provide appraise practice and devise strategies that would result in improved quality of health care services. This descriptive cross-sectional study which audited laboratory practice in haematology and blood transfusion at Muhimbili National Hospital (MNH) aimed at assessing the pre-analytical stage of laboratory investigations including laboratory request forms and handling specimen processing in the haematology laboratory and assessing the chain from donor selection, blood component processing to administration of blood during transfusion. A national standard checklist was used to audit the laboratory request forms (LRF), phlebotomists' practices on handling and assessing the from donor selection to administration of blood during transfusion. Both interview and observations were used. A total of 195 LRF were audited and 100% of had incomplete information such as patients' identification numbers, time sample ordered, reason for request, summary of clinical assessment and differential diagnoses. The labelling of specimens was poorly done by phlebotomists/clinicians in 82% of the specimens. Also 65% (132/202) of the blood samples delivered in the haematology laboratory did not contain the recommended volume of blood. There was no laboratory request form specific for ordering blood and there were no guidelines for indication of blood transfusion in the wards/clinics. The blood transfusion laboratory section was not participating in external quality assessment and the hospital transfusion committee was not in operation. It is recommended that a referral hospital like MNH should have a transfusion committee to provide an active forum to facilitate communication between those involved with transfusion, monitor, coordinate and audit blood transfusion practices as per national guidelines. Hide abstract
STUDY OBJECTIVE: To test the hypothesis that low iron availability, measured as transferrin saturation, is associated with low nocturnal hemoglobin oxygen saturation (SpO(2)) in children with homozygous sickle cell anemia (SCA; hemoglobin SS). METHODS: This was a cross-sectional study of Tanzanian children with SCA who were not receiving regular blood transfusions. Thirty-two children (16 boys) with SCA (mean age 8.0, range 3.6-15.3 years) underwent motion-resistant nocturnal oximetry (Masimo Radical) and had steady state serum transferrin saturation and hematological indices assessed. RESULTS: Higher transferrin saturation, adjusted for age and α-thalassemia deletion, was associated with lower nocturnal mean SpO(2) (p = 0.013, r(2) = 0.41), number of SpO(2) dips/h > 3% from baseline (p = 0.008, r(2) = 0.19) and with min/h with SpO(2) < 90% (p = 0.026 r(2) = 0.16). Transferrin saturation < 16% (indicative of iron deficiency) was associated with a 2.2% higher nocturnal mean SpO(2). CONCLUSIONS: Contrary to our hypothesis, higher iron availability, assessed by transferrin saturation, is associated with nocturnal chronic and intermittent hemoglobin oxygen desaturation in SCA. Whether these associations are causal and are driven by hypoxia-inducible factor and hepcidin-mediated upregulation of demand for iron warrants further investigation. Hide abstract
BACKGROUND: The World Health Organization has declared Sickle Cell Anemia (SCA) a public health priority. There are 300,000 births/year, over 75% in Africa, with estimates suggesting that 6 million Africans will be living with SCA if average survival reaches half the African norm. Countries such as United States of America and United Kingdom have reduced SCA mortality from 3 to 0.13 per 100 person years of observation (PYO), with interventions such as newborn screening, prevention of infections and comprehensive care, but implementation of interventions in African countries has been hindered by lack of locally appropriate information. The objective of this study was to determine the incidence and factors associated with death from SCA in Dar-es-Salaam. METHODS AND FINDINGS: A hospital-based cohort study was conducted, with prospective surveillance of 1,725 SCA patients recruited from 2004 to 2009, with 209 (12%) lost to follow up, while 86 died. The mortality rate was 1.9 (95%CI 1.5, 2.9) per 100 PYO, highest under 5-years old [7.3 (4.8-11.0)], adjusting for dates of birth and study enrollment. Independent risk factors, at enrollment to the cohort, predicting death were low hemoglobin (<5 g/dL) [3.8 (1.8-8.2); p = 0.001] and high total bilirubin (≥102 µmol/L) [1.7 (1.0-2.9); p = 0.044] as determined by logistic regression. CONCLUSIONS: Mortality in SCA in Africa is high, with the most vulnerable period being under 5-years old. This is most likely an underestimate, as this was a hospital cohort and may not have captured SCA individuals with severe disease who died in early childhood, those with mild disease who are undiagnosed or do not utilize services at health facilities. Prompt and effective treatment for anemia in SCA is recommended as it is likely to improve survival. Further research is required to determine the etiology, pathophysiology and the most appropriate strategies for management of anemia in SCA. Hide abstract
British Journal of Haematology, 155 (4), pp. 522-524. | Read more2011. Global arginine bioavailability in Tanzanian sickle cell anaemia patients at steady-state: A nested case control study of deaths versus survivors
BACKGROUND: Reduced growth is common in children with sickle cell anemia, but few data exist on associations with long-term clinical course. Our objective was to determine the prevalence of malnutrition at enrollment into a hospital-based cohort and whether poor nutritional status predicted morbidity and mortality within an urban cohort of Tanzanian sickle cell anemia patients. DESIGN AND METHODS: Anthropometry was conducted at enrollment into the sickle cell anemia cohort (n=1,618; ages 0.5-48 years) and in controls who attended screening (siblings, walk-ins and referrals) but who were found not to have sickle cell anemia (n=717; ages 0.5-64 years). Prospective surveillance recorded hospitalization at Muhimbili National Hospital and mortality between March 2004 and September 2009. RESULTS: Sickle cell anemia was associated with stunting (OR=1.92, P<0.001, 36.2%) and wasting (OR=1.66, P=0.002, 18.4%). The greatest growth deficits were observed in adolescents and in boys. Independent of age and sex, lower hemoglobin concentration was associated with increased odds of malnutrition in sickle cell patients. Of the 1,041 sickle cell anemia patients with a body mass index z-score at enrollment, 92% were followed up until September 2009 (n=908) or death (n=50). Body mass index and weight-for-age z-score predicted hospitalization (hazard ratio [HZR]=0.90, P=0.04 and HZR=0.88, P=0.02) but height-for-age z-score did not (HZR=0.93, NS). The mortality rate of 2.5 per 100 person-years was not associated with any of the anthropometric measures. CONCLUSIONS: In this non-birth-cohort of sickle cell anemia with significant associated undernutrition, wasting predicted an increased risk of hospital admission. Targeted nutritional interventions should prioritize treatment and prevention of wasting. Hide abstract
Fetal hemoglobin (HbF, α(2)γ(2)) is a major contributor to the remarkable phenotypic heterogeneity of sickle cell anemia (SCA). Genetic variation at 3 principal loci (HBB cluster on chromosome 11p, HBS1L-MYB region on chromosome 6q, and BCL11A on chromosome 2p) have been shown to influence HbF levels and disease severity in β-thalassemia and SCA. Previous studies in SCA, however, have been restricted to populations from the African diaspora, which include multiple genealogies. We have investigated the influence of these 3 loci on HbF levels in sickle cell patients from Tanzania and in a small group of African British sickle patients. All 3 loci have a significant impact on the trait in both patient groups. The results suggest the presence of HBS1L-MYB variants affecting HbF in patients who are not tracked well by European-derived markers, such as rs9399137. Additional loci may be identified through independent genome-wide association studies in African populations. Hide abstract
Although malaria is widely considered a major cause of death in young children born with sickle cell anemia (SCA) in sub-Saharan Africa, this is poorly quantified. We attempted to investigate this question through 4 large case-control analyses involving 7164 children living on the coast of Kenya. SCA was associated with an increased risk of admission to hospital both with nonmalaria diseases in general (odds ratio [OR] = 4.17; 95% confidence interval [CI], 1.95-8.92; P < .001) and with invasive bacterial diseases in particular (OR = 8.73; 95% CI, 4.51-16.89; P < .001). We found no evidence for a strongly increased risk of either uncomplicated malaria (OR = 0.43; 95% CI, 0.09-2.10; P = .30) or malaria complicated by a range of well-described clinical features of severity (OR = 0.80; 95% CI, 0.25-2.51; P = .70) overall; nevertheless, mortality was considerably higher among SCA than non-SCA children hospitalized with malaria. Our findings highlight both the central role that malaria plays in the high early mortality seen in African children with SCA and the urgent need for better quantitative data. Meanwhile, our study confirms the importance of providing all children living with SCA in malaria-endemic areas with effective prophylaxis. Hide abstract
Approximately 280,000 children are born with sickle cell anemia (SCA) in Africa annually, yet few survive beyond childhood. Falciparum malaria is considered a significant cause of this mortality. We conducted a 5-year prospective surveillance study for malaria parasitemia, clinical malaria, and severe malarial anemia (SMA) in Dar-es-Salaam, Tanzania, between 2004 and 2009. We recorded 10,491 visits to the outpatient clinic among 1808 patients with SCA and 773 visits among 679 patients without SCA. Similarly, we recorded 691 hospital admissions among 497 patients with SCA and 2017 in patients without SCA. Overall, the prevalence of parasitemia was lower in patients with SCA than in patients without SCA both at clinic (0.7% vs 1.6%; OR, 0.53; 95% CI, 0.32-0.86; P = .008) and during hospitalization (3.0% vs 5.6%; OR, 0.46; 95% CI, 0.25-0.94; P = .01). Furthermore, patients with SCA had higher rates of malaria during hospitalization than at clinic, the ORs being 4.29 (95% CI, 2.63-7.01; P < .001) for parasitemia, 17.66 (95% CI, 5.92-52.71; P < .001) for clinical malaria, and 21.11 (95% CI, 8.46-52.67; P < .001) for SMA. Although malaria was rare among patients with SCA, parasitemia during hospitalization was associated with both severe anemia and death. Effective treatment for malaria during severe illness episodes and further studies to determine the role chemoprophylaxis are required. Hide abstract
BACKGROUND: In sub-Saharan Africa, more than 90% of children with sickle-cell anaemia die before the diagnosis can be made. The causes of death are poorly documented, but bacterial sepsis is probably important. We examined the risk of invasive bacterial diseases in children with sickle-cell anaemia. METHODS: This study was undertaken in a rural area on the coast of Kenya, with a case-control approach. We undertook blood cultures on all children younger than 14 years who were admitted from within a defined study area to Kilifi District Hospital between Aug 1, 1998, and March 31, 2008; those with bacteraemia were defined as cases. We used two sets of controls: children recruited by random sampling in the same area into several studies undertaken between Sept 1, 1998, and Nov 30, 2005; and those born consecutively within the area between May 1, 2006, and April 30, 2008. Cases and controls were tested for sickle-cell anaemia retrospectively. FINDINGS: We detected 2157 episodes of bacteraemia in 38 441 admissions (6%). 1749 of these children with bacteraemia (81%) were typed for sickle-cell anaemia, of whom 108 (6%) were positive as were 89 of 13 492 controls (1%). The organisms most commonly isolated from children with sickle-cell anaemia were Streptococcus pneumoniae (44/108 isolates; 41%), non-typhi Salmonella species (19/108; 18%), Haemophilus influenzae type b (13/108; 12%), Acinetobacter species (seven of 108; 7%), and Escherichia coli (seven of 108; 7%). The age-adjusted odds ratio for bacteraemia in children with sickle-cell anaemia was 26.3 (95% CI 14.5-47.6), with the strongest associations for S pneumoniae (33.0, 17.4-62.8), non-typhi Salmonella species (35.5, 16.4-76.8), and H influenzae type b (28.1, 12.0-65.9). INTERPRETATION: The organisms causing bacteraemia in African children with sickle-cell anaemia are the same as those in developed countries. Introduction of conjugate vaccines against S pneumoniae and H influenzae into the childhood immunisation schedules of African countries could substantially affect survival of children with sickle-cell anaemia. FUNDING: Wellcome Trust, UK. Hide abstract
Globally, sickle cell disease (SCD) has its highest prevalence and worst prognosis in sub-Saharan Africa. Nevertheless, relatively few studies describe the clinical characteristics of children with SCD in this region. We conducted a prospective observational study of children with SCD attending a specialist out-patient clinic in Kilifi, Kenya. A total of 124 children (median age 6.3 years) were included in the study. Splenomegaly was present in 41 (33%) subjects and hepatomegaly in 25 (20%), both being common in all age groups. A positive malaria slide was found at 6% of clinic visits. The mean haemoglobin concentration was 73 g/l, compared to 107 g/l in non-SCD controls (P < 0.001). Liver function tests were elevated; plasma bilirubin concentrations were 46 micromol/l and aspartate aminotransferase was 124 iu/l. Forty-eight (39%) children were admitted to hospital and two died. Children with SCD in Kilifi have a similar degree of anaemia and liver function derangement to patients living in developed countries, but splenomegaly persists into later childhood. The prevalence of malaria was lower than expected given the prevalence in the local community. This study provides valuable data regarding the clinical characteristics of children living with SCD in a rural setting in East Africa. Hide abstract
BACKGROUND: To date, it has been widely assumed that malaria is a common cause of morbidity and mortality in children with sickle cell disease (SCD) in malaria-endemic countries, and as a result, malarial prophylaxis is commonly recommended. Nevertheless, few data are available that support this practice. METHODS: We conducted a retrospective analysis of the data collected prospectively from children aged 0-13 years who were admitted to Kilifi District Hospital during the period from July 1998 through June 2005. We studied the prevalence, clinical features, and outcome of malarial infections in these children, stratified by SCD status. RESULTS: Although we estimated the prevalence of SCD in children to be only 0.8% (71 of 8531 children) during the period from August 2006 through September 2008 in the community surrounding the hospital, 555 (1.6%) of 34,529 children admitted to the hospital during the study period (i.e., from July 1998 through June 2005) were children with SCD; in fact, a total of 309 children with SCD were admitted 555 times. The prevalence of Plasmodium falciparum parasitemia was lower among children with SCD than it was among children without SCD (86 [15.6%] of 551 children vs. 13,835 [41.3%] of 33,500 children; P < .001). Similarly, among those infected with P. falciparum parasites, the mean parasite density was significantly lower among children with SCD than it was among children without SCD (2205 vs. 23,878 parasites/microL; P < .001). Fourteen (16.3%) of 86 parasitemic patients with SCD had features consistent with severe malaria, compared with 3424 (24.7%) of 13,835 parasitemic patients without SCD (odds ratio, 0.59; P < .07). We found no association between malarial parasitemia and death. CONCLUSIONS: We found no evidence to support the conclusion that the risk of malaria is higher among children with SCD than it is among children without SCD in a rural area on the coast of Kenya. Further studies should be undertaken to help policy makers develop appropriate guidelines regarding malarial prophylaxis for patients with SCD in malaria-endemic regions. Hide abstract
We report a genome-wide association (GWA) study of severe malaria in The Gambia. The initial GWA scan included 2,500 children genotyped on the Affymetrix 500K GeneChip, and a replication study included 3,400 children. We used this to examine the performance of GWA methods in Africa. We found considerable population stratification, and also that signals of association at known malaria resistance loci were greatly attenuated owing to weak linkage disequilibrium (LD). To investigate possible solutions to the problem of low LD, we focused on the HbS locus, sequencing this region of the genome in 62 Gambian individuals and then using these data to conduct multipoint imputation in the GWA samples. This increased the signal of association, from P = 4 × 10(-7) to P = 4 × 10(-14), with the peak of the signal located precisely at the HbS causal variant. Our findings provide proof of principle that fine-resolution multipoint imputation, based on population-specific sequencing data, can substantially boost authentic GWA signals and enable fine mapping of causal variants in African populations. Hide abstract
High cerebral blood flow velocity (CBFv) and low haemoglobin oxygen saturation (SpO(2)) predict neurological complications in sickle cell anaemia (SCA) but any association is unclear. In a cross-sectional study of 105 Kenyan children, mean CBFv was 120 +/- 34.9 cm/s; 3 had conditional CBFv (170-199 cm/s) but none had abnormal CBFv (>200 cm/s). After adjustment for age and haematocrit, CBFv > or =150 cm/s was predicted by SpO(2) < or = 95% and history of fever. Four years later, 10 children were lost to follow-up, none had suffered neurological events and 11/95 (12%) had died, predicted by history of fever but not low SpO(2). Natural history of SCA in Africa may be different from North America and Europe. Hide abstract
Large-scale studies of genomic variation could assist efforts to eliminate malaria. But there are scientific, ethical and practical challenges to carrying out such studies in developing countries, where the burden of disease is greatest. The Malaria Genomic Epidemiology Network (MalariaGEN) is now working to overcome these obstacles, using a consortial approach that brings together researchers from 21 countries. © 2008 Macmillan Publishers Limited. All rights reserved. Hide abstract
PLoS Med, 4 (4), pp. e95. | Read more2007. Valid consent for genomic epidemiology in developing countries.
Sickle cell disease (SCD) has recently been recognised as a problem of major public-health significance by the World Health Organization. Despite the fact that >70% of sufferers live in Africa, expenditure on the related care and research in the continent is negligible, and most advances in the understanding and management of this condition have been based on research conducted in the North. In order to target limited resources, African countries need to focus research and interventions on areas that will lead to the maximum impact. This review details the epidemiological and clinical background of SCD, with an emphasis on Africa, before identifying the research priorities that will provide the necessary evidence base for improving the management of African patients. Malaria, bacterial and viral infections and cerebrovascular accidents are areas in which further research may lead to a significant improvement in SCD-related morbidity and mortality. As patients with high concentrations of foetal haemoglobin (HbF) appear to be protected from all but mild SCD, the various factors and pharmacological agents that might increase HbF levels need to be assessed in Africa, as options for interventions that would improve quality of life and reduce mortality. Hide abstract
DEVELOPMENTAL MEDICINE AND CHILD NEUROLOGY, 48 pp. 13-14.2006. Spectrum of cerebral blood flow velocities measured by transcranial Doppler ultrasonography in children with sickle cell disease in Africa
East Afr Med J, 81 (12), pp. 657-659. Read abstract2004. Stroke in sickle cell disease in Africa: case report.
Stroke, including asymptomatic cerebrovascular events, is a significant cause of morbidity and mortality in sickle cell disease, occurring with an incidence of 10 to 25%. Extensive research has established that cerebral stenosis, involving the circle of Willis, is the most common mechanism in children. We report a child with sickle cell disease who presented with cortical blindness and right-sided hemiplegia. Computerised tomography of the brain revealed an infarct involving the left parietal region and extending to the occipital region. Stroke in SCD is multifactorial, but high-risk individuals can be identified by simple well-established strategies such as transcranial doppler ultrasonography. There are approaches for both primary and secondary interventions, which have been shown to be effective and need to be incorporated into management guidelines for SCD patients. Before schemes are recommended into health care policies, research in the appropriate setting is required. Hide abstract
BACKGROUND: Cerebral malaria is commonly diagnosed in adults in endemic areas in Africa, both in hospitals and in the community. This presents a paradox inconsistent with the epidemiological understanding that the development of immunity during childhood confers protection against severe disease in adult life. AIM: To establish the contribution of Plasmodium falciparum infection in adults admitted with neurological dysfunction in an endemic area, to assess the implications of an admission clinical diagnosis of 'cerebral malaria' on the treatment and clinical outcome, and to describe the clinical features of patients with malaria parasitaemia. DESIGN: Prospective observational study. METHODS: We studied adult patients admitted with neurological dysfunction to Muhimbili National Hospital, Dar-es-Salaam, Tanzania from October 2000 to July 2001. A full blood count was done and serum creatinine, blood glucose and P. falciparum parasite load were measured. RESULTS: Of 199 patients (median age 34.6 years), 38% were diagnosed as 'cerebral malaria' on admission, but only 7.5% had detectable parasitaemia, giving a positive predictive value of 13.3%. Only 1% fulfilled the WHO criteria for cerebral malaria. The prevalence of parasitaemia (7.5%) was less than that observed in a group of asymptomatic controls (9.3%), but distribution of parasite densities was higher in the patients. Mortality was higher in patients with no parasitaemia (22.3%) than in those with parasitaemia (13%). DISCUSSION: Cerebral malaria was grossly overdiagnosed, resulting in unnecessary treatment and insufficient investigation of other possible diagnoses, which could lead to higher mortality. Extension of this misperception to the assessment of cause of death in community surveys may lead to an overestimation of the impact of malaria in adults. Hide abstract