Socio-economic determinants are not major risk factors for severe malaria in Gambian children

Receipt of antimalarials among children aged 6-59 months in Nigeria from 2010 to 2021

BACKGROUND

Nigeria has the highest malaria burden globally, and anti-malarials have been commonly used to treat malaria without parasitological confirmation. In 2012, Nigeria implemented rapid diagnostic tests (RDTs) to reduce the use of anti-malarials for those without malaria and to increase the use of artemisinin-based combination therapy (ACT) for malaria treatment. This study examined changes in anti-malarial receipt among children aged 6-59 months during a 12-year period of increasing RDT availability.

METHODS

A cross-sectional analysis was conducted using the Nigeria Malaria Indicator Survey (NMIS) data from 2010 (before RDT implementation in 2012), 2015, and 2021. The analysis assessed trends in prevalence of malaria by survey RDT result, and fever and anti-malarial/ACT receipt in the 2 weeks prior to the survey. A multivariable logistic regression was used to account for the complex survey design and to examine factors associated with anti-malarial receipt, stratified by survey RDT result, a proxy for recent/current malaria infection.

RESULTS

In a nationally-representative, weighted sample of 22,802 children aged 6-59 months, fever prevalence remained stable over time, while confirmed malaria prevalence decreased from 51.2% in 2010 to 44.3% in 2015 and 38.5% in 2021 (trend test p < 0.0001). Anti-malarial use among these children decreased from 19% in 2010 to 10% in 2021 (trend test p < 0.0001), accompanied by an increase in ACT use (2% in 2010 to 8% in 2021; trend test p < 0.0001). Overall, among children who had experienced fever, 30.6% of survey RDT-positive and 36.1% of survey RDT-negative children had received anti-malarials. The proportion of anti-malarials obtained from the private sector increased from 61.8% in 2010 to 80.1% in 2021 for RDT-positive children; most of the anti-malarials received in 2021 were artemisinin-based combinations. Factors associated with anti-malarial receipt for both RDT-positive and RDT-negative children included geographic region, greater household wealth, higher maternal education, and older children.

CONCLUSION

From 2010 to 2021 in Nigeria, both malaria prevalence and anti-malarial treatments among children aged 6-59 months decreased, as RDT availability increased. Among children who had fever in the prior 2 weeks, anti-malarial receipt was similar between children with either positive or negative survey RDT results, indicative of persistent challenges in reducing inappropriate anti-malarials uptake.

Estimating the malaria transmission over the Indian subcontinent in a warming environment using a dynamical malaria model

Malaria is a major public health problem in India. The malaria transmission is sensitive to climatic parameters. The regional population-related factors also influence malaria transmission. To take into account temperature and rainfall variability and associated population-related effects (in a changing climate) on the malaria transmission over India, a regional dynamical malaria model, namely VECTRI (vector-borne disease community model) is used. The daily temperature and rainfall data derived from the historical (years 1961-2005) and representative concentration pathway (years 2006-2050) runs of the Coupled Model Intercomparison Project Phase 5 models have been used for the analysis. The model results of the historical run are compared with the observational data. The spatio-temporal changes (region-specific as well as seasonal changes) in the malaria transmission as a result of climate change are quantified over the India. The parameters related to the breeding cycle of malaria as well as those which estimate the malaria cases are analyzed in the global warming scenario.

Reproductive-Age Women's Knowledge and Care Seeking for Malaria Prevention and Control in Ghana: Analysis of the 2016 Malaria Indicator Survey

INTRODUCTION

Malaria is a major cause of morbidity and mortality worldwide, requiring individual and environmental level controls to prevent its adverse morbidity effects. This study examined reproductive-aged women's knowledge and care-seeking practices for malaria prevention and control in Ghana.

METHODS

The 2016 Ghana Malaria Indicator Survey data for reproductive-age women was analysed (n=5,150). Multilevel mixed-effects logistic regression model was used to determine factors associated with reproductive-aged women's knowledge and care-seeking practices for malaria.

RESULTS

62.3%, 81.3%, and 64.6% knowledge levels on causes, signs/symptoms, and prevention of malaria were found, respectively, among respondents. Age, wealth and educational status, religion, region, and place of residence (rural) were found to significantly influence respondents' knowledge of causes, signs/symptoms, and care-seeking practices for malaria. A 15% differential among Insecticide Treated Nets (ITNs) awareness and use was found. Increasing age (≥35 years) was associated with increasing knowledge of malaria. Regional variations were observed to significantly influence knowledge of malaria treatment.

CONCLUSION

Though ownership of ITNs and knowledge of malaria prevention were high, it did not necessarily translate into use of ITNs. Thus, there is a need to intensify education on the importance and the role of ITNs use in the prevention of malaria.

Demographic, Socioeconomic, and Geographic Factors Leading to Severe Malaria and Delayed Care Seeking in Ugandan Children: A Case-Control Study

We studied associations between delayed care seeking, demographic, socioeconomic, and geographic factors and likelihood of severe malaria in Ugandan children. The study was based at Jinja Hospital, Uganda. We enrolled 325 severe malaria cases and 325 uncomplicated malaria controls matched by age and residence. Patient details, an itinerary of events in response to illness, household information, and location of participants' residences were captured. Conditional logistic regression was used to determine risk factors for severe malaria and delayed care seeking. Delayed care seeking (≥ 24 hours after fever onset; odds ratio [OR] 5.50; 95% confidence interval [CI] 2.70, 11.1), seeking care at a drug shop as the initial response to illness (OR 3.62; 95% CI 1.86, 7.03), and increasing distance from place of residence to the nearest health center (OR 1.45; 95% CI 1.17, 1.79) were independent risk factors for severe malaria. On subgroup analysis, delayed care seeking was a significant risk factor in children with severe malaria attributable to severe anemia (OR 15.6; 95% CI 3.02, 80.6), but not unconsciousness (OR 1.13; 95% CI 0.30, 4.28). Seeking care at a drug shop (OR 2.84; 95% CI 1.12, 7.21) and increasing distance to the nearest health center (OR 1.18; 95% CI 1.01, 1.37) were independent risk factors for delayed care seeking. Delayed care seeking and seeking care at a drug shop were risk factors for severe malaria. Seeking care at a drug shop was also a predictor of delayed care seeking. The role of drug shops in contributing to delayed care and risk of severe malaria requires further study.

House Structure Is Associated with Plasmodium falciparum Infection in a Low-Transmission Setting in Southern Zambia

House structure may influence the risk of malaria by affecting mosquito entry and indoor resting. Identification of construction features associated with protective benefits could inform vector control approaches, even in low-transmission settings. We examined the association between house structure and malaria prevalence in a cross-sectional analysis of 2,788 children and adults residing in 866 houses in a low-transmission area of Southern Province, Zambia, over the period 2008-2012. Houses were categorized according to wall (brick/cement block or mud/grass) and roof (metal or grass) material. Malaria was assessed by point-of-care rapid diagnostic test (RDT) for Plasmodium falciparum. We identified 52 RDT-positive individuals residing in 41 houses, indicating an overall prevalence in the sample of 1.9%, ranging from 1.4% to 8.8% among the different house types. Occupants of higher quality houses had reduced odds of P. falciparum malaria compared with those in the lowest quality houses after controlling for bed net use, indoor insecticide spraying, clustering by house, cohabitation with another RDT-positive individual, transmission season, ecologic risk defined as nearest distance to a Strahler-classified third-order stream, education, age, and gender (adjusted odds ratio [OR]: 0.26, 95% confidence interval [CI]: 0.09-0.73, P = 0.01 for houses with brick/cement block walls and metal roof; OR: 0.22, 95% CI: 0.09-0.52, P < 0.01 for houses with brick/cement block walls and grass roof). Housing improvements offer a promising approach to vector control in low-transmission settings that circumvents the threat posed by insecticide resistance, and may confer a protective benefit of similar magnitude to current vector control strategies.

Knowledge, attitudes and practices of malaria in Colombia

Background

Although Colombia has witnessed an important decrease in malaria transmission, the disease remains a public health problem with an estimated ~10 million people currently living in areas with malaria risk and ~61,000 cases reported in 2012. This study aimed to determine and compare the level of knowledge, attitudes and practices (KAP) about malaria in three endemic communities of Colombia to provide the knowledge framework for development of new intervention strategies for malaria elimination.

Methods

A cross-sectional KAP survey was conducted in the municipalities of Tierralta, Buenaventura and Tumaco, categorized according to high risk (HR) and moderate risk (MR) based on the annual parasite index (API). Surveys were managed using REDCap and analysed using MATLAB and GraphPad Prism.

Results

A total of 267 residents, mostly women (74%) were surveyed. Although no differences were observed on the knowledge of classical malaria symptoms between HR and MR regions, significant differences were found in knowledge and attitudes about transmission mechanisms, anti-malarial use and malaria diagnosis. Most responders in both regions (93.5% in MR, and 94.3% in HR areas) indicated use of insecticide-treated nets (ITNs) to protect themselves from malaria, and 75.5% of responders in HR indicated they did nothing to prevent malaria transmission outdoors. Despite a high level of knowledge in the study regions, significant gaps persisted relating to practices. Self-medication and poor adherence to treatment, as well as lack of both indoor and outdoor vector control measures, were significantly associated with higher malaria risk.

Conclusions

Although significant efforts are currently being made by the Ministry of Health to use community education as one of the main components of the control strategy, these generic education programmes may not be applicable to all endemic regions of Colombia given the substantial geographic, ethnic and cultural diversity.

Significance of travel to rural areas as a risk factor for malarial anemia in an urban setting

The epidemiology of malaria in urban environments is poorly characterized, yet increasingly problematic. We conducted an unmatched case-control study of risk factors for malarial anemia with high parasitemia in urban Kisumu, Kenya, from June 2002 through February 2003. Cases (n = 80) were hospital patients with a hemoglobin level < or = 8 g/dL and a Plasmodium parasite density > or = 10,000/microL. Controls (n = 826) were healthy respondents to a concurrent citywide knowledge, attitude, and practice survey. Children who reported spending at least one night per month in a rural area were especially at risk (35% of cases; odds ratio = 9.3, 95% confidence interval [CI] = 4.4-19.7, P < 0.0001), and use of mosquito coils, bed net ownership, and house construction were non-significant, potentially indicating that malaria exposure during rural travel comprises an important element of risk. Control of severe malaria in an urban setting may be complicated by Plasmodium infections acquired elsewhere. Epidemiologic studies of urban malaria in low transmission settings should take travel history into account.

Malaria is associated with poor school performance in an endemic area of the Brazilian Amazon

Background

Approximately 40% of the world's population is at risk for malaria. In highly endemic tropical areas, malaria is a major cause of morbidity and mortality during infancy. There is a complex interrelationship between malaria, malnutrition and intestinal helminths, and this may impair cognitive development in children. The aim of this study was to determine the relationship between malaria and school performance in children living in an endemic area where Plasmodium vivax is the species responsible for most of the cases.

Methods

The study was conducted in the Municipality of Careiro, Amazonas, Brazil, with five to14 year-old children, studying the first eight grades of public school, during the year 2008. After an initial active case detection, during nine months of follow-up, passive malaria cases detection was instituted, through a thick blood smear performed in every child with fever. School performance was evaluated by the final notes in Mathematics and Portuguese Language. Performance was considered poor when either of the final notes in these disciplines was below the 50^th percentile for the respective class and grade.

Results

The total number of students followed-up in the cohort was 198. Malarial attacks were reported in 70 (35.4%) of these students, with no cases of severe disease. Plasmodium vivax was detected in 69.2% of the attacks, Plasmodium falciparum in 25.5% and both species in 5.3%. In the multivariate analysis, adjusting for age, mother's education, time living in the study area and school absenteeism, presenting with at least one episode of malaria independently predicted a poor performance at school [OR = 1.91 (1.04-3.54); p = 0.039].

Conclusion

Non-severe malaria compromises the school performance of children even during a nine-month follow-up, potentially contributing to the maintenance of underdevelopment in countries endemic for malaria. This is the first evidence of such impact in Latin America, where P. vivax is responsible for the majority of the cases.

Socio-economic status is inversely related to bed net use in Gabon

BACKGROUND

Insecticide-treated bed nets (ITNs) range among the most effective measures of malaria prophylaxis, yet their implementation level in sub-Saharan Africa is still low. The goal of this study was to investigate the influence of socio-economic factors on the use of bed nets by mothers in Gabon.

METHODS

A cross-sectional study was conducted completing pre-tested, interviewer-administered questionnaires exploring socioeconomic proxy measures with 397 mothers or guardians of young children. Respondents were grouped according to their socio-economic situation, using scores. The condition of the bed nets was evaluated during a home visit.

RESULTS

Socio-economic factors of wellbeing were negatively associated with bed net use, such as living in a stone house (OR 0.26, 95% CI 0.14-0.48), running water in the house (OR 0.44, 95% CI 0.21-0.92), shower/flush toilet in the house (OR 0.39/0.34, 95% CI 0.21-0.75/0.16-0.73), ownership of a freezer (OR 0.50, 95% CI 0.26-0.96) and belonging to the highest group in the economic score (OR 0.32, 95% CI 0.15-0.67). In contrast, similar factors were positively associated with a good maintenance condition of the bed nets: higher monthly income (OR 5.64, 95% CI 2.41-13.19) and belonging to the highest group in the economic score (OR 2.55, 95% CI 1.19 - 5.45).

CONCLUSION

Among the poorest families in Lambaréné the coverage with untreated nets (UTNs) is the highest, but the condition of these UTNs is the worst. To achieve a broad implementation of ITNs in Lambaréné, there is an urgent need for educational programmes as well as need-tailored marketing strategies for ITNs.

Who develops severe malaria? Impact of access to healthcare, socio-economic and environmental factors on children in Yemen: a case-control study

OBJECTIVE

To investigate the impact of socio-economic and environmental factors on developing severe malaria in comparison with mild malaria in Yemen.

METHOD

Case-control study comparing 343 children aged 6 months to 10 years diagnosed with WHO-defined severe malaria (cases) at the main children's hospital in Taiz and 445 children with mild malaria (controls) diagnosed in the health centres, which serve the areas where the cases came from.

RESULTS

In univariate analysis, age <1 year, distance from health centre, delay to treatment and driving time to health centre were associated with progression from mild to severe malaria. In multivariate analysis, distance to nearest health centre >2 km was significantly associated with progression to severe disease. Environmental and vector control factors associated with protection from acquiring malaria (such as sleeping under bednets) were not associated with protection from moving from mild to severe disease.

CONCLUSIONS

Innovative ways to improve access to antimalarial treatment for those living more then 2 km away from health centres such as home management of malaria, especially for infants and young children, should be explored in malaria-endemic areas of Yemen.

Malaria and helminth interactions in humans: an epidemiological viewpoint

In the tropics, helminths are among the most common chronic infections of humans and Plasmodium infections the most deadly. As these two groups of parasites have similar geographical distributions, co-infection is commonplace. It has increasingly been speculated that helminth infections may alter susceptibility to clinical malaria, and there is now increasing interest in investigating the consequences of co-infection, with studies yielding contrasting results. The immunological interactions between helminths and malarial parasites are unclear, although several hypotheses have been proposed. This review provides an epidemiological overview of the possible interactions between helminths and malarial parasites, in relation to geographical distributions and disease patterns, and provides a critical discussion of the results of the epidemiological studies that have so far been conducted to investigate the possible associations. Future studies that might be considered, in order to address the gaps in knowledge, are also considered.

The co-distribution of Plasmodium falciparum and hookworm among African schoolchildren

Background

Surprisingly little is known about the geographical overlap between malaria and other tropical diseases, including helminth infections. This is despite the potential public health importance of co-infection and synergistic opportunities for control.

Methods

Statistical models are presented that predict the large-scale distribution of hookworm in sub-Saharan Africa (SSA), based on the relationship between prevalence of infection among schoolchildren and remotely sensed environmental variables. Using a climate-based spatial model of the transmission potential for Plasmodium falciparum malaria, adjusted for urbanization, the spatial congruence of populations at coincident risk of infection is determined.

Results

The model of hookworm indicates that the infection is widespread throughout Africa and that, of the 179.3 million school-aged children who live on the continent, 50.0 (95% CI: 48.9–51.1) million (27.9% of total population) are infected with hookworm and 45.1 (95% CI: 43.9–46) million are estimated to be at risk of coincident infection.

Conclusion

Malaria and hookworm infection are widespread throughout SSA and over a quarter of school-aged children in sub-Saharan Africa appear to be at risk of coincident infection and thus at enhanced risk of clinical disease. The results suggest that the control of parasitic helminths and of malaria in school children could be viewed as essential co-contributors to promoting the health of schoolchildren.

Pallor as a sign of anaemia in small Tanzanian children at different health care levels

BACKGROUND

Anaemia is a major complication of Plasmodium falciparum malaria among small children in sub-Saharan Africa. We studied the performance of the Integrated Management of Childhood Illness (IMCI) recommended assessment of no/some/severe pallor as predictor of anaemia in health surveys at community level and in clinical practice in an out patient department (OPD) and in a hospital ward in rural Tanzania.

METHODS

The study was undertaken among 6-36 months old children. Pallor was evaluated as a combined assessment of conjunctiva, tongue and palms and categorised as no, some or severe pallor. Packed cell volume (PCV) was measured and related to pallor.

FINDINGS

A total of 740 examinations were performed at village, OPD and in the hospital ward. The prevalences of severe pallor were 0%, 1.5% and 7% respectively. The prevalences of any pallor were 14%, 41% and 86%. The prevalences of severe anaemia (PCV<21%) were 1%, 5% and 81% and of any anaemia (PCV<33%) 68%, 73% and 98%. Severe pallor could not detect severe anaemia. The sensitivities were only 0%, 0% and 8%. The sensitivities of any pallor to detect severe anaemia were however 86% and 98% for children at the health care facility level, but still of relatively poor predictive values since the specificities were only 61% and 68%.

INTERPRETATION

Division of pallor into some or severe degrees was of no use at any health care level. The identification of any pallor was of no use at village level, but it may possibly be of some value as a screening test for severe anaemia at health care facilities, if additional assessment is included in view of the low specificity and positive predictive value of the finding.

C, Pineros J. JG, Arboleda N. M, Blair T. S, Carmona-Fonseca J. Epidemiologia de la malaria falciparum complicada: estudio de casos y controles en Tumaco y Turbo, Colombia, 2003

OBJETIVOS: Identificar aspectos del hospedero, del parásito y del ambiente asociados con ocurrencia de malaria por Plasmodium falciparum complicada. MÉTODOS: Estudio de casos y controles en pacientes de Tumaco y Turbo (Colombia) aplicando los criterios de complicación de la Organización Mundial de la Salud. RESULTADOS: Entre noviembre 2002 y julio 2003 se captaron 64 casos (malaria complicada) y 135 controles (malaria no complicada). Las complicaciones fueron: hiperparasitemia (40%), falla hepática (36%), síndrome dificultad respiratoria aguda (7%), falla renal (4%), trombocitopenia grave (3%), anemia grave (2%), malaria cerebral (2%) e hipoglicemia grave (1%). Se encontraron como factores de riesgo para malaria falciparum complicada: a) Los antecedentes de malaria falciparum durante el último año fueron menores en los casos (OR= 7.0 (1.2-43.6) P=0.019); b) Mayor uso previo de antimaláricos en los casos (OR=2.2 (1.1-4.4) P=0.031) y c) mayor uso de cloroquina en los casos (OR=7.4 (1.1-7.8) P=0.017). Se hallaron los alelos MAD-20 y K1 del gen msp1 y FC-27 e IC-1 del gen msp2, cuya distribución de frecuencias fue similar entre casos y controles, aunque el alelo K1 mostró una variación importante entre grupos (casos: 9.4%, controles: 3.5%). La frecuencia de "signos de peligro" fue significativamente mayor en los casos (OR= 3.3, (1.5-7.4) P=0.001). Los criterios de complicación malárica de la Organización Mundial de la Salud se comparan con otros y se discuten algunas implicaciones. CONCLUSIÓN: Se identificaron como factores de riesgo para malaria falciparum complicada, la ausencia de antecedentes de malaria falciparum en el último año y el uso de antimaláricos antes de llegar al hospital.

Household decision-making process and childhood cerebral malaria in The Gambia

Mortality from childhood cerebral malaria remains unacceptably high in endemic regions. This survey was conducted between June and December 2001 among 69 primary caregivers of children admitted for cerebral malaria in Bansang Hospital, Central River Division (CRD), The Gambia to describe decision-making process at the family level that could have impact on malaria mortality. Thirty two percent of children presented in coma after 24 h of onset of illness. The eldest person in the compound or the father was responsible for taking decision on when hospital treatment was necessary in 85% of the cases. Mothers who were the primary caregivers made such decisions only in 7% of the cases. Cultural norms in a community are important factors affecting preferences at the household level and could influence important medical decisions. This survey suggests that patriarchs and/or fathers are important target groups for health education and project implementation programs.

Malaria in southern Mozambique: incidence of clinical malaria in children living in a rural community in Manhiça district

We estimated the incidence of clinical malaria episodes by weekly home-based active case detection between December 1996 and July 1999 in 2 groups of children in Manhiça district in southern Mozambique. Cohort 1 comprised a random sample of children aged <10 years at recruitment and cohort 2 comprised newborns. A blood slide was taken if the axillary temperature was 7.5 degrees C or if the child was reported to have been febrile over the previous 24 h. A total of 1966 children were followed-up. Malaria occurred all year round. The number of clinical malaria episodes ranged from 0 to 6 per child. No clinical malaria episodes were detected in 71% of children or in children aged <2 months. Those aged 6 months to <4 years showed the highest incidence ranging from 0.65 to 0.74 episodes per 100 person-weeks at risk, indicating that infants and young children were at highest risk. Malaria transmission is perennial in this district of Mozambique with some seasonality. Significant differences were observed in the spatial incidence of malaria episodes in regions just a few miles apart with a higher incidence in children living near the river or in swampy areas. These findings strengthen the need for improved control measures targeted at infancy and early childhood.

Carriage of chloroquine-resistant parasites and delay of effective treatment increase the risk of severe malaria in Gambian children

Two hundred thirty-four Gambian children with severe falciparum malaria who were admitted to the pediatric ward of a rural district hospital each were matched for age with a same-sex control subject presenting as an outpatient with uncomplicated falciparum malaria. Severe malarial anemia (SMA) was the most common presentation (152 cases), followed by cerebral malaria (38 cases) and hyperparasitemia (26 cases). Children presenting with SMA were significantly younger and more likely to carry gametocytes than were children with other severe presentations. Alleles of the genes pfcrt and pfmdr1 associated with chloroquine-resistant parasites occurred together among cases presenting with SMA alone more often than among their matched controls (odds ratio, 2.08 [95% confidence interval, 1.04-4.38]; P=.039). Costs of travel to the hospital of more than US $0.20, use of mosquito repellents, and carriage of resistant parasites were identified as independent risk factors for severe malaria in the case-control analysis. We conclude that, in this setting, poor access to the hospital and a high prevalence of chloroquine-resistant parasites lead to a delay of adequate treatment for young children with malaria, who may then develop SMA.

Risk factors for severe malaria in Bamako, Mali: a matched case-control study

The aim of this case-control study was to identify epidemiological risk factors for severe malaria among children living in Bamako, a malaria-endemic area. For this, 260 healthy community controls were matched to 130 patients with severe malaria. Conditional multiple logistic regression analysis indicated that all examined independent factors associated with severe malaria are directly related to characteristics of the child's mother, with the exception of the child's own yellow fever vaccination history (odds ratio (OR): 1.93, 95% confidence intervals (CI(95%)) [1.10-3.37]). The following characteristics were all associated with a decreased risk of severe malaria in the child: maternal education (OR: 0.52, CI(95%) [0.31-0.86]), the mother's adequate knowledge about malaria (OR: 0.46, 95% CI(95%) [0.25-0.86]), her use of mosquito bed nets (OR: 0.53, CI(95%) [0.30-0.92]) and breast-feeding for at least 2 years (OR: 0.57, CI(95%) [0.33-0.94]). Conversely, chronic maternal disease (OR: ?3.16, CI(95%) [1.31-7.61]) was associated with an increased risk of severe malaria. These findings strongly support the hypothesis that maternal factors are central to the development of severe malaria in children. Programmes aiming to improve both maternal health and maternal education may reduce the incidence of severe malaria in children and should therefore be advocated in Bamako and in areas with similar epidemiological patterns for malaria.

Malaria parasitaemia in relation to HIV status and vitamin A supplementation among pre-school children

OBJECTIVES

To ascertain whether malaria parasitaemia in children is associated with HIV status. To examine the effect of vitamin A supplementation on malaria parasitaemia in children.

METHODS

We studied the cross-sectional associations between HIV status and malaria parasitaemia among 546 children 6-60 months of age who participated in a double-blind, randomized clinical trial of vitamin A supplementation. Prevalence ratios and 95% confidence intervals (CI) were estimated for the presence of malaria parasites at baseline by HIV status in uni- and multivariate models that adjusted for sociodemographic and environmental variables. Among children with malaria, correlates of high parasite loads were identified. Next, we examined the effect of vitamin A supplementation on the risk of malaria parasitaemia and high parasite density at 4-8 months of the first dose in a subset of children.

RESULTS

The prevalence of malaria parasitaemia was 11.4% among HIV-infected children, compared with 27.6% among uninfected. After adjusting for season, anaemia, use of bednets, maternal education and indicators of socioeconomic status, we found some evidence for lower prevalence of parasitaemia among HIV positive compared with HIV-negative children (prevalence ratio=0.56; 95% CI=0.29, 1.09; P=0.09). Other important correlates of malaria parasitaemia at baseline included low level of maternal education, poor quality of water supply, and the presence of animals at home. Vitamin A supplementation did not have a significant effect on malaria parasitaemia at 4-8 months of follow-up, overall or within levels of potential effect modifiers.

CONCLUSION

HIV infection appears to be negatively correlated with malaria parasitaemia in this group of children. Investing in women's education is likely to decrease the prevalence of malaria parasitaemia in children. Vitamin A supplementation does not seem to have an effect on malaria parasitaemia in this population; possible benefits against clinical episodes and severe malaria deserve further examination.

Which children come to the health centre for treatment of malaria?

Malaria remains one of the major public health problems for children in Guinea-Bissau and the major reason for using the health services. Little is known about factors with impact on whether the mothers seek malaria treatment for their children at a health centre. Mothers of children coming to the Bandim Health Centre in Bissau and age-matched controls selected from the registration system of the Bandim Health Project were interviewed about treatment habits, socio-economic standards and other factors associated with the mother seeking treatment for her child at a health centre. In a multivariate analysis, the controls were more often found to have chloroquine at home and had more often taken home treatment for suspected malaria. On average 2.97 persons among cases shared bed as opposed to only 2.02 among controls, bed-crowding thus, being a factor determining health seeking behaviour (P=0.0001). Low socio-economic status, as measured by the non-availability of electricity, was also a significant predicting factor (P=0.02). The possibilities of promoting home treatment should be further evaluated, not only to avoid unnecessary visits to the professional health system, but also to decrease the morbidity from acute malaria.

The contribution of health-care services to a sound and sustainable malaria-control policy

HIV and AIDS, tuberculosis, and malaria, besides presenting a large mortality and morbidity burden in developing countries, are also responsible for poor economic development. In the past international agencies devoted resources and efforts to control malaria and other diseases without taking into account health-system performance and sustainability. Even assuming that the Global Fund to Fight AIDS, Tuberculosis, and Malaria (GFATM)--a recent international initiative--would provide the necessary funds, a poorly performing health-care system will not be able to use these funds optimally. Moreover, even if all interventions are cost-effective, their impact on mortality and morbidity will only be marginal if access to proper care is not guaranteed. It is the responsibility of scientists and health managers to highlight to donor agencies the importance of an accessible and well functioning health-care system at all levels for the control of specific diseases.

Risk factors for presentation to hospital with severe anaemia in Tanzanian children: a case-control study

In malaria endemic areas anaemia is a usually silent condition that nevertheless places a considerable burden on health services. Cases of severe anaemia often require hospitalization and blood transfusions. The objective of this study was to assess risk factors for admission with anaemia to facilitate the design of anaemia control programmes. We conducted a prospective case-control study of children aged 2-59 months admitted to a district hospital in southern Tanzania. There were 216 cases of severe anaemia [packed cell volume (PCV) < 25%] and 234 age-matched controls (PCV > or = 25%). Most cases [55.6% (n = 120)] were < 1 year of age. Anaemia was significantly associated with the educational level of parents, type of accommodation, health-seeking behaviour, the child's nutritional status and recent and current medical history. Of these, the single most important factor was Plasmodium falciparum parasitaemia [OR 4.3, 95% confidence interval (CI) 2.9-6.5, P < 0.001]. Multivariate analysis showed that increased recent health expenditure [OR 2.2 (95% CI 1.3-3.9), P = 0.005], malnutrition [OR 2.4 (95%CI 1.3-4.3), P < 0.001], living > 10 km from the hospital [OR 3.0 (95% CI 1.9-4.9), P < 0.001], a history of previous blood transfusion [OR 3.8 (95% CI 1.7-9.1), P < 0.001] and P. falciparum parasitaemia [OR 9.5 (95% CI 4.3-21.3), P < 0.001] were independently related to risk of being admitted with anaemia. These findings are considered in terms of the pathophysiological pathway leading to anaemia. The concentration of anaemia in infants and problems of access to health services and adequate case management underline the need for targeted preventive strategies for anaemia control.

Intestinal helminths and malnutrition are independently associated with protection from cerebral malaria in Thailand

Although human infection with Ascaris appears to be associated with protection from cerebral malaria, there are many potential socio-economic and nutritional confounders related to helminth infection that need to be considered. In a hospital-based study, 37 cases of cerebral malaria and 61 cases of non-severe malaria with high parasite biomass (i.e. hyperparasitaemia and/or circulating schizonts) answered a structured questionnaire and were screened for intestinal helminths. Logistic regression was then used to adjust for the potential confounders. The adjusted odds ratios (OR) and their 95% confidence intervals (CI) still showed a significant protective association for helminths (OR = 0.24; CI = 0.07-0.78, P = 0.02) and malnutrition (OR = 0.11; CI = 0.02-0.58; P = 0.01), with no evidence of interaction between the two. There was also a significant dose-effect trend for the helminth infections (P = 0.048). These results, despite coming from a hospital-based study, indicate that the apparent association between helminths and protection from cerebral malaria is not the result of socio-economic or nutritional confounders.

Case-control studies on host factors in severe malaria

Although molecular biology has illustrated the phenotypic heterogeneity of Plasmodium falciparum, there are still no specific markers of virulence. As parasite virulence is an important determinant of severe malaria, the choice of comparison groups in the study of host factors influencing severity is a delicate issue. Ignoring parasite factors in the selection of controls potentially leads to biased comparisons between a majority of cases with virulent parasites and a majority of controls with non-virulent parasites. This article discusses how to avoid this virulence bias in the absence of specific markers of virulence.

Socio-economic and environmental protective/risk factors for severe malaria in Thailand

We conducted a cross-sectional study to identify the socio-economic and environmental protective/risk factors for severe malaria in Thailand. Forty-six cases of severe malaria, 72 cases of non-severe malaria with high parasite biomass and 40 mild malaria cases were included. When comparing severe malaria and non-severe malaria with high parasite biomass, specific logistic regression models showed a significant protective effect for helminths, adjusted odds ratio 0.24 (0.07-0.78) for low body mass index (BMI), adjusted odds ratio 0.11 (0.02-0.58). When comparing severe and mild malaria, a longer residence duration, adjusted odds ratio 0.36 (0.09-0.83) and the use of antimalarial self-medication, adjusted odds ratio 0.08 (0.009-0.84) were associated with protection from severe malaria. Using stepwise logistic regression with all the variables inserted in the model yielded similar results. These findings suggest specific immunity and self-medication control parasite multiplication whereas helminths and malnutrition more specifically affect the pathogenesis of severe malaria.

No influence of socioeconomic factors on severe malarial anaemia, hyperparasitaemia or reinfection

Malaria is responsible for nearly 500 million clinical cases per year, only a small proportion of whom will become severely ill. Socioeconomic risk factors may play a role in the development of severe malaria in African children and in their susceptibility to reinfection. In Gabon, 100 children suffering from severe malaria, defined as hyperparasitaemia and/or severe anaemia, were matched for sex, age and provenance to 100 children with mild malaria. Socioeconomic factors were assessed using a standard questionnaire and compared between the 2 groups. The children were followed-up and the time to first reinfection was recorded. No significant influence of socioeconomic factors could be detected on the severity of disease or the time to first reinfection. Socioeconomic factors are not major determinants of severe malarial anaemia and hyperparasitaemia in children in Gabon.

Nutritional status of children admitted to hospital with different diseases and its relationship to outcome in The Gambia, West Africa

Admission records from two paediatric units in The Gambia were used to explore the relationship between admission weight and different diseases. In total 13579 hospitalized children were analysed. For comparison, 7399 children were recruited from several surveys of well subjects to provide anthropometric values for healthy Gambian children. Compared to the control children, mean admission weights were lower for malaria (weight for age z-score: -1.602), cerebral malaria (-1.547), transfused malarial anaemia (-1.764), pneumonia (-1.725), meningitis (-1.362), gastro-enteritis (-2.497) and malnutrition (-3.786). Children with bronchiolitis did not have a significantly different weight for age than the controls. Outcome of the hospital admission was recorded and related to the weight on admission. In all disease categories the death rate rose with decreasing admission weight with the exception of bronchiolitis. For all diseases taken together, case fatality was 7.2% for children with a weight for age z-score above -2 Standard Deviations (SD), 9.3% between -2 and -3 SD, 15.6% between -3 and -4 SD and 22.7% for children with weight for age SD z-scores less than -4. Malnourished children are more susceptible to several infectious diseases frequently seen in developing countries and nutritional interventions, as well as standard treatment, may improve outcome.

Environmental and entomological risk factors for the development of clinical malaria among children on the Kenyan coast

Several malariometric studies have examined the impact on human-vector contact of house construction, demographics, bed net and insect repellent use. However, few studies have documented the significance of these proximate determinants on the risks of clinical disease. We undertook a matched case-control study of the risks of both mild clinical malaria and severe life-threatening malaria according to a range of putative factors which would influence the frequency of child-vector encounters in Kilifi district on the Kenyan coast. Among 394 severe disease cases, 380 age-matched mild disease cases, and their respective location and age-matched community controls, we were unable to demonstrate any statistically significant effect upon disease outcome of house construction, presence of domestic animals, or bed net use. Higher population density within a 250 m radius of the homes conferred significant protection from the risks of developing severe malaria compared to community controls. The risks of developing severe malaria compared to the community controls and the transition from mild to severe disease were statistically significantly lower in those who reported use of mosquito coils, local repellents or aerosol insecticides. We concluded that it is likely that the impact of household features on disease outcome is dependent upon both the density of infecting mosquitoes and acquired immunity within a given locality.

The Gambian National Impregnated Bed Net Programme: evaluation of effectiveness by means of case-control studies

Two case-control studies, one on mortality and the other on malaria morbidity, were carried out in order to evaluate the impact of the Gambian National Insecticide Bed Net Programme during the second year of intervention and to explore the feasibility of such a study for the evaluation of programme effectiveness. For the mortality study, children 1-9 years old who died during the 1993 rainy season were matched by age and sex with 2 healthy controls from the same village. For the morbidity study, children 1-9 years old attending Fatoto or Jahalia Health Centres in The Gambia and who had fever and parasitaemia > or = 5000/microL were matched by age with a child attending the health centres without fever or parasitaemia. An additional healthy control was recruited from the case's village. No impact of insecticide-treated bed nets on mortality was detected and this was in keeping with the results obtained by prospective surveillance. A protective effect of insecticide-treated nets on malaria morbidity was detected when cases were compared with controls recruited at the health centres. However, this disappeared when cases were compared with controls recruited from the cases' villages. The mortality case-control study suggested that reducing the time between onset of disease and treatment may have an important impact on childhood mortality. In order to calculate programme cost-effectiveness, important for informed resource allocations to be made by health managers, it is essential to obtain evidence of effectiveness. This can be done by means of case-control studies, which are easier to carry out and require fewer resources than prospective surveillance. Nevertheless, it is necessary to be conscious of their pitfalls, particularly of the bias involved in the choice of cases and controls. The measurement of insecticide on the nets of the cases or controls is essential for such studies.

Host-parasite interaction and morbidity in malaria endemic areas

Severe morbidity due to Plasmodium falciparum is a major health problem in African children. The patterns of morbidity in endemic areas are modified by the immune response, and vary markedly with transmission intensity. Severe disease falls into three overlapping syndromes: coma, respiratory distress, and severe anaemia. Recently, it has become clear that metabolic acidosis plays a major role in the pathogenesis of severe disease and is particularly important in the overlap between the different clinical syndromes. We propose that the different manifestations of severe malarial morbidity arise from the interaction of a limited number of pathogenic processes: red cell destruction, toxin-mediated activation of cytokine cascades, and infected cell sequestration in tissue microvascular beds. The pattern of severe morbidity varies with age within any one endemic area, with severe anaemia predominating in the youngest children and coma having its highest incidence in older children. Between endemic areas there is a marked variation in mean age of children with severe malaria, and therefore in the importance of different clinical syndromes. The shift in mean age is due to a combination of increased challenge and more rapid development of immunity at higher levels of transmission. Recent comparative studies indicate that at higher levels of transmission the net effect of these shifts may be a paradoxical reduction in total severe malarial morbidity.

Plasmodium falciparum malaria: some epidemiological implications of parasite and host diversity

Observations are accumulating concerning: (1) the antigenic diversity of Plasmodium falciparum; (2) the diversity of the genetic immuno-competence of human hosts; (3) the associations between these diversities and disease, protection and defined immune responses; and (4) the possible mechanisms of acquired protection at different steps of the host-parasite interaction. These observations have led to speculations concerning the distribution of disease, the acquisition of protection, and vaccination prospects. Speculations on the latter have varied from pessimism about the possibility of developing a vaccine that would protect most people against most parasites, to optimism based on the hypothesis that a local P. falciparum population is composed of a few discrete subpopulations. If this hypothesis is correct, it may be possible to prevent most severe disease with a narrow-spectrum vaccination against a virulent minority of the subpopulations, or transmission could be interrupted by a relatively low coverage of a broad-spectrum vaccination. A conceptual model that might accommodate the observations is outlined. Its plausibility and testability are considered, as well as some of its implications for the planning and interpretation of epidemiological surveys and intervention trials, and perhaps for selection of antigens for inclusion in vaccines.

Dynamic interactions in malaria: host heterogeneity meets parasite polymorphism

The spectrum of disease severity in Plasmodium falciparum malaria can be attributed to heterogeneity in parasite virulence or to heterogeneity in host factors. However, the two are not necessarily separate explanations for the same phenomena: they may actually complement each other. The conjoint effects of host and parasite heterogeneity can serve to explain certain intriguing epidemiological observations, such as, why there is a reduction in incidence of severe malaria in certain host genotypes without a concomitant reduction in mild disease. By assuming that severe disease is caused by a rare independently transmitted parasite strain, and that the probability of disease is nonlinearly related to the number of effective infections by a certain strain, the disproportionate reduction in the rate of the rarer disease within resistant host genotypes may be explained. Conversely, heterogeneity in host resistance may, under certain circumstances, facilitate the maintenance of diversity in parasite virulence. In this paper we discuss the coevolutionary consequences of heterogeneity in host resistance and diversity in parasite virulence by using a simple mathematical model that attempts to integrate the population genetics of the system with its ecological dynamics. This allows a unified perspective on malaria transmission that synthesises current evidence regarding the effects of host and parasite heterogeneities on malarial disease.