Malaria and asymptomatic parasitaemia in Gabonese infants under the age of 3 months

Antimalarial treatment in infants

INTRODUCTION

Malaria in infants is common in high-transmission settings, especially in infants >6 months. Infants undergo physiological changes impacting pharmacokinetics and pharmacodynamics of anti-malarial drugs and, consequently, the safety and efficacy of malaria treatment. Yet, treatment guidelines and evidence on pharmacological interventions for malaria often fail to address this vulnerable age-group. This review aims to summarise the available data on anti-malarial treatment in infants.

AREAS COVERED

The standard recommended treatments for severe and uncomplicated malaria are generally safe and effective in infants. However, infants have an increased risk of drug-related vomiting and have distinct pharmacokinetic parameters of antimalarials compared with older patients. These include larger volumes of distribution, higher clearance rates and immature enzyme systems. Consequently, infants with malaria may be at increased risk of treatment failure and drug toxicity.

EXPERT OPINION

Knowledge expansion to optimize treatment can be achieved by including more infants in antimalarial drug trials and by reporting separately on treatment outcomes in infants. Additional evidence on the efficacy, safety, tolerability, acceptability and effectiveness of ACTs in infants is needed, as well as population pharmacokinetics studies on antimalarials in the infant population.

HIV infection and placental malaria reduce maternal transfer of multiple antimalarial antibodies in Mozambican women

OBJECTIVES

Maternal Plasmodium falciparum-specific antibodies may contribute to protect infants against severe malaria. Our main objective was to evaluate the impact of maternal HIV infection and placental malaria on the cord blood levels and efficiency of placental transfer of IgG and IgG subclasses.

METHODS

In a cohort of 341 delivering HIV-negative and HIV-positive mothers from southern Mozambique, we measured total IgG and IgG subclasses in maternal and cord blood pairs by quantitative suspension array technology against eight P. falciparum antigens: Duffy-binding like domains 3-4 of VAR2CSA from the erythrocyte membrane protein 1, erythrocyte-binding antigen 140, exported protein 1 (EXP1), merozoite surface proteins 1, 2 and 5, and reticulocyte-binding-homologue-4.2 (Rh4.2). We performed univariable and multivariable regression models to assess the association of maternal HIV infection, placental malaria, maternal variables and pregnancy outcomes on cord antibody levels and antibody transplacental transfer.

RESULTS

Maternal antibody levels were the main determinants of cord antibody levels. HIV infection and placental malaria reduced the transfer and cord levels of IgG and IgG1, and this was antigen-dependent. Low birth weight was associated with an increase of IgG2 in cord against EXP1 and Rh4.2.

CONCLUSIONS

We found lower maternally transferred antibodies in HIV-exposed infants and those born from mothers with placental malaria, which may underlie increased susceptibility to malaria in these children.

Treatment-seeking behavior and practices among caregivers of children aged ≤5 y with presumed malaria in rural Uganda

BACKGROUND

We aimed to determine the rate of herbal medicine usage and the treatment-seeking patterns of children aged ≤5 y with presumed or confirmed malaria in an endemic area of Uganda.

METHODS

We interviewed guardians of 722 children aged 6 months to 5 y, who had experienced an episode of presumed malaria in the previous 3 months, about the illness history.

RESULTS

Overall, 36.1% of patients took herbal medicines but most also sought modern medical care; 79.2% received Artemether-Lumefantrine (AL), but only 42.7% received the correct AL dose. Of the 36.6% of patients treated in drug shops, 9.8% had a diagnostic test and 30.2% received the correct dose of AL. Antibiotics were frequently provided with AL at drug shops (62%) and formal health centers (45%). There were no significant differences in the self-reported outcomes associated with different treatments.

CONCLUSION

Almost all of the patients who took herbal medicine also took modern antimalarials, so further research is needed to explore potential interactions between them. Although formal health facilities provided the correct diagnosis and dose of AL to a majority of children with malaria, many children still received inappropriate antibiotics. Quality of care was worse in drug shops than in formal health facilities.

Reliability of rapid diagnostic tests in diagnosing pregnancy and infant-associated malaria in Nigeria

BACKGROUND

The effective management of maternal and infant malaria requires rational and prompt diagnosis. This study aims to determine the diagnostic efficiency of malaria RDT in infants and pregnant women.

METHODS

The study was conducted on infants (n=200), pregnant women (n=80) and non-pregnant women (n=100) who were recruited from two hospitals in Lagos, Nigeria. Plasmodium falciparum infections were assessed in the febrile subjects by microscopic examinations of blood smears and by RDT.

RESULTS

The lowest (44.3%) and the highest (83.3%) sensitivity (SS) values were recorded in the infants and pregnant women, respectively. Other diagnostic parameters, including the specificity (SP, 97.5%), positive predictive value (PPV, 92.1%) and negative predictive value (NPV, 72.8%), in the infants were greater than the values recorded in non-pregnant (SP=77.5%, PPV=83.9%, NPV=70.5%) and pregnant women populations (SP=65.6%, PPV=78.4%, NPV=72.4%). The diagnostic efficiency of malaria RDT exhibited higher sensitivity in women in early gestational stages (1st trimester=78.6% and 2nd trimester=88.0%) compared with those in the 3rd trimester (71.4%). The sensitivity of malaria RDT (100.0%) was significantly higher in the multigravid women than in the primigravida (78.6%) and secundigravida women (77.8%, P<0.05). The sensitivity of the RDT significantly increased with the intensity of the malarial parasites (P<0.05).

CONCLUSION

Malaria is endemic in the study populations. Malaria RDT can serve as a first-line of diagnosis for pregnant women in early gestational stages and multigravid women and can aid the differential diagnoses of other diseases due to its high specificity in infants.

Dynamics and role of antibodies to Plasmodium falciparum merozoite antigens in children living in two settings with differing malaria transmission intensity

BACKGROUND

Young infants have reduced susceptibility to febrile malaria compared with older children, but the mechanism for this remains unclear. There are conflicting data on the role of passively acquired antibodies. Here, we examine antibody titres to merozoite surface antigens in the protection of children in their first two years of life in two settings with differing malaria transmission intensity and compare these titres to previously established protective thresholds.

METHODS

Two cohorts of children aged four to six weeks were recruited in Banfora, Burkina and Keur Soce, Senegal and followed up for two years. Malaria infections were detected by light microscopic examination of blood smears collected at active and passive case detection visits. The titres of antibodies to the Plasmodium falciparum recombinant merozoite proteins (AMA1-3D7, MSP1-19, MSP2-Dd2, and MSP3-3D7) were measured by enzyme-linked immunosorbent assay at 1-6, 9, 12, 15 and 18 months of age and compared with the protective thresholds established in Kenyan children.

RESULTS

Antibody titres were below the protective thresholds throughout the study period and we did not find any association with protection against febrile malaria. Antibodies to AMA1 and MSP1-19 appeared to be markers of exposure in the univariate analysis (and so associated with increasing risk) and adjusting for exposure reduced the strength and significance of this association.

CONCLUSION

The antibody levels we measured are unlikely to be responsible for the apparent protection against febrile malaria seen in young infants. Further work to identify protective antibody responses might include functional assays and a wider range of antigens.

Genetic determinants of anti-malarial acquired immunity in a large multi-centre study

Background

Many studies report associations between human genetic factors and immunity to malaria but few have been reliably replicated. These studies are usually country-specific, use small sample sizes and are not directly comparable due to differences in methodologies. This study brings together samples and data collected from multiple sites across Africa and Asia to use standardized methods to look for consistent genetic effects on anti-malarial antibody levels.

Methods

Sera, DNA samples and clinical data were collected from 13,299 individuals from ten sites in Senegal, Mali, Burkina Faso, Sudan, Kenya, Tanzania, and Sri Lanka using standardized methods. DNA was extracted and typed for 202 Single Nucleotide Polymorphisms with known associations to malaria or antibody production, and antibody levels to four clinical grade malarial antigens [AMA1, MSP1, MSP2, and (NANP)₄] plus total IgE were measured by ELISA techniques. Regression models were used to investigate the associations of clinical and genetic factors with antibody levels.

Results

Malaria infection increased levels of antibodies to malaria antigens and, as expected, stable predictors of anti-malarial antibody levels included age, seasonality, location, and ethnicity. Correlations between antibodies to blood-stage antigens AMA1, MSP1 and MSP2 were higher between themselves than with antibodies to the (NANP)₄ epitope of the pre-erythrocytic circumsporozoite protein, while there was little or no correlation with total IgE levels. Individuals with sickle cell trait had significantly lower antibody levels to all blood-stage antigens, and recessive homozygotes for CD36 (rs321198) had significantly lower anti-malarial antibody levels to MSP2.

Conclusion

Although the most significant finding with a consistent effect across sites was for sickle cell trait, its effect is likely to be via reducing a microscopically positive parasitaemia rather than directly on antibody levels. However, this study does demonstrate a framework for the feasibility of combining data from sites with heterogeneous malaria transmission levels across Africa and Asia with which to explore genetic effects on anti-malarial immunity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-015-0833-x) contains supplementary material, which is available to authorized users.

Malaria Prevalence among Young Infants in Different Transmission Settings, Africa

The prevalence and consequences of malaria among infants are not well characterized and may be underestimated. A better understanding of the risk for malaria in early infancy is critical for drug development and informed decision making. In a cross-sectional survey in Guinea, The Gambia, and Benin, countries with different malaria transmission intensities, the overall prevalence of malaria among infants <6 months of age was 11.8% (Guinea, 21.7%; The Gambia, 3.7%; and Benin, 10.2%). Seroprevalence ranged from 5.7% in The Gambia to 41.6% in Guinea. Mean parasite densities in infants were significantly lower than those in children 1-9 years of age in The Gambia (p<0.0001) and Benin (p = 0.0021). Malaria in infants was significantly associated with fever or recent history of fever (p = 0.007) and anemia (p = 0.001). Targeted preventive interventions, adequate drug formulations, and treatment guidelines are needed to address the sizeable prevalence of malaria among young infants in malaria-endemic countries.

In vitro growth of Plasmodium falciparum in neonatal blood

BACKGROUND

Children below the age of six months suffer less often from malaria than older children in sub-Saharan Africa. This observation is commonly attributed to the persistence of foetal haemoglobin (HbF), which is considered not to permit growth of Plasmodium falciparum and therefore providing protection against malaria. Since this concept has recently been challenged, this study evaluated the effect of HbF erythrocytes and maternal plasma on in vitro parasite growth of P. falciparum in Central African Gabon.

METHODS

Umbilical cord blood and peripheral maternal blood were collected at delivery at the Albert Schweitzer Hospital in Gabon. Respective erythrocyte suspension and plasma were used in parallel for in vitro culture. In vitro growth rates were compared between cultures supplemented with either maternal or cord erythrocytes. Plasma of maternal blood and cord blood was evaluated. Parasite growth rates were assessed by the standard HRP2-assay evaluating the increase of HRP2 concentration in Plasmodium culture.

RESULTS

Culture of P. falciparum using foetal erythrocytes led to comparable growth rates (mean growth rate = 4.2, 95% CI: 3.5 - 5.0) as cultures with maternal red blood cells (mean growth rate =4.2, 95% CI: 3.4 - 5.0) and those from non-malaria exposed individuals (mean growth rate = 4.6, 95% CI: 3.8 - 5.5). Standard in vitro culture of P. falciparum supplemented with either maternal or foetal plasma showed both significantly lower growth rates than a positive control using non-malaria exposed donor plasma.

CONCLUSIONS

These data challenge the concept of HbF serving as intrinsic inhibitor of P. falciparum growth in the first months of life. Erythrocytes containing HbF are equally permissive to P. falciparum growth in vitro. However, addition of maternal and cord plasma led to reduced in vitro growth which may translate to protection against clinical disease or show synergistic effects with HbF in vivo. Further studies are needed to elucidate the pathophysiology of innate and acquired protection against neonatal malaria.

Malaria in infants aged less than six months - is it an area of unmet medical need?

Despite the protection provided by several factors, including maternal antibodies, the burden of malaria in young infants may be higher than previously thought. Infants with congenital or neonatal malaria may have a different clinical presentation than older children, and diagnosis may be confused with other neonatal diseases due to an overlap of clinical manifestations. In addition, there is little information on the use of artemisinin-based combination therapy in young infants. There is the need for a more accurate estimate of the parasite prevalence and the incidence of clinical malaria in infants under 6 months old, as well as a better characterization of risk factors, pharmacokinetic profiles, safety and efficacy of currently available anti-malarial treatments, in order to develop evidence-based treatment guidelines for this population.

Foetal haemoglobin and the dynamics of paediatric malaria

Background

Although 80% of malaria occurs in children under five years of age, infants under six months of age are known to have low rates of infection and disease. It is not clear why this youngest age group is protected; possible factors include maternal antibodies, unique nutrition (breast milk), and the presence of foetal haemoglobin (HbF). This work aims to gain insight into possible mechanisms of protection, and suggest pathways for focused empirical work, by modelling a range of possible effects of foetal haemoglobin and other red blood cell (RBC) developmental changes on parasite dynamics in infants.

Methods

A set of ordinary differential equations was created to investigate the leading hypotheses about the possible protective mechanisms of HbF-containing red blood cells, in particular whether HbF suppresses parasite population growth because parasite multiplication in individual RBCs is lower, slower or absent. The model also incorporated the intrinsic changes in blood volume and haematocrit that occur with age, and the possibility of parasite affinities for HbF-containing RBCs or reticulocytes.

Results

The model identified several sets of conditions in which the infant remained protected, or displayed a much slower growth of parasitaemia in the first few months of life, without any intervening immune response. The most protective of the hypothesized mechanisms would be the inhibition of schizont division in foetal RBCs so that fewer merozoites are produced. The model showed that a parasite preference for HbF-containing RBCs increases protective effects for the host, while a preference for reticulocytes has little effect.

Conclusions

The results from this simple model of haematological changes in infants and their effects on Plasmodium falciparum infection dynamics emphasize the likely importance of HbF and RBC number as an explanatory factor in paediatric malaria, and suggest a framework for organizing related empirical research.

Survey for asymptomatic malaria cases in low transmission settings of Iran under elimination programme

Background

In malaria endemic areas, continuous exposure to Plasmodium parasites leads to asymptomatic carriers that provide a fundamental reservoir of parasites, contributing to the persistence of malaria transmission. Therefore, in the present investigation, the presence and prevalence of malaria asymptomatic cases were determined to evaluate the reservoir of infection in two malaria endemic areas with a previous history of malaria transmission in the south of Iran, Bashagard and Ghale-Ganj districts of Hormozgan and Kerman provinces, respectively, where malaria transmission has been drastically reduced in the recent years.

Methods

The population samples (n=500 from each of the studied areas) were randomly collected from non-febrile, long-term residing, aged two to over 60years, during 20092010. Three identical surveys were carried out in both study areas and in each phase all the consent participants were interviewed and clinically examined. In all, three surveys to detect hidden parasite reservoirs (both Plasmodium falciparum and Plasmodium vivax), thick and thin blood smears and a highly sensitive nested-PCR were applied. In addition, the sero-prevalence survey for detecting malaria exposure was done by using a serological marker.

Results

In this study, P. vivax and P. falciparum parasites were not detected by light microscopy and nested-PCR assay in all three surveys of samples. Antibody responses against P. vivax and P. falciparum were detected in 1 % and 0.2 % of the total examined individuals, respectively, in Bashagard district. Regarding to Ghale-Ganj district, about 0.9% of the individuals had IgG -specific antibody to P. vivax at the first and second surveys, but at the third survey 0.45% of the participants had positive antibody to P. vivax parasite. IgG -specific antibody to P. falciparum was detected in 0.2% of the participants at the first and follow-up surveys. The overall regional differences were not statistically significant (P>0.05).

Conclusion

Taken together, the lack of asymptomatic carrier with the evidence of extremely low sero-positive to both P. vivax and P. falciparum among examined individuals supported the limited recent transmission in the studied areas and, therefore, these parts of Iran have potential to eliminate the disease in the next few years. However, continued follow up and action are still needed in both studied areas and also in their neighbouring province, Sistan and Baluchistan, which has the highest reported cases of malaria in Iran and also, has the largest border line with Afghanistan and Pakistan, with no elimination activities. This data will provide useful information for managing elimination activities in Iran.

Malaria in infants below six months of age: retrospective surveillance of hospital admission records in Blantyre, Malawi

Background

Information on the burden of malaria in early infancy is scarce. Young infants are relatively protected against clinical malaria during the first six months of life due to the presence of maternal antibodies and foetal haemoglobin, and have received relatively little attention with respect to research and treatment guidelines. The World Health Organization provides treatment guidelines for children from six months onwards, without specific treatment guidelines for the younger infants. A number of recent reports however suggest that the burden in this young age group may be underestimated.

Methods

A retrospective review of paediatric hospital records at the Queen Elizabeth Central Hospital in Blantyre from 1998 to 2008 from three data sources was carried out. The number of admitted infants <6 months and ≤ 15 years was obtained from the registry books of the Paediatric-Nursery-Department and the Malaria Research Laboratory. For the period 2001 - 2004, more detailed malaria related admission information was available as part of an ongoing study on severe malaria, allowing a calculation of the proportion of infants < 6 months of age among admissions in children < 5 years.

Results

Retrospective analysis of hospital records showed that over the course of these years, the average annual proportion of paediatric admissions in children ≤ 15 years with confirmed malaria aged <6 months was 4.8% and ranged between 2.8%-6.7%. This proportion was stable throughout the seasons. Between 2001-2004, 9.9% of admissions with confirmed malaria in children <5 years occurred in infants <6 months, with numbers increasing steadily during the first six months of life.

Conclusions

These findings are consistent with recent reports suggesting that the burden of malaria during the six first months of life may be substantial, and highlight that more research is needed on dose-optimization, safety and efficacy of anti-malarials that are currently used off-label in this vulnerable patient group.

Impact of Plasmodium falciparum infection on the frequency of moderate to severe anaemia in children below 10 years of age in Gabon

Background

Improving the understanding of childhood malarial anaemia may help in the design of appropriate management strategies.

Methods

A prospective observational study over a two-year period to assess the burden of anaemia and its relationship to Plasmodium falciparum infection and age was conducted in 8,195 febrile Gabonese children.

Results

The proportion of children with anaemia was 83.6% (n = 6830), higher in children between the ages of six and 23 months. Those under three years old were more likely to develop moderate to severe anaemia (68%). The prevalence of malaria was 42.7% and P. falciparum infection was more frequent in children aged 36–47 months (54.5%). The proportion of anaemic children increased with parasite density (p < 0.01). Most of infected children were moderately to severely anaemic (69.5%, p < 0.01). Infants aged from one to 11 months had a higher risk of developing severe malarial anaemia. In children over six years of age, anaemia occurrence was high (>60%), but was unrelated to P. falciparum parasitaemia.

Conclusion

Malaria is one of the main risk factors for childhood anaemia which represents a public health problem in Gabon. The risk of severe malarial anaemia increases up the age of three years. Efforts to improve strategies for controlling anaemia and malaria are needed.

Placental malaria increases malaria risk in the first 30 months of life

BACKGROUND

Plasmodium falciparum infection during pregnancy is associated with stillbirth, fetal growth restriction, and low birth weight. An additional consequence may be increased risk of malaria in early life, although the epidemiological evidence of this consequence is limited.

METHODS

A cohort of 527 children were observed actively every month for 30 months after delivery. Offspring of mothers with microscopically detectable placental P. falciparum infection at the time of delivery were defined as exposed. The outcome measure was malaria (parasitemia and fever). Analyses were performed using Cox proportional hazard models and were stratified by gravidity.

RESULTS

Overall, offspring of mothers with placental P. falciparum infection had a significantly higher risk of clinical malaria during the first 30 months of life (adjusted hazard ratio, 2.1; 95% confidence interval [CI], 1.2-3.7). The adjusted hazard ratio for offspring of multigravidae was 2.6 (95% CI, 1.3-5.3), and that for primigravidae was 1.5 (95% CI, 0.6-3.8). The offspring of placenta-infected primigravidae had no episodes of malaria during the first year of life.

CONCLUSIONS

Our findings show that active placental P. falciparum infection detected at delivery is associated with an approximately 2-fold greater risk of malaria during early life, compared with noninfection. The fact that persons born to infected multigravidae rather than primigravidae appear to be at greater risk emphasizes the importance of preventing malaria in mothers of all gravidities.

Blood coagulation, inflammation, and malaria

Malaria remains a highly prevalent disease in more than 90 countries and accounts for at least 1 million deaths every year. Plasmodium falciparum infection is often associated with a procoagulant tonus characterized by thrombocytopenia and activation of the coagulation cascade and fibrinolytic system; however, bleeding and hemorrhage are uncommon events, suggesting that a compensated state of blood coagulation activation occurs in malaria. This article (i) reviews the literature related to blood coagulation and malaria in a historic perspective, (ii) describes basic mechanisms of coagulation, anticoagulation, and fibrinolysis, (iii) explains the laboratory changes in acute and compensated disseminated intravascular coagulation (DIC), (iv) discusses the implications of tissue factor (TF) expression in the endothelium of P. falciparum infected patients, and (v) emphasizes the procoagulant role of parasitized red blood cells (RBCs) and activated platelets in the pathogenesis of malaria. This article also presents the Tissue Factor Model (TFM) for malaria pathogenesis, which places TF as the interface between sequestration, endothelial cell (EC) activation, blood coagulation disorder, and inflammation often associated with the disease. The relevance of the coagulation-inflammation cycle for the multiorgan dysfunction and coma is discussed in the context of malaria pathogenesis.

WHO 2006 child growth standards: implications for the prevalence of stunting and underweight-for-age in a birth cohort of Gabonese children in comparison to the Centers for Disease Control and Prevention 2000 growth charts and the National Center for Health Statistics 1978 growth references

OBJECTIVES

To assess the proportion of children being stunted and underweight-for-age at 3, 9 and 15 months in Lambaréné, Gabon, using the WHO child growth standards released in 2006 as compared with the Centers for Disease Control and Prevention (CDC) 2000 and the National Center for Health Statistics (NCHS) 1978 child growth charts/references.

DESIGN AND SETTING

Prospective birth cohort in Lambaréné, Gabon.

SUBJECTS

Two hundred and eighty-nine children from birth to 15 months of age.

METHODS

Weight and length were recorded at 3, 9 and 15 months. Corresponding Z scores for stunting and underweight-for-age were calculated for the three different standards/references. Children with a height-for-age or weight-for-age below -2 SD of the corresponding reference median (Z score < or = -2) were classified as stunted or underweight-for-age, respectively.

RESULTS

With the new WHO 2006 standards a higher proportion (4.0%) of 3-month-old infants were underweight compared with the CDC (1.0%) or the NCHS (0.7%) child growth charts/references. In contrast to the NCHS references or the CDC charts, this proportion did not increase from 3 to 9 months or from 9 to 15 months. The proportion of children being stunted was highest (above 20%) with the WHO 2006 standards at all three ages. Again, in contrast to the old standards, this proportion did not increase from 3 to 9 months or from 9 to 15 months.

CONCLUSIONS

The present results show considerably different growth faltering patterns for Gabonese children depending on the growth charts used to assess the prevalence of stunting and underweight. Shifting to the new WHO child growth standards may have important implications for child health programmes.

Intermittent preventive treatment against malaria in infants in Gabon--a randomized, double-blind, placebo-controlled trial

BACKGROUND

Intermittent preventive treatment aims to maximize the protective effects of malaria chemoprophylaxis while minimizing the deleterious effects.

METHODS

In Gabon, 1189 infants received either sulfadoxine-pyrimethamine (SP; 250 and 12.5 mg, respectively) or placebo at 3, 9, and 15 months of age. Children were actively followed-up until 18 months of age.

RESULTS

In the intention-to-treat population at 18 months of follow-up, 84 children (17%) in the SP group had > or =1 episode of anemia, versus 108 (21%) in the placebo group (protective efficacy, 22% [95% confidence interval {CI}, -1% to 40%]; P=.06). In the intervention group, there were 66 episodes during 485 person-years at risk, compared with 79 episodes during 497 years in the placebo group (protective efficacy, 17% [95% CI, -24% to 45%; P=.36). The effects were similar at 12 months of follow-up. The study drug was safe and well tolerated.

CONCLUSIONS

The intervention was efficacious, producing a reduction in risk for anemia but a smaller effect against malaria. It is a valuable additional tool to control malaria in a highly vulnerable age group. Remaining important questions are currently being addressed in further studies.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT00167843.