The Malaria-High Blood Pressure Hypothesis

Immune and inflammatory mechanisms in hypertension

Hypertension is a global health problem, with >1.3 billion individuals with high blood pressure worldwide. In this Review, we present an inflammatory paradigm for hypertension, emphasizing the crucial roles of immune cells, cytokines and chemokines in disease initiation and progression. T cells, monocytes, macrophages, dendritic cells, B cells and natural killer cells are all implicated in hypertension. Neoantigens, the NLRP3 inflammasome and increased sympathetic outflow, as well as cytokines (including IL-6, IL-7, IL-15, IL-18 and IL-21) and a high-salt environment, can contribute to immune activation in hypertension. The activated immune cells migrate to target organs such as arteries (especially the perivascular fat and adventitia), kidneys, the heart and the brain, where they release effector cytokines that elevate blood pressure and cause vascular remodelling, renal damage, cardiac hypertrophy, cognitive impairment and dementia. IL-17 secreted by CD4+ T helper 17 cells and γδ T cells, and interferon-γ and tumour necrosis factor secreted by immunosenescent CD8+ T cells, exert crucial effector roles in hypertension, whereas IL-10 and regulatory T cells are protective. Effector mediators impair nitric oxide bioavailability, leading to endothelial dysfunction and increased vascular contractility. Inflammatory effector mediators also alter renal sodium and water balance and promote renal fibrosis. These mechanisms link hypertension with obesity, autoimmunity, periodontitis and COVID-19. A comprehensive understanding of the immune and inflammatory mechanisms of hypertension is crucial for safely and effectively translating the findings to clinical practice.

Hypertension Increases Susceptibility to Experimental Malaria in Mice

Global prevalence of hypertension is on the rise, burdening healthcare, especially in developing countries where infectious diseases, such as malaria, are also rampant. Whether hypertension could predispose or increase susceptibility to malaria, however, has not been extensively explored. Previously, we reported that hypertension is associated with abnormal red blood cell (RBC) physiology and anemia. Since RBC are target host cells for malarial parasite, Plasmodium, we hypothesized that hypertensive patients with abnormal RBC physiology are at greater risk or susceptibility to Plasmodium infection. To test this hypothesis, normotensive (BPN/3J) and hypertensive (BPH/2J) mice were characterized for their RBC physiology and subsequently infected with Plasmodium yoelii (P. yoelii), a murine-specific non-lethal strain. When compared to BPN mice, BPH mice displayed microcytic anemia with RBC highly resistant to osmotic hemolysis. Further, BPH RBC exhibited greater membrane rigidity and an altered lipid composition, as evidenced by higher levels of phospholipids and saturated fatty acid, such as stearate (C18:0), along with lower levels of polyunsaturated fatty acid like arachidonate (C20:4). Moreover, BPH mice had significantly greater circulating Ter119+ CD71+ reticulocytes, or immature RBC, prone to P. yoelii infection. Upon infection with P. yoelii, BPH mice experienced significant body weight loss accompanied by sustained parasitemia, indices of anemia, and substantial increase in systemic pro-inflammatory mediators, compared to BPN mice, indicating that BPH mice were incompetent to clear P. yoelii infection. Collectively, these data demonstrate that aberrant RBC physiology observed in hypertensive BPH mice contributes to an increased susceptibility to P. yoelii infection and malaria-associated pathology.

Sickle cell allele HBB-rs334(T) is associated with decreased risk of childhood Burkitt lymphoma in East Africa

Burkitt lymphoma (BL) is an aggressive B-cell lymphoma that significantly contributes to childhood cancer burden in sub-Saharan Africa. Plasmodium falciparum, which causes malaria, is geographically associated with BL, but the evidence remains insufficient for causal inference. Inference could be strengthened by demonstrating that mendelian genes known to protect against malaria-such as the sickle cell trait variant, HBB-rs334(T)-also protect against BL. We investigated this hypothesis among 800 BL cases and 3845 controls in four East African countries using genome-scan data to detect polymorphisms in 22 genes known to affect malaria risk. We fit generalized linear mixed models to estimate odds ratios (OR) and 95% confidence intervals (95% CI), controlling for age, sex, country, and ancestry. The ORs of the loci with BL and P. falciparum infection among controls were correlated (Spearman's ρ = 0.37, p = .039). HBB-rs334(T) was associated with lower P. falciparum infection risk among controls (OR = 0.752, 95% CI 0.628-0.9; p = .00189) and BL risk (OR = 0.687, 95% CI 0.533-0.885; p = .0037). ABO-rs8176703(T) was associated with decreased risk of BL (OR = 0.591, 95% CI 0.379-0.992; p = .00271), but not of P. falciparum infection. Our results increase support for the etiological correlation between P. falciparum and BL risk.

Left ventricular function by strain in uncomplicated malaria: a prospective study from the Brazilian Amazon

We hypothesized that adults with uncomplicated malaria have lower left ventricular contractile function compared to the general population and that this improves after antimalarial treatment. We examined uncomplicated malaria and the general population from the Western part of the Brazilian Amazon Basin. All persons underwent an echocardiographic examination and peripheral blood smears. Left ventricular function was assessed by speckle tracking analysis of global longitudinal strain (GLS). Logistic regression models were used to assess the association between malaria status (yes/no) and GLS and improvement in GLS by follow-up was assessed using a paired T-test. We enrolled 99 adults with uncomplicated malaria (mean age 40 years, 46% female) of whom 75 had Plasmodium vivax, 22 Plasmodium falciparum and two had both species [median 1595 (528 to 6585) parasites/mm³]. Seventy adults completed a follow-up examination after standard malaria treatment (median 31 days). We examined 486 from the general population (mean age 41 years, 63% female). In persons with malaria at baseline, GLS was lower compared to the general population (18.7% vs. 19.4%, P = 0.002) and GLS improved at follow-up (19.2%, P = 0.032). In multivariable models adjusted for clinical, socioeconomic and echocardiographic confounders, baseline GLS remained significantly associated with malaria status [odds ratio 2.45 (95%CI 1.00 to 7.25), P = 0.023 per 1% increase]. Parasite density was associated with worsening in GLS [+ 16% (+ 0% to + 34%), P = 0.047 per 1 unit increase in GLS]. Adults with uncomplicated malaria had lower GLS compared to the general population and this improved after completed antimalarial treatment. Our results suggest that malaria infection may affect left ventricular contractile function, however, further studies are needed to fully elucidate such a relationship.

Temporal trends in the burden of non-communicable diseases in countries with the highest malaria burden, 1990–2019: Evaluating the double burden of non-communicable and communicable diseases in epidemiological transition

Background

Non-communicable diseases (NCDs) are rapidly increasing in sub-Saharan African countries, where 96% of global malaria deaths occur. This study aimed to investigate the disease burden of NCDs in countries with the current highest malaria mortality.

Methods

Data for this study were obtained from the Global Burden of Disease 2019 study (1990–2019). We selected the ten countries with malaria’s highest age-standardised mortality rate (ASMR) and identified and ranked the five NCDs with the highest ASMR in each country. Measures of the NCDs disease burden included ASMR, age-standardised disability-adjusted life-years (DALY), years of life lost (YLL) and years lost due to a disability (YLD). The Estimated annual percentage change (EAPC) was used to examine the trends of the NCDs disease burden from 1990 to 2019.

Results

As of 2019, the ASMR of chronic liver disease, kidney disease, diabetes mellitus, Alzheimer’s disease and other dementias, hypertensive heart disease and stroke were higher than the global average. From 1990 to 2019, the ASMR for Alzheimer’s disease and other dementias, type II diabetes mellitus, and chronic kidney disease increased by 3.0%, 10.8%, 13.3%, and the age-standardised DALY rate increased by 3.7%, 27.6%, 6.3%, and the increases tended to be in younger populations.

Conclusion

The double burden of non-communicable and communicable diseases is crippling the health systems of many sub-Saharan African countries and is often neglected. The prevention, surveillance, and control of diseases require an integrated strategy, with governments and non-government organisations aligned and supported by the global initiative.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12992-022-00882-w.

The Global Epidemiological Transition in Cardiovascular Diseases: Unrecognised Impact of Endemic Infections on Peripheral Artery Disease

An epidemiological transition in the prevalence of peripheral artery disease (PAD) is taking place especially in low- and middle-income countries (LMICs) where an ageing population and adoption of western lifestyles are associated with an increase in PAD. We discuss the limited evidence which suggests that infection, potentially mediated by inflammation, may be a risk factor for PAD, and show by means of an ecological analysis that country-level prevalence of the major endemic infections of HIV, tuberculosis and malaria are associated with the prevalence of PAD. While further research is required, we propose that scientists and health authorities pay more attention to the interplay between communicable and non-communicable diseases, and we suggest that limiting the occurrence of endemic infections might have some effect on slowing the epidemiological transition in PAD.

Evolutionary trilogy of malaria, angiotensin II and hypertension: deeper insights and the way forward

Despite clinical and pathological distinctions between malaria and hypertension, accumulated epidemiological and evolutionary evidence indicate the need of deeper understanding how severe malaria contributes to elevated hypertension risk. Malaria is said to exert strong selection pressure on the host genome, thus selecting certain genetic polymorphisms. Few candidate polymorphisms have also been reported in the RAS (ACE I/D and ACE2 rs2106809) that are shown to increase angiotensin II (ang II) levels in a combinatorial manner. The raised ang II has some antiplasmodial actions in addition to protecting against severe/cerebral malaria. It is hypothesized that RAS polymorphisms may have been naturally selected over time in the malaria-endemic areas in such a way that hypertension, or the risk thereof, is higher in such areas as compared to non-malaria endemic areas. The purpose of this review is to gain deeper insights into various sparse evidence linking malaria and hypertension and suggesting a way forward.

Heart failure associated with imported malaria: a nationwide Danish cohort study

AIMS

Despite adequate treatment, recent studies have hypothesized that malaria may affect long-term cardiovascular function. We aimed to investigate the long-term risk of cardiovascular events and death in individuals with a history of imported malaria in Denmark.

METHODS

Using nationwide Danish registries, we followed individuals with a history of malaria for the risk of incident heart failure (HF), myocardial infarction (MI), cardiovascular death and all-cause death (1 January 1994 to 1 January 2017). The population was age- and sex-matched with individuals without a history of malaria from the Danish population (ratio 1:9). We excluded patients with known HF and ischaemic heart disease at inclusion.

RESULTS

We identified 3912 cases with a history of malaria (mean age 33 ± 17 years, 57% male, 41% Plasmodium falciparum infections). The median follow-up was 9.8 years (interquartile range 3.9-16.4 years). Event rates per 1000 person-years for individuals with a history vs. no history of malaria were HF: 1.84 vs. 1.32; MI: 1.28 vs. 1.30; cardiovascular death: 1.40 vs. 1.77; and all-cause death: 5.04 vs. 5.28. In Cox proportional hazards models adjusted for cardiovascular risk factors, concomitant pharmacotherapy, region of origin, household income and educational level, malaria was associated with HF (HR: 1.59 [1.21-2.09], P = 0.001), but not MI (HR: 1.00 [0.72-1.39], P = 1.00), cardiovascular death (HR: 1.00 [0.74-1.35], P = 0.98) or all-cause death (HR 1.11 [0.94-1.30], P = 0.21). Specifically, P. falciparum infection was associated with increased risk of HF (HR: 1.64 [1.14-2.36], P = 0.008).

CONCLUSION

Individuals with a history of imported malaria, specifically P. falciparum, may have an increased risk of incident HF.

Seasonal and socio-demographic patterns of self-reporting major disease groups in north-west Burkina Faso: an analysis of the Nouna Health and Demographic Surveillance System (HDSS) data

Background

Sub-Saharan Africa (SSA) is facing a rapid growth of non-communicable diseases (NCDs), while communicable diseases still prevail. For rural SSA, evidence for this development is scarce. We aimed at quantifying self-reported major disease groups according to season, and determining the associations with socio-economic factors in rural Burkina Faso.

Methods

This study used data of 4192 adults (age range: 18–101 years; male: 49.0%) from the Nouna Health and Demographic Surveillance System (HDSS) in north-west Burkina Faso, rainy season of 2010 and dry season of 2011. We assessed the proportions and their 95% confidence intervals (CIs) of self-reported major disease groups as defined by the World Health Organization. For their associations with socio-economic factors, odds ratios (OR), 95% CIs and p-values were calculated by logistic regression.

Results

The surveys were completed by 3949 adults in 2010 (mean age: 37.5 ± 14.9 years, male: 48.8%) and by 4039 adults in 2011 (mean age: 37.3 ± 16.2 years, male: 49.1%). The proportions of self-reported communicable diseases were 20.7% (95% CI: 19.4–21.9%) in the rainy season and 11.0% (10.0–11.9%; McNemar’s p < 0.0001) in the dry season. Self-reported NCDs amounted to 5.3% (4.6–6.0%) and 4.5% (3.8–5.1%; p = 0.08), respectively. In each year, less than 1% reported injuries (p = 0.57). Few individuals reported an overlap of communicable diseases and NCDs: 1.4% in 2010 and 0.6% in 2011. In the multiple-adjusted models, formal education (vs. lack of education) showed the strongest association with self-reporting of communicable diseases in both seasons. For NCD-reporting, non-manual occupation (vs. manual) was positively associated, only in the rainy season.

Conclusions

Self-reporting of communicable diseases is subject to seasonal variation in this population in north-west Burkina Faso. The exact reasons for the low overall self-reporting of NCDs and injuries, apart from a low socio-demographic position, require further investigation.

Elevated Levels of the Endothelial Molecules ICAM-1, VEGF-A, and VEGFR2 in Microscopic Asymptomatic Malaria

Background

In malaria, clinical disease has been associated with increased levels of endothelial activation due to the sequestration of infected erythrocytes. However, the levels and impact of endothelial activation and pro-angiogenic molecules such as vascular endothelial growth factor (VEGF)–A and its receptor vascular endothelial growth factor receptor 2 (VEGFR2) in asymptomatic malaria have not been well characterized.

Methods

Blood samples were obtained from community children for malaria diagnosis using microscopy and polymerase chain reaction. A multiplex immunoassay was used to determine the levels of intracellular adhesion molecule (ICAM)–1, vascular endothelial growth factor (VEGF)–A, and VEGFR2 in the plasma of children with microscopic or submicroscopic asymptomatic parasitemia and compared with levels in uninfected controls.

Results

Levels of ICAM-1, VEGF-A, and VEGFR2 were significantly increased in children with microscopic asymptomatic parasitemia compared with uninfected controls. Also, levels of VEGF-A were found to be inversely associated with age. Additionally, a receiver operating characteristic analysis revealed that plasma levels of ICAM-1 (area under the curve [AUC], 0.72) showed a moderate potential in discriminating between children with microscopic malaria from uninfected controls when compared with VEGF-A (AUC, 0.67) and VEGFR2 (AUC, 0.69).

Conclusions

These data imply that endothelial activation and pro-angiogenic growth factors could be one of the early host responders during microscopic asymptomatic malaria and may play a significant role in disease pathogenesis.

Prevalence of Cardiovascular Complications in Malaria: A Systematic Review and Meta-Analysis

Recent studies have suggested that malaria may affect the cardiovascular system. The aim of this systematic review and meta-analysis was to determine the prevalence of cardiovascular complications in symptomatic malaria patients. We searched databases such as Pubmed, Embase, Cochrane, and Web of Science (January 1950-April 2020) for studies reporting on cardiovascular complications in adults and children with malaria. Cardiovascular complications were defined as abnormalities in electrocardiogram (ECG), cardiac biomarkers, and echocardiography on admission or during outpatient examination. Studies of patients with known heart disease or cardiovascular evaluation performed after the start of intravenous antimalarial medication were excluded. The study was registered in International Prospective Register of Systematic Reviews (PROSPERO) (No.: CRD42020167672). The literature search yielded 1,243 studies, and a total of 43 studies with symptomatic malaria patients were included. Clinical studies (n = 12 adults; n = 5 children) comprised 3,117 patients, of which a majority had Plasmodium falciparum (n = 15) and were diagnosed with severe malaria (n = 13). In random-effects models of adults, the pooled prevalence estimate for any cardiovascular complication was 7% (95% CI: 5-9). No meta-analysis was conducted in children, but the range of abnormal ECG was 0-8%, cardiac biomarkers 0-57%, and echocardiography 4-9%. We analyzed 33 cases (n = 10 postmortem), in which the most common cardiovascular pathologies were myocarditis and acute coronary syndrome. All histopathological studies found evidence of parasitized red blood cells in the myocardium. Cardiovascular complications are not uncommon in symptomatic adults and children with malaria. Additional studies investigating malaria and cardiovascular disease are encouraged.

Malaria link of hypertension: a hidden syndicate of angiotensin II, bradykinin and sphingosine 1-phosphate

In malaria-endemic countries, the burden of hypertension is on the rise. Although malaria and hypertension seem to have no direct link, several studies in recent years support their possible link. Three bioactive molecules such as angiotensin II (Ang II), bradykinin (BK) and sphingosine 1-phosphate (S1P) are crucial in regulating blood pressure. While the increased level of Ang II and S1P are responsible for inducing hypertension, BK is arthero-protective and anti-hypertensive. Therefore, in the present review, based on available literatures we highlight the present knowledge on the production and bioavailability of these molecules, the mechanism of their regulation of hypertension, and patho-physiological role in malaria. Further, a possible link between malaria and hypertension is hypothesized through various arguments based on experimental evidence. Understanding of their mechanisms of blood pressure regulation during malaria infection may open up avenues for drug therapeutics and management of malaria in co-morbidity with hypertension.

Teoría sindémica como un enfoque para explicar la interacción entre problemas de salud pública

La teoría sindémica proporciona un marco innovador que permite comprender ¿por qué ciertos problemas de salud pública se concentran geográfica y temporalmente?, y ¿cómo estos problemas interactúan biológica y socialmente?, generando efectos nocivos en grupos vulnerables. Sin embargo, la evidencia empírica que pone a prueba esta teoría aún es escasa y la existente tiene ciertas limitaciones en el enfoque y medición de conceptos claves. Por este motivo, este artículo tiene como propósito generar una discusión sobre algunas implicaciones conceptuales y metodológicas del uso de la teoría sindémica. El correcto abordaje de la teoría sindémica permite direccionar futuras investigaciones en este tema y promueve su importancia para el estudio de problemas de salud en el contexto de Latinoamérica.

The Malaria-High Blood Pressure Hypothesis: Revisited

Malaria etiologies with pathophysiological similarities to hypertension currently constitute a major subject of research. The malaria-high blood pressure hypothesis is strongly supported by observations of the increasing incidence of hypertension in malaria-endemic, low- and middle-income countries with poor socioeconomic conditions, particularly in sub-Saharan African countries. Malnutrition and low birth weight with persistent symptomatic malaria presentations in pregnancy correlate strongly with the development of preeclampsia, gestational hypertension and subsequent hypertension in adult life. Evidence suggest that the link between malaria infection and high blood pressure involves interactions between malaria parasites and erythrocytes, the inflammatory process, effects of the infection during pregnancy; effects on renal and vascular functions as well as effects in sickle cell disease. Possible mechanisms which provide justification for the malaria-high blood pressure hypothesis include the following: endothelial dysfunction (reduced nitric oxide (NO) levels), impaired release of local neurotransmitters and cytokines, decrease in vascular smooth muscle cell viability and/or alterations in cellular calcium signaling leading to enhanced vascular reactivity, remodeling, and cardiomyopathies, deranged homeostasis through dehydration, elevated intracellular mediators and proinflammatory cytokine responses, possible genetic regulations, activation of the renin-angiotensin-aldosterone system mechanisms and renal derangements, severe anemia and hemolysis, renal failure, and end organ damage. Two key mediators of the malaria-high blood pressure association are: endothelial dysfunction (reduced NO) and increased angiotensin-converting enzyme activity/angiotensin II levels. Sickle cell disease is associated with protection against malaria infection and reduced blood pressure. In this review, we present the state of knowledge about the malaria-blood pressure hypothesis and suggest insights for future studies.

Epidemiological links between malaria parasitaemia and hypertension: findings from a population-based survey in rural Côte d'Ivoire

Background:

Although potential links between malaria parasitaemia and hypertension have been hypothesized, there is paucity of epidemiologic evidence on this link. We investigated in a population-based survey, the association between malaria parasitaemia and hypertension in Ivorian adults.

Methods:

We estimated the adjusted odds ratios (OR) and 95% confidence intervals (CI) of hypertension in relation to malaria parasitaemia using multinomial regression, in 997 randomly selected adults in the ‘Côte d’Ivoire Dual Burden of Disease Study’ (CoDuBu), in south-central Côte d’Ivoire. We defined malaria parasitaemia as a positive rapid diagnostic test or identification of Plasmodium spp. on microscopy. Using the mean of the last two of three blood pressure (BP) measurements and questionnaire data, we defined hypertension as SBP at least 140 mmHg or DBP at least 90 mmHg or clinician-diagnosed hypertension.

Results:

Prevalence of malaria parasitaemia and hypertension were 10 and 22%, respectively. Malaria parasitaemia was negatively associated with hypertension in participants with body temperature 36.5 °C or less [OR 0.23 (95% CI 0.06–0.84)]. Contrastingly, microscopic malaria parasitaemia showed positive associations with hypertension in participants with elevated body temperature [>36.5 °C; OR: 2.93 (95% CI 0.94–9.14)]. Participants having microscopic malaria parasitaemia with elevated body temperature had three-fold higher odds of hypertension [OR: 3.37 (95% CI 1.12–10.0)] than malaria parasitaemia-negatives with lower body temperature.

Conclusion:

Malaria parasitaemia and hypertension are prevalent and seemingly linked comorbidities in African settings. This link may depend on malaria parasitaemia symptomaticity/latency where individuals with more latent/asymptomatic malaria parasitaemia have lower risk of hypertension and those with more acute/symptomatic malaria parasitaemia have a tendency toward higher BP. The cross-sectional nature of the study limited the distinction of short-term BP elevation (interim pathophysiological stress) from hypertension development. Future longitudinal studies considering malaria/hypertension phenotypes and host molecular variations are needed to clarify involved biological mechanisms, toward comorbidity management.

Histopathological lesions and exposure to Plasmodium falciparum infections in the placenta increases the risk of preeclampsia among pregnant women

Preeclampsia (PE) is a placental disorder with different phenotypic presentations. In malaria-endemic regions, high incidence of PE is reported, with debilitating foeto-maternal effects, particularly among primigravid women. However, the relationship between placental pathology and Plasmodium falciparum infection in the placenta with PE is underexplored. Placentas from 134 pregnant women were examined after delivery for pathological lesions and placental malaria (PM). They comprised of 69 women without PE (non-PE group) and 65 women diagnosed with PE (PE group). The presence of placental pathology increased the risk of PE, with particular reference to syncytial knots. Placental malaria was 64 (48.1%) and 21 (15.8%) respectively for active and past infections and these proportions were significantly higher in the PE group compared to the non-PE group. Further multivariate analyses showed placental pathology (adjusted (aOR) 3.0, 95% CI = 1.2-7.5), active PM (aOR 6.7, 95% CI = 2.3-19.1), past PM (aOR 12.4, 95% CI = 3.0-51.0) and primigravidity (aOR 6.6, 95% CI 2.4-18.2) to be associated with PE. Our findings suggest that placental histological changes and PM are independent risk factors for PE particularly in primigravida. These findings might improve the management of PE in malaria-endemic regions.

Pharmacotherapy for hypertension in Sub-Saharan Africa: a systematic review and network meta-analysis

BACKGROUND

The highest burden of hypertension is found in Sub-Saharan Africa (SSA) with a threefold greater mortality from stroke and other associated diseases. Ethnicity is known to influence the response to antihypertensives, especially in black populations living in North America and Europe. We sought to outline the impact of all commonly used pharmacological agents on both blood pressure reduction and cardiovascular morbidity and mortality in SSA.

METHODS

We used similar criteria to previous large meta-analyses of blood pressure agents but restricted results to populations in SSA. Quality of evidence was assessed using a risk of bias tool. Network meta-analysis with random effects was used to compare the effects across interventions and meta-regression to explore participant heterogeneity.

RESULTS

Thirty-two studies of 2860 participants were identified. Most were small studies from single, urban centres. Compared with placebo, any pharmacotherapy lowered SBP/DBP by 8.51/8.04 mmHg, and calcium channel blockers (CCBs) were the most efficacious first-line agent with 18.46/11.6 mmHg reduction. Fewer studies assessing combination therapy were available, but there was a trend towards superiority for CCBs plus ACE inhibitors or diuretics compared to other combinations. No studies examined the effect of antihypertensive therapy on morbidity or mortality outcomes.

CONCLUSION

Evidence broadly supports current guidelines and provides a clear rationale for promoting CCBs as first-line agents and early initiation of combination therapy. However, there is a clear requirement for more evidence to provide a nuanced understanding of stroke and other cardiovascular disease prevention amongst diverse populations on the continent.

TRIAL REGISTRATION

PROSPERO, CRD42019122490. This review was registered in January 2019.

Serious infection may systemically increase noradrenergic signaling and produce psychological effects

Serious infection elicits inflammatory processes that act through a range of molecular pathways, including cytokine signaling. It is not established however that noradrenaline (NA), a widely distributed neurotransmitter in the brain that is also a principal output molecule of the sympathetic nervous system, can produce psychological effects associated with infection. This paper puts forth the hypothesis that through neural-immune crosstalk, serious infection increases noradrenergic signaling, both in the central nervous system and in peripheral organs. In this manner, elevated noradrenergic transmission may help produce basic symptoms of infection such as fever, fatigue, aches and pains (including headache), nausea, and loss of appetite. NA may also promote cognitive impairment, major depression, unipolar mania, and even epileptic seizures in some cases. The paper focuses on three major types of infection: influenza (viral), tuberculosis (bacterial), malaria (parasitic), while also summarizing the potential relationship between NA and human immunodeficiency virus (HIV) infection. Four lines of evidence are used to test association between NA and influenza, tuberculosis, and malaria: direct measures of NA and its metabolites; and incidence of hypertension, bipolar mania, and epileptic seizures, since the latter three conditions may be associated with elevated NA. In addition, heart rate variability data are examined with respect to a number of infectious diseases, since those data provide information on sympathetic nervous system activity. While the data do not unequivocally support elevated noradrenergic signaling promoting psychological symptomatology with infection, many studies are consistent with this view.

Asymptomatic Plasmodium infection and glycemic control in adults: Results from a population-based survey in south-central Côte d'Ivoire

AIMS

We investigated the cross-sectional associations of Plasmodium infection (PI) with fasting glucose (FG) and glycated hemoglobin (HbA1c) in malaria-endemic south-central Côte d'Ivoire.

METHODS

We studied 979 participants (non-pregnant; no treated diabetes; 51% males; 18-87 years) of the Côte d'Ivoire Dual Burden of Disease study. Fasting venous blood was obtained for PI, FG, and HbA1c assessment. We defined PI as a positive malaria rapid diagnostic test (RDT) or microscopic identification of Plasmodium species. We applied multivariable linear regressions to assess beta coefficients (β) and 95% confidence intervals (CIs) of PI positivity for FG and HbA1c independent of diabetes risk factors.

RESULTS

Prevalence of PI was 10.1% (5.5% microscopy; 9.7% RDT) without clinical fever. Prevalence of FG-based prediabetes (45.8%) and diabetes (3.6%) were considerably higher than HbA1c-based values (2.7% and 0.7%, respectively). PI was independently associated with FG among participants with higher body temperature (β 0.34, 95% CI 0.06-0.63, p_{heterogeneity} = 0.028), or family history of diabetes (β 0.88, 95% CI 0.28-1.47, p_{heterogeneity} = 0.009). Similar patterns observed with HbA1c were obliterated on accounting for FG. We also observed consistent associations with parasite density.

CONCLUSIONS

FG-based diabetes diagnosis in the presence of asymptomatic PI may misclassify or overestimate diabetes burden in malaria-endemic settings. Longitudinal studies are needed to confirm these findings and determine the risk for diabetes.

Effect of Previous Exposure to Malaria on Blood Pressure in Kilifi, Kenya: A Mendelian Randomization Study

Background Malaria exposure in childhood may contribute to high blood pressure ( BP ) in adults. We used sickle cell trait ( SCT ) and α+thalassemia, genetic variants conferring partial protection against malaria, as tools to test this hypothesis. Methods and Results Study sites were Kilifi, Kenya, which has malaria transmission, and Nairobi, Kenya, and Jackson, Mississippi, where there is no malaria transmission. The primary outcome was 24-hour systolic BP. Prevalent hypertension, diagnosed using European Society of Hypertension thresholds was a secondary outcome. We performed regression analyses adjusting for age, sex, and estimated glomerular filtration rate. We studied 1127 participants in Kilifi, 516 in Nairobi, and 651 in Jackson. SCT frequency was 21% in Kilifi, 16% in Nairobi, and 9% in Jackson. SCT was associated with -2.4 (95% CI , -4.7 to -0.2) mm Hg lower 24-hour systolic BP in Kilifi but had no effect in Nairobi/Jackson. The effect of SCT in Kilifi was limited to 30- to 59-year-old participants, among whom it was associated with -6.1 mm Hg ( CI , -10.5 to -1.8) lower 24-hour systolic BP. In pooled analysis allowing interaction by site, the effect of SCT on 24-hour systolic BP in Kilifi was -3.5 mm Hg ( CI , -6.9 to -0.1), increasing to -5.2 mm Hg ( CI , -9.5 to -0.9) when replacing estimated glomerular filtration rate with urine albumin to creatinine ratio as a covariate. In Kilifi, the prevalence ratio for hypertension was 0.86 ( CI , 0.76-0.98) for SCT and 0.89 ( CI , 0.80-0.99) for α+thalassemia. Conclusions Lifelong malaria protection is associated with lower BP in Kilifi. Confirmation of this finding at other sites and elucidating the mechanisms involved may yield new preventive and therapeutic targets.

Blood pressure risk factors in early adolescents: results from a Ugandan birth cohort

We aimed to investigate life-course factors associated with blood pressure (BP) among Ugandan adolescents. Between 9th April 2003 and 24th November 2005, 2507 pregnant women from Entebbe municipality and Katabi sub-county were enrolled into a deworming trial. The resulting 2345 live-born offspring were followed to age 10 or 11 years, when between 20th May 2014 to 16th June 2016, BP was measured following standard protocols. Factors associated with BP were assessed using multivariable linear regression. BP was measured in 1119 adolescents with a median age of 10.2 years. Mean systolic BP and diastolic BP was 105.9 mmHg (standard deviation (SD) 8.2) and 65.2 mmHg (SD 7.3), respectively. Maternal gestational body mass index (BMI), higher maternal education status and family history of hypertension were positively associated with adolescent BP. Childhood (age ≤5 years) malaria was associated with lower adolescent systolic BP. Factors measured at time of BP measurement positively associated with systolic BP were age, BMI, waist circumference and Trichuris trichiura (whipworm) infection; higher vegetable consumption was associated with lower systolic BP. Results for diastolic BP were similar, except higher fruit, rather than higher vegetable consumption was associated with lower diastolic BP and there was no association with waist circumference or Trichuris trichiura infection. In summary, life-course exposures were associated with adolescent BP in this tropical birth cohort. Malaria early in life could impact later BP. Interventions initiated early in life targeting individuals with family history of hypertension, aiming to reduce adiposity (in pregnancy and adolescence) and promoting fruit and vegetable consumption might contribute to reducing the risk of high BP and subsequent cardiovascular diseases.

Natural selection and local adaptation of blood pressure regulation and their perspectives on precision medicine in hypertension

Prevalence of hypertension (HTN) varies substantially across different populations. HTN is not only common - affecting at least one third of the world's adult population - but is also the most important driver for cardiovascular diseases. Yet up to a third of hypertensive patients are resistant to therapy, contributed by secondary hypertension but more commonly the hitherto inability to precisely predict response to specific antihypertensive agents. Population and individual genomics information could be useful in guiding the selection and predicting the response to treatment - an approach known as precision medicine. However this cannot be achieved without the knowledge of genetic variations that influence blood pressure (BP). A number of evolutionary factors including population demographics and forces of natural selection may be involved. This article explores some ideas on how natural selection influences BP regulation in ethnically and geographically diverse populations that could lead to them being susceptible to HTN. We explore how such evolutionary factors could impact the implementation of precision medicine in HTN. Finally, in order to ensure the success of precision medicine in HTN, we call for more initiatives to understand the genetic architecture within and between diverse populations with ancestry from different parts of the world, and to precisely classify the intermediate phenotypes of HTN.

Cardiovascular Diseases in India Compared With the United States

This review describes trends in the burden of cardiovascular diseases (CVDs) and risk factors in India compared with the United States; provides potential explanations for these differences; and describes strategies to improve cardiovascular health behaviors, systems, and policies in India. The prevalence of CVD in India has risen over the past 2 decades due to population growth, aging, and a stable age-adjusted CVD mortality rate. Over the same time period, the United States has experienced an overall decline in age-adjusted CVD mortality, although the trend has begun to plateau. These improvements in CVD mortality in the United States are largely due to favorable population-level risk factor trends, specifically with regard to tobacco use, cholesterol, and blood pressure, although improvements in secondary prevention and acute care have also contributed. To realize similar gains in reducing premature death and disability from CVD, India needs to implement population-level policies while strengthening and integrating its local, regional, and national health systems. Achieving universal health coverage that includes financial risk protection should remain a goal to help all Indians realize their right to health.

Blood Pressure and Arterial Stiffness in Kenyan Adolescents With the Sickle Cell Trait

The potential association between sickle cell trait (SCT) and increased arterial stiffness/blood pressure (BP) has not been evaluated in detail despite its association with stroke, sudden death, and renal disease. We performed 24-hour ambulatory BP monitoring and arterial stiffness measurements in adolescents raised in a malaria-free environment in Kenya. Between December 2015 and June 2016, 938 randomly selected adolescents (ages 11–17 years) who had been continuous residents of Nairobi from birth were invited to participate in the study. Standard clinic BP measurement was performed, followed by 24-hour ambulatory BP monitoring and arterial stiffness measurement using an Arteriograph24 (TensioMed Ltd., Budapest, Hungary) device. SCT status was determined using DNA genotyping in contemporaneously collected blood samples. Of the 938 adolescents invited to participate, 609 (65%) provided complete data for analysis. SCT was present in 103 (15%). Mean 24-hour systolic and diastolic BPs were 116 (standard deviation (SD), 11.5) mm Hg and 64 (SD, 7) mm Hg, respectively, in children with SCT and 117 (SD, 11.4) mm Hg and 64 (SD, 6.8) mm Hg, respectively, in non-SCT children. Mean pulse wave velocity (PWV) was 7.1 (SD, 0.8) m/second and 7.0 (SD, 0.8) m/second in SCT and non-SCT children, respectively. We observed no differences in PWV or in any clinic or ambulatory BP-derived measures between adolescents with and without SCT. These data suggest that SCT does not independently influence BP or PWV.

Evaluating the Causal Link Between Malaria Infection and Endemic Burkitt Lymphoma in Northern Uganda: A Mendelian Randomization Study

Background

Plasmodium falciparum (Pf) malaria infection is suspected to cause endemic Burkitt Lymphoma (eBL), but the evidence remains unsettled. An inverse relationship between sickle cell trait (SCT) and eBL, which supports that between malaria and eBL, has been reported before, but in small studies with low power. We investigated this hypothesis in children in a population-based study in northern Uganda using Mendelian Randomization.

Methods

Malaria-related polymorphisms (SCT, IL10, IL1A, CD36, SEMA3C, and IFNAR1) were genotyped in 202 eBL cases and 624 controls enrolled during 2010–2015. We modeled associations between genotypes and eBL or malaria using logistic regression.

Findings

SCT was associated with decreased risk of eBL (adjusted odds ratio [OR] 0·37, 95% CI 0·21–0·66; p = 0·0003). Decreased risk of eBL was associated with IL10 rs1800896-CT (OR 0·73, 95% CI 0·50–1·07) and -CC genotypes (OR 0·53, 95% CI 0·29–0·95, p_trend = 0·019); IL1A rs2856838-AG (OR 0·56, 95% CI 0·39–0·81) and -AA genotype (OR 0·50, 95% CI 0·28–1·01, p_trend = 0·0016); and SEMA3C rs4461841-CT or -CC genotypes (OR 0·57, 95% CI 0·35–0·93, p = 0·0193). SCT and IL10 rs1800896, IL1A rs2856838, but not SEMA3C rs4461841, polymorphisms were associated with decreased risk of malaria in the controls.

Interpretation

Our results support a causal effect of malaria infection on eBL.

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Mendelian randomization analysis was done to assess a causal relationship between malaria infection and endemic Burkitt lymphoma in Uganda

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Carriage of the sickle cell trait was associated with decreased risk of endemic Burkitt lymphoma

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Heterozygous or homozygous minor alleles of IL10 rs1800896, IL1A rs2856838, and SEMA3C rs4461841 were associated with decreased risk of endemic Burkitt lymphoma

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The inverse association between sickle cell trait and endemic Burkitt lymphoma supports a causal role of malaria in endemic Burkitt lymphoma

In utero exposure to malaria is associated with metabolic traits in adolescence: The Agogo 2000 birth cohort study

OBJECTIVES

Malaria in pregnancy (MiP) contributes to fetal undernutrition and adverse birth outcomes, and may constitute a developmental origin of metabolic diseases in the offspring. In a Ghanaian birth cohort, we examined the relationships between MiP-exposure and metabolic traits in adolescence.

METHODS

MiP at delivery was assessed in 155 mother-child pairs. Among the now teenaged children (mean age, 14.8 years; 53% male), we measured fasting plasma glucose (FPG), body mass index (BMI), and systolic and diastolic blood pressure (BP). Associations of MiP with the adolescents' FPG, BMI, and BP were examined by linear regression.

RESULTS

At delivery, 45% were MiP-exposed, which increased FPG in adolescence, adjusted for mother's age at delivery, parity and familial socio-economic status (infected vs. uninfected: mean ΔFPG = 0.20 mmol/L; 95% confidence interval (CI): 0.01, 0.39; p = 0.049). As a trend,this was discernible for BP, particularly for microscopic infections (mean Δsystolic BP = 5.43 mmHg; 95% CI: 0.00, 10.88; p = 0.050; mean Δdiastolic BP = 3.67 mmHg; 95% CI: -0.81, 8.14; p = 0.107). These associations were largely independent of birth weight, gestational age and teenage BMI. Adolescent BMI was not related to MiP.

CONCLUSIONS

In rural Ghana, exposure to malaria during fetal development contributes to metabolic conditions in young adulthood.

Blood Pressure and Arterial Stiffness in Kenyan Adolescents With α+Thalassemia

Background

Recent studies have discovered that α‐globin is expressed in blood vessel walls where it plays a role in regulating vascular tone. We tested the hypothesis that blood pressure (BP) might differ between normal individuals and those with α⁺thalassemia, in whom the production of α‐globin is reduced.

Methods and Results

The study was conducted in Nairobi, Kenya, among 938 adolescents aged 11 to 17 years. Twenty‐four‐hour ambulatory BP monitoring and arterial stiffness measurements were performed using an arteriograph device. We genotyped for α⁺thalassemia by polymerase chain reaction. Complete data for analysis were available for 623 subjects; 223 (36%) were heterozygous (−α/αα) and 47 (8%) were homozygous (−α/−α) for α⁺thalassemia whereas the remaining 353 (55%) were normal (αα/αα). Mean 24‐hour systolic BP ±SD was 118±12 mm Hg in αα/αα, 117±11 mm Hg in −α/αα, and 118±11 mm Hg in −α/−α subjects, respectively. Mean 24‐hour diastolic BP ±SD in these groups was 64±8, 63±7, and 65±8 mm Hg, respectively. Mean pulse wave velocity (PWV)±SD was 7±0.8, 7±0.8, and 7±0.7 ms⁻¹, respectively. No differences were observed in PWV and any of the 24‐hour ambulatory BP monitoring‐derived measures between those with and without α⁺thalassemia.

Conclusions

These data suggest that the presence of α⁺thalassemia does not affect BP and/or arterial stiffness in Kenyan adolescents.

The High Blood Pressure-Malaria Protection Hypothesis

RATIONALE

A recently proposed hypothesis states that malaria may contribute to hypertension in endemic areas,¹ but the role of angiotensin II (Ang II), a major regulator of blood pressure, was not considered. Elevated levels of Ang II may confer protection against malaria morbidity and mortality, providing an alternative explanation for hypertension in malaria endemic areas.

OBJECTIVE

To discuss a possible alternative cause for hypertension in populations who have been under the selective pressure of malaria.

METHODS AND RESULTS

We reviewed published scientific literature for studies that could establish a link between Ang II and malaria. Both genetic and functional studies suggested that high levels of Ang II may confer protection against cerebral malaria by strengthening the integrity of the endothelial brain barrier. We also describe strong experimental evidence supporting our hypothesis through genetic, functional, and interventional studies.

CONCLUSIONS

A causal association between high levels of Ang II and protection from malaria pathogenesis can provide a likely explanation for the increased prevalence in hypertension observed in populations of African and South Asian origin. Furthermore, this potential causative connection might also direct unique approaches for the effective treatment of cerebral malaria.