Spleen volume and clinical disease manifestations of severe Plasmodium falciparum malaria in African children

Ultrasound as a triaging tool for the diagnosis of malaria and typhoid in a resource constrained setting: A proposed frame-work

INTRODUCTION

Ultrasound has proven to have great potentials in the diagnosis and work-up of patients affected by tropical diseases. Its role in the diagnosis of malaria and typhoid abounds, but its value as a triaging tool in a resource-constrained settings is indistinct. Our review aimed is aimed at assessing the utility of ultrasound in diagnosis and prognosis of malaria and typhoid.

MATERIALS AND METHOD

Extensive literature search was conducted using the PubMed electronic database, for original peer reviewed articles in English language within 1964-2023. Keywords like "malaria", "typhoid", "S. Typhi", "Salmonella Typhi", "enteric fever", "ultrasound", "sonography" and "ultrasonography" were searched, using Boolean operators such as (OR, AND) applying the following filters (English, Human). A systematic synthesis of the literature was done.

RESULT

Our initial search yielded 749 potentially relevant references out of which 55 were found to be eligible. Organs assessed include the liver, spleen, kidneys, intestines, mesenteric lymph nodes, among others. For malaria, pathognomonic conditions like splenic enlargement, hepatomegaly, renal abnormalities as well as mesenteric lymph nodes and intestinal wall thickening in patients with typhoid fever.

CONCLUSION

Ultrasound by experienced clinicians adds significantly to the diagnosis and work-up of patients with malaria and typhoid fever. However, it is important to note that ultrasound alone may not be sufficient for definitive diagnosis as laboratory tests may still be required for confirmatory diagnosis.

IMPLICATION FOR PRACTICE

This study provide information on ultrasound in diagnosis of Malaria and typhoid by evaluating the morphological changes in abdominal and other organs of the body. This can be a guide to clinicians and other healthcare providers for early diagnosis and work-up of patients in endemic areas where resources are scarce.

Retention of uninfected red blood cells causing congestive splenomegaly is the major mechanism of anemia in malaria

Splenomegaly frequently occurs in patients with Plasmodium falciparum (Pf) or P. vivax (Pv) malarial anemia, but mechanisms underlying this co-occurrence are unclear. In malaria-endemic Papua, Indonesia, we prospectively analyzed red blood cell (RBC) concentrations in the spleen and spleen-mimetic retention in 37 subjects splenectomized for trauma or hyperreactive splenomegaly, most of whom were infected with Plasmodium. Splenomegaly (median 357 g [range: 80-1918 g]) was correlated positively with the proportion of red-pulp on histological sections (median 88.1% [range: 74%-99.4%]; r = .59, p = .0003) and correlated negatively with the proportion of white-pulp (median 8.3% [range: 0.4%-22.9%]; r = -.50, p = .002). The number of RBC per microscopic field (>95% uninfected) was correlated positively with spleen weight in both Pf-infected (r = .73; p = .017) and Pv-infected spleens (r = .94; p = .006). The median estimated proportion of total-body RBCs retained in Pf-infected spleens was 8.2% (range: 1.0%-33.6%), significantly higher than in Pv-infected (2.6% [range: 0.6%-23.8%]; p = .015) and PCR-negative subjects (2.5% [range: 1.0%-3.3%]; p = .006). Retained RBCs accounted for over half of circulating RBC loss seen in Pf infections. The proportion of total-body RBC retained in Pf- and Pv-infected spleens correlated negatively with hemoglobin concentrations (r = -.56, p = .0003), hematocrit (r = -.58, p = .0002), and circulating RBC counts (r = -.56, p = .0003). Splenic CD71-positive reticulocyte concentrations correlated with spleen weight in Pf (r = 1.0; p = .003). Retention rates of peripheral and splenic RBCs were correlated negatively with circulating RBC counts (r = -.69, p = .07 and r = -.83, p = .008, respectively). In conclusion, retention of mostly uninfected RBC in the spleen, leading to marked congestion of the red-pulp, was associated with splenomegaly and is the major mechanism of anemia in subjects infected with Plasmodium, particularly Pf.

Human ApoE2 protects mice against Plasmodium berghei ANKA experimental cerebral malaria

IMPORTANCE

Cerebral malaria (CM) is the deadliest complication of malaria infection with an estimated 15%-25% mortality. Even with timely and effective treatment with antimalarial drugs such as quinine and artemisinin derivatives, survivors of CM may suffer long-term cognitive and neurological impairment. Here, we show that human apolipoprotein E variant 2 (hApoE2) protects mice from experimental CM (ECM) via suppression of CD8+ T cell activation and infiltration to the brain, enhanced cholesterol metabolism, and increased IFN-γ production, leading to reduced endothelial cell apoptosis, BBB disruption, and ECM symptoms. Our results suggest that hApoE can be an important factor for risk assessment and treatment of CM in humans.

Hydroxyurea treatment is associated with lower malaria incidence in children with sickle cell anemia in sub-Saharan Africa

Realizing Effectiveness Across Continents with Hydroxyurea (REACH, NCT01966731) provides hydroxyurea at maximum tolerated dose (MTD) for children with sickle cell anemia (SCA) in sub-Saharan Africa. Beyond reducing SCA-related clinical events, documented treatment benefits include ∼50% reduction in malaria incidence. To identify associations and propose mechanisms by which hydroxyurea could be associated with lower malaria rates, infections were recorded across all clinical sites (Angola, Democratic Republic of Congo, Kenya, and Uganda). Hazard ratios (HR) with 95% confidence intervals (CIs) for baseline demographics, and time-varying laboratory and clinical parameters were estimated in a modified Cox gap-time model for repeated events. Over 3387 patient-years of hydroxyurea treatment, 717 clinical malaria episodes occurred in 336 of 606 study participants; over half were confirmed by blood smear and/or rapid diagnostic testing with 97.8% Plasmodium falciparum. In univariate analysis limited to 4 confirmed infections per child, malaria risk was significantly associated with absolute neutrophil count (ANC), splenomegaly, hemoglobin, and achieving MTD; age, malaria season, MTD dose, fetal hemoglobin, α-thalassemia, and glucose-6-phosphate dehydrogenase deficiency had no effect. In multivariable regression of confirmed infections, ANC was significant (HR, 1.37 per doubled value; 95% CI, 1.10-1.70; P = .0052), and ANC values <3.0 × 109/L were associated with lower malaria incidence. Compared with nonpalpable spleen, 1- to 4-cm splenomegaly also was associated with higher malaria risk (HR, 2.01; 95% CI, 1.41-2.85; P = .0001). Hydroxyurea at MTD is associated with lower malaria incidence in SCA through incompletely defined mechanisms, but treatment-associated mild myelosuppression with ANC <3.0 × 109/L is salutary. Splenomegaly is an unexplained risk factor for malaria infections among children with SCA in Africa.

Stroke Prevention with Hydroxyurea Enabled through Research and Education: A Phase 2 Primary Stroke Prevention Trial in Sub-Saharan Africa

INTRODUCTION

Stroke is a severe complication of sickle cell anemia (SCA), with devastating sequelae. Transcranial Doppler (TCD) ultrasonography predicts stroke risk, but implementing TCD screening with suitable treatment for primary stroke prevention in low-resource environments remains challenging. SPHERE (NCT03948867) is a prospective phase 2 open-label hydroxyurea trial for SCA in Tanzania.

METHODS

After formal training and certification, local personnel screened children 2-16 years old; those with conditional (170-199 cm/s) or abnormal (≥200 cm/s) time-averaged mean velocities (TAMVs) received hydroxyurea at 20 mg/kg/day with dose escalation to maximum tolerated dose (MTD). The primary study endpoint is change in TAMV after 12 months of hydroxyurea; secondary endpoints include SCA-related clinical events, splenic volume and function, renal function, infections, hydroxyurea pharmacokinetics, and genetic modifiers.

RESULTS

Between April 2019 and April 2020, 202 children (average 6.8 ± 3.5 years, 53% female) enrolled and underwent TCD screening; 196 were deemed eligible by DNA testing. Most had numerous previous hospitalizations and transfusions, with low baseline hemoglobin (7.7 ± 1.1 g/dL) and %HbF (9.3 ± 5.4%). Palpable splenomegaly was present at enrollment in 49 (25%); average sonographic splenic volume was 103 mL (range 8-1,045 mL). TCD screening identified 22% conditional and 2% abnormal velocities, with hydroxyurea treatment initiated in 96% (45/47) eligible children.

CONCLUSION

SPHERE has built local capacity with high-quality research infrastructure and TCD screening for SCA in Tanzania. Fully enrolled participants have a high prevalence of elevated baseline TCD velocities and splenomegaly. SPHERE will prospectively determine the benefits of hydroxyurea at MTD for primary stroke prevention, anticipating expanded access to hydroxyurea treatment across Tanzania.

The Human Spleen in Malaria: Filter or Shelter?

The human spleen is an immune sentinel and controls red blood cell (RBC) quality. By mechanically retaining subsets of infected RBCs, the spleen may reduce the pace at which the parasite biomass increases before the adaptive immune response operates. Conversely, the spleen may contribute to malaria pathogenesis, particularly anemia that is associated with splenomegaly. Large spleens may also shelter parasites in chronic carriers. Upon treatment with artemisinins, the spleen clears circulating parasites by pitting and releases 'once-infected' RBCs in circulation. This triggers postartesunate delayed hemolysis and explains the long post-treatment positivity of histidine-rich protein 2 (HRP2)-based dipsticks. Importantly, splenic retention of RBCs also applies to gametocytes, the clearance of which may be enhanced by stiffening them with drugs, a potential way to block malaria transmission.

Is there a role for bedside ultrasound in malaria? A survey of the literature

PURPOSE

Point-of-care ultrasound (POCUS) has proven utility in the evaluation and treatment of many tropical diseases. Its role in malaria has been studied, but its value for the clinician at the bedside is unclear. Our review aimed at summarizing the existing studies to assess the usefulness, if any, of POCUS in treating malaria.

METHODS

We used Boolean operators using keywords "malaria", "acoustic", "ultrasound", "echography", and "ultrasonography" to search PubMed, Scopus, and Science Direct in three languages (Italian, French, and English).

RESULTS

We found 22 eligible references. Organs explored include the liver, spleen, heart, optic nerve sheath diameter (ONSD), kidney, lungs, and cerebral vasculature. Multiple pathologic findings by ultrasound are reported, but few demonstrate clinical utility. Current studies involve small numbers of patients, and a few trends emerge when studies are compared. The ability to combine study results is limited due to the significant heterogeneity that exists between studies in regards to both methods of evaluation and the reporting of organ pathology and malaria severity.

CONCLUSIONS AND ASSESSMENT

A review of the current literature indicates that the use of ultrasound by clinicians adds little to the diagnostic evaluation of patients with malaria. Our review did find that measurements of the spleen, lungs, optic nerve sheath diameter, and cerebral blood flow have potential utility in specific patient populations. Further studies are needed to evaluate whether this utility persists when a larger sample size is used.

Asymptomatic Plasmodium Parasites among Adults in Eastern Uganda: A Case of Donor Blood Screening at Mbale Regional Blood Bank

Background

There is a paucity of data on asymptomatic carriage of Plasmodium parasite among adult population in Eastern Uganda, an area of perennial high transmission of malaria. In this study, we estimated the prevalence of Plasmodium parasites in donor blood units at Mbale Regional Blood Bank (Mbale RBB), a satellite centre of the Uganda Blood Transfusion Service (UBTS).

Method

This was a cross-sectional descriptive study in which 380 screened donor blood units were examined for the presence of Plasmodium parasites. A systematic random sampling technique using the interval of 7 was used in selecting the screened blood units for testing. Two experienced malaria slide microscopists (MC1 and MC2) independently examined each thick and thin blood slide under high power magnification of X400 and then X1000 as stated on the study standard operation procedure (SOP). Each slide was examined for 100 oil immersion fields before the examiner declared them negative for Plasmodium parasites. The results by each microscopist's examination were tallied separately, and finally, the two tallies were compared. The third independent microscopist (MC3) was blinded to the results from MC1 and MC2, but whose role was to perform quality control on the slides randomly sampled and read 38 (10%) of all the slides and was available to examine any slides with inconsistent findings by MC1 or MC2.

Results

All the microscopists were unanimous in all the slide readings. Five of the thick smears (1.3%) confirmed the presence of Plasmodium parasites among donor blood units. Of these, 4/5 were from male donors. Plasmodium falciparum was identified in 4 positive samples, while Plasmodium malariae was identified in one of the donor units.

Conclusion

The 1.3% prevalence of Plasmodium malaria parasites in screened donor blood units represents risk of malaria blood transfusion transmitted infection and a pool of community transmittable malaria infections, respectively.

The Best Single Measurement for Assessing Splenomegaly in Patients with Cirrhotic Liver Morphology

RATIONALE AND OBJECTIVES

There is little agreement within the radiology literature as to the best single measurement for assessing splenomegaly. In this study, we evaluate the correlation of multiple unidirectional measurements of the spleen with splenic volume in patients with cirrhotic liver morphology on computed tomography (CT).

MATERIALS AND METHODS

Splenic volume was retrospectively calculated from CT examinations of 179 adult patients, 47 of whom were approved as renal donors, and 132 of whom were referred for various other indications, and were found to have cirrhotic liver morphology on CT. Seven unidimensional measurements (long-axis, cranial-caudal, width, and four measures of thickness) of each spleen were evaluated to identify which most closely correlated with the calculated volume.

RESULTS

The splenic width had the best correlation with splenic volume for mild-to-moderate splenomegaly, and the splenic cranial-caudal measurement had the best correlation with splenic volume for massive splenomegaly. Receiver operating characteristic analysis demonstrates that a splenic width measurement of approximately 10.5 cm has a sensitivity of 89% and a specificity of 78% for mild-to-moderate splenomegaly, and a cranial-caudal measurement of 14.6 cm has a sensitivity of 92% and a specificity of 91% for massive splenomegaly.

CONCLUSIONS

A splenic width threshold of 10.5 cm is the most sensitive (89%) and specific (78%) single measurement for mild-to-moderate splenomegaly in patients with cirrhotic liver morphology, whereas a cranial-caudal height threshold of 14.6 cm is the most sensitive (92%) and specific (91%) single measurement for massive splenomegaly.

Malaria parasite clearance

Following anti-malarial drug treatment asexual malaria parasite killing and clearance appear to be first order processes. Damaged malaria parasites in circulating erythrocytes are removed from the circulation mainly by the spleen. Splenic clearance functions increase markedly in acute malaria. Either the entire infected erythrocytes are removed because of their reduced deformability or increased antibody binding or, for the artemisinins which act on young ring stage parasites, splenic pitting of drug-damaged parasites is an important mechanism of clearance. The once-infected erythrocytes returned to the circulation have shortened survival. This contributes to post-artesunate haemolysis that may follow recovery in non-immune hyperparasitaemic patients. As the parasites mature Plasmodium vivax-infected erythrocytes become more deformable, whereas Plasmodium falciparum-infected erythrocytes become less deformable, but they escape splenic filtration by sequestering in venules and capillaries. Sequestered parasites are killed in situ by anti-malarial drugs and then disintegrate to be cleared by phagocytic leukocytes. After treatment with artemisinin derivatives some asexual parasites become temporarily dormant within their infected erythrocytes, and these may regrow after anti-malarial drug concentrations decline. Artemisinin resistance in P. falciparum reflects reduced ring stage susceptibility and manifests as slow parasite clearance. This is best assessed from the slope of the log-linear phase of parasitaemia reduction and is commonly measured as a parasite clearance half-life. Pharmacokinetic-pharmacodynamic modelling of anti-malarial drug effects on parasite clearance has proved useful in predicting therapeutic responses and in dose-optimization.

Ultrasonographic assessment of splenic volume at presentation and after anti-malarial therapy in children with malarial anaemia

Background

Splenic enlargement is a component of the host response to malaria and may also influence the genesis and progression of malarial anaemia. Few cross-sectional and no longitudinal studies have assessed the relationship between splenic volume measured ultrasonographically and haemoglobin concentrations in children with malaria.

Methods

Fifteen Papua New Guinean children with severe malarial anaemia (SMA; haemoglobin <50 g/L) and ten with moderate malarial anaemia (MMA; 51–99 g/L) were recruited. The SMA patients were given intramuscular artemether followed by oral artemisinin combination therapy (ACT), and were transfused one unit of packed cells 0.3-4.0 days post-admission. The MMA patients were treated with ACT. Splenic enlargement (Hackett’s grade, subcostal distance and ultrasonographically determined volume) and haemoglobin concentrations were measured on days 0, 1, 2, 3, 7, 14, 28, and 42.

Results

Associations between Hackett’s grade, subcostal distance and splenic volume were modest (r_s ≤ 0.62, P <0.001). Baseline splenic volume was not associated with age or haemoglobin (P ≥0.90). Mean splenic volume had fallen by approximately 50 % at day 14 in children with MMA (P ≤0.011 vs days 0, 1 and 2), but there was no change in the SMA group (P ≥0.30). There was no change in haemoglobin in the MMA group during follow-up but a rise in the SMA group to day 7 (P ≤0.05 vs days 0, 1, 2, and 3) which paralleled the packed cell volume transfused.

Conclusions

Clinical assessment of splenomegaly is imprecise compared with ultrasonography. Serial splenic volumes and haemoglobin concentrations suggest that the spleen does not influence post-treatment haemoglobin, including after transfusion.

Plasmodium falciparum malaria and invasive bacterial co-infection in young African children: the dysfunctional spleen hypothesis

Children with recent or acute malaria episodes are at increased risk of invasive bacterial infections (IBI). However, the exact nature of the malaria-IBI association is still unclear. Young children have an age-related spleen immunologic immaturity, mainly due to the still ongoing development of the marginal zone (MZ) B cell subset. By mounting a rapid antibody response against encapsulated bacteria, these cells are critical for the defence against highly pathogenic microorganisms that do not elicit classical T cell-dependent responses. There is increasing evidence that the anatomy of the spleen becomes disorganized during malaria infection, with complete dissolution of the MZ and apoptosis of MZ B cells. Correspondingly, a reduction in the frequency of the peripheral equivalent of the MZ B cells has been found in malaria endemic areas. A remarkable similarity exists in IBI susceptibility between African children with malaria and hyposplenic or splenectomized patients. However, studies specifically assessing the immune function of the spleen in controlling bacterial infections in young children with malaria are scarce.

Here, it is hypothesized that Plasmodium falciparum malaria infection constitutes a detrimental factor in the still immature spleen function of young children, resulting in a factually hyposplenic state during malaria episodes, putting children with malaria at a high risk to develop life-threatening bacterial infections. Studies to confirm or reject this hypothesis are greatly needed, as well as the development of affordable and feasible tools to assess the immune spleen function against encapsulated bacteria in children with malaria.