Prakaykaew Charunwatthana

Direct In Vivo Assessment of Microcirculatory Dysfunction in Severe Falciparum Malaria

BACKGROUND This study sought to describe and quantify microcirculatory changes in the mucosal surfaces of patients with severe malaria, by direct in vivo observation using orthogonal polarization spectral (OPS) imaging. METHODS The microcirculation in the rectal mucosa of adult patients with severe malaria was assessed by use of OPS imaging, at admission and then daily. Comparison groups comprised patients with uncomplicated falciparum malaria, patients with bacterial sepsis, and healthy individuals. RESULTS Erythrocyte velocities were measured directly in 43 adult patients with severe falciparum malaria, of whom 20 died. Microcirculatory blood flow was markedly disturbed, with heterogeneous obstruction that was proportional to severity of disease. Blocked capillaries were found in 29 patients (67%) and were associated with concurrent hyperdynamic blood flow (erythrocyte velocity, >750 mm/s) in adjacent vessels in 27 patients (93%). The proportion of blocked capillaries correlated with the base deficit in plasma and with the concentration of lactate. Abnormalities disappeared when the patients recovered. In healthy individuals and in patients with uncomplicated malaria or sepsis, no stagnant erythrocytes were detected, and, in patients with sepsis, hyperdynamic blood flow was prominent. CONCLUSION Patients with severe falciparum malaria show extensive microvascular obstruction that is proportional to the severity of the disease. This finding underscores the prominent role that microvascular obstruction plays in the pathophysiology of severe malaria and illustrates the fundamental difference between the microvascular pathophysiology of malaria and that of bacterial sepsis.

A Simple Score to Predict the Outcome of Severe Malaria in Adults

BACKGROUND World Health Organization treatment guidelines recommend that adults with severe malaria be admitted to an intensive care unit (ICU). However, ICU facilities are limited in the resource-poor settings where most malaria occurs. Identification of patients at greater risk of complications may facilitate their triage and resource allocation. METHODS With use of data from a trial conducted in Southeast Asia (n=868), a logistic regression model was built to identify independent predictors of mortality among adults with severe malaria. A scoring system based on this model was tested in the original dataset and then validated in 2 series from Bangladesh (n=188) and Vietnam (n=292). RESULTS Acidosis (base deficit) and cerebral malaria (measured as Glasgow Coma Score) were the main independent predictors of outcome. The 5-point Coma Acidosis Malaria (CAM) score was simply derived from these 2 variables. Mortality increased steadily with increasing score. A CAM score <2 predicted survival with a positive predictive value (PPV) of 95.8% (95% confidence interval [CI], 93%- 97.7%). Of the 14 of 331 patients who died with a CAM score <2, 11 (79%) had renal failure and death occurred late after hospital admission (median, 108 h; range, 40-360 h). Substitution of plasma bicarbonate as the measure of acidosis only slightly reduced the prognostic value of the model. Use of respiratory rate was inferior, but a score <2 still predicted survival with a PPV of 92.2% (95% CI, 89.1%-94.7%). CONCLUSIONS Patients with a CAM score <2 at hospital admission may be safely treated in a general ward, provided that renal function can be monitored.

N-Acetylcysteine as adjunctive treatment in severe malaria: A randomized double blinded placebo controlled clinical trial

Objective:Markers of oxidative stress are reported to be increased in severe malaria. It has been suggested that the antioxidant N-acetylcysteine (NAC) may be beneficial in treatment. We studied the efficacy and safety of parenteral NAC as an adjunct to artesunate treatment of severe falciparum malaria. Design:A randomized, double-blind, placebo-controlled trial on the use of high-dose intravenous NAC as adjunctive treatment to artesunate. Setting:A provincial hospital in Western Thailand and a tertiary referral hospital in Chittagong, Bangladesh. Patients:One hundred eight adult patients with severe falciparum malaria. Interventions:Patients were randomized to receive NAC or placebo as an adjunctive treatment to intravenous artesunate. Measurements and Main Results:A total of 56 patients were treated with NAC and 52 received placebo. NAC had no significant effect on mortality, lactate clearance times (p = 0.74), or coma recovery times (p = 0.46). Parasite clearance time was increased from 30 hours (range, 6–144 hours) to 36 hours (range, 6–120 hours) (p = 0.03), but this could be explained by differences in admission parasitemia. Urinary F2-isoprostane metabolites, measured as a marker of oxidative stress, were increased in severe malaria compared with patients with uncomplicated malaria and healthy volunteers. Admission red cell rigidity correlated with mortality, but did not improve with NAC. Conclusion:Systemic oxidative stress is increased in severe malaria. Treatment with NAC had no effect on outcome in patients with severe falciparum malaria in this setting.

Severe malaria is associated with a deficiency of von Willebrand factor cleaving protease, ADAMTS13

Severe falciparum malaria remains a major killer in tropical countries. Central in the pathophysiology is mechanical obstruction in the microcirculation caused by cytoadherence and sequestration of parasitized erythrocytes. However, the pathogenesis of many features complicating severe malaria, including coma, renal failure and thrombocytopenia, remains incompletely understood. These disease manifestations are also key features of thrombotic thrombocytopenic purpura, a life-threatening disease strongly associated with a deficiency of the von Willebrand factor (VWF) cleaving protease, ADAMTS13. We measured plasma ADAMTS13 activity, VWF antigen and VWF propeptide levels in 30 patients with severe falciparum malaria, 12 patients with uncomplicated falciparum malaria and 14 healthy Bangladeshi controls. In patients with severe malaria ADAMTS13 activity levels were markedly decreased in comparison to normal controls (mean [95%CI]: 23% [20-26] vs. 64% [55-72]) and VWF antigen and propeptide concentrations were significantly elevated (VWF antigen: 439% [396-481] vs. 64% [46-83]; VWF propeptide: 576% [481-671] vs. 69% [59-78]). In uncomplicated malaria VWF levels were also increased compared to healthy controls but ADAMTS13 activity was normal. The results suggest that decreased ADAMTS13 activity in combination with increased VWF concentrations may contribute to the complications in severe malaria.

Levamisole Inhibits Sequestration of Infected Red Blood Cells in Patients with Falciparum Malaria

BACKGROUND Sequestration of infected red blood cells (iRBCs) in the microcirculation is central to the pathophysiology of falciparum malaria. It is caused by cytoadhesion of iRBCs to vascular endothelium, mediated through the binding of Plasmodium falciparum erythrocyte membrane protein-1 to several endothelial receptors. Binding to CD36, the major vascular receptor, is stabilized through dephosphorylation of CD36 by an alkaline phosphatase. This is inhibited by the alkaline phosphatase-inhibitor levamisole, resulting in decreased cytoadhesion. METHODS Patients with uncomplicated falciparum malaria were randomized to receive either quinine treatment alone or treatment with a single 150-mg dose of levamisole as an adjunct to quinine. Peripheral blood parasitemia and parasite stage distribution were monitored closely over time. RESULTS Compared with those in control subjects, peripheral blood parasitemias of mature P. falciparum parasites increased during the 24 h after levamisole administration (n=21; P=.006). The sequestration ratio (between observed and expected peripheral blood parasitemia) of early trophozoite and midtrophozoite parasites increased after levamisole treatment, with near complete prevention of early trophozoite sequestration and >65% prevention of midtrophozoite sequestration. CONCLUSION These findings strongly suggest that levamisole decreases iRBC sequestration in falciparum malaria in vivo and should be considered as a potential adjunctive treatment for severe falciparum malaria. TRIAL REGISTRATION Current Controlled Trials identifier: 15314870.

The spectrum of retinopathy in adults with Plasmodium falciparum malaria

Summary A specific retinopathy has been described in African children with cerebral malaria, but in adults this has not been extensively studied. Since the structure and function of the retinal vasculature greatly resembles the cerebral vasculature, study of retinal changes can reveal insights into the pathophysiology of cerebral malaria. A detailed observational study of malarial retinopathy in Bangladeshi adults was performed using high-definition portable retinal photography. Retinopathy was present in 17/27 adults (63%) with severe malaria and 14/20 adults (70%) with cerebral malaria. Moderate or severe retinopathy was more frequent in cerebral malaria (11/20, 55%) than in uncomplicated malaria (3/15, 20%; P = 0.039), bacterial sepsis (0/5, 0%; P = 0.038) or healthy controls (0/18, 0%; P < 0.001). The spectrum of malarial retinopathy was similar to that previously described in African children, but no vessel discolouration was observed. The severity of retinal whitening correlated with admission venous plasma lactate (P = 0.046), suggesting that retinal ischaemia represents systemic ischaemia. In conclusion, retinal changes related to microvascular obstruction were common in adults with severe falciparum malaria and correlated with disease severity and coma, suggesting that a compromised microcirculation has important pathophysiological significance in severe and cerebral malaria. Portable retinal photography has potential as a valuable tool to study malarial retinopathy.

Relative contributions of macrovascular and microvascular dysfunction to disease severity in falciparum malaria

BACKGROUND Sequestration of parasitized erythrocytes in the microcirculation is considered the central pathophysiological process in severe falciparum malaria. Hypovolemia with reduced oxygen delivery and microvascular obstruction have different implications for patient management; however, their relative contributions to disease severity are uncertain. METHODS Adult patients (n = 28) with severe Plasmodium falciparum malaria were enrolled in a prospective hemodynamic study. Volume status and oxygen delivery were assessed using transpulmonary thermodilution. Microvascular sequestration was measured using orthogonal polarized spectroscopy. FINDINGS Duration of therapy before study enrollment was correlated with the amount of directly visualized and quantitated microvascular sequestration (P = .03). The amount of sequestration correlated with plasma lactate (r(s )= 0.55; P = .003) and disease severity (r(s )= 0.41; P = .04). In patients who had received artesunate for <10 hours, sequestration was higher in fatal cases than in survivors: median (range) 45% (32-50) vs 15% (0-40); P = .03). Parasite biomass estimated from plasma P. falciparum histidine-rich protein 2 correlated positively with disease severity (r(s )= 0.48; P = .01) and was significantly higher in patients who died (P = .046). There was no relationship between oxygen delivery and disease severity (P = .64) or outcome (P = .74). INTERPRETATION Vital organ dysfunction in severe malaria results primarily from sequestration of parasitized erythrocytes in the microvasculature rather than reduction in circulating blood volume and oxygen delivery.

Fluid resuscitation of adults with severe falciparum malaria: effects on acid-base status, renal function, and extravascular lung water

Objective:To evaluate the efficacy and safety of liberal fluid resuscitation of adults with severe malaria. Design, Setting, Patients, and Methods:Twenty-eight Bangladeshi and Indian adults with severe falciparum malaria received crystalloid resuscitation guided by transpulmonary thermodilution (PiCCO) in an intensive care setting. Systemic hemodynamics, microvascular indices and measures of acidosis, renal function, and pulmonary edema were followed prospectively. Results:All patients were hypovolemic (global end-diastolic volume index < 680 mL/m2) on enrollment. Patients received a median (range) 3230 mL (390–7300) of isotonic saline in the first 6 hours and 5450 mL (710–13,720) in the first 24 hours. With resuscitation, acid-base status deteriorated in 19 of 28 (68%), and there was no significant improvement in renal function. Extravascular lung water increased in 17 of 22 liberally resuscitated patients (77%); eight of these patients developed pulmonary edema, five of whom died. All other patients survived. All patients with pulmonary edema during the study were hypovolemic or euvolemic at the time pulmonary edema developed. Plasma lactate was lower in hypovolemic patients before (rs = 0.38; p = 0.05) and after (rs = 0.49; p = 0.01) resuscitation but was the strongest predictor of mortality before (chi-square = 9.9; p = 0.002) and after resuscitation (chi-square = 11.1; p < 0.001) and correlated with the degree of visualized microvascular sequestration of parasitized erythrocytes at both time points (rs = 0.55; p = 0.003 and rs = 0.43; p = 0.03, respectively). Persisting sequestration was evident in 7 of 15 patients (47%) 48 hours after enrollment. Conclusions:Lactic acidosis—the strongest prognostic indicator in adults with severe falciparum malaria—results from sequestration of parasitized erythrocytes in the microcirculation, not from hypovolemia. Liberal fluid resuscitation has little effect on this sequestration and does not improve acid-base status or renal function. Pulmonary edema—secondary to increased pulmonary vascular permeability—is common, unpredictable, and exacerbated by fluid loading. Liberal fluid replacement of adults with severe malaria should be avoided.

Characterization of G6PD Genotypes and Phenotypes on the Northwestern Thailand-Myanmar Border

Mutations in the glucose-6-phosphate dehydrogenase (G6PD) gene result in red blood cells with increased susceptibility to oxidative damage. Significant haemolysis can be caused by primaquine and other 8-aminoquinoline antimalarials used for the radical treatment of Plasmodium vivax malaria. The distribution and phenotypes of mutations causing G6PD deficiency in the male population of migrants and refugees in a malaria endemic region on the Thailand-Myanmar border were characterized. Blood samples for G6PD fluorescent spot test (FST), G6PD genotyping, and malaria testing were taken from 504 unrelated males of Karen and Burman ethnicities presenting to the outpatient clinics. The overall frequency of G6PD deficiency by the FST was 13.7%. Among the deficient subjects, almost 90% had the Mahidol variant (487G>A) genotype. The remaining subjects had Chinese-4 (392G>T), Viangchan (871G>A), Açores (595A>G), Seattle (844G>C) and Mediterranean (563C>T) variants. Quantification of G6PD activity was performed using a modification of the standard spectrophotometric assay on a subset of 24 samples with Mahidol, Viangchan, Seattle and Chinese-4 mutations; all samples showed a residual enzymatic activity below 10% of normal and were diagnosed correctly by the FST. Further studies are needed to characterise the haemolytic risk of using 8-aminoquinolines in patients with these genotypes.

Pharmacokinetic interactions between primaquine and chloroquine

ABSTRACT Chloroquine combined with primaquine has been the standard radical curative regimen for Plasmodium vivax and Plasmodium ovale malaria for over half a century. In an open-label crossover pharmacokinetic study, 16 healthy volunteers (4 males and 12 females) aged 20 to 47 years were randomized into two groups of three sequential hospital admissions to receive a single oral dose of 30 mg (base) primaquine, 600 mg (base) chloroquine, and the two drugs together. The coadministration of the two drugs did not affect chloroquine or desethylchloroquine pharmacokinetics but increased plasma primaquine concentrations significantly (P ≤ 0.005); the geometric mean (90% confidence interval [CI]) increases were 63% (47 to 81%) in maximum concentration and 24% (13 to 35%) in total exposure. There were also corresponding increases in plasma carboxyprimaquine concentrations (P ≤ 0.020). There were no significant electrocardiographic changes following primaquine administration, but there was slight corrected QT (QTc) (Fridericia) interval lengthening following chloroquine administration (median [range] = 6.32 [−1.45 to 12.3] ms; P < 0.001), which was not affected by the addition of primaquine (5.58 [1.74 to 11.4] ms; P = 0.642). This pharmacokinetic interaction may explain previous observations of synergy in preventing P. vivax relapse. This trial was registered at ClinicalTrials.gov under reference number NCT01218932.