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

  1. Arjen M. Dondorp1,2,
  2. Kamolrat Silamut1,
  3. Prakaykaew Charunwatthana1,
  4. Sunee Chuasuwanchai1,
  5. Ronnatrai Ruangveerayut3,
  6. Somyot Krintratun3,
  7. Nicholas J. White1,2,
  8. May Ho4 and
  9. Nicholas P. J. Day1,2
  1. 1 Faculty of Troical Medicine, Mahidol University, Bangkok, Thailand
  2. 2 Mae Sot Hospital, Mae Sot, Tak Province, Thailand
  3. 3 Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
  4. 4 Department of Microbiology and Infectious Diseases, Health Sciences Centre, Calgary, Alberta, Canada
  1. Reprints or correspondence: Dr. A. M. Dondorp, Deputy Director, Mahidol-Oxford Tropical Medicine Research Unit (MORU), Faculty of Tropical Medicine, Mahidol University, 4206 Rajvithi Rd., Bangkok 10400, Thailand (arjen{at}tropmedres.ac).

  1. Presented in part: Joint International Tropical Medicine Meeting, Bangkok, 29 November–1 December 2006.

 
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Abstract

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.

Plasmodium falciparum is a protozoan that infects human erythrocytes. Infected red blood cells (iRBCs) are in intimate contact with vascular endothelium throughout the parasite's 48-h life cycle, particularly during the second two-thirds of the life cycle, when erythrocytes containing mature parasites adhere to endothelium through parasite proteins that are transported to the erythrocyte surface [1]. This process, termed “cytoadherence,” is important for parasite survival and provides a mechanism for evasion of splenic clearance. Unfortunately, extensive sequestration may also kill the human host through obstruction of microcirculatory blood flow, hypoxia, tissue damage, and, ultimately, multiorgan failure.

The molecular basis of cytoadherence has been intensively studied over the past 2 decades. Research on the role played by endothelial cells in this process has focused mainly on the identification of receptor molecules under static conditions and on the regulation of adhesion molecule expression and, hence, cytoadherence by proinflammatory cytokines that are produced during an acute P. falciparum infection [1-3]. This approach has led to the endothelium being viewed merely as a provider of points of attachment for iRBCs, not as an important regulator of immune and inflammatory responses. Consequently, the possibility that endothelial cells may respond directly to iRBCs or their products and, thus, play a dynamic role in the pathogenesis of severe falciparum malaria has only been explored sporadically.

To investigate the interaction between parasitized erythrocytes and host vascular endothelium in malaria, we recently examined the effect of iRBC adhesion on primary human dermal microvascular endothelial cells (HDMECs) under flow conditions in vitro [4]. It was shown that the adhesion of iRBCs to HDMECs induces an intracellular signal that up-regulates subsequent iRBC adhesion via an Src-family kinase- and alkaline phosphatase-dependent mechanism. In further experiments, it was shown that endothelial CD36 is constitutively phosphorylated and that the target of the phosphatase activity triggered by the initial interaction with iRBCs is the ectodomain of CD36 at threonine-92 [5]. As with its natural ligand, thrombospondin-1, dephosphorylated CD36 appears to have a higher affinity for iRBCs under flow conditions [6]. Inhibition of phosphatase activity by the specific alkaline phosphatase inhibitor levamisole resulted in a 2-fold decrease in the number of adherent iRBCs. These experimental findings suggested that inhibition of CD36 dephosphorylation may constitute a novel therapeutic modality to reduce iRBC sequestration and, hence, pathology in falciparum malaria. To test the clinical potential of this approach in vivo, we studied the effect of levamisole on iRBC sequestration in patients with uncomplicated falciparum malaria. Levamisole is already widely used in humans as an immunomodulatory agent and as an antihelminthic.

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Patients, Materials, and Methods

Ethics approval for the present study was obtained from the Ministry of Public Health of the Royal Government of Thailand and from the Oxford Tropical Research Ethical Committee. The study was conducted in 2005. Consecutive adult patients (16 years old) with slide-proven falciparum malaria admitted to Mae Sot Hospital, Tak Province, Thailand, were enrolled in the study, provided that written informed consent was given by the patient or attending relative. Patients with any sign of severe disease, determined on the basis of World Health Organization criteria, were not eligible [7]. Other exclusion criteria were evidence of antimalarial treatment within 1 week of admission; contraindications to levamisole, quinine, or doxycycline therapy; documented allergies to any of the drugs; and pregnancy. Patients were randomized to receive either adjuvant therapy with a single 150-mg dose of levamisole hydrochloride (Janssen-Cilag) on admission or no adjuvant therapy. Randomization was open and was done by a computerized random-number generator. Antimalarial treatment was with oral quinine sulfate (10 mg of saltevery 8 h) in combination with doxycycline (4 mg) for 7 days. An artemisinin combination therapy was not used, because the broad stage specificity and the rapid onset of action of the artemisinins prevents maturation and subsequent sequestration of ring-form parasites, thus obscuring the effects of levamisole. On admission, samples for routine hematology and biochemistry were taken; peripheral blood parasitemia and staging were assessed in thin films at 0, 1, 2, 3, 4, 5, 6, 8, 10, and 12 h after admission and then every 6 h thereafter until complete parasite clearance. Microscopists were blinded with regard to treatment allocation. Differences in sequestration between levamisole and the control group were evaluated by comparing the integrated numbers (in parasites per microliter) and parasitemia (in percentages) of trophozoite-and schizont-stage parasites seen in the peripheral blood over time up to 72 h, determined as the area under the time-parasitemia curve. This was defined as the primary end point. Moreover, differences in sequestration were assessed through calculation of stage-specific sequestration ratios (SQRs) at various sample times, defined as follows: SQR p observed number of parasites (expected number of parasites × C f), where the observed number of parasites is the peripheral blood parasitemia (in parasites per microliter) of a well-defined developmental stage; the expected number of parasites of that developmental stage is the number expected to be present in the peripheral blood if the matching cohort of circulating younger-form parasites on admission had developed unrestricted, without either sequestration in the microvasculature or splenic clearance; and C f is the factor by which parasites are cleared by the spleen and through antimalarial drug action. Matching developmental-stage cohorts at different times after admission were derived from the parasite developmental ages bordering the morphological stages [8]. The well-defined morphological stages of the parasite consist of the following: tiny rings, small rings, large rings, early trophozoites, midtrophozoites, late trophozoites, and schizonts [9]. The parasite asexual-stage ages (from merozoite invasion) bordering the morphological stages, as assessed by in vitro culture, are, respectively, 12, 17, 22, 28, 37, and 42 h [8]. Assuming similar development rates in vivo, a cohort of large-ring forms on admission will evolve to the early trophozoite stage 6 h later (figure 1). Other matching cohorts include tiny rings on admission and small and large rings combined after 12 h, small rings on admission and large rings after 6 h, early trophozoites after 12 h and midtrophozoites after 18 h, and large rings on admission and either mid-trophozoites after 12 h or late trophozoites after 18 h. Although the midtrophozoite stage at 6 h matches with the early trophozoite stage on admission, this was not included in the analysis, because 3 patients had no early trophozoite stages on the admission blood slide. A decrease in SQR, thus, represents an increase in sequestration, if C f is constant. Parasite clearance time was defined as the interval between the start of treatment and the time of the first of 2 sequential negative thick films. Parasite reduction ratios (PRRs) at 24 and 48 h were defined as the ratio of the parasite count at admission to that at 24 and 48 h, respectively [10].

Figure 1.
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Figure 1.

Explanation of the sequestration ratio (SQR) as a measure of sequestration in falciparum malaria. A cohort of free-circulating young parasites of well-defined morphological stages can be quantified on admission in the peripheral blood of a patient with malaria. After 6 h, the same cohort of parasites will have matured to the next stage (black arrows) . The reduction in size of the cohort at 6 h is a measure of sequestration combined with parasite clearance and can be expressed as SQR = observed no. of parasites(expected no. of parasites × C f), where the observed no. of parasites is the peripheral blood parasitemia of a well-defined developmental stage; the expected no. of parasites of that developmental stage is the no. expected to be present in the peripheral blood if the matching cohort of circulating younger-form parasites on admission had developed unrestricted, without either sequestration in the microvasculature or splenic clearance; and Ci0 f is the factor by which parasites are cleared by the spleen and through antimalarial drug action. The SQR of more-mature stages can be calculated in a similar manner at 18 h after admission (in the shown example, midtrophozoites and late trophozoites).

The power calculation for this study was difficult, because there were no previous in vivo data on which to rely. The calculated sample size was 40 patients (total), on the basis of an expected standardized difference of 1 in the area under the time-parasitemia curves, a power of 85%, and a significance level of 5%. Differences between treatment groups were compared by Student’s t test for normally distributed variables and by the Mann-Whitney U test for the remainder, using the SPSS statistical software package (version 11; SPSS).

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Results

A planned interim analysis after 1 malaria season, at which time 21 patients with uncomplicated falciparum malaria had been randomized to receive either quinine treatment alone (n = 9) or levamisole in addition to quinine ( n = 12), showed highly significant differences in the primary end point between the 2 study groups. In our view, we felt it was warranted to stop the trial and publish the results to be able to proceed to a follow-up study. The baseline clinical parameters of the 2 groups of patients are summarized in table 1. New symptoms appearing within the first 2 days after admission included nausea (3 in the levamisole and 2 in the control group), vomiting (6 in the levamisole and 1 in the control group; P = .07), headache (1 in both groups), dizziness (2 in both groups), and tinnitus (3 in the levamisole and 2 in the control group), and 1 patient in the control group developed a papulomacular rash on the second day after admission. These symptoms are also known to be associated with malaria (headache, nausea, and vomiting) and quinine therapy (dizziness and tinnitus). Adjunctive treatment with levamisole was associated with the appearance of more-mature parasite stages in the peripheral blood (figures 2 and 3). The median integrated number of late-stage parasites (trophozoites and schizonts) seen on peripheral blood slides during the first 72 h after admission was 585,000 parasitesμL(interquartile range [IQR], 253,000–1,273,000 parasitesμL) in the levamisole group and was 95,300 parasitesμL(IQR, 29,100–362,000 parasitesμL) in the control group (P = .015 ). This difference represents the continued circulation in the levamisole group of late-stage parasites that would normally have sequestered. The observation could not be explained by differences in admission parasitemia, given that it was not significantly different between the 2 study groups.

Figure 2.
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Figure 2.

Effect of a single 150-mg dose of levamisole as adjunctive treatment to quinine on parasite sequestration in a patient with falciparum malaria, compared with sequestration in a patient treated with quinine alone. In the patient receiving levamisole, light microscopy of a peripheral blood slide shows late stages of Plasmodium falciparum 8 and 12 h after the drug is given (lower part of upper panel) . Late stages are not present after treatment with quinine alone (upper part of upper panel) . In the lower panel, this is quantified over time. The dark gray areas represent late-stage parasites (trophozoites and schizonts), and the light gray areas represent ring forms of P. falciparum . Unlike after treatment with quinine alone (upper part of lower panel), late-stage parasites are present in significant nos. between 4 and 24 h after levamisole treatment (lower part of lower panel), indicating their lack of sequestration.

Figure 3.
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Figure 3.

Late-stage parasites (trophozoites) of Plasmodium falciparum as a percentage of the total no. of parasites in the peripheral blood of patients treated with levamisole as adjunctive treatment to quinine (light gray bars), compared with that for patients treated with quinine alone (dark gray bars) . Box plots represent median, quartiles, and extreme values.

To quantify more clearly the inhibitory effects of levamisole on sequestration, the ratios between the observed and expected peripheral blood parasite densities of defined parasite age groups determined on the basis of validated morphological assessment were calculated at 6, 12, and 18 h after admission [8]. This ratio represents the product of the SQR ( 1 the sequestered fraction of parasites of a particular stage) and a clearance factor (C f; 1 the fraction of parasites of a particular stage cleared by the spleen), SQR × C f (see Patients, Materials, and Methods). Table 2 shows the differences in SQR × C f between the 2 treatment groups. A higher SQR × C f indicates prevention of sequestration if clearance (C f) is assumed to be similar in both groups. Six hours after the administration of levamisole and quinine, the mean SQR × C f for early trophozoites was close to 1, implying the almost complete inhibition of sequestration and the absence of significant splenic clearance. In the control group, the mean SQR × C f for early trophozoites was 0.26. Given that splenic clearance was still low at this time point (C f close to 1), on the basis of the data from the levamisole-treated group, this implies that 26% of the total number of early trophozoites were circulating and that 74% were sequestered. If it is assumed that, after 12 h, the nonsequestered fraction of early trophozoites (SQR) remained 0.26 in the control group, the corresponding splenic clearance factor (C f) was 0.130.26 = 0.5.If C f was unaffected by levamisole, this would imply that, after 12 h, the sequestration of early trophozoites was still completely inhibited in the levamisole-treated patients, because the SQR = 0.55C f = 0.550.5 = 1.1. After 12 and 18 h, the mean SQR × C f for midtrophozoites was 0.60 and 0.75, respectively, in the levamisole group and was significantly higher than that in the control group. This translates to the prevention of sequestration of at least 60%-70% of midtrophozoites in the levamisole-treated patients (because 0 ⩽ C f ⩽ 1). After 6 and 12 h, there was no significant difference in the SQR × C f of small-and large-ring forms, stages of parasite development that normally sequester to a much lesser extent than the more-mature trophozoites. At these time points, the SQR × C f for the ring forms is underestimated, because the cohort of small rings on admission does not overlap completely with the large-ring cohort after 6 h; however, this underestimation will be equal in both treatment arms, assuming that levamisole has no effect on parasite maturation (figure 1). The SQR × C f of trophozoites after 18 h, at which time mature-stage forms had disappeared from the peripheral circulation in most patients, was similar in both treatment arms. Schizont-stage parasites were detected only sporadically in the peripheral blood, with a median SQR × C f of 0, even after levamisole treatment. This suggests either that cytoadherence of this most-mature stage is not affected by levamisole or that these rigid schizont-infected red cells are cleared very effectively from the circulation by the spleen. In the peripheral blood samples obtained 18 h after start of quinine treatment, mature stages beyond late trophozoites could not be detected in the peripheral blood of most patients, presumably because the antimalarial drug action of quinine precluded assessment of the antiadhesive effects of levamisole at these later time points. Quinine mainly affects the more-mature stages of the parasites, starting at the early trophozoite to midtrophozoite stage [11].

Figure 4.
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Figure 4.

Peripheral blood parasite clearance curves for patients treated with levamisole as adjunctive treatment to quinine (light gray symbols), compared with those for patients treated with quinine alone (dark gray symbols) . Bars represent geometric mean parasite no. per microliter and SEs.

Table 1.
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Table 1.

Baseline characteristics of patients with uncomplicated malaria treated with quinine plus adjunctive levamisole vs. quinine alone (control).

Table 2.
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Table 2.

Comparison of sequestration ratios (SQRs) times a clearance factor (C f) at 3 time points after admission between patients treated with quinine plus adjunctive levamisole vs. quinine alone (control).

A linear regression model was constructed to determine whether the number of late-stage parasites (trophozoites and schizonts) over time was dependent on differences in sequestration (expressed as SQR × C f), independent of admission parasitemia. In a stepwise regression model with the total number of late-stage parasites over time as the dependent variable and with admission parasitemia and SQR × C f for trophozoites at different sample times as independent variables, both admission parasitemia ( t = 7.80 ; P = .001 ) and the SQR × C f of early trophozoites ( t = 3.55 ; P = .003) at 12 h contributed independently to the model. The SQR × Cf of midtrophozoites did correlate with the integrated number of trophozoites but dropped out in the stepwise analysis.

The median parasite clearance time was 72 h (IQR, 44–72 h) in the levamisole group, versus 36 h (IQR, 26–66 h) in the control group ( P = .023). The median PRRs at 24 and 48 h were respectively 3.7 (IQR, 1.8–8.3) and 2035 (IQR, 4-∞) in the levamisole group, versus 6.0 (3.5–366) and 1319 (73-∞) in the control group, both not significantly different ( P = .22 and P = .19 , respectively). The median time to 50% reduction of peripheral blood parasitemia was 12.5 h (IQR, 4.3–21.3 h) in the levamisole group, versus 7.5 h (IQR, 3.3–14.5 h) in the control group ( P = .28), and the median time to 90% reduction was significantly longer in the levamisole group (43.1 h [IQR, 26.4–65.8 h] vs. 27.1 h [IQR, 13.0–28.8 h]; P = .015 ) (figure 4). These differences reflect the higher numbers of circulating parasites in levamisole-treated patients, because the PRRs were not significantly different between the 2 groups.

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Discussion

Impairment of the microcirculation by sequestered, parasitized erythrocytes causing local tissue hypoxia, acidosis, and metabolic dysfunction is central to the pathogenesis of severe malaria. Of the human malarial pathogens, only P. falciparum sequesters in vital organs, and it is the species responsible for the vast majority of deaths from malaria. Autopsy studies in fatal adult falciparum malaria show convincing correlations between the extent of sequestration in the brain and the depth of coma on presentation [12, 13]. Preventing sequestration might save lives. Both the assessment of the SQR for late stages at different time points as well as the absolute and relative numbers of mature stages appearing in the peripheral blood strongly suggest that sequestration of mature parasite stages is to a large extent prevented after a single 150-mg dose of levamisole.

It is unlikely that the increase in the numbers of late-stage parasites in the peripheral blood is caused by decreased splenic clearance rather than by prevention of sequestration. Trophozoites and schizonts are rarely observed in the peripheral blood of patients with falciparum malaria, because of the efficiency of sequestration in the microcirculation. In vitro experiments show that, under febrile conditions (which enhance P. falciparum erythrocyte membrane protein-1 expression), cytoadhesion begins at ∼12 h of parasite development, 50% of the maximum effect is observed at 14–16 h, and adherence is highly effective during the second half of the parasite life cycle [14]. The high degree of sequestration of mature forms is also apparent from autopsy studies and from estimations of the sequestered as opposed to circulating parasite biomass based on plasma histidine-rich protein-2 [15]. In the levamisole-treated patients analyzed in the present study, the number of circulating early trophozoites 6 h after admission equaled the number expected from continued maturation of the cohort of large ring-stage parasites on admission. This can only be explained by the near absence of sequestration of early trophozoites and not by decreased splenic clearance. Also, the prolonged parasite clearance time in the levamisole group can be explained by the increased number of circulating trophozoites prevented from sequestering rather than decreased splenic clearance, whereas in the control group a portion of these late stages were hidden in the microcirculation as sequestered iRBCs. That the parasite reduction rate was similar in the 2 treatment groups supports this.

Schizont-infected erythrocytes were only very rarely detected in the peripheral blood, even after levamisole therapy. Although the deformability of trophozoite-infected erythrocytes is affected only a little, schizont-infected erythrocytes are rigid and rapidly cleared by the spleen [16], which might obscure the detection of reduced sequestration. Alternatively, schizonts may demonstrate highly efficient sequestration, which is unaffected by levamisole.

In summary, our findings show that levamisole inhibits the sequestration of P. falciparum -infected erythrocytes. This makes the drug a possible candidate for adjunctive treatment for severe malaria, which still carries a mortality rate of ∼20%. This present study was small, and, although it indicates that sequestration can be prevented, further studies are required to determine the magnitude of this effect and whether it can be translated into a therapeutic advantage. A study of the use of levamisole as adjunctive treatment for severe malaria is under way.

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Footnotes

  • Potential conflicts of interest: none reported.

  • Financial support: Wellcome Trust of Great Britain.

  • Received August 11, 2007.
  • Accepted March 2, 2007.
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References

  1. ↵
    1. Magowan C,
    2. ollish W,
    3. Anderson L,
    4. Leech J
    . Cytoadherence by Plasmodium falciparum -infected erythrocytes is correlated with the ex. Magowan C, Wollish W, Anderson L, Leech J.
    1. Ho M,
    2. White NJ
    . Molecular mechanisms of cytoadherence in malaria. Am J Physiol 1999;276:C1231-42.
    MedlineWeb of Science
  3. ↵
    1. Yipp BG,
    2. Anand S,
    3. Schollaardt T,
    4. et al
    . Synergism of multiple adhesion molecules in mediating cytoadherence of Plasmodium falciparum -infected erythrocytes to microvascular endothelial cells under flow. Blood 2000;96:2292-8.
    Abstract/FREE Full Text
  4. ↵
    1. Yipp BG,
    2. Robbins SM,
    3. Resek ME,
    4. et al
    . Src-family kinase signaling modulates the adhesion of Plasmodium falciparum on human microvascular endothelium under flow. Blood 2003;101:2850-7.
    Abstract/FREE Full Text
  5. ↵
    1. Ho M,
    2. Hoang HL,
    3. Lee KM,
    4. et al
    . Ectophosphorylation of CD36 regulates cytoadherence of Plasmodium falciparum to microvascular endothelium under flow conditions. Infect Immun 2005;73:8179-87.
    Abstract/FREE Full Text
  6. ↵
    1. Asch AS,
    2. Liu I,
    3. Briccetti FM,
    4. et al
    . Analysis of CD36 binding domains: ligand specificity controlled by dephosphorylation of an ectodomain. Science 1993;262:1436-40.
    Abstract/FREE Full Text
  7. ↵
    1. World Health Organization
    . Severe and complicated malaria. Trans R Soc Trop Med Hyg 1990;84(Suppl 2):1-65.
  8. ↵
    1. Desakorn V,
    2. Dondorp AM,
    3. Silamut K,
    4. et al
    . Stage-dependent production and release of histidine-rich protein 2 by Plasmodium falciparum . Trans R Soc Trop Med Hyg 2005;99:517-24.
    MedlineWeb of Science
  9. ↵
    1. Silamut K,
    2. Phu NH,
    3. Whitty C,
    4. et al
    . A quantitative analysis of the microvascular sequestration of malaria parasites in the human brain. Am J Pathol 1999;155:395-410.
    MedlineWeb of Science
  10. ↵
    1. White NJ
    . Assessment of the pharmacodynamic properties of antimalarial drugs in vivo. Antimicrob Agents Chemother 1997;41:1413-22.
    FREE Full Text
  11. ↵
    1. ter Kuile F,
    2. White NJ,
    3. Holloway P,
    4. Pasvol G,
    5. Krishna S
    . Plasmodium falciparum: in vitro studies of the pharmacodynamic properties of drugs used for the treatment of severe malaria. Exp Parasitol 1993;76:85-95.
    CrossRefMedlineWeb of Science
  12. ↵
    1. MacPherson GG,
    2. Warrell MJ,
    3. White NJ,
    4. Looareesuwan S,
    5. Warrell DA
    . Human cerebral malaria: a quantitative ultrastructural analysis of parasitized erythrocyte sequestration. Am J Pathol 1985;119:385-401.
    MedlineWeb of Science
  13. ↵
    1. Pongponratn E,
    2. Turner GD,
    3. Day NP,
    4. et al
    . An ultrastructural study of the brain in fatal Plasmodium falciparum malaria. Am J Trop Med Hyg 2003;69:345-59.
    Abstract/FREE Full Text
  14. ↵
    1. Udomsangpetch R,
    2. Pipitaporn B,
    3. Silamut K,
    4. et al
    . Febrile temperatures induce cytoadherence of ring-stage Plasmodium falciparum -infected erythrocytes. Proc Natl Acad Sci USA 2002;99:11825-9.
    Abstract/FREE Full Text
  15. ↵
    1. Dondorp AM,
    2. Desakorn V,
    3. Pongtavornpinyo W,
    4. et al
    . Estimation of the total parasite biomass in acute falciparum malaria from plasma PfHRP2. PLoS Med 2005;2:e204.
    CrossRefMedline
  16. ↵
    1. Cranston HA,
    2. Boylan CW,
    3. Carroll GL,
    4. et al
    . Plasmodium falciparum maturation abolishes physiologic red cell deformability. Science 1984;223:400-3.
    Abstract/FREE Full Text
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  1. J Infect Dis. (2007) 196 (3): 460-466. doi: 10.1086/519287
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