Severe Plasmodium falciparum Malaria Is Associated with Circulating Ultra-Large von Willebrand Multimers and ADAMTS13 Inhibition

Plasmodium falciparum infection results in adhesion of infected erythrocytes to blood vessel endothelium, and acute endothelial cell activation, together with sequestration of platelets and leucocytes. We have previously shown that patients with severe infection or fulminant cerebral malaria have significantly increased circulatory levels of the adhesive glycoprotein von Willebrand factor (VWF) and its propeptide, both of which are indices of endothelial cell activation. In this prospective study of patients from Ghana with severe (n = 20) and cerebral (n = 13) P. falciparum malaria, we demonstrate that increased plasma VWF antigen (VWF∶Ag) level is associated with disproportionately increased VWF function. VWF collagen binding (VWF∶CB) was significantly increased in patients with cerebral malaria and severe malaria (medians 7.6 and 7.0 IU/ml versus 1.9 IU/ml; p<0.005). This increased VWF∶CB correlated with the presence of abnormal ultra-large VWF multimers in patient rather than control plasmas. Concomitant with the increase in VWF∶Ag and VWF∶CB was a significant persistent reduction in the activity of the VWF-specific cleaving protease ADAMTS13 (∼55% of normal; p<0.005). Mixing studies were performed using P. falciparum patient plasma and normal pooled plasma, in the presence or absence of exogenous recombinant ADAMTS13. These studies demonstrated that in malarial plasma, ADAMTS13 function was persistently inhibited in a time-dependent manner. Furthermore, this inhibitory effect was not associated with the presence of known inhibitors of ADAMTS13 enzymatic function (interleukin-6, free haemoglobin, factor VIII or thrombospondin-1). These novel findings suggest that severe P. falciparum infection is associated with acute endothelial cell activation, abnormal circulating ULVWF multimers, and a significant reduction in plasma ADAMTS13 function which is mediated at least in part by an unidentified inhibitor

Current Role of Community-Acquired Methicillin-Resistant Staphylococcus Aureus among Children with Skin and Soft Tissue Infections

Community-acquired methicillin-resistant Staphylococcus aureus has become a wellestablished pathogen with alarming rates during the last decade. The current situation of this bacteria in pediatric infections is very limited and motivated us to conduct this study. This is a retrospective and analytical study including patients less than 18 years of age with the diagnosis of skin or soft tissue infections in 2008 and 2009 meeting the criteria of Community-acquired infection. A prevalence of 41.9% among skin and soft tissue infections was found. Inducible resistance to clindamycin was detected in 1.3% of the strains and the infection shows a seasonal predilection for summer (P=0.003); 57.8% of the cases required hospitalization with a mean stay of 3.3±2.5 days. The susceptibility to clindamycin and co-trimoxazole is 88 and 97% respectively. The resistance to erythromycin has reached 92%. The main diagnoses at presentation was gluteal abscess plus cellulitis (34.2%). The prevalence of CA-MRSA is trending up and seems to become a large burden for the health system in our community. Clindamycin is still an excellent option in the community setting since inducible clindamycin resistance is extremely low in this community. Co-trimoxazole should be kept as a reserved drug to avoid the rapid resurgence resistance in the community

von Willebrand factor propeptide in malaria: evidence of acute endothelial cell activation

The pathogenicity of Plasmodium falciparum is thought to relate to the unique ability of infected erythrocytes to adhere to and subsequently activate the vascular endothelium. To study the state of endothelial activation during falciparum malaria, we measured plasma levels of both von Willebrand factor (VWF) and its propeptide, indices of chronic and acute endothelial cell perturbation, respectively. Results were correlated with clinical and biochemical markers of disease severity, including plasma lactate. Our data show that acute endothelial cell activation is a hallmark of malaria in children, indicated by a significant rise in VWF and VWF propeptide. The highest VWF and propeptide levels were seen in cerebral and non-cerebral severe malaria, and associations found between VWF propeptide level and lactate (P < 0.001). Mean VWF propeptide levels (nmol/l) were in cerebral malaria 33.4, non-cerebral severe malaria 26.3, mild malaria 22.1, non-malaria febrile illness 10.2, and controls 10.1. Differences between patient and control groups were highly significant (P < 0.005). Follow-up of 26 cerebral malaria cases showed that levels of VWF propeptide, but not VWF fell by 24 h, following the clinical course of disease and recovery. These novel findings potentially implicate acute, regulated exocytosis of endothelial cell Weibel-Palade bodies in the pathogenesis of Plasmodium falciparum malari

Plasma ADAMTS13 activity inhibition in <i>P. falciparum</i> malaria.

<p>(A&B) To investigate further the mechanisms responsible for the marked and discrepant increase in plasma VWF∶CB, and the significant reduction in ADAMTS13 activity, we investigated the effects of mixing malaria plasma with normal plasma. Plasma from four different children (□, ●, △, ◆) with SM (each with baseline ADAMTS13 activities of ∼0.4 U/dl) were mixed in various proportions with pooled normal plasma, and ADAMTS13 activity determined. No evidence of an immediate ADAMTS13 inhibitor effect was observed (<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1000349#ppat-1000349-g004" target="_blank">Fig 4A</a>). However following incubation at 37°C for 15 min or 30 min (<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1000349#ppat-1000349-g004" target="_blank">Fig 4B</a>), significant ADAMTS13 inhibition was observed in malaria plasmas at either 75%∶25% (▲), or 50%∶50% (●), but not in normal control plasma (□). All results represent mean±SEM. (C) To further investigate whether malarial plasma contained an ADAMTS13 inhibitor, individual malaria plasma samples (n = 4) and control plasmas (n = 4) were spiked with recombinant human ADAMTS13. Again, significant inhibition of rADAMTS13 activity (means±SEM) was observed only in malaria plasma (◆) but not in normal plasma (■).</p

Severe <i>Plasmodium falciparum</i> malaria influences plasma VWF antigen level and collagen binding activity.

<p>(A) Plasma VWF∶Ag levels (<i>white bars – left Y axis</i>) were measured by ELISA, and VWF activity by collagen binding activity (VWF∶CB) (<i>grey bars – right Y axis</i>). Each plasma sample was tested in duplicate at three dilutions, and median values for each group are shown. VWF∶Ag and VWF∶CB levels were markedly elevated in patients with cerebral malaria and in children with severe malaria at presentation compared to levels in healthy control children. (B) In a cohort of children with cerebral malaria (CM), the time-course of VWF∶Ag and VWF∶CB levels following admission and commencement of anti-malarial therapy was assessed using follow-up plasma samples collected after 24 and 72 hours respectively. (C) Although both VWF∶Ag and VWF∶CB were increased in all cases of <i>P. falciparum</i> malaria, the relative increase observed in plasma VWF∶CB levels was significantly higher (p<0.05), such that the ratio of CB to Ag was consistently >1 in children with CM (n = 13; ●) or SM (n = 20; ▲) at presentation compared to healthy control subjects (n = 25; □). (<i>Hashed line indicates 1∶1 ratio</i>).</p