Pandemic H1N1 Influenza Infection and Vascular Thrombosis

Abstract

During the summer and fall of 2009, significant thrombotic events were observed in patients infected with the pandemic H1N1 influenza A virus. In a retrospective chart review of 119 individuals admitted to the hospital with H1N1 virus infection, 7 patients (5.9%) were found to have experienced thrombotic vascular events.

Influenza virus H1N1 activates platelets through FcγRIIA signaling and thrombin generation

“…Consistent with the autopsies of H 1 N 1 -infected patients, which have documented platelets in the affected lungs, [33][34][35] we observed an accumulation of platelets in bronchoalveolar lavages of H 1 N 1 -infected mice (supplemental Figure 3). The interaction between platelets and H 1 N 1 may thus take place in blood during viremia in critically ill patients or in the inflamed lungs where immune complexes against H 1 N 1 are present, 23 when vascular permeability is increased 65 and/or when the integrity of lung capillaries is compromised.…”

“…Platelets are an important source of inflammatory mediators, which are either stored or can be produced de novo upon activation. 3,4 Intrigued by the presence of activated platelets in the blood of critically ill influenza H 1 N 1 infected patients, [33][34][35]37 we aimed to study the activation of platelets by the H 1 N 1 IAV.…”

“…17 Indeed, the autopsy of patients with fatal influenza infection revealed pulmonary vascular thrombosis. [33][34][35] Previous work indicating that incubation of human platelets with H 3 N 2 virus induces antibody-and complementdependent platelet lysis could also possibly explain the thrombocytopenia observed in patients. 36 Alternatively, the lower platelet count in IAV-infected patients might result from the direct or indirect platelet activation by the virus, promoting platelet-leukocyte aggregation.…”

Emerging roles for platelets as immune and inflammatory cells

“…In the 2009 H1N1A pandemic, ;6% of patients experienced a thrombotic event. 162 Platelet activation in H1N1A infection exceeded platelet activation noted in bacterial pneumonia. 163 Similar to HIV infection, platelet-monocyte aggregates are elevated in influenza infection suggesting that platelets affect viral immune responses.…”

Coagulation profile in patients with H1N1 influenza A infection undergoing treatment for haematological malignancies

“…In one report, thrombotic vascular events were detected in 5.6% of cases during the H1N1 pandemic in 2009 [13]. Recent evidence suggests that endothelial activation, loss of barrier function, and consequent microvascular leak may also contribute to the pathogenesis of severe influenza, observed in different subtypes of the disease [14].…”