Cytokine release and endothelial dysfunction: a perfect storm in orbivirus pathogenesis.

Abstract

Although bluetongue viruses (BTV) and epizootic haemorrhagic disease viruses (EHDV) are closely related, there are differences in susceptibility to these viruses both between and within a species. White‑tailed deer are susceptible to disease by both BTV and EHDV, sheep are susceptible to BTV, but resistant to EHDV, and cattle can be infected with both viruses but disease is usually subclinical. Host genetics probably play a role in the disease outcome, but cytokine and endothelial responses are likely to determine if subclinical or clinical disease develops. Dendritic macrophages deliver virus to lymph nodes following the bite of an infected Culicoides. The virus then disseminates to many organs replicating in mononuclear phagocytes and endothelium. Initially, an interferon‑1 response probably determines if the disease develops. Replication in mononuclear cells and endothelium results in the release of cytokines and vasoactive mediators, and may result in endothelial cell death leading to the clinical features of fever, hyperaemia, exudation of fluid, and haemorrhage. Disease outcome may also be linked to virus binding Toll‑like receptor‑3 and upregulation of endothelial surface receptors potentiating cytokine release and allowing transmigration of inflammatory cells, respectively. Despite a wealth of information, host genetics involved in resistance to BTV and EHDV and how variations in cytokines and endothelial responses determine clinical outcome still need further elucidation.