Resp tract. Aerosol virus replicates in the upper respiratory tract epithelium and then reaches the bronchii and pulmonary lymph nodes in 24h.to cause coughing. More virulent strains of virus replicate in pulmonary blood vessels and cause pulmonary thrombosis. Infected horses can shed virus for up to 10 days.

Viraemia. There is a cell associated viraemia, with virus infecting predominantly T cells, monocytes and dendritic cells.