(A) PVM is a negative sense non-segmented single stranded RNA virus, family Paramyxoviridae, genus Pneumovirus, gene order as shown. (B) Challenge with a minimal inoculum (<100 pfu) results in a severe respiratory infection, with macroscopic evidence of hemorrhage and (C) microscopic pathology including profound granulocytic inflammation and edema. (D) Immunoreactive virus can be detected in bronchiolar epithelial cells. Panels (A), (B), (C), and (D) reprinted with permission from references [29], [37], [38], and [33], respectively.