viruses of the genus Paramyxovirus, of four types: type 1 (hemadsorption virus type 2), which includes sendai virus, causes acute laryngotracheitis in children and occasionally adults; type 2 (croup-associated virus) is associated especially with acute laryngotracheitis or croup in young children and minor upper respiratory infections in adults; type 3 (hemadsorption virus type 1; shipping fever virus) has been isolated from small children with pharyngitis, bronchiolitis, and pneumonia, and causes occasional respiratory infection in adults; bovine strains have been isolated from cattle with shipping fever, and the virus has also been isolated from sheep; type 4 has been isolated from a very few children with minor respiratory illness.