Pathogenicity and cross-protection of pigeon paramyxovirus-1 and Newcastle disease virus in young chickens.

Avian paramyxovirus-1 (PMV-1) isolates from Delaware racing pigeons were compared with Newcastle disease virus (NDV) in pathogenicity and cross-protection studies in young chickens. The pathogenicity of pigeon PMV-1 isolates was more closely related to mesogenic (Roakin) NDV than to lentogenic (La Sota) or velogenic (Texas GB) NDV strains. Pigeon PMV-1 produced 100% mortality in 1-day-old NDV-susceptible chickens following intratracheal and intracerebral inoculation. Laboratory tests often used in conjunction with chicken pathogenicity procedures for patho-typing NDV gave conflicting results. Pigeon PMV-1 isolates produced large clear plaques (up to 3.5 mm) in chicken-embryo-fibroblast cultures. Chicken embryo mean death times were considerably greater for pigeon PMV-1 (88 and 109 hr) than for Roakin (66 hr) and Texas GB (48 hr). B1 strain NDV and pigeon PMV-1 produced complete cross-protection in challenge studies in chickens. Extensive cross-reaction between pigeon PMV-1 and NDV occurred in hemagglutination-inhibition tests using polyclonal antisera. However, pigeon PMV-1 and NDV were readily distinguishable using a NDV monoclonal antibody, 2F12.