Neurotropic velogenic Newcastle disease in cormorants in Michigan: pathology and virus characterization.

Excessive unexplained mortality was observed in flocks of double-crested cormorants located at Snake Island in Green Bay, Michigan, in June 1992. Clinical signs included weakness, lethargy, diarrhea, respiratory distress, paralysis of the wings and legs, torticollis, and incoordination. The most significant and consistent gross lesions included edema of the eyelids and periocular tissues, pulmonary edema and congestion, marked splenomegaly, hepatic necrosis, and scattered hemorrhages in visceral organs. Histologically, the principal alterations were severe lymphocytic meningoencephalitis and myelitis, as well as splenic lymphoid necrosis with hemorrhage. A type 1 paramyxovirus was isolated from the affected birds and characterized as a velogenic neurotropic strain of Newcastle disease virus. Since the infection occurred in free-living migratory birds, there exists the potential for spread of the virus over a large area, thus posing a hazard to domestic poultry.