The Viscerotropic Pathotype of Newcastle Disease Virus

SUMMARY The viscerotropic form of Newcastle disease is defined and the history of the present panzootic of this disease is reviewed. Evidence is presented to support the concept that the viscerotropic form is genetically different from established enzootic forms of Newcastle disease. Ways of differentiating the pathologic forms are described. Transmission of the virus is discussed so as to identify problems of controlling its spread and preventing further introductions.