Identification and grouping of Newcastle disease virus strains by restriction site analysis of a region from the F gene

A 75% region of the F gene (between nucleotides 334 and 1682) of Newcastle disease virus (NDV) RNA was amplified by reverse transcription-polymerase chain reaction (RT-PCR). PCR products were cleaved by three restriction endonucleases and the positions of thirty cleavage sites were mapped in more than 200 NDV strains. Restriction site analysis established six major groups of NDV isolates and unique fingerprints of vaccine strains. Group I comprised lentogenic strains isolated mainly from waterfowl with some from chickens. ''Old'' (prior to 1960s) North American isolates of varying virulence including lentogenic and mesogenic vaccine strains belonged to group II. Group III included two early isolates from the Far East. Early European strains (Herts 33 and Italien) of the first panzootic (starting in the late 1920s) and their descendants with some modifications were placed into group IV. NDV strains isolated during the second panzootic of chickens (starting in the early 1960s) were classified into two groups. Group V included strains originating in imported psittacines and in epizootics of chickens at the early 1970s. Group VI comprised strains from the Middle East in the late 1960s and later isolates from Asia and Europe. Pigeon paramyxovirus-l strains that were responsible for the third panzootic formed a distinct subgroup in group VI. Our grouping of NDV strains has confirmed group differences established by monoclonal antibodies. It is concluded that restriction site analysis off gene PCR amplicons is a relatively fast, simple and reliable method for the differentiation and identification of NDV strains.