PHYLOGENETIC-RELATIONSHIPS AMONG HIGHLY VIRULENT NEWCASTLE-DISEASE VIRUS ISOLATES OBTAINED FROM EXOTIC BIRDS AND POULTRY FROM 1989 TO 1996

Newcastle disease virus {NDV (avian paramyxovirus type 1 [APMV1])} iso lates were recovered from imported exotic birds confiscated following importation into the United States, from waterbirds in the United Stat es, and from poultry. The exotic birds probably originated from Centra l and South America, Asia, and Africa. The NDV isolates were initially characterized as highly virulent because of a short mean death time i n embryonated chicken eggs. The isolates were typed as neurotropic or viscerotropic velogenic by intracloacal inoculation of adult chickens. Intracerebral pathogenicity index values for the virulent NDV isolate s ranged from 1.54 to 1.90, compared to a possible maximum value of 2. 0. These isolates had a dibasic amino acid motif in the fusion protein cleavage site sequence required for host systemic replication. Sequen ce differences were detected surrounding the fusion protein cleavage s ite and the matrix protein nuclear localization signal, indicating evo lution of highly virulent NDV. Phylogenetically, these isolates were c ategorized with other highly virulent NDV strains that caused outbreak s in southern California poultry during 1972 and in cormorants in the north central United States and southern Canada during 1990 and 1992. These isolates are related to NDV that may have the APMV1 strain chick en/Australia/AV/32 or a related virus as a possible progenitor. Recent virulent NDV isolates and those recovered during disease outbreaks si nce the 1970s are phylogenetically distinct from current vaccine virus es and standard challenge strains.