|Marin, M. - UNIVERSITY OF GEORGIA|
|Villegas, Pedro - UNIVERSITY OF GEORGIA|
Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 15, 1995
Publication Date: N/A
Interpretive Summary: Several field isolates of the virus that causes Newcastle disease in chickens were isolated from healthy birds in Georgia, Alabama, Mississippi, Texas and Puerto Rico. Biological properties of these viruses indicated they were a variety of this agent that does not cause disease and were more typical of live-virus vaccine types. Using techniques to amplify and analyze genetic material from the virus also pointed to the fact these were vaccine type viruses. Although these viruses were similar to vaccine types, there was a small amount of variation detected in the genetic material as compared to live-virus vaccines. Consequently, some genetic differences do arise following replication of these virus types after vaccination of chickens with live- virus. However, these differences do not change the virus enough to cause disease in birds.
Technical Abstract: Nine Newcastle disease virus (NDV) isolates obtained from Puerto Rico, Georgia, Alabama, Mississippi, and Texas were analyzed for in vivo pathogenicity, biological properties (hemagglutination of mammalian erythrocytes), and for sequence variation at the amino acid and sense RNA level of the fusion protein cleavage site. Intracerebral pathogenicity index values ranged from 0 to 0.3 and the intravenous pathogenicity index obtained from all isolates was 0. Four isolates hemagglutinated bovine erythrocytes, while no hemagglutination was observed using equine erythrocytes. By direct sequencing of reverse transcription polymerase chain reaction products, all the isolates had the predicted fusion cleavage sequence comparable to lentogenic NDV strains. Based on nucleotide sequence, the viruses could be grouped phylogenetically with the B1 vaccine type virus. However, nucleotide sequences were not 100% similar to the B1 or La Sota NDV strains indicating that minor genetic heterogeneity occurs among lentogenic field isolates of NDV.