[Properties of local velogenic strains of Newcastle disease virus in poultry]

Studies were carried out on four strains of the Newcastle disease virus, isolated in Bulgaria and referred, as typed by the routinely used methods, to the velogenic group. The strains proved to be hemagglutinin - thermostable. Two of the local virus strains (Rosa and Toutrakan) belonged to the velogenic-neurotropic pathogenic type, and two (Bregovo and Haskovo) - to the velogenic - viscerotropic pathogenic one. All four strains were slowly eluated from chicken erythrocytes. Full immunologic similarity was established between these strains by means of the live vaccines used in this country for the specific prevention of Newcastle disease, produced with the lentogenic strains Hitchner B1 and La Sota and the mesogenic Komarov.