[Study of the immunogenic properties of 3 lentogenic strains of the Newcastle disease virus isolated in Bulgaria].

Three local strains of lentogenic type of the Newcastle disease were used to produce live liquid vaccines. These were given per os to broiler chickens in order to test their immunogenicity (first vaccination at the age of 25 days and vaccination when 70 days old). The immunity thus acquired was followed serologically by the titer of the antihemagglutinins and the resistance manifested by the birds at the control infection with a proven lethal dose of a highly virulent velogenic strain of the Newcastle disease virus. The results obtained were compared with those observed with the use of liquid vaccines of the strains Hitchner-B1 and La Soto. It was concluded that the vaccines of the local Newcastle disease strains are completely harmless and immunogenic. The vaccinal strains are excreted by the immunized birds and serve to immunize the contact control chickens.