| dc.description.abstract | Seven commercial lentogenic Newcastle disease vaccines, three of the B¹ strain and four of the La Sota strain, produced by four different manufacturers, covering nearly 80% of the brazilian poultry vaccine market were studied. All the vaccines were tested to evaluate their efficacy, being submitted to the following tests: purity, potency, antigen content, innocuity and stability. The lentogenic strains were identified on the basis of their response to five tests: Mean Death Time (MDT), Intracerebral Pathogenicity Index for day old chicks (ICPI), heat stability of the hemagglutinin, stability of infectivity at pH 3 and agglutination of horse erytrocytes. No differences were found in the resistance to intramuscular challenge exposure with 105 Embryo Lethal Dose50 (ELD50) of a velogenic viscerotropic Newcastle strain isolated from a field case, neither between the strains nor the producing laboratories. Two La Sota vaccines and one B¹ vaccine from three laboratories, exhibited 90% protection or higher. Under carefully controlled conditions, chicks with congenital passive immunity, vaccinated at twelve days of age, elicited average responses of 89,3% protection for 10 6.59 EID50/dose and 87.5%protection for vaccinal titers of 10 5.87 EID50/dose. Three La Sota vaccines were stable in their vaccinal titer until the expiration date. All of the vaccines were satisfactory, both in the innocuity and purity tests. The IH antibodies showed the greater rise in titer 19 days after vaccination, being significantly higher for La Sota strain. The passive immunity interfered with the formation of active immunity, in all the B1 vaccines and in one La Sota vaccine. The SN antibodies showed better correlation with the immunity affordaiby the vaccines than the IH antibodies. Differences were found in the typing of the lentogenic strains as compared with the standard values. | |
