[Evaluation of the immune state of poultry against Newcastle virus via various serological reactions].

Studied were 336 sera of vaccinated and challenged chickens, 76 egg extracts, and 36 birds following challenge for the presence of serum antibodies against the Newcastle disease virus, using the hemagglutination-inhibition reaction, the agar gel diffusion precipitation reaction, and the virus-neutralizing test. The values of the antihemagglutinins, precipitins, and virus-neutralizing antibodies were investigated in relation to the immunobiologic resistance of birds to a velogenic Newcastle disease virus. A correlation was found between the antihemagglutinins and the neutralizing antibodies in broilers, aged 30-60 days, treated with an aerosol vaccine La Sota, and in henlayers treated muscularly with the Komarov vaccine. The presence of antihemagglutinin titers of 1:40 and higher values or positive neutralizing indices in the investigated birds were able to provide immunobiologic protection in challenging with a velogenic virus. Precipitins were detected in the blood sera of the challenged birds, which made reasonable their use as a sign pointing to the passage of a velogenic virus through the birds. The lower number of cases with positive precipitin reactions in the vaccinated birds speaks against using objectively this index for the evaluation of the immunologic status.