[Cases of atypical pseudoplague among birds in a vaccinated flock]

Epizootiological, clinical, morphological, and virological investigations have indisputably demonstrated the persistence of the Newcastle disease virus (NDV) in vaccinated flocks of layers at the age of 5-6 months for a period of three months. The influence was followed up of NDV on mortality rate and the egg performance of birds that had built immunity after ocular/nasal instillation of the Komarov vaccine, birds that had been simultaneously vaccinated and infected, and birds that had been infected and then subjected to i/m treatment with Komarov vaccine. An attempt was made to elucidate the persistence of the virus in various organs and tissues of birds manifesting variations in their immune status as well as to demonstrate it at different intervals of time through isolation in chick embryos. It has been suggested to investigate virologically tracheal swabs or the trachea itself and the nasopharinx of birds that have recently contracted the disease when respiratory troubles are established in vaccinated flocks. The hemagglutination-inhibition test is a valuable adjunct also in the case of employing it as a diagnostic reaction. The difference between the agglutination titers of log2-2 and more in newly affected birds and survivals may dependably serve in establishing the presence of a virulent virus. The atypical course of the Newcastle disease at the rhythmical course of the technologic processes contributes to the creation of a rather dangerous, 'smouldering' focus of NDV.