The pathology of velogenic viscerotropic Newcastle disease virus infection was compared in 7-and 20-week-old groups of non-immune birds and birds with two levels of immunity as determined by the haemagglutinin inhibition test. In non-immune birds the bursa at 7 and 20 weeks was the only lymphoreticular organ to show sustained reticular and lymphoid cell reactions until death took place. Caecal tonsil and spleen were extensively necrotized on day 4 after contact exposure, and similar changes occurred in lung and proventriculus. There was evidence of lymphoid recovery in birds which survived for 18 days. In immune birds the spleen showed two main responses. The first, acute reticular cell response around the ellipsoids indicated that renewed exposure to antigen was often associated with localized cell degeneration. The second, immunological, reaction was rapid formation of germinal centres which occurred somewhat earlier in 20-week-old birds (4-5 days). Especially from the second week, reticular (dendritic) cell and lymphoid hyperplasia occurred diffusely in the bursal medulla of both age groups although marked atrophy and cellular depletion, probably of physiological origin, was a feature of 20-week-old birds with high antibody levels. In the gastro-intestinal tract, germinal centre formation was most marked in the caecal tonsils at 20 weeks. With the Indonesian ITA strain of ND virus, degenerative and inflammatory changes in the brain were mild in all groups up to day 18 irrespective of immune status.

Seven-week-old chickens infected oro-nasally with the lentogenic V4 strain of Newcastle disease virus showed no clinical signs and minimal gross pathology. There was slight ulcerative tracheobronchitis but the main system response was a rapid and progressive lymphoproliferative hyperplasia in the respiratory system, gastrointestinal tract, bursa and spleen which tended to peak after three weeks. By using an indirect immunoperoxidase technique with antibody prepared against homologous virus, viral antigen was localised chiefly in the cytoplasm of lymphoreticular cells, persisting for at least 28 days in the caecal tonsil. Positive cells were not seen in the bursa or brain.

This study was performed to detect reticuloendotheliosis virus (REV) as a contaminant in fowl pox vaccines. A total of 30 fowl pox vaccine samples for the presences of REV using the in vitro a total and in vivo methods. In the in vitro test, the fowl pox vaccine samples were inoculated into chicken embryo fibroblast (CEF) cultures prepared from SPF embryonated chichen egg and examined by PCR test for detection of REV. In the in vivo test, each fowl pox vaccine sample was inoculated in five days old SPF chicks and kept under observation up to 12 weeks post inoculation (PI); serum samples were collected on 15th , 30th and 45th day PI for the detection of antibodies against REV by commercial ELIZA kit, and tissue specimens were collected at 8th and 12th weeks PI for histopathological examination. The results revealed that: only one imported vaccine sample gave positive results by PCR test a product of 291-bp was obtained by the vaccine sample.