A total of 18 Newcastle disease virus (NDV) isolates that were recovered from 1949 through 1997 were characterized and pathotyped. All viruses were highly virulent as determined by intracerebral pathogenicity indices greater-than or equal to 1.81 in day-old. These pathotypes are typical for viscerotropic velogenic NDV (VVNDV) pathotype viruses. Some differences were observed for the chicken red blood cell elution rate and thermostability of the hemagglutinin at 56℃. Three antigenic groups were identified by a hemagglutination-inhibition assay using NDV monoclonal antibodies. And the predominant gross lesions were as follows: discharge from the nasal cavity, tracheal mucus, petechial hemorrhage in the heart fat, kidney urates and hemorrhage with or without necrosis in the gastrointestinal tract. Severe hemorrhagic or necrotic lesions were also noted in the lymphoid organs and were localized primarily in the spleen and cecal tonsil. However, differences in the occurrence and frequency of the gross lesions were observed between the virus strains. Among them, NDV strains that induced neurological symptoms belonged only to genotype Ⅵ. This strain had spread throughout Korea during the late 1980s to the 1990s, which suggests that specific VVNDVs genotypes might result in neurological symptoms.

Newcastle disease (ND) is a highly contagious disease of poultry that can cause severe economic losses throughout the world. Vaccination has been used for a long time and proved as one of the most effective method to reduce the economic loss due to ND virus infection. The measurement of antibody titer such as hamagglutination-inhibition (HI) test with sera has been used as a useful method to evaluate the immunity leve of host. However, HI test is gradually being replaced by the enzyme linked-immunosorbent assay (ELISA).

In the conditions of the Republic of Belarus there was studied the activity of alaninaminotranspherase (AIT) and aspartate aminotransferases (AsT), alkaline phosphatase, lactic dehydrogenase, cholinesterase, alpha amylase in blood serum, liver and pancreas of 130-158-day old replacement chicks vaccinated against Newcastle disease. Research results showed that the most essential changes were observed from such enzymes, as AsT and AIT. Increasing of AIT activity in a liver, pancreas and blood serum of immunized hens was stated on the seventh day after vaccine administration. Character of changes can testify both the increasing of synthesis of the mentioned enzymes, and also their posttransmitting activation which took place due to intensification of transamination processes. Changes of activity of alkaline phosphatase, cholinesterase and alpha amylase were the most expressed on the 14th and 21st days of research. It was possible to assume, that there was a stimulation of synthetic function of hepatocytes under the influence of the vaccine. It was possibly the decreasing of enzymatic functions pancreas.

Investigation of immunity of broiler chickens of Kobb-500 cross vaccinated by national associated viral vaccine and foreign (ABIC, Israel; Vitex XXI vek Seva) vaccines against Newcastle disease and infectious bronchitis was investigated in the conditions of the Republic of Belarus. In course of studies there was analyzed the content of immunoglobulin in blood serum, as well as the influence of living vaccines on immunity formation. Research results showed that broiler chickens immunization against Newcastle disease and infectious bronchitis by national and foreign vaccine produced by ABIC company made it possible to increase the phagocytic activity of pseudoeosinophils, bactericidalal and lysozyme activity of blood serum, that proved the activation of nonspecific protection factors. At the same time in blood serum there was stated the increasing of immunoglobulin number in 1,5-3,0 times in comparison with control groups. Economic efficiency of all analyzed vaccines was analyzed