Pathogenicity Of Velogenic Newcastle Disease Viruses Of Different Genotypes In Geese And Chickens

The pathogenicity of velogenic Newcastle disease (ND) viruses of different genotypes in geese and chickens was compared in the present study. The transmissibility of ND viruses of diferent origin between chickens and geese was evaluated, and the F protein of the ND viruses in tissues from the infected birds was detected.23 day-old goslings were inoculated with velogenic ND viruses of 5 different genotypes, respectively, through both oral and oculonasal routes. The challenges of these viruses caused 10%~100% morbidity, and 0~70% mortality in the infected geese. While four NDV field isolates and reference strain of chicken origin which fell into genotype respectively, caused severe clinical disease in geese, and led to substantial death, similar to those of naturally or experimentally diseased animals infected with isolate of goose origin-genotype; geese inoculated with strain Herts/33 (genotype) and isolate PB9601(b) exhibited no overt disease, though depres sion and diarrhea was observed in very few cases. The localization and distribution of the viral antigen in tissues from the infected goslings were investigated by using immunohistochemical (IHC) staining for the detection of NDV F protein. The viral antigen could be detected frequently in 17 organs and tissues. Specific staining was localized in the cytoplasma of lymphocytes, reticulocytes, macrophages, hepatocytes as well as various epithelial cells. The positive staining was less intensive in several tissues of goslings infected with Herts/33 and PB9601, compared to that from the same tissue of goslings inoculated with genotype indicative of the differences of the histotropism of different genotypes of ND viruses. The results of the present study showed that different genotypes of velogenic ND viruses have different pathogenicity to geese. 25 day-old chickens were inoculated with with velogenic ND viruses of 3 genotypes respectively, through the same routes montionedabove. As a result, both the morbidity and mortality of the challenged chickens was 100%. Chickens showed clinical signs and pathological alternations similar to those of chickens infected with viscerotropic strains of NDV. By using IHC staining for the detection of NDV F protein, the localization and distribution of the viral antigen in tissues from the infected chickens was similar to those of geese infected with isolate of goose origin-genotype. While, in chickens, there was marked preferential viral tropism for the lymphoid aggregates associated with the gastrointestinal (GI) tract rather than for nearby epithelial cells. Pathologic findings in association with IHC staining showed that the velogenic ND viruses of 3 genotypes caused systemic illness involving many organs and tissues in chickens.The transmissibility of ND viruses of different origin in chickens and geese was investigated. Oral and oculonasal inoculation with 105 EID50 of two field NDV isolates of JS/1/97/Go and ZJ/1/00/Go resulted in 75%~100% and 50%~100% morbidity, 0~25% and 25%~50% mortality in the infected geese, respectively. Transmission of the two goose-originated NDV isolates by contact with infected geese and goose feces both resulted in infection of all chicekens with 100% mortality. Transmission from infected geese to chickens occurred by aerosol spread, but none of the chickens died despite acquiring infection. The reference challenge strain F48E8 and virulent isolate XJ/2/97/Ch challenge caused 100% morbidity and 100% mortality in the infected chickens, respectively. Transmission of the ND viruses of chicken origin from infected chickens to geese by either fecal or aerosol spread resulted in infection of 50%~75% and 100% birds, which showed 0~25% and 50%~75% mortality, respectively. Viruses were isolated more consistently from cloacal samples than from tracheal samples on 5 days after infection. The result showed that mutual transmission in chickens and geese of some velogenic ND viruses of different origin could occur by either aerosol or fecal contact.In the last experiment, 23 day-old goslings were inocula...