Study On Pathogenicity Of Duck Paramyxovirus

Duck Paramyxovirus is a member of the order Mononegavirales in the family Paramyxoviridae and has been designated an Rubulavirus. Paramyxovirus infected chicken only and waterfowls were resistant to the virus before. However, many strains had been isolated from geese by Wang yongkun first in 1997 and proved to Avian Paramyxovirusâ… . Thus, the theory that Paramyxovirus never infected waterfowls is changed. The report of Duck Paramyxovirus desease increased gradually at present and viruses were isolated from duckling by zhangxunhai, Chenshaoying, Heyongqiang. The pathogenicity of DPMV to ducks is enhanced, waterfowls (goose, duck, penguin et al.) are not only the host and reservoir of Avian Paramyxovirusâ… , but also are susceptible to this virus.In recent years, the infection of Duck Paramyxovirus was on the rise, which was lead to substantial loss in the poultry industry. Studying on Pathogenicity of duck Paramyxo- virus has great importence in controlling Duck Paramyxovirus disease and protecting the development of ducking industry. Based on the detection of Duck Paramyxovirus MDT, ICPI, and ELD50, we studied the pathological changes and histological changes of the infected chickens and ducks to approach the pathogenic mechanism of duck paramyxo- virus, combined with virus antigen targeting to detect the tissue tropism of DPMV.A strain virus isolated from duckling was identified as paramyxovirus by HA, HI. The strain was able to agglutinate chicken red blood cells, which can be inhibited by Newcastle disease virus (NDV) classic antiserum, but can't be inhibited by avian influenza virus (AIV) classic antiserum (H5, H7, H9 subtype). The virus was identificated by RT-PCR and named SDFC strain. The MDT, ICPI and IVPI for SDFC strain were 58h, 1.37 and 2.19 respectively. LD₅₀ of duck embryos is 10^-8.5. The results indicated that SDFC isolate was virulent strain.To study the incidence, clinical symptom and compare the pathohistological changes on ducks and chickens which were sampled at different time, 30 healthy non-immune Cherry Valley ducks and 30 SPF chickens were challenged with duck Paramyxovirus in 21day-old. The results showed that the morbidity and mortality were 100% and 43.3% respectively in ducks and 100% in chickens. Histopathological results showed that in ducks group, the heart, lung, liver, kidney, spleen, bursa completely suffered with hemo- rrhage and degeneration, but the pathological changes in digestive tract were observed slightly; In chickens group, the extensive hemorrhage were found in tissues. The degener- ation and necrosis at different degree were observed in spleen, thymus, bursa, liver, pancreas, kidney and cordiac muscle tissues. The extensive hemorrhage was discovered in oesophagus, stomachus glandularis and all intestinal canals, which accompanied with mucosa desquamation. The results showed that the DPMV caused high pathogenicity to ducks and chickens. Compared with that to chickens, the pathogenicity of DPMV to ducks was slighter.An immuno-fluorescence assay by NDV monoclonal antibody was developed to detect antigen of Duck paramyxovirus in paraffin sections. The IFA was applied to detect the DPMV antigen in different organs of the artificially infected ducks. The results showed that DPMV antigen can be detected in all the tissues which were sampled. Just only sampled at different time, the distribution of positive signals were in different tissues. The research suggested that the positive detection rate was high in spleen, thymus, bursa of Fabricius, intestine, liver and lung, which are the main target organs of DPMV. The antigens distributed in the cytoplasm of the infected cells. IFA should be a sensitive and specific method for detecting DPMV antigen in paraffin sections and could be used in diagnosis and antigen location of DPMV.