Clinical Symptoms And Antibody Dynamics Of Immunized Chicken Flocks Infected With Newcastle Disease

Newcastle disease (ND), also called Asian fowl plague or pseud-fowl plague, is an avianacute, highly contacted, contagious disease. It is caused by Newcastle disease virus (NDV)which belongs to Paramyxoviridae. The main symptoms are the respiratory symptoms andnervous system disorders, i.e., pulmonary cerebral type. Since Outbreak of Newcastle diseasefirst reported in1926, it was defined as a list A disease by the Office International desEpizooties (OIE). ND severely damages the development of cultivation industry and causesthe increase of infectious flocks, which lead to great economic losses. Our experiments wereconducted in a layer farm in Shanxi. Clinical symptoms of immunized chicken flocks wererecorded before and after the occurrence of a typical Newcastle disease. Productionperformances of laying hens were investigated. We tested ND antibody titer of immunizedchicken flocks and summarized antibody dynamics of the chickens before and after infection.We hope that these efforts could provide some basis for the prevention and treatment of ND.Experience results suggest that:1. The clinical symptoms after infection are as follows. Firstly, the typical symptoms areslight hemorrhage at the proventriculus and papillary. Moreover, date pit shape convex bodyand hemorrhage can be seen at the ileocecal orifice. Secondly, before the infection, the deathrate is0.02%. However, the death rate increased to0.5%after the infection. After theemergency immunization, the death rate decreased to0.1%. In the early stage of Newcastledisease infection, weekly average laying rate does not exist significant difference withstandard average laying rate (p>0.05); During the stage of incidence and diseaseregression, the weekly average laying rate and egg weight was significantly lower than thestandard weekly average laying rate (p <0.01). 2. Using HA/HI method to test the NDV antigen in two hen houses, we found that mostof the mean antibody titers values are between9~10and have a big dispersion. Beforeinfection, the antibody titer of the chicken flocks was212and they had strong immunologicalprotection. However, in the absence of immunity, antibody levels rised rapidly and thecoefficient of variation was17%~25%, then the infection of Newcastle disease in chickenoccurs. At the beginning of the infection, antibody titer was more than213. After emergencyimmunity, the antibody level decreased to the best protection value9~11.Immune chickens after infection presented the clinical symptoms of atypical ND.Although the production performances such as laying rate and egg weight increased to someextent after emergency immunization, they didn’t reach the peak level. The productionperformances in the convalescence are significantly lower than the standard level.(p <0.01)Due to the fact that the production performances in the convalescence are significantly lower,we get the conclusion that infection of ND causes irreparable loss to the farming enterprises.The infection in the immunized chicken flocks may be caused by the irregular antibody titerlevel. The antibody level could reach as high as213and this could be popular wild straininfection. From these results we know that: We can conduct timely and accurate immuneprevention and treatment of Newcastle disease based on the antibody dynamics of HA/HItest.