Application of Monoclonal Antibody Based on ELISA Kit for Detection of Virulent Newcastle Disease Virus Infection in Vaccinated Chicken Flock

The ELISA kit based on Monoclonal Antibodies(MABs)for rapid diagnosis of Newcastle disease virus(NDV)was applied to detect virulent NDV in cloacal swab specimens from the vaccinated chicken flock in continuous surveillance for a long time.Haemagglutination inhibition(HI)was parallelly measured.A total of 2317 matched specimens of cloacal swab and blood were taken from two vaccinated chicken flocks.The result in this experiment showed that viral antigen might be detected in cloacal swabs of the chickens with HI titers between 2 to 14.The infection rate of virulent NDV was higher between 2_6 and 11_14 than those between 6 to 10.Those chickens with titers of HI above 6 can still be infected with virulent NDV.The result demonstrated the trend of fall and rise of HI was that the lower were rose more rapidly than the higher before virulent NDV infection.It showed that the high HI titers of infected chickens was caused by virulent NDV infection.In general,the infected individual excreted virus for 3 weeks or so.Once virulent NDV invaded a chicken flock,the susceptible individual in the flock would become infected,then the virus was excreted from the infected and cycled within the flock coninuously.