Studies And Application On Monitoring Technique Of Agar-gel Precipitation (AGP) Test For Virulent MDV-infection Of Chickens

Soluble antigen of Marek's disease virus(MDV) was concentrated about 100 folds with50% saturated ammonium sulfate cell culture fluids. The antigen were identified for thepresence of MDV vaccine CVI988/Rispens strain examined by agar-gel precipitation (AGP)test and its titre to 1:4. Some specific pathogen free(SPF) and commercial Lohmann chicksvaccinated respectively, with the commercial vaccine CVI988/Rispens and the viral antigen ofthe feather tips were always negative at 3 to 8 weeks post-vaccination(PV) by AGP test.However, when 10 to 30 feather-tips were pooled and cut into pieces in 2ml phosphatebuffered saline(PBS), the suspension after incubation was centrifuged and the buffer decreasedto about 1/15~ 1/20 times in volume was detected by AGP for viral antigens.lt showed that theviral antigens in the feather was recovered and always positive at 3 to 4 weeks PV, whereas itwas positive partly for the antigen at 5 or 6 week and none at 6 to 8 or 7 to 8 weeks PV in theSPF and Lohmann chicks, respectively. Both the feather tips and serum, obtained fromchickens vaccinated with the commercial vaccine CVI988/Rispens or turkeyherpesvirus(HVT), its chickens vaccinated infected and unvaccinated infected with a virulentMDV strain Beijing-1(BJ-1) at 14 days of age, were detected by agar-gel precipitation (AGP)test for the viral antigen and either viral antigen and/or viral antibody. Results showed thegroups of birds vaccinated alone were rarely positive for the presence either precipitatingantigen or precipitating antibody at 3 to 8 weeks of age. The precipitating antigens wereidentified at 1 week post-infected(PI) in the feather tip of birds CVI988-vaccinated infectedand were about 2 weeks earlier than the presence of HVT-vaccinated infected. However, theprecipitating antibodies in the serum of birds CVI988-vaccinated infected were identified later2 weeks than that of HVT-vaccinated infected, similar to birds infected alone with BJ-1 at thesame time. In addition, the precipitating antigens could be requently found in the serum ofbirds infected alone with BJ-1 range about 9~18 days PI. The reasons of all above result andapplications are discussed in our article. The two immunoassay was developed to identifychickens infected with pathogenic MDV. The assay for Marek's disease (MD) of chicken wascarried out in 29 counties ( or cities ) distributed mainly in Anhui Province. 93 flocks ofopening or half-opening breeding chicken were surveyed, including 8 varieties of breeding fordifferent purpose and scope of age from 31 to 434 days with a total number of 2071 chickensunimmunized or immunized with different serotye vaccines. The results showed that 76(81.7%) of 93 flocks tested were positive for MDV-infection. Viral antigen positive rates and viral antibody positive rates were 24.2%(472/1947, cut out 124 not tested) and 42.9%(879/2071), while in the positive flocks of MDV-infection tested, the viral antigen positive rates and viral antibody positive rates were 34.1%(472/1386) and 64.7%(866/1386), respectively. However, the total identified positive rates of MDV-infection were increased significantly to 88.3%(1223/1386, removed over 115 overlapping identification) by the AGP test using both the precipitating antigen and the precipitating antibodies. The results obtained in this survey are in general agreement with the results of survey obtained in Guangxi Province by Wang guijun et al.detected using a PCR technique who found that MD was 84.91% positive of the flocks and 73.33% positive of the birds.Our results above and involved published suggest confirmly that the viral antigens could be found at low levels in feather tips of chickens vaccinated with either the CVI988/Rispens vaccine or HVT(Fc-126) vaccine, but couldn' t be covered directly by the conventional AGP test. The precipitating antibodies as the same as the precipitating antigens was specific for specific diagnosis of virulent MDV-infection of chickens. And vaccination of chicks with ei...