Synergistic Pathogenicity Of Chicken Infectious Anemia Virus And Newcastle Disease Attenuated Vaccine LaSota Strain On SPF Chickens

Chicken Infectious anaemia is an immunosuppressive disease caused by infectious anaemia virus.The clinical manifestations of infectious anaemia in chickens are anaemia and other symptoms.It has been widely distributed and prevalent in major poultry-raising countries all over the world,causing increasing losses to poultry industry and gradually developing into a global problem.The transmission mode of CIAV mainly includes horizontal transmission and vertical transmission,but as one of the common exogenous viruses in avian attenuated vaccine,the use of attenuated vaccine contaminated with CIAV is also a very important way of transmission.Previously,we observed that low-dose CIAV contamination in attenuated vaccines can also cause very typical symptoms of CIAV,while the same dose of CIAV directly attacked can hardly observe any obvious symptoms.We used systematic animal experiments to confirm that CIAV contaminated in vaccines and vaccine strains played a synergistic pathogenic role.In this study,typical anemia symptoms appeared in a farm after vaccination with attenuated Newcastle disease vaccine,while chickens without attenuated Newcastle disease vaccine did not show typical symptoms.Is this related to CIAV infection and epidemic in chickens.Will immunization with attenuated Newcastle disease vaccine enhance the pathogenicity of CIAV infection.The synergistic pathogenicity of CIAV infection and immunization with Newcastle disease attenuated vaccine was confirmed by systematic animal experiments on the basis of epidemiological investigation of infected chickens.The clinical symptoms of CIAV appeared in some chickens immunized with attenuated Newcastle disease vaccine in a farm,but the incidence of CIAV in chickens without attenuated vaccine was relatively low.In response to this phenomenon,we first carried out an epidemiological survey of vertical transmission of chicken infectious anemia virus(CIAV)by Real-time PCR,DNA dot blot and RAA detection methods in 240 blood samples of chickens of different original breeds and 240 blood samples of parental breeding birds.The resultsshowed that 1 of 60 blood samples of B line chickens was CIAV positive,the positive rate was 1.7%;4 of 60 blood samples of C line were CIAV positive,the positive rate was 6.7%;14of 60 blood samples of D line were CIAV positive,the positive rate was 23.3%;3 of 60 blood samples of E line were CIAV positive,the positive rate was 5%;14 of 240 parental chickens were CIAV positive,the positive rate was 5.8%.A total of 36 blood samples were CIAV positive,the overall positive rate was 7.5%.The data showed that there was an epidemic of chicken infectious anemia virus CIAV in different strains of chicken flocks in this farm.It is speculated that vaccination with La Sota vaccine in chickens infected with CIAV can promote the replication and proliferation of CIAV in vivo and make chickens show more typical clinical symptoms.Therefore,we observed the interaction of SPF chickens congenitally infected with CIAV after vaccination with La Sota vaccine through systematic animal experiments.Fifty SPF chicken embryos were randomly selected to simulate CIAV infection through vertical transmission through yolk sac inoculation,and the same amount of SPF chicken embryos were inoculated with normal saline as control.After hatching,20 SPF chickens were inoculated with Newcastle Disease IV attenuated vaccine(La Sota strain)at 7days of age in the inoculated group and control group respectively.At the same time,the other chickens in each group were inoculated with the same amount of PBS as the control group.The mortality rate,1-6W body weight and red blood cell number were monitored and recorded after hatching.Anticoagulant nucleic acid was extracted from chickens at 1-6W intervals to detect the viremia level of CIAV;antibody blood was collected at each week interval to detect the antibody level of Newcastle disease and analyze the changes of antibody level;spleen,thymus and bursa of Fabricius were collected at 3W and 6W intervals to measure the immune organ index of chickens.The results showed that compared with other groups,the mortality rate,body weight,erythrocyte count,antibody titer of Newcastle disease and viral load of CIAV in the group of congenital infection with CIAV and immunized with La Sota vaccine increased significantly.Therefore,CIAV and La Sota strain of Newcastle disease attenuated vaccine have synergistic pathogenicity in chickens.This effect not only affects the immune effect of Newcastle disease attenuated vaccine,but also enhances the pathogenicity of CIAV,causing huge economic losses to the breeding industry.