Synergistic Pathogenicity Of Avian Retrovirus With Newcastle Disease Attenuated Vaccine La Sota Strain

Both Avian leukosis virus and Reticuloendotheliosis virus are avian retroviruses that cause tumors and severe immunosuppression in chickens and infect them primarily through vertical transmission.Flocks infected with ALV or REV through vertical transmission of chicken embryos usually produce severe immunosuppression.On the one hand,it can cause chickens to other vaccine immune response levels drop and cannot produce enough protective efficacy.On the other hand,it results in the decrease of the chicken body resistance to other diseases,therefore increases the risk of the other secondary infections.In order to prevent and control Newcastle disease virus and other virulent pathogens,we need a large number of immune against NDV inactivated vaccine and attenuated vaccine in the clinical.In the practice of the clinical application,We find that certain REV and ALV appeared latent infection of virus symptoms occur in broiler immune Newcastle disease after attenuated vaccine,speculated that La Sota vaccine immunization will accelerate REV and ALV replication and disease in the body.To this end,this study systematically observed the synergistic pathogenic effects of REV and ALV(two vertically transmitted retroviruses)on SPF chicks infected by chicken embryos after inoculation with La Sota strain of Newcastle disease vaccine.From 100 SPF chicken embryos,50 SPF chicken embryos were randomly selected to be inoculated with ALV-J through the yolk sac,and the remaining 50 SPF chicken embryos were inoculated with the yolk sac to sterilize PBS.After hatching,20 SPF chickens in the embryo inoculation group and the blank embryo control group were inoculated with PBS at the age of7 days,and 20 SPF chickens in the embryo inoculation group and the blank embryo control group were inoculated with PBS at the age of 7 days.The results showed that the body weight of the incubated SPF chickens infected with ALV-J after embryo inoculation was lower than that of the control group inoculated with PBS,it indicates that the infection of ALV-J through chicken embryo has a strong inhibitory effect on the weight gain of chickens,and this weight difference tends to increase over time,in the 3W/4W/5W/6W four time point the average weight of the two groups are respectively 14.48 g,13.99 g,50.60 g and 56.85 g.When the above infected chickens were immunized with La Sota vaccine,the weight loss trend was more obvious,that is,the weight of the chickens in the ALV-J/La Sota group was lower than that inthe ALV-J group,indicating that the synergistic effect of La Sota vaccine immunization with ALV-J intensified the inhibition of weight gain in the chickens.Compared with the control group inoculated with PBS,significant splenic enlargement and thymus atrophy were observed in the SPF chickens hatched after inoculation with ALV-J,and the splenic enlargement was aggravated after immunization with La Sota vaccine,especially at 6W.After La Sota vaccine immunized uninfected SPF chickens,the NDV antibody reached titer peaks at 3W and gradually decreased.The NDV titers of SPF chickens infected with ALV-J in the same period were lower than those of the control group.The mean values of NDV antibody titers at 3W,4W and 5W differed by 1.369,1.682 and 0.215 log2,respectively.The ALV-J viral load in the blood was detected by fluorescence quantitative PCR.Before 3W,there was almost no difference in the viral load in the blood of the two groups of SPF chickens.At 4W,the ALV-J viral load in the blood of the immune La Sota vaccine group was higher than that in the non-immune group,indicating that the immune La Sota vaccine can promote the replication of ALV-J in the body.According to the grouping and experimental operation similar to the above experiment,we further observed the synergistic pathogenic effect of REV and the Newcastle disease attenuated vaccine La Sota strain through animal experiments and observed similar rules.None of the four treated SPF chickens died before they were immunized with the La Sota vaccine at 7 days of age,and no deaths occurred in the La Sota group alone or in the complete blank group(PBS group)throughout the trial.The chicks infected with REV were the first to die on the 10 th day after immunization,and only the chicks infected with REV and not immune to La Sota began to die after a long interval,indicating that La Sota immunization accelerated the death of the chicks infected with REV.In the 2 to 6 weeks after infection,the body weight of SPF chickens in the REV group alone was consistently significantly lower than that of the control group without the REV,and the difference became more significant over time.In particular,SPF chickens in the REV-infected group gained weight more slowly after they were immunized with La Sota,and they were always the lowest in each group.Compared with the completely blank group,SPF chicks infected with REV through chicken embryos showed damage to their immune organs,including enlargement of the spleen,atrophy of the thymus and bursa of fabricus.When SPF chickens infected with REV were inoculated with La Sota vaccine,the damage to immune organs of SPF chickens was more obvious,which indicated that the presence of both REV and immune attenuated La Sota in SPF chickens significantly aggravated the damage to immune organs.The results of antibody titer determination against NDV showed that the level of NDV antibody in the infectedchickens with REV showed a significant and continuous decrease compared with that in the blank SPF chickens.In particular,the early infection of REV had a significant impact on NDV vaccine.Fluorescence quantification method was used to detect the REV viral load in different organs.The REV viral load of La Sota/REV group was always higher than that of the REV-infected group,indicating that La Sota immunity can promote the replication of REV in SPF chickens.This research by simulation animal experiment observed the chicken embryos vertically transmitted infections ALV-J or REV to La Sota vaccine had significant inhibitory effect.The immune La Sota vaccine enhanced the replication of ALV-J or REV in chickens and the synergistic effect of enhanced both the inhibitory effect of SPF chicken weight and immune organ damage.It suggested that we should attach great importance to the provenance vertical transmission venereal purification of the original work.