Development Of A Newcastle Disease (Lasota) And Infectious Bursal Disease (NF₈) Combined Live Vaccine

The Newcastle disease vires (NDV) strain Lasota bought from China Institute ofVeterinary Drug Control was characterized according to the methods of OIE and "themanufacture and inspection regulations for newcastle disease low virttlence livevaccine" in "Regulations of the people's republic of china on biological products foranimal use(edition 2000)" (Thereafter called "the regulations"). The NDV swainLasota was rejuvenated and passaged for several generations by inoculation of SPFchicken embryos. The mean death time of the chicken embryos (MDT), theintracerbral pathogenicity index (ICPI), the pathogenicity and viral fiter of the NDVstrain Lasota were determined, and inspection of the safety, purity, specificity andimmunogenicity of the NDV strain Lasota were also performed. The results showed thatNDV strain Lasota we used was steady and suitable for producing NDV live vaccine.The infectious bursal disease virus (IBDV) strain NFs from the key laboratory ofanimal infectious disease, ministry of agriculture, Yangzhou University wascharacterized according to the methods of OIE and "manufacture and inspectionregulations for chicken infections bursal disease middling virulence live vaccine" in theregulations. The tests included determination of the purity, specificity, stability, titer,virulence, immunogenicity, immune suppression of IBDV sWain NF₈. The resultsshowed that the infectious bursal disease vires strain NF₈ we used was steady, and it has no immune suppression, it could break through the maternal antibody, it'simmunogenicity was good enough for producing IBDV live vaccine.The above NDV strain Lasota and IBDV strain NF₈ were inoculated into SPFchicken embryos separately. Then the allantoic fluid from NDV infected embryos andCAM and chick embryos from IBDV infected embryos were collected. After the axenicinspection and titer test, the two kinds of semi-finished products were mixed in a 1:1ratio, and stabilizer were added. We gained a batch of ND-IBD two-combined livevaccine (Thereafter called the two-combined live vaccine) through lyophilization.Whereafter the batch of vaccine was evaluated for physical character, axenic inspection,exogenous virus inspection and mycoplasma inspection, and all test were passed. TheNDV and IBDV titers in the vaccine were 10^7.0EID₅₀/dose and 10^4.5EID₅₀/dose,respectively.Seven-day-old SPF chickens were vaccinated with 10 dose and 1 dose of thetwo-combined live vaccine for safety test, at same time the immunized SPF chickenswere kept in same isolator with unvaccinated SPF chicken for test of contacttransmission. We found them all in good health at 14 days. And there are no specificpathological lession of ND and IBD over all dissected body and the bursal ofimmunized chickens with 10-fold dosage and chickens in same isolator withoutimmunization, as well as in negative control group. Those data indictaed that thetwo-combined live vaccine was safe. Vaccinated chiken were bled for ND HI tests andIBD serum neutralization (SN) antibody tests at 1 week, 2 weeks and 3 weeks intervals.At 3 weeks post-vaccination the vaccinated groups and the nonimmune group werechallenged with virulent NDV or IBDV separately. The results showed: UnvaccinatedSPF chicken could produce relevant IBD SN antibody and ND HI antibody when theunvaccinated SPF chicken were contacted with the chickens vaccinated by thetwo-combined live vaccine for some times. The protection index (PI) of vaccinated andunvaccinated chickens against vNDV or vlBDV are all 100%. So the chickens could be infected by two-combined live vaccine.Seven-day-old SPF chicken were immunised by the two-combined live vaccine ingroups, the dosage of ND was 10⁴EID₅₀, 5000EID₅₀, 10³EID₅₀. respectively; anddosage of IBD was 300 ELD₅₀,200ELD₅₀, and 100ELD₅₀, respectively. The first threevaccinated groups were challenged by vNDV and the last three vaccinated groups werechallenged by vIBDV at 3 weeks post-vaccination. The results showed that theminimum immunal dosage of the two-combined live vaccine was 5000EID₅₀ for ND,and 200ELD₅₀ for IBD respectively.Seven-day-old SPF chicken and chicken with maternal antibody were grouped andimmunised by the two-combined live vaccine, ND monovalent vaccine and IBDmonovalent vaccine, respectively. For the chicken with maternal antibody, the test wasdivided into 2 trials. The 1st trail was same as 7-day-old SPF chicken. The abovevaccinated chicken were bled for ND HI tests and IBD SN antibody tests at 1 week, 2weeks and 3 weeks intervals. At 3 weeks post-vaccination the vaccinated groups and thecontrol group were challenged by vNDV or vIBDV separately. The 2st trail was carriedout using boost immunization at 10 days after prime immunization, and the other stepswas same as the 1st trail. For 7-day-old SPF chickens, there is no siginificant different inantibody response between the two-combined live vaccine group and the correspondingmonovalent vaccine group. For the chickens with maternal antibody, the immuneefficiency was good enough for the NDV strain Lasota, but not so good for IBDV strainNF₈ to protect all chicken. Moreover, referring to the antibody level and protection ratio,there is no significant difference between the two-combined live vaccine group and thecorresponding monovalent vaccine groups if they were boosted at 10 dayspost-vaccination. All groups could provide 100% protection against ND and IBD.Seven-day-old SPF chickens were grouped and immunised by the two-combinedlive vaccine. The vaccinated groups and the control group were challenged for vNDVor vIBDV separately at six weeks, seven weeks, eight weeks, nine weeks post-vaccination. The data indicated the immune duration of the two combinatedvaccine was at least 9 weeks for ND and 7 weeks for IBD, respectively.