Comparison of the Efficacy and Transmissibility of Conventional NDV Vaccines and Vaccines Prepared After Back-Passage Through Chickens

In laboratory trials B1 and Lasota stains of Newcastle disease virus (NDV) back-passaged in chickens were found to have a greater spreading potential than presently available B1 and Lasota vaccines. Although the regular B1 and Lasota strains of NDV gave a routine serologic response when administered to 4-week-old chickens via the water, both vaccines had a low spreading potential since the geometric mean titer of the birds in contact with the B1 vaccinated birds did exceed 3.4 and the HI response of the nonvaccinated birds placed with the Lasota vaccinated birds did not exceed 4.1. The results from this study also indicate that these back-passaged vaccines elicit higher HI titers and are possibly more invasive than the regular B1 and Lasota vaccines. The data also suggest that the Lasota strain possesses a slightly greater spreading potential than the B1 strain of NDV.