Alternative methods to compare safety of live‐attenuated respiratory Newcastle disease vaccines in young chicks

Abstract

The work reported here is an initial attempt to find an alternative method by which the safety of live-attenuated Newcastle disease virus (NDV) vaccines for the respiratory tract of young chickens can be assessed. The current recommended methods involve either the subjective assessment of respiratory signs, or raise ethical concerns, as in the case of the intracerebral pathogenicity index. The two methods considered here were the use of tracheal organ cultures to assess the level of ciliostasis which the vaccines caused to the ciliated epithelium of the trachea and the incorporation of a pathogenic strain of in the inoculum in order to induce colibacillosis. Both methods were successful in confirming the safety of the two vaccines. However, these results are only preliminary and more studies need to be performed to determine whether one or both methods have potential, either to replace the existing statutory tests, or provide a test which might be useful during the development stages of a new live-attenuated NDV vaccine.

Effect of Pullet Vaccination on Development and Longevity of Immunity

“…The lack of ciliostasis observed in NDV B1-infected positive controls contrasts with previous reports demonstrating that NDV caused ciliostasis in tracheal explants. Butler, et al [40] demonstrated that NDV caused ciliostasis within 2 to 6 days after infection of tracheal explants, and Malo, et al [41] reported that following vaccination of one-day-old chicks with lentogenic NDV, the peak of ciliostasis occurred at 5 and 7 dpv and waned by 13 dpv. The discrepancy between our results and the previous studies may be explained by the use of a different lentogenic NDV strain; B1 in our studies and LaSota in previous reports [41].…”

“…Butler, et al [40] demonstrated that NDV caused ciliostasis within 2 to 6 days after infection of tracheal explants, and Malo, et al [41] reported that following vaccination of one-day-old chicks with lentogenic NDV, the peak of ciliostasis occurred at 5 and 7 dpv and waned by 13 dpv. The discrepancy between our results and the previous studies may be explained by the use of a different lentogenic NDV strain; B1 in our studies and LaSota in previous reports [41]. It is well established that the LaSota vaccine strain is more virulent than B1 [42], which may explain the ciliostasis observed in LaSota-vaccinated chicks or LaSota-infected tracheal explants, whereas ciliostasis was not observed in our study using B1 vaccine.…”