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

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 Escherichia coli 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.