Efficacy and transmissibility of Newcastle disease I-2 vaccine strain against a field isolate of virulent ND virus (JF820294.1) in village chicken.

This study was conducted to assess efficacy of heat-stable I-2 vaccine against Newcastle diseases in vaccinated and vaccinated in contact birds group following challenge against virulent Newcastle disease (ND) virus in village chicken. Also, to assess whether birds that have been exposed to vaccine virus-shedding, birds were protected against mortality and clinical signs after infection with a virulent strain of the ND virus (NDV). One hundred fifty one-day-old native chickens were divided into seven groups (4 experimental groups of 30 birds/group and 3 control groups (unvaccinated unchallenged, challenged, and just vaccinated). Birds in experimental groups were vaccinated either via drinking water or as food carrier with thermostable I-2 vaccine and then challenged with virulent isolate of NDV (JF820294.1), and eight birds were added as in-contact birds to vaccinated groups. Following challenge, seven extra birds were added to each group as in contact with vaccinated and challenged birds. Survival rate, clinical signs, necropsy finding, and mean antibody titer were evaluated in different experimental and control groups. Birds vaccinated via drinking water showed 100% survival rate. However, birds vaccinated with food carrier vaccine showed less than 50% survival rate. Based on the results obtained from this study, it can be recommended that I-2 vaccination via drinking water can effectively prevent ND in village chicken, since I-2 strain has been able to transmit to non-vaccinated-sensitive birds more effectively than velogenic NDV.