Efficacy of Thermostable Newcastle Disease Virus Strain I-2 in Broiler Chickens Challenged with Highly Virulent Newcastle Virus.

Newcastle disease (ND) is a major threat to poultry industry production throughout developing countries. The Newcastle disease viruses (NDVs) infecting industrialized and indigenous poultry in Iran are velogenic strains and responsible for the frequent outbreaks of ND in poultry farms even in vaccinated flocks causing serious economic losses in the commercial and indigenous poultry. However, vaccination is the only way to protect against endemic ND, and the conventional vaccines are not heat stable and consequently require complex cold-chains to be transferred to users leading to not much resistance. The present study aimed to evaluate the efficacy of thermostable NDV strain I-2 in broiler chickens vaccinated via drinking water and coated on oiled wheat grain. The horizontal transmission of I-2 strain and transmission of disease from vaccinated to unvaccinated chickens were also evaluated in this study. The obtained results showed that both routes of administration, following primary and/or secondary dose, provoked the production of necessary antibody titer and adequate protective immunity in broiler chickens. Moreover, the horizontal transmission of I-2 strain from vaccinated to unvaccinated chickens housed together induced an antibody response and protected unvaccinated chickens against a local field isolate of a virulent strain of NDV (The intravenous pathogenicity index 2.46, mean death time 59 h). Nevertheless, all unvaccinated and Newcastle challenged broilers chickens against the NDV died in this study. It is noteworthy that the transmission of the virus from challenged broiler chickens was very low to induce clinical signs in susceptible chickens. The obtained results of this study revealed the efficacy of NDV strain I-2 coated on the oiled wheat and via drinking water as it protects broiler chickens from highly virulent NDV.