Assessment of type I interferons, clinical signs and virus shedding in broiler chickens with pre and post challenge Newcastle disease vaccination.

BACKGROUND: Newcastle disease (ND) causes devastating economic losses in poultry industry. AIMS: This study evaluates the plausible effect of prior or post challenge vaccination with a live commercial vaccine on some pathogenic aspects of velogenic Newcastle disease virus (vNDV) infection in broilers with an emphasis on elucidating type I interferons (IFNs) response trends.
METHODS: Chicks (n=250) were randomly allocated into 5 equal groups including negative control (NC), positive control (PC) (challenged with vNDV), and treatment (T1-T3) groups: (T1) only received Villegas-Glisson/University of Georgia (VG/GA) strain of NDV vaccine, (T2) vaccinated 24 h prior to vNDV challenge, and (T3) vaccinated 24 h post vNDV challenge. Samples from trachea, cloacal content, and serum were collected at different time points to evaluate virus shedding or IFNs levels.
RESULTS: Although clinical signs and lesions were not completely blocked by administration of vaccine prior to or post vNDV inoculation, the disease severity diminished as demonstrated by an increase in bird's survival rate and median survival days (MSDs). Moreover, prior to or post challenge VG/GA live vaccine administration, modified viral shedding patterns by decreasing the vNDV shedding period especially from the gastrointestinal (GI) system. Strong early type I IFNs response was observed in the trachea and sera of chickens vaccinated prior to or post-infection (pi) as compared to birds that received vaccine or vNDV alone. In trachea, IFN-α response was more pronounced than IFN-β, while both IFNs showed a considerable change in serum.
CONCLUSION: It seems that vaccination after challenge with vNDV can improve bird's health similar to prior administration and reduces virus shedding which may be due to type I IFNs production.