Aerosol vaccination against Newcastle disease: factors affecting the serological response in chickens

The effects of vaccine diluent and virus concentration on the immune response following aerosol vaccination against Newcastle Disease (ND) were studied. Four diluents (saline, tap water, distilled water and 2% casitone in distilled water) were used with various concentrations of LaSota strain virus. At low virus concentrations 2% casitone produced a higher HI antibody response than the other diluents. However, when the virus was administered in concentrations exceeding 7.4 +/- 0.4 logioEID50/m3, the recommended field dosage, virus suspensions in 2% casitone, distilled water and non-chlorinated tap water produced similar responses. The effect of virus concentration on the immune response was studied in 12- to 14-week-old chickens with or without residual immunity. Tenfold dilutions of ND virus of the LaSota strain were applied intratracheally or by aerosol and haemagglutination inhibition titres measured 2 and 4 weeks later. The dose producing an antibody response in 50% of the chickens was calculated both after intratracheal application and after aerosol vaccination. After intratracheal application doses of 0.9 log(10) EID50 and 1.8 log(10)EID50 were required to obtain a 50% response in specific pathogen free chickens and chickens with residual immunity respectively. When the virus was applied by aerosol 5.0 and 6.0 to 7.0 log(10)EID50/m3 were required to produce a 50% response in chickens without and with residual immunity, respectively.