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.