Overdose Administration of Thermostable Newcastle Disease Vaccines to Naïve Unvaccinated 6 Weeks Old Cockerels at NVRI, Vom Plateau state, Nigeria

One hundred and fifty (150) unvaccinated 6 weeks old cockerel were divided into six groups of 25 birds each. Pre-vaccination haemagglutination inhibition (HI) mean titers values of 21.4, <21, 21 <21 21 and 21.6 were observed for groups A, B, C, D E and F respectively. Two batches of Newcastle Disease vaccine (NDVI-2) of 50 and 200 doses produced at National Veterinary Research Institute Vom, with EID50 value of 7.7 and 7.6 per dose were administered to groups B and D at 10x (10 times the normal dose) of NDVI-2 via the intra-ocular and intranasal routes. The rest of the groups were administered normal doses of NDVI-2 through the intra-ocular route. Consequently, 40% of the vaccinated birds were randomly selected and sero-monitored twice at 2 and 4 weeks intervals. No observable ND clinical signs were seen in both groups B and D irrespective of the vaccine over dosage. Post-vaccination (HI) immune profiling of the vaccinated flock revealed steady increase in the HI mean titer value per group, while groups B and D which had 10x the normal dose showed high response in comparison to groups that had NDVI-2 standard dose. HI immune profile results 2 weeks post-vaccination revealed HI mean titer values of 23.0, 24.0, 23.2 24.2 23.6 and 24.4 for groups A, B, C, D, E and F respectively; week 4 post-vaccination haemagglutination inhibition mean titer values of 23.6, 25.4, 23.0 25.7 25.2 and 24.0 for the respective groups. Week 8 HI mean titer values of 22.2, 21.8, 22.4 22.5 23.2 and 21.8 were equally observed. While week 12 HI mean titer values of 22.0, 21.8, 22.0 22.0 21.8 and 21.8 were recorded. Post-vaccination HI mean titer values showed that groups B and D with 10x the normal dose had no observable adverse clinical signs but rather high ND antibody response was observed in groups where overdose of standard NDVI-2 vaccine were administered and evidence of ND antibody depletion was equally observed in all the vaccinated groups irrespective of the dose administrated.