Abstract

This study was designed to characterize a field isolate of Newcastle disease virus (NDV) to check its suitability as an inactivated vaccine and to determine the comparative efficacy of this inactivated NDV vaccine with conventional live vaccines, Baby Chick Ranikhet Disease Vaccine (BCRDV, F strain) and Ranikhet Disease Vaccine (RDV, Mukteswar strain). The field isolate of NDV was identified as velogenic strain based on the pathogenicity indices {mean death time (MDT), intracerebral pathogenicity index (ICPI) and intravenous pathogenicity index (IVPI)}. Formalin precipitated inactivated NDV vaccine was prepared from the field isolate and adjuvanted with aluminium hydroxide. The comparative efficacy of three distinct vaccination schedules (Group A, inactivated vaccine three times only; group B, BCRDV followed by inactivated and group C, BCRDV followed by RDV) was then evaluated on the basis of haemagglutination inhibition (HI) antibody titre of sera samples collected at day 4, 27, 55 and 72 of post vaccinated chicks. The prepared inactivated vaccine with the field isolate induced satisfactory level of antibody following vaccination in chicken. Combined vaccination in chickens with live BCRDV followed by inactivated NDV vaccine induced better immune response than the live or inactivated NDV vaccine alone. The antibody titre though differed significantly (P <0.05, group B versus group C at 55- and 72-days and group B versus group A at 72 days) in the chickens among the vaccinated groups, the protection rate was 100% in all groups following virulent challenge infection.

Key words:  Newcastle disease virus, vaccine, velogenic, haemagglutination inhibition (HI), antibody.