ABSTRACT
Aim: For a simpler, more rapid and more accurate method of characterizing new isolates of Newcastle disease virus (NDV), agglutination of mammalian erythrocytes (HA) plus heat stability test and agglutination of mammalian erythrocytes plus erythrocytes elution time (EET) were compared with use of Intra-cerebral pathogenicity index (ICPI) to characterize the isolates. Materials and Methods: NDV isolates characterized by their ICPI were re-characterized by HA of mammalian erythrocytes plus heat stability test and by HA of mammalian erythrocytes plus EET. Rate of agreement of each of the two combinations with ICPI was calculated. Results: HA of mammalian erythrocytes plus heat stability agreed with ICPI in characterizing 10 of the 12 NDV isolates (83.3%) while use of HA of mammalian erythrocytes plus EET agreed with ICPI in all the 12 isolates (100%). Conclusion: It was concluded that use of combination of agglutination of mammalian erythrocytes and EET to characterize NDV isolates has better agreement with use of ICPI to characterize the virus than use of combination of agglutination of mammalian erythrocytes and heat stability test.
ABSTRACT
Aim: Relationship between virus titers of live Infectious Bursal disease (IBD) vaccines and their serum-conversion abilities was studied. Study design and Methodology: Five batches of each, of five IBD vaccine brands used in Nigeria, were tested for virus titers. Each of the vaccine brands was also used to vaccinate a group of fifteen 12-days old chicks to study their serum-conversion abilities. Mean antibody titers of the groups of chicks were plotted, on a graph, against virus titers of the vaccine brands used to vaccinate them. Results: Mean Modified Passive Haemagglutination titers of IBD virus in the vaccines,were:1,065.60±780.03,1,472.00±748.55,2,112.00±1984.00,2,176.00±1920. 00 and 2,585.00±926.92 while mean antibody titers they elicited were, 1,356.80±241.51, 1,280.00±174.88, 448.00±79.25, 998.40±196.27 and 332.80±51.20, respectively. Line of best fit of graph of antibody titers of vaccinated chicks on vaccine titers, showed that reducing titers of the live IBD vaccines improved their immunogenicity. Conclusions: The inverse relationship between virus titers of the vaccines and their serum conversion abilities, suggests that, if viral titers of live IBD vaccines are too high, immune-suppression instead of enhancement of immune response may occur.