|Dudnikov, Leonid - NARVAC, MOSCOW, RUSSIA|
Submitted to: World Poultry Congress Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: August 20, 2000
Publication Date: N/A
Technical Abstract: Vaccines against Marek's disease (MD) have historically been prepared from viral strains biologically and, in some cases serologicaly, distant from the field strains that provide the natural challenge. Although these heterologous vaccines have been effective, it is possible that vaccines prepared from closely related or autologous serotype 1 strains would be advantageous. To test this hypothesis, chickens were vaccinated at hatch with three different serotype 1 MD vaccine strains, R2/23, 584A/70 and 648A/100, each attenuated by passage in cell culture and determined to provide significant protection against virulent challenge. Vaccinated groups were challenged at day 6 with low passage, fully virulent parent strains (Md11, 584A and 648A). The strains were isolated from different flocks at different times, and represented vv (Md11) and vv+ (584A and 684A) pathotypes. Vaccines were considered to be autologous to the low passage virus of the same strain and heterologous to low passage viruses o other strains. Data from 3 replicate trials showed that all three vaccines provided high levels of protection against all three challenge viruses. The highest level of protection (mean 82%) was against Md11 challenge and the lowest level (mean 66%) was against 648A challenge. However, no differences were noted in protection by autologous and heterologous vaccines against the same challenge virus (P>0.05). Also, no serological differences were found among the 3 serotype 1 strains by immunofluorecent or neutralizaion tests. The findings show that autologous vaccination with cell-culture attenuated strains offer no better protection compared to heterologous vaccination and suggests that antigenic differences among serotype 1 vaccines are less important than other determinants of vaccine efficacy.