The present invention provides methods and reagents for inducing active immunity in animals. In particular, the present invention provides recombinant herpesviruses having foreign DNA that are capable of inducing immunity to the herpesvirus and/or the source of the foreign DNA. The present invention also provides mutant herpesviruses having portions of their genome deleted. Preferably, foreign DNA is introduced, or portions of the genome are deleted, in the UL54.5 open reading frame of avian herpesviruses or the UL43 open reading frame of Marek's disease virus.
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