ANTIGENICITY, PATHOGENICITY, AND IMMUNOGENICITY OF SMALL AND LARGE PLAQUE INFECTIOUS BURSAL DISEASE VIRUS CLONES

A serotype 1 variant strain of infectious bursal disease virus designa ted IN was passaged 40 times in BGM-70 cell line. A small plaque (SP) clone and a large plaque (LP) clone were then isolated and plaque puri fied four times. The SP and LP viruses formed circular plaques about 0 .5 mm and 6.0 mm in diameter, respectively. Both clones lost their pat hogenicity for specific-pathogen-free (SPF) chickens and did not elici t significant levels of virus-neutralizing antibody titers. However, t he SP and LP clones maintained their immunogenicity when used as inact ivated vaccines in SPF chickens. The restriction enzyme profiles of bo th clones were similar. Back passage of the SP and LP clones once in S PF chickens resulted in loss of their phenotypic characteristics.