| characteristics of a very virulent infectious bursal disease virus from california. | an outbreak of infectious bursal disease (ibd) in two california layer flocks resulted in the isolation of two infectious bursal disease viruses designated ra and rb. increased mortality plus gross and histopathology in the layer flocks suggested ra and rb could be very virulent infectious bursal disease virus (vvibdv). preliminary studies indicated that high mortality resulted when bursa homogenates from the layer farms were used to inoculate specific-pathogen-free (spf) chicks. in addition, ra ... | 2009 | 20095162 |