Marek's disease virus-induced transient paralysis in chickens. 1. Time course association between clinical signs and histological brain lesions.

Association between Marek's disease virus (MDV)-induced clinical signs of transient paralysis (TP) and brain. histological lesions (vasogenic oedema and perivascular mononuclear cell cuffs) were evaluated in TP-susceptible line G-B2 chickens in a time sequence study. The most consistent histological lesions were seen in the cerebellum. Leakage of albumin and vacuolation were parallel in development with clinical signs, but preceded the clinical signs by 6 to 12 h. During resolution of signs, a parallel decline in vacuolation, but not in extra-vascular albumin content was observed. The extravascular albumin shifted from an extracellular to intracellular location. No association was seen between the IgG leakage and vasogenic oedema or clinical signs. Perivascular mononuclear cell cuffing was statistically associated with clinical signs, but evaluation of plotted data indicated the slope for the cuffs was less than the slope for corresponding clinical signs. In addition, cuffing began 2 days prior to clinical signs. Thus, perivascular mononuclear cell cuffing was not causally associated with the TP syndrome.