Submitted to: American Veterinary Medical Association Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 25, 1998
Publication Date: N/A
Technical Abstract: A novel syndrome was observed following inoculation of 3-week old chickens with highly virulent Marek's disease virus (MDV strains. This syndrome was characterized by the acute onset of neurological signs including flaccid paralysis of neck and limbs 9-10 days post inoculation, typically resulting in death 1-3 days after the onset of clinical signs. Most affected birds died and spontaneous recovery was rare. There were few if any gross tissue changes. Histologic brain lesions included acute vasculitis and vasogenic edema and perivascular cuffing. The syndrome was influenced by the virus strain and dose, and by chicken strain and B haplotype. It was prevented by vaccination with herpesvirus. Chickens up to 18 weeks of age were susceptible. Based on clinical signs and histopathology, the syndrome was determined to be an acute form of transient paralysis (TP); its more acute nature and virtual lack of spontaneous recovery differentiated this syndrome from classical TP. Affected birds were viremic and brains were positive for viral DNA by polymerase chain reaction assays, but these tests were also positive in inoculated chickens without clinical signs and may have limited value for diagnosis. Although acute TP should only rarely in MD-vaccinated commercial flocks, this syndrome may be important in laboratory studies where it could not only interfere with pathogenesis trials but could also serve as a marker for highly pathogenic MDV strains. Acute TP may also be involved in the pathogenesis of the early mortality syndrome (EMS), a previously-described immunodepressive disease induced by inoculation of 1-day-old chicks with highly virulent MDV.