Systematic Veterinary Virology

LESIONS

• As with clinical signs, no gross or microscopic lesions can be considered pathognomonic for any form of ND. Carcasses of birds dying as a result of virulent ND usually have a fevered, dehydrated appearance. Gross lesions vary with the infecting virus.
• Virulent ND viruses cause haemorrhagic lesions of the intestinal tract. These are most easily seen if the intestine is opened and may vary considerably in size.
• Haemorrhages are seen in the proventriculus, duodenum, jejunum and ileum. Haemorrhages and necrotic lesions in proventriculus and ileo-caecal junction are considered as specific for ND.
• Even in birds showing neurological signs prior to death, minimal gross lesions are seen in the central nervous system. Changes in the central nervous system are nonpurulent encephalomyelitis.
• Lesions are usually present in the respiratory tract when respiratory signs are observed. These generally appear as haemorrhagic lesions and congestion in lungs, tracheitis and airsacculitis. Egg peritonitis is seen in laying hens infected with virulent NDV.
• Ovaries may be edematous, hemorrhagic, or degenerated. Microscopic lesions are not considered to have any diagnostic significance. In most tissues and organs where changes occur, they consist of hyperaemia, necrosis, cellular infiltration and oedema.