(1) Sudden death in 3 - 8 week-old puppies.
This presented as sudden death or as a "fading puppy syndrome". The virus had a predilection for myocardial cells where intranuclear inclusion bodies developed. Heart failure resulted and this could be sudden in onset and fatal. Partial heart failure resulted in poor exercise tolerance and pulmonary oedema. This disease pattern has largely disappeared because maternal immunity is now common in the dog population.
(2) Enteritis in dogs > 8 week-old.
Serious shortening of the villi occurs because of viral destruction of crypt epithelial cells. Initially, a grey, persistent, foul-smelling diarrhea was associated with infection. More recently, haemorrhagic lesions are found. Morbidity high; mortality around 10%.
The former syndrome appears more rarely now, probably due to widespread passive maternal immunity.