[citation needed] The disease has acute and chronic forms, and can range from severe, with high mortality, to mild or even unapparent.

[citation needed] In the acute form of the disease, in all age groups, there is fever, huddling of sick animals, loss of appetite, dullness, weakness, conjunctivitis, constipation followed by diarrhoea, and an unsteady gait.

Several days after the onset of clinical signs, the ears, abdomen and inner thighs may show a purple discoloration.

With low-virulence strains, the only expression may be poor reproductive performance and the birth of piglets with neurologic defects such as congenital tremor.

[9] It was believed to have been eradicated in the United Kingdom by 1966 (according to the Department for Environment, Food and Rural Affairs), but an outbreak occurred in East Anglia in 2000.

[11] Other regions believed free of CSF include Australia, Belgium (1998), Canada (1962), Ireland, New Zealand, and Scandinavia.

[citation needed] Less virulent strains can give rise to subacute or chronic infections that may escape detection, while still causing abortions and stillbirths.