PMWS tends to be slow and progressive with a high fatality rate in affected pigs. Clinical cases may occur in a herd over many months, reaching a peak after 9 - 12 months and then gradually decline. A high proportion of cases of PMWS are associated with continuous production and the mixing of different sources of pigs. The clinical signs are quite variable. Affected pigs may show signs of chronic wasting, respiratory distress, diarrhea, incoordination, paralysis, pale skin color and blue ears .
Pigs usually demonstrate a decrease in growth rate and, occasionally, jaundice.
The carcass is emaciated with enlarged spleen, lymph nodes and kidneys. The lungs are usually rubbery and mottled. It appears that most infections are subclinical. It is not known why some infections result in clinical manifestation of the syndrome. The diagnosis of PMWS is based on the age of affected pigs, typical wasting appearance, and necropsy lesions.