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Antigens persist in the tissues, especially the joints, long after infection has resolved, stimulating '''auto-immune mechanisms''' which further damage the joints, causing damage which may be permanent.
 
Antigens persist in the tissues, especially the joints, long after infection has resolved, stimulating '''auto-immune mechanisms''' which further damage the joints, causing damage which may be permanent.
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==Disease==
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==Clinical signs==
 
The main presentation is as a chronic '''progressive polyserositis''' in pigs under 10 weeks old. '''Lameness and swollen joints''' are common and congenital arthrogryposis may be seen in young stock.
 
The main presentation is as a chronic '''progressive polyserositis''' in pigs under 10 weeks old. '''Lameness and swollen joints''' are common and congenital arthrogryposis may be seen in young stock.