Chronic disease
This is the normal picture where the organism has been present in the herd for some considerable time. Maternal antibody is passed via colostrum to the piglets and it disappears from seven to twelve weeks of age after which clinical signs start to appear. A prolonged non-productive cough, at least seven to eight coughs per episode, is a common sign around this time, with some pigs breathing heavily ("thumps") and showing signs of pneumonia. 30 to 70% of pigs will have lung lesions at slaughter.