The incubation period is 10 days or more after exposure to carrier swine. The pigs have a dry, nonproductive cough that is most noticeable after exercise. Pigs may cough for only 1-3 weeks, or the coughing may persist indefinitely. Other conditions such as influenza, pasteurella pneumonia and lungworms also cause pigs to cough and should be considered in making a differential diagnosis. In general, pigs with mycoplasmal pneumonia continue to eat reasonably well, but some do not grow at a normal rate if lesions are extensive or secondary bacterial pneumonias occur.
Pigs are also more severely affected when lungworms are present.
Growth retardation due to mycoplasmal pneumonia is variable. Generally, the more severe the lesions the greater the effect. Adequate treatment of established mycoplasmal pneumonia is not currently available. Several promising treatments are being investigated. Sulfas and antibiotics are very useful in the control of secondary bacterial pneumonias.