The disease: enzootic pneumonia caused by Mycoplasma hyopneumoniae

Porcine enzootic pneumonia, caused by Mycoplasma hyopneumoniae, is one of the most prevalent diseases affecting swine production today. The economic impact in the US has been estimated at $200 million to $1 billion every year.1 It can affect pigs of all ages, but infection and clinical disease normally occur during the finishing phase.


The organism that causes enzootic pneumonia, Mycoplasma hyopneumoniae, attaches itself to the epithelial cells lining the upper respiratory tract. The cells colonize there, resulting in the destruction of cilia, the hair-like structures that help remove foreign material from the lungs. This elicits an inflammatory response, which predisposes the lung to further infections and complicated pneumonia.  


Mycoplasma hyopneumoniae is normally transmitted by contact with affected, carrier pigs. Overcrowding, large group size, and poor air circulation can contribute to infection rates.

  • Animal to animal
  • Nasal secretions
  • Infection by airspread
  • Transmission possible by tools/equipment, boots, etc.
  • No transmission through sow milk or by boars (semen)


Clinical signs associated with Mycoplasma hyopneumoniae vary, depending on the presence of secondary infections and other viruses. Normal signs of a simple infection include:

  • Deep, non-productive cough
  • Thumping
  • Mild to moderate fever
  • Rough coat
  • Decreased appetite/feed intake
  • Reduction in Average Daily Gain


Infection and clinical disease normally occur in the finishing phase of production, from 10- to 12-weeks of age to market. However, the infection can occur at any stage of production. 

Seroconversion typically begins 2 to 3 weeks following infection. Serologic profiling can be used to identify the onset of infection and schedule appropriate vaccination timing.

Diagnosis of Mycoplasma hyopneumoniae is based on clinical signs and diagnostic testing.


Herd management practices can help reduce the severity of Mycoplasma hyopneumoniae in a population, but vaccination aids in prevention of the disease.


1. Clark, L.K., Armstrong, C.H., Freeman, M.J., Scheidt, A.B., Sands-Freeman, L., Knox, K., 1991. Investigating the transmission of Mycoplasma hyopneumoniae in a swine herd with enzootic pneumonia. Veterinary Medicine 86:543-550.