Pathogenesis
M. hyopneumoniae has been found to attach to the cilia of epithelial cells in the lungs of swine. They cause cilia to stop beating (ciliostasis), clumping and loss of cilia, eventually leading to epithelial cell death; which is the source of the lesions found in the lungs of pigs with porcine enzootic pneumonia. This damage impedes normal ciliary clearance and often secondary infections develop. On a cellular level, mononuclear infiltration of peribronchiolar and perivascular areas occurs.
Sadly, the immune response caused by the presence of M. hyopneumoniae in pigs is slow and ineffective (Minion, 2002); it is also believed to cause much of the damage that is seen in pigs with the disease. This mycoplasma is not known to produce any specifically harmful toxin like many other disease-causing bacteria, but some mildly toxic by-products have been observed (Geary et al., 1985).
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