Carrier pigs are common source of infection
Transmission of Enzootic Pneumonia occurs via nose-to-nose contact between pigs and can persist for months in the lungs of infected pigs. Transmission between herds is unlikely due to this organism’s incredibly slow growth and limited ability to survive in the environment. The organism is passed from sow to piglet, but the frequency of pathogen shedding by the sow decreases with increased parity: 73% of parity 1 sows, 50% of parity 6-7 sows, and only 6% of parity 8-11 sows can be found to shed the bacteria.
Early weaning at 7-10 days of age can decrease the transmission of pathogen to young suckling piglets. While signs of infection with Mycoplamsa hyopneumoniae (M. hyo) are not generally seen in pigs less than 6 weeks of age, any age of pig can become infected with this pathogen. Clinical symptoms of the disease tend to occur in pigs around 2-6 months of age.
The incubation period is dose-dependent. For high doses, the incubation period is 11 days, and for moderate doses, it is approximately 4-6 weeks. Low doses cause subclinical chronic infections.
The organism attaches to the cilia in the airways. This causes clumping of cilia, loss of cilia and excessive production of mucous. The mucociliary apparatus is thus impaired, causing reduced clearance of inhaled particles and making the respiratory tract more susceptible to opportunistic infections. M. hyo infection is often found in conjunction with other viral infections (especially PRRS and PCV2) and bacterial infections (P. multocida, B. bronchiseptica, S. suis, H. parasuis, A. pyogenes) as part of PRDC.
M. hyo also modulates the immune response of the host. It is both immunosuppressive and stimulatory to lymphocytes. M. hyo induces the production of pro-inflammatory cytokines, including IL-1 TNF, and IL-6, which are responsible for much of the inflammation and chronic nature of mycoplasmal pneumonia.