Swine Enzootic Pneumonia

Mycoplasma hyopneumoniae is one of the most important contributors to respiratory diseases in pigs.

It interacts with other infections, damaging the cilia and epithelia of the airways of the lower respiratory tract, making way for invasion by secondary pathogens. Viral infection can complicate the picture even further. PRRS-virus is known to aggravate M. hyopneumoniae infection.

About M. Hyopneumoniae

• Pathogenesis
• Clinical signs
• Diagnosis
• Treatment and prevention

Pathogenesis
Transmission of Mycoplasma hyopneumoniae occurs via direct contact with affected pigs. There is little transmission from sow to piglets. Pigs older than 6 weeks are mainly affected.

The incubation period is dose dependent. High doses, the incubation period is 11 days, moderate doses 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 mucociliar 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 seen in conjunction with other viral (especially PRRS and PCV2) infections 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 pneumoniae.

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Clinical signs
The severity of the clinical signs and the degree of economic loss depend on the agents involved, secondary bacterial infections and/or other viruses, as well as environmental and management factors.

In uncomplicated infections Mycoplasma hyopneumoniae causes:

• mild chronic pneumonia with a non-productive cough
• rough hair coat
• reduced growth rate and feed efficiency.

With secondary bacterial infections clinical signs are more severe.

• increased coughing
• laboured breathing
• elevated temperatures
• prostration

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Diagnosis of M. hyopneumoniae infection
Diagnosis is based on:

• Clinical signs - chronic non-productive coughing
• Lung lesions at necropsy- lungs are meat-like and purple-grey in colour. Lesions are typically seen in the cranio-ventral regions of the lungs, though Influenza virus can cause similar lesions.
• Laboratory tests
  

  Histpathology of lung tissue infected with M. hyopneumoniae

  • ELISA is often used to detect antibodies, use is limited as antibodies may only be present 6 weeks after infection
  • PCR testing is done on lung tissue or lung flushes to demonstrate the M. hyopneumoniae antigen.
  • Histological examination of lung tissue can be useful, revealing alveolar inflammation and peribronchiolar accumulations of lymphocytes.

To accurately diagnose M. Hyopneumoniae infection a combination of diagnostic tests is advised.

Macroscopic lung lesions in a pig infected with M. hyopneumoniae

Cross section of lung lobe - multiple pale foci within the affected lobules indicating bronchiolar orientation of the pneumonia.

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Treatment and Prevention of M. Hyopneumoniae infections

• Prevention is very dependent on good management to provide an optimal environment - attention to air quality, ventilation, temperature and stocking density. Age segregation
  and a strict all-in-all-out policy are also very important.
• Antibiotics are also used in the treatment and prevention of M. hyopneumoniae infections, but timing is a real problem. Treating too late or too early is ineffective, so it often needs to be continued over an extended period. Medicated Early Weaning will produce litters free of M. hyopneumonia.
• The use of SPF pig programs

Vaccination

Vaccination of piglets before the infection occurs can be an efficient strategy for preventing damage from M. hyopneumoniae infections.

Two vaccine options are available from Intervet/Schering-Plough Animal Health:

• Porcilis M Hyo - a two shot vaccination program
• M + PAC - one or two shot vaccination program

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Confluent consolidation of cranioventral lung lobes