Mycoplasma hyopneumoniae is a bacterium that causes a chronic respiratory disease in pigs. It is a primary agent of enzootic pneumonia, a significant health concern in swine production. Infections are highly prevalent globally, leading to considerable economic losses due to increased medication use and reduced animal performance.
Understanding Mycoplasma hyopneumoniae
Mycoplasma hyopneumoniae is a bacterium notable for its lack of a cell wall, which makes it susceptible to environmental changes and certain disinfectants. This characteristic also means it requires a host to obtain essential metabolites for survival. It only infects pigs.
This bacterium is the causative agent of Porcine Enzootic Pneumonia (PEP), a chronic respiratory disease that frequently affects finishing pigs. PEP is characterized by its persistent nature and often plays a significant role in the Porcine Respiratory Disease Complex (PRDC), a multifactorial respiratory illness in swine. Mycoplasma hyopneumoniae primarily targets the respiratory system, specifically attaching to and damaging the ciliated epithelial cells lining the trachea, bronchi, and bronchioles. This damage hinders the cilia’s ability to clear foreign substances, including other bacteria, from the respiratory tract, thereby weakening the lung’s defenses and making pigs more susceptible to secondary infections.
Recognizing the Signs and Spread
Clinical signs of Porcine Enzootic Pneumonia include a dry, non-productive cough that can persist for weeks to months. This cough is often more noticeable when pigs are roused. Other common signs include decreased growth rates, reduced feed efficiency, and a rough hair coat.
While Mycoplasma hyopneumoniae alone may cause mild disease, symptoms often worsen when secondary bacterial or viral infections occur. In such complicated cases, pigs may exhibit increased coughing, labored breathing, elevated body temperatures, prostration, and even death. The incubation period for the disease can range from two to eight weeks before clinical signs become apparent.
Transmission of Mycoplasma hyopneumoniae primarily occurs through direct nose-to-nose contact between infected and susceptible pigs. Vertical transmission from infected sows to their piglets is common, typically through close contact. Horizontal transmission can also occur between pigs in the same or different pens. The bacterium can also spread via aerosol over short distances. Factors influencing the spread and severity of the disease include pig density, poor ventilation, variable temperatures, high dust levels, and stress from pig movement or mixing.
Detection and Management Approaches
Diagnosing Mycoplasma hyopneumoniae infection involves a combination of methods. Clinical observation of a chronic, persistent, non-productive cough, especially in grower and finisher pigs, often suggests the presence of the disease. Serological tests, such as Enzyme-Linked Immunosorbent Assay (ELISA), can detect antibodies to Mycoplasma hyopneumoniae, though antibodies may not be present until six weeks post-infection. Polymerase Chain Reaction (PCR) is a widely used and sensitive method for detecting the bacterium’s genetic material in samples like tracheal swabs, bronchoalveolar lavage fluid (BALF), or lung tissue from dead animals. Post-mortem examinations often reveal characteristic lung lesions, typically dark-red-to-purple (acute) or tan-grey (chronic) areas of consolidation in the cranioventral lobes of the lungs.
Managing Mycoplasma hyopneumoniae involves a multi-faceted approach focused on prevention. Vaccination programs are a primary preventive strategy, aiming to reduce clinical symptoms and lung lesions. Various commercial vaccines are available, with differing schedules, all designed to reduce infection impact. Biosecurity measures are also important and include practices like all-in/all-out production systems, which involve moving groups of pigs through facilities together, then completely emptying, cleaning, and disinfecting the barns before introducing a new group. Testing source animals for the bacterium before introduction into a herd can prevent new infections.
Environmental control plays a role in minimizing disease impact. Maintaining good air quality, ensuring proper ventilation, and controlling temperature fluctuations within pig housing can reduce irritation to airways and decrease susceptibility to infection. While antibiotics can be used to treat Mycoplasma hyopneumoniae infections, their role is primarily to manage secondary bacterial infections that often complicate the disease, rather than to eliminate Mycoplasma hyopneumoniae itself. The bacterium can persist in the respiratory tract for months, even after clinical signs resolve.