Mycoplasma hyopneumoniae is the cause of swine enzootic pneumonia, which has a serious impact on pig farming worldwide.

Respiratory diseases are a problem of significant impact in pig farming. The origin of these respiratory tract pathologies can have different origins. Some causes of pneumonia in swine are produced by bacterial, viral, parasitic, or fungal agents. Other causes of swine pneumonia are of traumatic, physical, or chemical origin.

In many cases, the respiratory symptoms of swine production are the result of the interaction of all these possible agents and the environment. In pneumonia outbreaks, more than one infectious agent may be involved. For this reason, it is called Porcine Respiratory Complex, considering the multiple and diverse etiology.

Characteristics of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is a bacterium of the Mycoplasmataceae family and has no defined cell wall, which is why it is called pleomorphic. In culture, Mycoplasma spp. is noted for having a demanding and slow growth, which complicates its diagnosis by this method.

Mycoplasma hyopneumoniae together with Porcine Reproductive and Respiratory Syndrome Virus (PRRS) are the main respiratory pathogens that a vaccination program tries to control.

Triggering factors of Swine Enzootic Pneumonia

The environment plays a decisive role in the occurrence of respiratory diseases in pigs. Some characteristics and conditions can favor the multiplication of infectious agents that cause pneumonia in pigs, such as Mycoplasma hyopneumoniae.

1. Population density: an excessive density generates stress in the animals, which debilitates them at the immune level and predisposes the pigs to suffer respiratory diseases such as Swine Enzootic Pneumonia.
2. Co-infections: the presence of pathogens such as Haemophilus parasuis, Haemophilus somnus, Actinobacillus pleuropneumoniae and Pasteurella multocida are known as the “PAH Group”. These infectious agents cause lesions of the respiratory tract that favor entry and disease by Mycoplasma hyopneumoniae.
3. Feeding: inadequate feeding can generate nutritional imbalances that end up weakening the pig’s organism and favoring the appearance of infections such as PRRS or Mycoplasma hyopneumoniae.
4. Ammonia concentrations and poor ventilation: physicochemical traumas generated by ammonia and a deficit in ventilation affect the respiratory epithelium of pigs. This damage to the respiratory protective barrier is the entrance door for pathogenic microorganisms.
5. Temperature: in swine farming, it is a frequent problem that there is heat stress in pigs, which weakens them at the immune level and predisposes them to respiratory diseases.
6. Immunity of the population: infectious diseases have more severe impacts when the affected population does not have defenses and has not been confronted with these agents. The presence of antibodies in the population is a great help to the herd when infectious agents increase in the environment.
7. Farm management: some poor management conditions and animal welfare failures can generate stress in animals. This stress decreases the capacity of the animals’ immune systems.

You may also be interested in: Heat stress in pigs: How to avoid it?

All these characteristics influence the severity of an eventual outbreak of Mycoplasma hyopneumoniae in pigs.

The clinical picture of Swine Enzootic Pneumonia

Among the causes of pneumonia in pigs, one of the most frequent and problematic is caused by Mycoplasma hyopneumoniae. This infectious agent causes Porcine Enzootic Pneumonia (PEN). EPN is a chronic respiratory disease with high prevalence and high morbidity. However, low mortality rates are reported.

Porcine Enzootic Pneumonia in animals generates chronic, dry, and non-productive cough. The most affected age group is usually the fattening group, between 16 and 22 weeks of age, decreasing their body condition. This infection causes a delay in the growth of the pigs, in addition to a lower feed conversion rate. This consequence of infection has a serious economic impact on the swine industry.

Mycoplasma binds to the respiratory tract cilia, causing their loss. Over time, this bacterium advances through the bronchial tract, predisposing to other respiratory infections and the Porcine Respiratory Complex.

Transmission of Swine Enzootic Pneumonia

The sow is the main reservoir of Mycoplasma hyopneumoniae and transfers it to piglets during lactation. The pathogen continues to circulate in vaccinated animals, making eradication difficult.

Transmission occurs mainly by direct contact with nasal secretions between infected and non-infected animals. Airborne transmission is also reported to occur, and the bacteria can travel a few kilometers in the air between one farm and another.

After the bacterium enters pigs, it has a variable incubation period ranging from 10 days to 10 months. Commonly, the infection spreads very slowly, and the most affected population group is usually fattening pigs.

Diagnosis of Mycoplasma in pigs

To achieve the diagnosis of swine enzootic pneumonia, aspects of the disease such as the affected population, symptomatology and available laboratory tests must be considered.

• History and signs: they are a great help for the diagnosis of Swine Respiratory Complex.
• Necropsy: lesions are observed on carcasses in slaughterhouses. There are areas of purple to gray pulmonary consolidation, predominantly in the cardiac, apical, intermediate, and anterior regions of the diaphragmatic lobes.
• Histopathology: broncho-interstitial pneumonia with hyperplasia of lymphoid-alveolar tissue (BALT) can be found.
• ELISA: from a blood serum sample, exposure to natural infection by Mycoplasma hyopneumoniae or vaccination is determined.
• PCR: determines the presence of the bacterium from nasal or bronchial swab and lung tissue.
• Immunofluorescence: it has proved useful in acute cases when there is a large amount of Mycoplasma in pigs. It is performed on bronchial and lung tissue.

How to prevent Mycoplasma hyopneumoniae?

The preventive approach against Swine Enzootic Pneumonia caused by Mycoplasma hyopneumoniae consists of a combination of different tools:

1. All-in-all-out system (AIAO): this system allows to cut the natural cycle of the disease and to avoid transmission between pigs of different ages. Each generation group is separated from the others and thus the contagion is avoided.
2. Vaccination: this is the main method to increase the immunity of the pig farm and prevent Mycoplasma hyopneumoniae. However, if the disease is already prevalent on the farm, it cannot be eradicated.
3. Pronutrients: Some substances can reinforce the mechanism of vaccination, such as pronutrients. These substances stand out for not having pharmacological action and do not generate residues or resistance, do not require withdrawal periods, and are an adequate alternative to the prophylactic use of antibiotics. There are immunostimulant pronutrients that are supplied in the diet of pigs, generating the activation of immune cells and tissues responsible for the response after vaccination. It has been demonstrated that, with the administration of pronutrients, the number of circulating antibodies against Mycoplasma has been increased.
4. Biosecurity: Swine farming should always consider quarantining new animals to rule out diseases such as Swine Enzootic Pneumonia.
5. Optimal population density: managing ideal densities in the farm allows reducing stress levels that may favor the development of the disease.
6. Improve ventilation: good ventilation reduces the effect of air irritants that affect the respiratory system. In addition, it avoids stress in pigs.
7. Population replacement: if Mycoplasma hyopneumoniae has become established on the farm, replacement animals should be purchased from farms free of this bacteria. In addition, they should be quarantined.
8. Reduce pathogen load: a mix of biosecurity, vaccination, and replacement animals allows to reduce the bacterial load in the environment and thus correctly prevent the disease.

CONCLUSIONS

Swine Enzootic Pneumonia is caused by Mycoplasma hyopneumoniae. This respiratory disease of bacterial origin has a great economic impact on the swine industry. Its control is mainly directed to prevention measures, including vaccination. Eradication of this disease is difficult, but a combination of preventive measures can help pig farms. Other pathogens of the Porcine Respiratory Complex should be controlled.