Pneumonia in pigs, characterized by inflammation of the lungs, represents a major health and economic challenge for swine producers globally. This condition is typically a component of the Porcine Respiratory Disease Complex (PRDC), where multiple factors interact to create illness rather than a single agent. While the disease can be mild, it frequently leads to chronic infections that severely impact the growth and efficiency of the herd. This article explores the biological agents, environmental stressors, and practical protocols involved in recognizing and controlling pneumonia in swine.
Identifying the Diverse Causes
Pneumonia in swine rarely results from a single infectious agent, usually involving a complex interplay between viruses and various bacteria. The disease is often initiated by primary pathogens that damage the respiratory tract, making the animal vulnerable to secondary invaders. The bacterium Mycoplasma hyopneumoniae, the cause of Enzootic Pneumonia, is considered a significant primary culprit worldwide. This organism attaches to and destroys the cilia lining the respiratory epithelium, impairing the pig’s natural defense mechanism for clearing inhaled particles and pathogens.
The damage caused by primary agents allows opportunistic bacteria, such as Pasteurella multocida, Streptococcus suis, and Actinobacillus pleuropneumoniae (APP), to establish severe, secondary infections. P. multocida frequently complicates M. hyopneumoniae infections, resulting in the severe form known as “common swine pneumonia.” A. pleuropneumoniae causes a severe and highly contagious form of pleuropneumonia, often leading to rapid onset of illness and high mortality in naive herds.
Viral infections also act as predisposing factors, significantly increasing the severity and duration of the disease. Viruses such as Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) and Swine Influenza Virus (SIV) suppress the immune system and cause direct tissue injury. This viral damage creates an open pathway for secondary bacterial pathogens to invade the lower respiratory tract.
Recognizing Clinical Signs and Symptoms
The manifestations of pneumonia vary widely depending on the causative agent, the pig’s age, and the presence of secondary infections. Acute cases, often seen during an initial outbreak or with highly virulent pathogens like APP, are characterized by sudden, severe signs. Affected pigs may develop a high fever, become lethargic, and exhibit labored breathing, sometimes described as “thumping”—a rapid, shallow movement of the abdomen and chest. A deep, moist cough may accompany these acute symptoms, and pigs may show a blue discoloration of the ears or snout due to poor oxygenation.
When the disease is caused by chronic agents like Mycoplasma hyopneumoniae, the signs are less dramatic but persist over a long period. The most common indication of chronic infection is a persistent, nonproductive cough, especially noticeable when pigs are roused from rest. These subclinical infections lead to a reduction in feed intake and a decrease in the daily weight gain of growing pigs. Affected animals often display uneven growth rates across a group and poor body condition, which extends the time required to reach market weight.
Environmental and Management Risk Factors
Non-infectious factors in the pig’s environment weaken the immune system and increase the likelihood of respiratory disease. Poor ventilation is a major contributor, leading to the accumulation of airborne irritants such as ammonia and dust. High levels of ammonia damage the delicate lining of the respiratory tract, impairing the function of the cilia that clear the airways. Dust particles, composed of feed, dried feces, and bacteria, further irritate the lungs and increase the overall pathogen load.
Management practices that create stress or allow for high pathogen transmission also increase the risk of disease outbreaks. High stocking density, or overcrowding, reduces the air space available per pig and increases direct contact transmission of infectious agents. Mixing groups of pigs from different sources or age groups introduces stress and exposes naive animals to new pathogens. Rapid or extreme temperature fluctuations, such as drafts or poor insulation, impose physical stress on the animals, diverting energy away from immune function.
Treatment Protocols and Veterinary Care
A suspected outbreak of pneumonia requires immediate veterinary consultation for accurate diagnosis, as treatment effectiveness depends on identifying the underlying cause. Laboratory diagnostics, such as PCR assays or culture, are necessary to determine which bacterial and viral agents are present in the herd. Once a bacterial cause is confirmed, antimicrobial therapy is the primary measure to reduce the severity of the illness and prevent mortality. The choice of antibiotic, such as tetracyclines, tiamulin, or amoxicillin, must be based on the sensitivity of the specific bacteria isolated.
Antibiotics may be administered individually via injection for severely affected pigs or through the feed or drinking water for mass treatment during a herd outbreak. Injectable treatment is preferred for sick, anorexic animals who may not be consuming enough medicated feed or water. Antibiotics are only effective against the bacterial components of the disease, such as Mycoplasma or Pasteurella, and do not treat viral infections like PRRSV or SIV.
For cases involving viruses, treatment focuses on supportive care to help the pig’s immune system fight the infection and control secondary bacterial complications. This includes ensuring pigs have easy access to fresh water and feed, reducing environmental stressors, and providing warmth and comfort. Non-steroidal anti-inflammatory drugs (NSAIDs) may be used under veterinary direction to reduce fever and inflammation, which can improve the pig’s appetite and overall well-being during recovery. Timely intervention is important, as delaying treatment can lead to chronic unthriftiness and increased mortality.
Strategies for Prevention and Herd Health
Long-term management of swine pneumonia relies on proactive prevention strategies that minimize pathogen exposure and bolster herd immunity. A comprehensive vaccination program tailored to the specific agents endemic to the farm is one of the most effective tools. Vaccines are commercially available for major bacterial pathogens like Mycoplasma hyopneumoniae and Actinobacillus pleuropneumoniae, as well as for viral agents like PRRSV and Swine Influenza. Vaccination aims to reduce the severity of clinical signs and lung damage.
Rigorous biosecurity measures are important to prevent the introduction and spread of disease within the herd. This involves strict quarantine protocols for all incoming breeding stock, who should be isolated for at least 30 days and tested before integration. Controlling pig flow through the facility using an all-in/all-out system minimizes the continuous exposure of younger, more susceptible pigs to older, potentially carrier animals. This system involves moving groups of pigs together through a facility, then thoroughly cleaning and disinfecting the area before the next group is introduced.
Optimizing the physical environment of the housing facility reduces the burden on the pigs’ respiratory systems. This includes improving ventilation systems to consistently remove harmful gases and humidity while avoiding drafts and extreme temperature swings. Maintaining appropriate stocking densities reduces stress and decreases the concentration of airborne pathogens. Overall, a combination of immunization, biosecurity, and facility improvements provides a strong defense against the economic losses associated with swine pneumonia.