Seems there’s a multitude of new swine respiratory diseases these days: porcine respiratory disease complex, porcine reproductive and respiratory syndrome, the 18-week wall, enzootic pneumonia, mycoplasmal pneumonia.

It begs the question: Is there truly a new pathogen to deal with?

Let’s step back and understand what the acronym PRDC is telling us. 

PRDC is not caused by one single infectious agent but by a combination of already recognized respiratory pathogens. Most people stop with that small amount of information and make the quantum leap to a treatment.

The “complex” part of PRDC is the management practices and other environmental influences that affect pneumonia severity. With that in mind, you need to know more about the pig’s respiratory system and go back to the basics of diagnosing the causative organism and management practices.

The lower respiratory tract (trachea, bronchus, bronchioles, alveolar ductals and alveoli) is protected from bacterial and viral invasion by a mechanical method, alveolar macrophages and the immune system. Your pigs will develop pneumonia if the mechanical system is damaged, the alveolar macrophages are overpowered, the immune system is suppressed and/or there is an overwhelming challenge. 

The first line of defense starts at the pig’s nose. Nasal turbinates filter large particles from inhaled air. Challenges occur from organisms that damage the turbinates, management practices that increase pathogens in the facilities or a hot environment that cause a pig to breath through its mouth.

The mechanical system in the trachea is the tiny, hair-like structures that line the airways. Mucus produces within the airways to trap bacteria, viruses, dust and so forth. The cilia move the mucus and trapped material up the trachea to the throat where it is swallowed. This mechanism will clear a normal lung of inhaled pathogens within 30 minutes.

Swine influenza virus, pseudorabies virus or Mycoplasma can damage this mechanism. Once that happens, naturally-occurring bacteria in a pig’s upper-respiratory system may overwhelm the lung’s macrophages and immune system, causing pneumonia.

The alveolar macrophages are cells within the lung’s air sacs (alveoli) that engulf bacteria and viruses. Some viruses (such as PRRS) can destroy or damage them. Since they are the primary defense mechanism at this level, the lungs are vulnerable without them.

Infectious organisms will always be part of pork production. There are no injectable or consumable cures for many of the respiratory organisms. You must optimize management to control, eliminate or reduce your pigs’ exposure to infectious agents.

While aerosol spread of organisms does occur, the primary mode is by direct contact with respiratory secretions. Management that increases pig contact or bacteria concentration in an airspace will increase the pneumonia incidence. For example, increased pneumonia is associated with high stocking density, large group size (150 to 200 pigs) per airspace, frequent mixing, exposure to older groups of pigs (continuous-flow management), multiple-source pigs, open partitions between pens, air space less than 3 cubic meters per finishing pig and low ventilation rates.

Management that hinders the clearance of organisms via mechanical means will increase pneumonia incidence. This includes chilling due to low ambient temperatures, wide fluctuations in ambient temperature, uninsulated concrete floors in the sleeping areas and ammonia levels greater than 50 parts per million. 

Primary respiratory pathogens include swine influenza, PRRS and pseudorabies viruses; Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae and Bordetella bronchiseptica. Secondary respiratory pathogens are Pasteurella multocida, Streptococcus suis, Hemophilus parasuis and Actinomyces pyogenes. 

Systemic infections that cause pneumonia are Salmonella choleraesuis, Actinobacillus suis, and A. pyogenes.

PRDC is rarely caused by a single infectious organism. It is an unpleasant blend of management, environment and infectious organisms. Therefore, it is your responsibility to have the “complex” identified using diagnostics, herd health evaluations and the courage to honestly evaluate your management.  

Nearly every pig is infected with potential disease-causing bacteria or viruses. Mycoplasma hyopneumoniae is present in virtually all U.S. swine herds. For some it causes no harm; in others the damage is severe.

What will be the cause of your PRDC? Take the time and make the investment to identify your herd’s  respiratory pathogens and management weaknesses. Formulate sound management practices, diagnose pneumonia causes in your herd. Judiciously use biological  and therapeutic treatments where needed.

The pathogens may not be new but they are certainly “complex”.

Angela Baysinger is a veterinarian with Swine Pro Associates in Columbus, Neb.