What You Need to Know About Porcine Respiratory Disease

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From my recent visits to intensive pig farms and conversations with other veterinarians, there appears to be a sharp increase in the number of porcine respiratory disease incidents over the past few months. Left untreated, porcine respiratory disease can cause mortality in young pigs at a rate of up to 50 percent. What’s more, survivors suffer from persistent cough, lung abscesses, bronchiectasis and reduced growth.

While producers and veterinarians work together to identify the specific causes behind fall swine respiratory disease, it’s important that everyone who works in the pork production sector has a basic understanding of the disease’s root causes and is armed with the appropriate information on proper diagnosis and treatment options.

The majority of respiratory infections in the late nursery to finishing phases can be attributed to the porcine reproductive and respiratory syndrome virus. According to the 2008 Iowa State University Animal Industry Report, PRRS cost the U.S. pork industry between $595 million and $687 million in 2007. 

First reported in 1987 as a mystery pig disease, PRRS has two distinct phases: first, as a reproductive ailment, and the other as a post-weaning respiratory disease.  In the respiratory phase, PRRS causes significant damage to the lungs, specifically the pulmonary macrophages. Vital to fighting off disease, pulmonary macrophages are immune-system cells found in the pig’s lungs that ingest foreign invaders such as infectious microorganisms. Damage to the pulmonary macrophages impairs the animal’s immune system and severely limits the ability to combat secondary bacterial infections such as Mycoplasma hyopneumoniae, Pasteurella multocida, Streptococcus suis, Haemophilus parasuis, Actinobacillus pleuropneumoniae, Actinobacillus suis, and Salmonella. Those are the more common pathogens of porcine respiratory diseases. Additionally, the normal flora of bacterial agents may become pathogenic when a pig contracts the PRRS virus.

While PRRS increases the likelihood of a pig contracting respiratory disease, animals may still develop pneumonia even without the presence of the virus. Stressors, such as crowding, moving and mixing pigs, temperature changes and poor air quality, contribute greatly to the contraction of pneumonia. When pigs from multiple sites are mixed together, those harboring subclinical pathogens spread them to other pigs, which have not yet been exposed. With management practices such as continuous pig flow, it is often impossible to completely prevent disease spread, which makes early diagnosis and proper treatment that much more important.

Regardless of how or why an animal becomes infected, it is vital for anyone who interacts with hogs on a daily basis to recognize the clinical signs of respiratory disease. First and foremost, it’s important to give attention to individual animals rather than the entire pen — simply walking through the barn to check out the herd as a whole is not enough. You need to check each animal for initial symptoms such as respiratory distress (commonly referred to as “thumping”), coughing, sneezing, nasal discharge, tearing and reduced water intake and feed consumption. As the infection becomes more severe or acute, blood-stained discharges from the nose and mouth appear, appetite and growth rate decline, and purple discoloration of the skin and tips of the ears occurs due to a lack of oxygen. Finally, the rate of sudden deaths increases. If the presence of respiratory disease seems likely, contact a veterinarian immediately. 

Once respiratory disease is properly diagnosed by a veterinarian, direct intervention with an antibiotic is a must because pneumonia may spread rapidly. Antibiotics to treat respiratory diseases are generally classified in two ways, bacteriostatic and bactericidal, and they work due to the potency of the dose or the length of the therapy. Always work with a veterinarian to determine the proper treatment, to stay updated on complications and the roles of bacteria or viruses (PRRS, circovirus and swine influenza viruses), and to better understand the potential treatment outcome.  Animals may need several treatments over a period of time to control secondary bacterial infections when viral challenges (like PRRS and circovirus) exist within an operation.

A bacteriostatic antibiotic will inhibit or slow down bacteria growth. Once the drug halts the growth of the disease, it can then allow the animal’s immune system to clear out the remaining infection. These drugs are typically time-dependant and require administration or release over a period of time. That’s because they need to remain in the pig’s body longer in order to repress the disease until the immune system can eliminate the infection on its own. One drawback of bacteriostatic antibiotics is that an animal’s immune system is already in a weakened state from the infection, so it will take it longer to clean-up any left over infection. 

Bactericidal is the other classification of antibiotics. These actually kill the bacteria quickly without relying as heavily on the animal’s immune system. Bactericidal drugs can be time-dependent or concentration-dependent. A concentration-dependent bactericidal drug kills infectious bacteria quickly by achieving peak concentration in a short time period. By administering treatment with a concentration-dependent antibiotic, it reduces the infection fast, allowing the animal to recover quickly.

With the increase in cases of porcine respiratory disease and its economic impact on operations, it is critical to build an understanding of the roots of the disease and recognize the early signs of infection. Paying close attention to individual animals and working closely with a veterinarian to determine the proper treatment are vital to any production system’s success.

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