Posted by Dr. Steve Dudley on November 15 2008 16:29
The pig industry has had multiple challenges over the past 2 to 3 years that include financial and environmental problems as well as severe challenges with respiratory disease. Porcine respiratory disease complex is a term that has been used to describe the interaction of multiple viruses and bacteria to create a severe respiratory disease. The clinical signs associated with PRDC include severe coughing, high fevers, and poor weight gain due to animals being off feed as well as difficult breathing or thumping.
PRDC shows up in many different management styles and health statuses. The potential pathogens or disease causing bugs associated with PRDC are either viruses or bacteria. Viruses include swine influenza, porcine respiratory and reproductive syndrome virus and Pseudorabies. Bacteria include Mycoplasma hyopneumonia, Pasteurella multocida Type A, Streptococcus suis, Haemophilus parasuis and Actinobacillus pleuropneumonia. All of these bacteria can be associated with PRDC either as primary or secondary invaders. The third factor that contributes to PRDC is environmental and management practices. Large environmental temperature swings, poor air quality, over crowding and poor nutrition are all factors that lower the immune status of the pigs and increase the likelihood of PRDC.
Veterinary practitioners along with their producers and university diagnosticians have all been frustrated pursuing a consistent definitive diagnosis for the cause of PRDC. Because of the multiple pathogens present, the conventional diagnostic approach of doing individual post mortems seems to constantly change depending on the day, the week or the month. Diagnostic tools have improved over the years and currently a combination of bacteriology, histopathology, serology, and other special tests such as imunohistochemistry, and florescent antibody tests all help diagnosticians more definitively diagnosis and identify primary versus secondary pathogens. We have recently increased the use of serology as a tool to help clarify the involvement of the three primary pathogens; Mycoplasma hyopneumoniae, Swine Influenza, and PRRS virus. The increased use of serology has helped to:1. Improve the description and interpretation of which primary pathogens are associated with PRDC, 2. Improve our understanding of the timing of these disease pathogens and when they are occurring to assist with vaccination recommendations, This serological approach is combined with conventional postmortems utilizing specific lung tests and other diagnostic procedures.
I was called to a farm that was experiencing Porcine Respiratory Disease Complex. The pigs were approximately 18 weeks of age and had been in the finisher for 10 weeks. The pigs were coughing, had high fevers, and were off feed. This had been a problem for the last 3 groups that had gone through this producer’s finishing barn. We decided to do a serum profiling. Ten blood samples were collected from pigs that were 6, 10, 14, 18, and 22 weeks of age. The blood samples were tested for PRRS virus, Mycoplasma hyopneumoniae, and Swine Influenza (both H3N2 and H1N1). The following graph indicates that all of the PRRS samples were positive by 10 weeks of age, the Swine Influenza became 25% positive by 22 weeks. 20 % of the pigs tested in the 6 week group were positive for Mycoplasma and 80% of the group at 22 weeks were positive.
At this same time we sacrificed pigs and sent them to a diagnostic laboratory. Multiple bacteria were isolated such as Streptococcus suis, Pasteurellamultocida type A, and Haemophilus parasuis. Histopathology lesions indicated that Mycoplasma hyopneumoniae was involved. In combining all of the diagnostic information I felt that Mycoplasma was the primary contributor or trigger point. The fact that Mycoplasma titers were low until 22 weeks of age and the fact that histopathology lesions came back positive led us to prioritize Mycoplasma as the primary control point. We placed Lincomycin in the feed at 100g/ton for 3 weeks starting at 9 weeks into the finisher. In addition the pigs were vaccinated for Mycoplasma in future groups. There were no control methods put into play to control PRRS or Swine Influenza on this particular farm. The combination of Lincomycin and Mycoplasma vaccination has greatly helped to eliminate problems on this particular farm place.
I was called to a second farm that was also experiencing PRDC. This particular farm also had a severe respiratory problem through late finishing. Multiple diagnostic methods have been used on this farm to come up with a diagnosis. Mycoplasma hyopneumoniae, Swine Influenza, PRRS and bacteria such as Streptococcus suis, Haemophilus parasuis and Pasteurella multocida type A were all isolated. The question this producer asked was, “I cannot vaccinate for all of these problems, what can we do to prioritize which bug is causing the most problem?” The serology information was sampled like the other case with 10 blood samples taken at 6, 10, 14, 18, and 22 weeks of age. All of the laboratory testing was done and a composite picture was graphed to help analyze and prioritize what pathogens were causing most of the problem. Swine Influenza and Mycoplasma were the two pathogens that drastically increased following the clinical outbreak. Because of this serological picture, along with the traditional methods of diagnosis, an emphasis was placed on controlling these pathogens. A Mycoplasma vaccine, along with an autogenous Swine Influenza vaccine, was used and a pulse medication program was set up utilizing Lincomycin and Tetracycline.
Both of these farms have responded very effectively to the combination of vaccine and feed additive medications. PRDC has been extremely frustrating and economically significant to the swine industry as a whole. There continues to be new developments and improved diagnostic testing methods to assist veterinarians, university diagnosticians, and producers in the identification, prioritization, and control of respiratory disease. If you have specific problems on your farm, contact your veterinarian and have them set up a diagnostic and control program. In addition, we have attempted to use nasal swabs to identify if Mycoplasma hyopneumonia is actively being shed by the use of a nasal swab PCR test. Once the results are completed we look at the information in a combined overlay to help determine the increase in antibody titers in the blood for the various pathogens.