TREATMENT AND CONTROL OF SWINE RESPIRATORY DISEASE

Madonna E. Gemus
Swine Production Medicine
Michigan State University
East Lansing, MI 48824

Introduction

Respiratory disease in swine, despite the exponential adoption of All-In/All-Out production within United States and Canada, remains a major constraint to profitability. Today I would like to describe some of the control and treatment methods available in a disease outbreak. To control and treat disease we should understand the pig's protection mechanisms against respiratory pathogens and how this mechanism is broken down by contributing factors of respiratory disease. Through our discussion, we will understand how environmental and management practices are the most consistent means of control against repiratory disease.

Protective Mechanisms

The pig's protection mechanism consist of both physical and cellular barriers which prevent entry of infectious agents or destroy the agents that have come in contact with the pig. Nasal airways and the mucociliary apparatus are two physical barriers. The nasal passage provides a physical barrier to particles greater than 5 um in diameter and smaller particles are handled by a mucociliary clearance apparatus. This apparatus is composed of fine hair-like structures which move the particles back up toward the mouth of the pig where the particles are then swallowed. Within the lung there exists a cellular defense mechanism called pulmonary macrophage cells. Macrophage cells act to neutralize pathogens (bacteria or virus). If this is not effective then the macrophage will recruit another cell-type, neutrophils, to remove debris and pathogens. Antibodies and T-cell production are triggered by the presence of pathogens. An immune animal is one which has previous exposure via natural infection or vaccination. A nonimmune animal is one that has no previous exposure to the pathogen. Maternal antibodies or passive immunity is the protection that piglets receive from drinking the sow's colostrum. While the sow continues to be a major reservoir of pathogens, maternal antibodies transferred to the piglets prevents pathogens from penetrating the piglet's system. Maternal antibodies tend to breakdown near the time the piglet is developing it's own antibodies. Therefore there is a period at 3-5 weeks of age when the piglet has low levels of protection.

Transmission of Disease: 2 Primary Mechanisms

1) Pig to Pig: The nose, mouth and trachea is a habitat for many organisms. Organisms which do not promote an immune response are called commensal. Conversely, organisms which release toxins, destroy tissue or lower the immune system are deemed pathogens. Commensal organisms such as Haemophilus parasuis (Hpp) and Streptococcus suis (Strep. suis) can thrive when piglets are exposed while protected by maternal antibodies, without clinical signs of disease. However, nonimmune pigs (SPF or SEW pigs), not previously exposed to Hpp and Strep. suis may result in severe respiratory disease in the presence of primary pathogens.

2) Airborne Transmission: Organisms such as M. hyopneumonia (MH), Porcine Respiratory Coronavirus (PRCV), Swine Influenza Virus (SIV), and Pseudorabies virus (PRV) are capable of airborne transmission up to several kilometers in distance. Airborne spread is facilitated by prevailing wind velocity and direction, cloud cover and humidity.

Predisposing factors for Increased Risk of Respiratory Disease

Control Strategies

There are two primary goals to disease prevention:

Goal # 1) minimize the "dose" or number of pathogens to pigs by;

Goal # 2) to interrupt the natural build-up of pathogens within the pigs environment;

Treatment and Control of Disease

Management Strategies

Actinobacillus pleuropneumonia (App)

Subclinical carriers of App are the primary cause of outbreaks. Serology (30 samples) from pigs at 7-8 weeks of age is important to determine if App carriers are present, isolate App serotype, and determine sensitivity to antibiotics. Positive results from serology taken from 7-8 week old pigs denotes; a recent infection, presence of carriers, and an active infection in the herd.

1) IF your herd is Positive on serology but negative for clinical signs.

Use serology to measure presence of other pathogens which are contributing factors such as PRRS, M. hyo, salmonellosis, and atrophic rhinitis.

2) IF your herd is Positive on serology and positive for clinical signs.

Use serology to measure presence of other pathogens which are contributing factors such as PRRS, M. hyo, salmonellosis, and atrophic rhinitis.

Antibiotics: Injection of pigs as soon as they show clinical signs of anorexia, breathing difficulty and depression (dog sitting). Sick pigs should be injected twice a day for as long as they are sick. Compliance is difficult because this is labor intensive, time consuming and expensive. Mass medication using drinking water medication may be useful. Feed additive antibiotics are of little value against App because pigs are generally not eating and the minimum levels of antibiotic required in the blood to kill the organism is not attainable via feed grade regardless of dosage levels. Besides, feeding pigs at rates above the licensed levels is illegal.

Vaccination:Current vaccines do not reliably prevent pleuropneumonia but MAY reduce mortality rate if the vaccine serotype matches that of the serotype on your farm. Vaccine serotypes do not provide crossprotection against other serotypes. Vaccination of sows may reduce piglet protection by colostral immunity.

Replacement stock must be App negative. Serology on entry and again 30 days later.

Full or partial depopulation: Full: Cost effective when 30% + of unvaccinated sows are App positive.

Eradication: Not an effective method. Many eradication efforts fail. Takes about one year. Must empty the weaner and finishing facility in a farrow to finish operation. Test and cull sows which are positive for App.

Lung lesions resolve in 1-2 months, therefore slaughter checks may not be indicative of App.

3) IF your herd is Negative for clinical signs and negative on serology.

Ensure that breeding stock from supplier is negative and remains negative.

Question if App vaccine is used in gilts prior to entry

Serological Monitoring using ELISA tests for App.

Mycoplasma hyopneumoniae (M. hyo)

Transmission is primarily from pig to pig although long range aerosol transmission is possible. M. Hyo has been isolated from lungs of clinically normal pigs. Based on serology surveys, nearly all commercial swine herds have M. hyo. Clinical signs within the herd (coughing, depression and poor growth rate) are dependent on the dose of infection, contributing pathogens and environmental stress. Many producers are utilizing All-In/All-Out for the farrowing and nursery units. Therefore pigs are not affected until the finishing units when pigs of various ages are exposed to M. hyo carriers.

Antibiotics: Many antibiotics are shown to be effective in a laboratory setting but the effectiveness is questionable in the herd. While antibiotics may improve growth performance during administration, once the antibiotic has been removed, clinical signs and poor growth performance resume.

Vaccination: Commercial vaccines are available and tend to reduce to severity of clinical signs (i.e. coughing) but have not always demonstrated an advantage in growth rate.

Atrophic Rhinitis (AR)

The severe and progressive form is caused by a combination of two bacteria: Bordetella bronchiseptica and Pasteurella multocida. B. bronchiseptica lines the mucosa of the nasal passage allowing the adherence of toxin producing P. multocida which destroys the nasal cavity and turbinates. Some transmission of bacteria is from the sow to the piglet, but transmission after 3 weeks of age is generally from one pig to another via droplets.

Antibiotics: First and foremost, proper testing is required to determine drug sensitivity of the bacteria. Antibiotics such as oxytetracylines and sulfonamides can be used in feed medication in the last month of gestation to control the shedding of bacteria from sows to her subsequent litter. Injectable oxytetracyclines and potentiated sulphonamides (under a veterinary/client relationship) are often used under a program for piglets which consists of three to four injections in the first 21-28 days of life.

Vaccination: The vaccination program is targeted to protect piglets before infection. Vaccinate sows (prefarrow) with a vaccine containing the appropriate P. multocida toxin. Vaccination of piglets must be performed 2 weeks prior to natural exposure of the bacteria.

Salmonella cholerasuis: S. cholerasuis is a species specific organism transmitted by feces from clinically infected or carrier pigs. Diagnosis is based on clinical signs, necropsy, bacterial culture and histology results.

Antibiotics: Injectable antibiotics provide the most effective treatment in outbreak infections. Affected pigs may continue to eat and drink, therefore mass medications using appropriate antibiotics in the feed and/or drinking water may reduce death loss.

Porcine Respiratory Disease Complex(PRDC)

Porcine Reproductive and Respiratory Virus (PRRS), Swine Influenza Virus, Porcine Respiratory Coronavirus, and Pseudorabies.

Respiratory disease caused by PRRS, in itself, is infrequent in pigs. Concurrent respiratory infections of PRRS and bacteria are common. Pat Halbur at Iowa State University and David Zeman at South Dakota State University have determined that of the swine respiratory disease cases submitted, greater than 50 percent of the PRRS submissions where complicated with bacterial infections such as P. multocida, Strep. suis, Haemophilus parasuis and S. cholerasuis.

PRRS, Mycoplasma hyopneumonia, Swine Influenza Virus and Actinobacillus pleuropneumoniae are the most common primary agents involved in the Porcine Respiratory Disease Complex (PRDC). This complex tends to affect pigs at 18-20 weeks of age. Treatment and control of this complex is based on proper diagnosis using a combination of detailed clinical history, serology and necropsy. Long term control strategies include segregated weaning, All-In/All-Out in each stage of growth, ventilation modifications and biosecurity measures.

Take-Home Message

A poorly managed hog farm with a high incidence of respiratory disease was used in a clinical trial to determine whether use of a particular antibiotic would improve growth performance on this farm. The farm facilities were not large enough to replicate the trial, therefore some of the pigs from this farm were moved to the university farm. The original hog farm was continuous flow and of poor conditions in terms of ventilation, high pig density and inadequate sanitation procedures. The university facility had good sanitation and better management practices. As in the children's rhyme: some piggies stayed home, while others went off to the university. The pigs at the home farm treated with antibiotics improved in growth performance over the untreated pigs at home. The pigs which went off to university, both the treated and the untreated outperformed the treated stay at home pigs. The moral of the story is that management and environment is the better choice over medication for respiratory disease control. OR Be cool and stay in school.

Recommended Readings

Basics of Immunology. B. Straw, J. Roth, L. Saif: 10/89 Bulletin PIH-122 in Pork Industry Handbook. Purdue University Cooperative Extension Service.

Atrophic Rhinitis. B. Straw, G. M. Daniels: 12/92: Bulletin PIH-50 in Pork Industry Handbook. Purdue University Cooperative Extension Service.

Mycoplasma Pneumonia. B. Straw, L K. Clark: 12/92: Bulletin PIH-29 in Pork Industry Handbook. Purdue University Cooperative Extension Service.

Salmonella cholerasuis. J. Cole, J.C. Nietfeld, K. J. Schwartz: 6/93: Bulletin PIH-29 in Pork Industry Handbook. Purdue University Cooperative Extension Service.

Modern Disease Control Strategies. A. Baysinger: 1996 in The 37th George A. Young Swine Conference & Annual Nebraska SPF Swine Conference. University of Nebraska and Nebraska Cooperative Extension.

Control of PRRS in the US: A Systems Approach. S. Dee: 1996 in The 37th George A. Young Swine Conference & Annual Nebraska SPF Swine Conference. University of Nebraska and Nebraska Cooperative Extension.