HERD HEALTH
PIH-29
pork industry handbook
PURDUE UNIVERSITY • COOPERATIVE EXTENSION SERVICE • WEST LAFAYETTE, INDIANA
Mycoplasmal Pneumonia of Swine
Authors
Barbara Straw, University of Nebraska
L. Kirk Clark, Purdue University
Reviewers
Clyde and Connie Fischer, Optima, Oklahoma
Calvin and Lisa Nichols, Morrisville, New York
Richard Ross, Iowa State University
Timothy P. Trayer, Denver, Pennsylvania
Doug Weiss, Apple Valley, Minnesota
Causative Agents
Mycoplasmal pneumonia of swine also is called enzootic pneumonia. It is a chronic respiratory disease of swine that seldom kills pigs but causes considerable economic loss through depression in performance.

Mycoplasma hyopneumoniae is the primary infecting agent responsible for mycoplasmal or enzootic pneumonia of swine. M. hyopneumoniae is able to colonize the normal lung, depressing lung defense mechanisms thus allowing other bacteria to produce secondary infections.

Except for laboratory controlled cases, M. hyopneumoniae infections always are complicated by secondary bacteria. The most common secondary bacterium in cases of mycoplasmal pneumonia is Pasteurella multocida. Other bacteria such as Streptococi, Staphylococci, Bordetella bronchiseptica, Actinomyces pyogenes, Actinobacillus pleuropneumoniae, Klebsiella, and Salmonella also may be involved.

Transmission
Transmission of M. hyopneumoniae can occur from carrier sows to their offspring, but the major source is from pig-to-pig in older pigs. Evidence indicates that most young pigs do not become infected until they leave the nursery and are housed in the grow-finish space with older pigs. In some herds, pigs are infected in the nursery especially if it is operated on a continuous-flow basis and younger pigs are commingled with older pigs.
Transmission of M. hyopneumoniae primarily is through direct contact. While long range aerosol transmission of organisms is possible, most clinical spread is due to nose-to-nose contact between animals. Therefore, environmental adjustments are designed primarily to provide a comfortable living space for the pigs rather than to dilute the number of organisms suspended in the air.
Prevalence of Infection
Nearly all (approximately 99%) commercial swine herds have mycoplasmal pneumonia. In a herd in which there are no clinical signs of mycoplasmal pneumonia, typical lesions may be seen in the lungs at a slaughter check. M. hyopneumoniae has been isolated from clinically normal lungs so pigs that appear healthy may be carrying organisms that will cause disease under stressful situations.
Clinical Signs of Infection
There have been occasional reports of nursing pigs being affected with mycoplasmal pneumonia, typically, signs are seen in pigs aged 6 to 10 weeks and older. Affected pigs have a dry, nonproductive cough that is most noticeable after exercise. Coughing may persist for 1 to 2 months. Although pigs continue to eat, feed intake is usually depressed and pigs fail to grow at a normal rate particularly if lesions are extensive due to secondary bacterial complications. The extent of damage to the lung and effect on growth rate are variable depending on
Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U. S. Department of Agriculture Cooperating. H. A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the Acts of May 8 and June 30,1914. It is the policy of the Cooperative Extension Service of Purdue University that all persons shall have equal opportunity and access to our programs and facilities.