HERD HEALTH PIH-29
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 pneu-
monia. It is a chronic respiratory disease of swine that seldom
kills pigs but causes considerable economic loss through depres-
sion 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 Streptococci, Sta-
phylococci, Bordetella bronchiseptica, Actinomyces pyogenes,
Actinobacillus pleuropneumoniae, Klebsiella, and Salmonella also
may be involved.
Transmission
Transmission of M. hyopeumoniae can occur from carrier sows
to their offspring, but pig-to-pig transmission is more common 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 iso-
lated 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 secon-
dary bacterial complications. The extent of damage to the lung
and effect on growth rate are variable depending on the dose of
M. hyopneumoniae, number and kind of secondary infections and
degree of environmental stress.
Environmental Factors that
Influence Severity of Infection
Researchers have identified numerous factors that influence
the severity of clinical pneumonia in infected herds. These are
presented in Table 1.
Economic Effect
One study estimated that the cost per pig for enzootic pneu-
monia was $4.08, and the annual cost for the entire U.S. swine
herd was about $367,000,000. This cost excluded the costs of
drugs used to treat or reduce the effects of this disease (which
has been estimated to be about $100,000,000) and the disease
enhancing effects of poor management.
Diagnosis
Diagnosis of mycoplasmal pneumonia is best achieved by a
combination of procedures including clinical observation, post-
mortem and histological evaluations, and fluorescent antibody
examination. Isolation of M. hyopneumoniae is occasionally used
but is not routinely available. Serological tests such as the
complement fixation (CF) or the Enzyme Linked Immuno-Sorbent
Assay (ELISA) may be used on a herd basis to support a diagnosis
or to screen groups of animals in special situations. Use of the
CF test and ELISA is somewhat limited because each test yields
some low level cross reactions with other mycoplasmas. These
deficiencies are likely to be corrected with the development of
species specific cell membrane antigens.
Control Measures
Antibiotics. Antibiotics have been used since their
discovery in efforts to treat, control and prevent pneumonia in
pigs. Many antibiotics have been shown to be effective against M.
hyopneumoniae grown in the laboratory. However, the effect of
antibiotics on enzootic pneumonia in pigs remains questionable.
In one study researchers examined the effect of tiamulin, lycomy-
cin, and a combination of chlortetracycline and tiamulin on the
development of pneumonia and growth performance in naturally
exposed pigs and the results indicate that the antibiotics used
had little influence on the development of lesions of enzootic
pneumonia. Although these antibodies enhanced growth performance,
their use was not cost effective. In other studies, kitasomycin,
tiamulin, and lincomycin, used either before or after M. hyop-
neumoniae challenge, did not reduce the clinical signs or lesions
of mycoplasmal pneumonia. The newer quinolone antibiotics appear
to be effective against mycoplasmal pneumonia, but none of these
antibiotics are commercially available in the United States.
Vaccines. The fact that pigs that recovered from mycoplasmal
pneumonia were refractory to subsequent challenge led researchers
to investigate the possibilities of preparing an immunizing
agent. Commercial vaccines are available for the prevention of
mycoplasmal pneumonia in pigs. In two field studies using these
vaccines, vaccinated pigs had a 77% to 92% reduction in lung
lesions and were 5.5 lb to 11.5 lb heavier at market than unvac-
cinated controls. Other studies confirmed the improvement in lung
lesions, but have not always demonstrated an advantage in growth
rate.
The value of vaccination in relation to the cost of the pro-
cedure should be examined in each herd before initiating an
immunization program.
Management. Whenever possible, the farm manager should
attempt to incorporate sound management procedures into the pro-
duction system. Special attention should be given to the factors
listed in Table 1 especially the major influences designated with
3 pluses.
Elimination of Disease
Primary Specific Pathogen Free (SPF), Medicated Early Wean-
ing (MEW), Modified Medicated Early Weaning (MMEW), Secondary
SPF, MMEW plus 2- and 3-Site Multiplication (Isowean), and All-
In, All-Out (AIAO) programs were developed to prevent the
transmission of diseases from the sow to her pigs and from older
pigs to younger pigs. These programs used alone or in combination
have been shown to allow pigs to attain a growth rate near their
genetic potential if all other inputs are correctly managed.
These programs either prevent or control enzootic pneumonia, in
addition to most other diseases in pigs.
Seed stock suppliers heavily utilize these disease control
programs, however, because reinfection of herds free of enzootic
pneumonia has been common, these programs (except AIAO) are less
frequently implemented in commercial herds.
Table 1. Herd factors that exacerbate effects of respiratory
disease.*
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Degree of effect
Production system:
Large herd size +++
High stocking density +++
Conventional health system (not SPF, MEW, AIAO, etc.) +++
Introduction of animals of unknown or low health status +++
Continuous flow rather than batch movement of pigs +++
Low average age of the sows +++
Average age at weaning very low (less than 21 days) ++
medium (21 to 28 days) +
high (greater than 28 days) ++
use of more susceptible breeds +
Use of purebreds instead of crossbreds +
Housing:
Inadequately insulated & ventilated facilities (improper
regulation of temperature and air exchange, and drafts) +++
Housing of different aged pigs in same air space +++
Open spaces in pen dividers +++
Large growing-finishing rooms (more than 200/300 pigs) ++
Nutrition:
Caloric intake insufficient +
Improper content of macro/micro nutrients in feed +
Feed without added fat (dust from feed) +
Presence of non-respiratory diseases:
Colibacillosis and dysentery ++
Mange and roundworms +
Management Deficiencies:
Insufficient control of environment +++
Poor monitoring of signs of disease ++
Failure to treat or incorrect treatment of sick pigs ++
Absence of or incorrect preventive measures
(vaccinations, strategic medications, etc.) ++
Insufficient care of sick animals (isolation, handling) +
Poor hygiene ++
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*Adapted from Christensen and Mousing, Diseases of Swine,
7th ed, 1992. * +++ = great, ++ = moderate, + = small
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endorsement to the exclusion of others which may be similar. Persons
using such products assume responsibility for their use in accordance
with current directions of the manufacturer.
REV 12/92 (7M)
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