Mycoplasmal pneumonia in pigs
March 2103 Primefact 1274 first edition
Dr Amanda Lee, Pig Health Coordinator, Menangle
Mycoplasmal pneumonia in pigs is a respiratory
disease that is caused by Mycoplasma
hyopneumoniae. This organism predisposes pigs
to secondary infections of the lung with bacteria
including Pasteurella multocida, Streptococcus
suis, Haemophilus parasuis and Actinobacillus
pleuropneumoniae. M. hyopneumoniae infection
alone causes relatively mild disease in the
absence of environmental stressors, but when
complicated by secondary bacterial invaders the
resultant disease can cause obvious clinical
disease and severe production losses in
intensively reared pigs. This disease complex is
referred to as Enzootic Pneumonia (EP). If EP is
further complicated by viral pathogens, as seen
overseas with swine influenza virus, PRRS virus
and possibly PCV2, a syndrome known as the
porcine respiratory disease complex can occur.
M. hyopneumoniae and EP are widespread in pig
populations and endemic in most pig herds
around the world. Although infected sows and
gilts can transmit infection to their offspring, this
is less important than other sources of infection.
Transmission is most common between finisher
or older grower pigs to younger grower or weaner
pigs.
In diseased animals, the infected lung tissue
becomes consolidated (denser and darker) in a
typical pattern that affects the cranio-ventral
areas (front lobes and only the lower-most part of
the large diaphragmatic lobes), where the lower
lung is affected and much of the upper lung
(especially most of the diaphragmatic lobe) is
normal.
Clinical signs
Mycoplasmal pneumonia and EP usually have an
incubation period of two to eight weeks before
clinical signs are seen, but may be even longer.
Clinical signs of infection only appear in lactating
sows and piglets if disease is introduced into a
naïve herd for the first time.
Acute disease is usually only seen in new
breakdowns of disease in naïve herds.
Clinical signs are more pronounced if EP occurs,
in which case acute disease signs may include:

prolonged, non-productive cough

respiratory distress

fever

high mortality rate across all ages of stock.
Chronic disease is the more normal clinical
picture when the organism has been present in
the pig herd for a long time.
Maternal antibody is passed from sows to piglets
and passive immunity protects piglets for seven
to 12 weeks after which clinical signs start to
appear including:

prolonged, non-productive cough

heavy breathing (‘thumps’)

reduced growth rates

30 per cent to 70 per cent of pigs with lung
lesions at slaughter.
Contributing factors
Mycoplasma hyopneumoniae is often introduced
into a pig herd by carrier pigs showing no
apparent clinical signs.
Windborne aerosol transmission is also possible
over long distances (three kilometres or more)
with the right climatic conditions.
Mycoplasmal pneumonia in pigs
Increased clinical disease is associated with the
following:

overcrowding

continuous flow production systems

concurrent diseases

< 3 m3 air space per pig

< 0.7 m2 floor space per pig

poor air flow in pig housing

variable temperatures

poor insulation

variable wind speeds and chilling

high levels of carbon dioxide and ammonia

pig movement, stress and mixing

poor nutrition

dietary changes at susceptible times.
Diagnosis
Mycoplasmal pneumonia and EP are often
suspected if the clinical picture is one of coughing
grower/finisher pigs with low mortality.
At the abattoir, the lungs of individual pigs are
scored for the amount of damage in each lung
lobe. A total score out of 55 is then awarded to
each pig. An average lung score is then
calculated for the herd. At slaughter or postmortem examination, typical gross lesions
include well demarcated dark, consolidated
areas, particularly in the apical and cardiac lung
lobes.
Moderate Mycoplasma hyopneumoniae lung
lesions with consolidation at tips of the apical and
cardiac lobes. Photo courtesy of G. Eamens, NSW
DPI.
Very severe Mycoplasma hyopneumoniae lung
lesions showing extensive consolidation of the
apical and cardiac lobes and the ventral aspect of
the diaphragmatic lobe. Photo courtesy of G.
Eamens, NSW DPI.
Lung lesions become more widespread as
disease progresses, but do not extend to the
upper areas of the diaphragmatic lobe unless
complicated by organisms such as A.
pleuropneumoniae.
In complicated infections where P. multocida, H.
parasuis or A. pleuropneumoniae occur, pleurisy
and pericarditis may complicate the gross
appearance of the lungs at necropsy.
Lymph node enlargement and a catarrhal
exudate in the bronchial tree often accompany
these lesions, especially if EP occurs.
Microscopically, there is a lymphocytic infiltration
around the bronchioles and blood vessels known
as ‘cuffing’. Severity of the microscopic lesions
and increasing neutrophil presence is seen with
secondary pathogens.
Although characteristic, these pathological
lesions are not specific to Mycoplasmal
pneumonia or EP so does not provide a definitive
diagnosis. Isolation by culture is a gold standard
for diagnosis, but is technically difficult and may
take two to three weeks.
In herds, providing breeding stock or in certain
other situations, it may be necessary to carry out
further testing. Antibody detection using an
indirect or a blocking ELISA is the most effective
and commonly used serological test for detecting
M. hyopneumoniae antibodies.
Seroconversion after infection with M.
hyopneumoniae is relatively slower compared
with other bacterial pathogens and pigs may take
eight to nine weeks to seroconvert. Therefore,
testing of finisher age pigs is most useful.
2
NSW Department of Primary Industries, March 2013
Mycoplasmal pneumonia in pigs
Sensitivity can be low in low prevalence herds,
but specificity of the blocking ELISA is high. PCR
testing can confirm the presence of M.
hyopneumoniae in the nasal cavity, in lung
lesions and in bronchial washings. Nasal swab
PCR is the least reliable, as animals may excrete
intermittently.
Treatment
In herds where EP is endemic, a decision to
medicate feed with antibiotics (e.g.
chlortetracycline, tiamulin, tilmicosin) should be
made in consultation with a veterinarian and
based on the following:

Variable growth in pigs 10 to 20 weeks old

Lung scores > 15

Evidence of clinical disease.
Control
Vaccination is the most effective and common
method of controlling clinical disease, minimising
the severity of EP and reducing transmission of
Mycoplasma hyopneumoniae.
Ensure that the donor herd has maintained M.
hyopneumoniae free status before moving the
incoming stock into the main herd.
Eradication of Mycoplasma
hyopneumoniae
A partial depopulation is preferred by many
producers in order to maintain good genetics and
minimise production disruptions/costs.
Mycoplasma hyopneumoniae eradication is
feasible and highly successful (>90%) with partial
depopulations, but it is essential to plan carefully
in consultation with a veterinarian and consider
what other diseases can be reasonably expected
to be eradicated at the same time to improve the
disease status and performance of the herd.
Pigs < ten months of age are often found to be
highly infectious, shedding high levels of the
organism and are resistant to treatment so these
pigs should be destocked from the piggery during
the eradication program.
Maintain a broad parity breeding herd because
sows > parity 2 are more immune than parity 1
sows and pass on better immunity to their piglets.
Pigs > ten months of age generally have built up
high levels of immunity against M.
hyopneumoniae and shedding of the organism is
low so these pigs can remain on the piggery
during the eradication program and they should
be medicated in-feed with tiamulin or a
combination of tiamulin/chlortetracycline for two
weeks.
Maintaining a Mycoplasma
hyopneumoniae free herd
A period of two weeks with no farrowings should
coincide with the in-feed medication period and
all pens should be cleaned and disinfected.
Young piglets should be vaccinated as per
manufacturer’s instructions.
Location, regional pig density and topography are
all important in maintaining a M. hyopneumoniae
free herd.
Piggeries that are three kilometre+ away from
other piggeries in a low pig dense area with
screening trees/hills have a greater chance of
remaining M. hyopneumoniae free. However,
overseas evidence indicates that M.
hyopneumoniae can travel nine kilometres on
wind currents.
In addition, the pig herd should ideally be
‘closed’, introducing new genetics only by
artificial insemination or embryo transfer. If new
breeding stock is introduced, purchase only M.
hyopneumoniae free stock from a reputable
supplier and, if possible, from only one source
every time.
Incoming stock should be isolated for a minimum
of six weeks in facilities at least one kilometre
(and preferably further) away from the main herd.
3
NSW Department of Primary Industries, March 2013
Updates: www.dpi.nsw.gov.au/factsheets
© State of New South Wales through the Department of Trade and
Investment, Regional Infrastructure and Services 2013. You may copy,
distribute and otherwise freely deal with this publication for any
purpose, provided that you attribute the NSW Department of Primary
Industries as the owner.
Disclaimer: The information contained in this publication is based on
knowledge and understanding at the time of writing (March 2013).
However, because of advances in knowledge, users are reminded of
the need to ensure that information upon which they rely is up to date
and to check currency of the information with the appropriate officer of
the Department of Primary Industries or the user’s independent
adviser.
Published by the Animal biosecurity unit, NSW Department of Primary
Industries.
ISSN 1832-6668
INT12/96309
Job track 11957