Enzootic Pneumonia (SEP) caused by Mycoplasma hyopneumoniae is
the most common respiratory disease seen in pigs both in the UK and
worldwide. It is estimated that the disease is present in
more than 80% of pig herds in the UK but at variable levels.
The causative agent is neither a bacteria nor a virus, occupying
a position somewhere between the two. The key features of the
organism are that it is physically small and thus easily spread by
the wind whilst still being susceptible to a wide range of
Fig 1 - Clinical pneumonia in a growing pig typical
of SEP with secondary bacteria
Fig 2: Consolidation typical of
Fig 3: '55' scoring system for SEP
In its uncomplicated form the disease has a relatively mild
appearance with a low grade dry non productive cough often the only
sign. In severe infection particularly in previously naïve
populations more drastic signs including lethargy, high
temperatures and inappetance can be seen. The age groups
typically affected are 8-20 weeks although initial infection can
occur earlier and disease can be seen in adults that are not
immune. In breeding animals meeting the disease for the first
time fertility can be severely compromised with failure to cycle
and elevated returns to oestrous evident.
Growth rates will be compromised by SEP. The most
susceptible parts of the lungs are the front 4 lobes and the front
tips of the main (diaphragmatic) lobe. 10% of this tissue damaged
by SEP will depress growth between 30 and 90kg by approximately
40gm/day. In a herd even moderately affected by the disease,
suppression in growth of double this is common.
The most significant clinical effect of SEP is to "open the
door" to secondary pathogens that can cause the severe compromised
pneumonic pig seen commonly on infected farms. Pasteurellas
and Streptococci are common secondaries but it is also possible for
Mycoplasma to exacerbate the effect of PRRS virus in the
lung. SEP and Swine Influenza will often co-exist and be
additive in their effect on the pig.
Furthermore, this association with complicating viral
respiratory pathogens is seen extensively in Porcine Circovirus
Associated Disease (PCAD) (previously referred to as PMWS).
These co-infections mean that any programme to control respiratory
disease in a herd must take account of the full range of pathogens
involved and not rely on treating or preventing only one.
In the herd known to be infected, diagnosis is simply achieved
by clinical inspection. A measure of the levels of disease
can be obtained by examining batches of pigs at slaughter and
measuring the levels of damage in the lungs of 30-50 pigs.
The lesions seen are plum coloured, fading to reddish grey as they
age, and solid, as shown in fig 2.
In herds not known to be infected, the disease can be confirmed
by examination of the affected lung tissue by histopathology and
PCR testing. Culture of the organism whilst possible is a
highly specialised technique and frequently unsuccessful.
PCR testing can also be done on nasopharyngeal swabs but these
are highly sensitive tests and should only be applied on the farm
affected; they can easily give false positive results if pigs are
tested in the abattoir, due to cross contamination.
A blood test exists for the detection of antibodies to M.
hyopneumoniae and, whilst false positive results can occur in
individuals, it can be used to confirm the presence of the organism
within a population. Conversely, seroconvention takes many
weeks following infection and testing too early can give false
Treatment of groups or individuals clinically affected is with
appropriate antibiotics. Tetracyclines, Lincomycin and
Tiamulin are highly effective against the organism but often
alternatives are needed to treat individuals due to the mixed
infection involving secondary bacteria that frequently occurs.
Long term medication via the feed has historically been needed
in finishing pigs to suppress the disease, although better methods
of control are now available.
Because SEP causes distinct changes in the lungs of slaughtered
pigs it is possible to monitor the levels of disease over time by
regularly assessing damage in the abattoir. The '55' scoring
system in which the percentage of vulnerable tissues affected are
assessed and added up to give a total score out of 55 for each pig
and batches of pigs assessed can give an average for the
herd. This scoring system is the basis of lung monitoring
under the British Pig Health Scheme.
An individual pig with a score of less than 10 may have
shown very limited clinical signs (despite suffering slowed growth)
whereas above this level pigs will cough, have difficulty breathing
and lose condition requiring individual treatment.
On a herd basis a 55 score of above 10 would represent a serious
disease problem likely to require repeated group medication to
control it. Well-controlled disease in the presence of SEP
would give a score of less than 3.
It should be noted that '55' scoring scheme is a guide to
assessing SEP levels. The damage (consolidation) seen at
slaughter can be caused by other agents either alone or in
association with SEP.
Prevention and Control
The organism has consistently been shown to have the ability to
spread 3km (2 miles) on the wind and, as such, any herd free of SEP
is vulnerable to infection not just from other established
neighbouring farms but also from pigs passing on lorries etc.
People are able to carry the organism in the nose for 48 hours and
are a potential source of infection.
Clearly infected pigs entering the herd will introduce SEP and
for established herds introducing stock, an extended off site
isolation period (6-8 weeks) is essential. The blood test or
nasal swabs could be used to screen pigs before removal from
Where the disease is present, control can be achieved by a
combination of management and pharmaceutical approaches.
1) Do not overstock pigs and limit group sizes in an air
2) Ensure adequate ventilation - FRESH AIR!
3) Separate age groups and operate an all in all out policy for
buildings or rooms.
4) Regularly wash and disinfect accommodation between
5) Ensure satisfactory thermal comfort.
6) Hospitalise affected pigs in air spaces separate from the
mainstream. Treat affected pigs rapidly.
7) Vaccinate young pigs against Mycoplasma hyopneumoniae.
8) Strategically medicate pigs at danger times (e.g. following
mixing and moving of accommodation) with appropriate antibiotics
either via feed or water.
Highly effective vaccines available for direct administration to
piglets as young as 7 days old have been available since the mid
1990s. A range of products are available in either single or
two dose formats to suit difficult management systems, preference
and challenges. There is no objective evidence to indicate
that either single dose or double dose programmes are better - both
can protect the pig through to normal slaughter weight even in the
face of maternal (colostral) immunity. Competition has
reduced the price of vaccines by 50% since they originally
appeared, making them highly cost effective.
A herd suffering SEP with a 55 score of 8-10 without major viral
complication would be expected to see that score drop to 2 or less
over 6-12 months following introduction of SEP vaccine.
The vaccine operates as a herd protection and it will not
eliminate disease or prevent every pig from suffering some
challenge. As with all vaccines, correct handling,
application and dosage are essential to success.
As a general policy it is advisable to avoid giving piglets more
than one vaccine at a time (if other diseases also require
vaccination) and this can present serious challenges to work out a
programme to give control of multiple infections.
Due to the ability of Mycoplasma to spread on the wind, where
pig density is high it is generally not feasible to remain free of
SEP. However, where units are geographically isolated,
freedom from Mycoplasma can be desirable. Eradication of the
disease can be achieved either by herd depopulation/repopulation or
by partial depopulation in combination with sow vaccination and
medication programmes with antibiotics such as
tetracycline/tiamulin combination or tilmicosin (Pulmotil:
Elanco). The veterinary surgeon can devise an appropriate
programme for the farm.
There is currently some interest in area disease elimination
where herds cooperate to "clean up" collectively.
A mild grumbling level of SEP producing a herd score of 5.5 will
undermine growth to the tune of 40gm/day extending the finishing
period by 4-5 days with its additional feed cost of £1.12 -
£1.40. Over a year such modest levels of disease can
represent a loss of £13000 - £16000 to a sow breeder feeder
farm. Any treatments required are added to this.
All producers should monitor the disease by way of membership of
BPHS and make cost based decisions on control policies with the
help of such information.