Post-weaning Multisystemic Wasting Syndrome
Other papers and Comments on PMWS
Other names |
PMWS |
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Causal agent |
At
present unknown. The most likely
suspect is a pig circovirus 'type II' which is antigenically distinct from
the widely distributed normal non-pathogenic pig circovirus 'type I'. Circovirus II (PCV II)
can be isolated on nearly every farm.
Circovirus are small non-enveloped |
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Distribution |
The
problem is recognised worldwide. |
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Age group |
Post
weaning from 4 to 16 weeks of age (15 -50 kg). Males more susceptible |
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Clinical
signs |
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Note
this affects pigs 1 to 2 weeks after weaning it is very different from the
wasting/poor weaner who fails to eat or drink adequately after weaning. These weaners have started to grow and then
collapse quickly. Extremely poor
response to antibiotics. |
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Many
pigs present with a high fever (40-42C) |
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Affected
pigs are listless and seek a cool area of the pen - near drinkers or along an
outside wall |
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Pigs
waste very rapidly and develop a hairy coat and runted appearance |
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Some
pigs also may develop a slight cough, difficulty breathing and a slight
diarrhoea, but this could be associated with secondary infections |
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The
lymph nodes may be palpable as grossly enlarged. Ensure that the lymph node is actually
enlarged and not just more prominent.
Normal superficial inguinal lymph node for a 25kg pig has an average length 38mm, width 19 mm and
weight 4.2g |
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Pigs
may go pale and yellow |
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Generally
this affects some 25% of the pigs in the pen, the remaining pigs can look
well and unaffected. Mortality rates
can exceed 25% |
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The
disease takes about 3 weeks to go through a group of pigs |
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Many
pigs will die although it will take several weeks. |
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Conjunctivitis
may be seen |
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There
increasing reports of latter abortion
- neonate myocarditis |
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Swollen
lymph nodes are seen in the inguinal
region and can be visualised and palpated Note
difference between enlarged and prominent |
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The
pigs are wasted. They are often
smaller than their pen mates.
Secondary infections are common such as Glassers. |
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Infectivity |
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Very
contagious. Circovirus is shed via
most routes. Clinical signs are
exacerbated with secondary diseases in particular active Parvovirus in
growing pigs. |
Post-mortem
Lesions |
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Post
mortems can grossly be very disappointing or only reveal secondary infections
with Pasteurella, streptococci or Haemophilus
parasuis. However more detailed
will reveal the swollen lymph nodes
cases which progress to lymph node necrosis and reduction. Specific histological changes - syncytial
formation (cells merging together) and cytoplasmic basophilic intracellular
inclusions. Macrophages ‘soak’ up Circovirus II without
significant change in their function.
Circovirus II particles are therefore found in all areas where macrophages
are active Histological examination
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There
may be very few post mortem signs. In
the pig above presented with enlarged lymph nodes. The liver was also a tan orange colour |
The
swollen lymph nodes in the inguinal region. |
H&E
section of lymph node. At histology intracytoplasmic inclusion bodies are
seen. There is also a proliferation of
cells in the lymph nodes. PCV II in immunohistochemistry |
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Diagnosis |
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Clinical
picture. There is no diagnostic test
for the live animal. Circovirus
serology is not useful. PCV2 and presence of virus is blood not
useful as PMWS positive and negative pigs are positive to PCV2. |
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Post-mortem
picture with swollen lymph nodes |
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The
histological picture from submitted lymph nodes, including IHC. Note that macrophages may carry the virus
in large numbers without causing any impact on the macrophage function. |
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Ruling
out other causes |
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Treatment – see separate
paper |
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The
circovacines are extremely effective in controlling the clinical signs of
PMWS and where possible should be urgently considered as part of the control
programme. The
vaccine can be administered to the sow pre-farrowing or the piglet between 2
and 5 weeks of age |
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This
is still under development as the disease becomes better understood more
specific protocols can be advised. The
following is a general guide only. |
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Mange
farm using all-in/all-out protocols.
Age segregation may help control. |
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Provide
pigs with a good environment to limit effects of secondary infections |
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Separate
weaners who show signs of the disease to reduce the level of the disease in the
pen |
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Have
good gilt introduction protocols to ensure gilts are well acclimatised before
entry into the main unit. |
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Feed-back
of on-site nursery faeces is essential.
Consider the use of tonsilar scrapes. |
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Minimise
cross-fostering |
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Common
differentials |
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Any
other cause of wasting in 15 to 60 kg pigs, Glassers, chronic pneumonia,
Ileitis, internal abscessation.
Lymphosarcoma tends to affect individual older animals. The mortality levels are very high in PMWS |
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Papers on PMWS
Treatment and control of PMWS –
personal observations