Post-weaning Multisystemic Wasting Syndrome

Other papers and Comments on PMWS


Other names


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 DNA virus containing a unique single-stranded circular genome.  There appears to be three major forms of PCV II referred to as a,b, and c– the b form is more commonly isolated from cases of clincal PMWS, however, the evidence is still being investigated to demonstrate any pathogenic differences.  All three types occur in Australia – where PMWS is not recognised as a herd problem.  Viral dendogram Australia


The problem is recognised worldwide.

Age group

Post weaning from 4 to 16 weeks of age (15 -50 kg).  Males more susceptible

Clinical signs

PMWS pigs 2

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.

Many pigs present with a high fever (40-42C)

Affected pigs are listless and seek a cool area of the pen - near drinkers or along an outside wall

Pigs waste very rapidly and develop a hairy coat and runted appearance

Some pigs also may develop a slight cough, difficulty breathing and a slight diarrhoea, but this could be associated with secondary infections

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

Pigs may go pale and yellow

Generally this affects some 25% of the pigs in the pen, the remaining pigs can look well and unaffected.  Mortality rates can exceed 25%

The disease takes about 3 weeks to go through a group of pigs

Many pigs will die although it will take several weeks.


PMWS swollen inguinal lymphnodes

Conjunctivitis may be seen

There increasing reports of latter abortion  - neonate myocarditis

Swollen lymph nodes are seen in  the inguinal region and can be visualised and palpated


Note difference between enlarged and prominent

PMWS pig italy 1

The pigs are wasted.  They are often smaller than their pen mates.  Secondary infections are common such as Glassers.



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


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

PMWS PM gross

PMWS PM Lymph nodes

Postweaning wasting inclusions HE

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



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.

Post-mortem picture with swollen lymph nodes

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.

Ruling out other causes

Treatment – see separate paper


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

This is still under development as the disease becomes better understood more specific protocols can be advised. 

The following is a general guide only.

Mange farm using all-in/all-out protocols.  Age segregation may help control.

Provide pigs with a good environment to limit effects of secondary infections

Separate weaners who show signs of the disease to reduce the level of the disease in the pen

Have good gilt introduction protocols to ensure gilts are well acclimatised before entry into the main unit.

Feed-back of on-site nursery faeces is essential.  Consider the use of tonsilar scrapes.

Minimise cross-fostering

Common differentials


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


Papers on PMWS
Treatment and control of PMWS – personal observations