Pathological findings within the group of animals

PMWS is a disease of the lymphoid tissues with secondary lesions in the other major organs.  Note PMWS cannot be diagnosed on postmortem findings only as these findings can be recognized on many farms without the clinical signs of PMWS.


The lymphoid tissues in the acute phase presents as enlargement and are more noticeable/prominent lymph nodes – often in areas where lymph nodes would not be noticed.  Three areas of lymphoid enlargement should be examined:


The superficial inguinal lymph node

The abdominal lymph nodes – mesenteric (which can be extremely variable), hepatic and gastrosplenic.

The bronchial lymph nodes

Superficial inguinal lymph node 

These may become more bilaterally prominent and may even be visible to the naked eye




Abdominal lymph nodes – in particular the mesenteric, hepatic and gastrosplenic lymph nodes demonstrate enlargement – this can be extremely variable.

Bronchial and chest lymph nodes are enlarged 


When there are respiratory problems the bronchial lymph nodes can become prominent.  The ones shown are only slightly enlarged.


Other gross pathological findings which are commonly associated with PMWS


Pericardial effusion – fluid around the heart

Rounding of the heart – enlarged right venticle – this may be the cause of the fluid around the heart and other organs

Pale enlarged liver – this may be associated with jaundice or icterus - a yellowing of the carcass

Gastric ulceration

Enlarged kidney

Kidney with “white spots” which are caused by nonpurulent interstitial nephritis.


With secondary infections becoming involved, the pig also presents with the range of pathology associated with each of these secondary infections which are then superimposed over the lesions described above.


Laboratory findings
Histological examination of the enlarged lymph nodes reveal a characteristic lesion.  Note however, this lesion can also be found in wasted/compromised pigs without PMWS, especially when only single lymph node is examined.  It is essential that at least tissues samples from at least 3 different enlarged lymph nodes are presented from each affected animal to demonstrate that the condition is systemic.


Normal lymph node

Each of the follicles (one highlighted by the circle) shown are a single B lymphocyte clone line of cells producing a single antibody

PMWS lymph node

In the infected lymph node the B cells have disappeared from the follicle and only the background remains – highlighted by the arrow

Overwhelming PCVII in tissues – example lung

The brown areas are areas of PCVII virus

Pictures Iowa State University

The depleted follicle is replaced with large histiocytic cells and giant multinucleate cells.  Cytoplasmic PCVII viral inclusion bodies may be seen in the histocytes or dendritic cells.  Note with time the lymph nodes may actually undergo atrophy (a reduction in size). 


Multinucleated cells in the lymph node

Cytoplasmic inclusion bodies (New Zealand)



When the lymph node is examined for the presence of PCV II in positive cases of PMWS there will be an overwhelming presence of PCV II in the macrophages of the lymph node.







Clinical findings



Gross pathological findings



Laboratory findings

Herd History



Treatment and control

PMWS negative

PMWS positive