Few cells in the lung, liver, kidney and lymph node stain positive for the replicative form of PCV2, showing that replication takes place in epithelial and endothelial cells.

Sequential studies in experimentally infected pigs have shown that from one day post infection PCV2 virus is present in the intestine, the upper respiratory tract and their associated lymphoid organs and is widespread in most tissues by 10-14 days after infection.

A new in-situ hybridization method allows differentiation between cells that contain virus and those that contain replicating PCV2 virus. In tissues of PMWS affected pigs virus labelling was most intense in macrophage like cells in lymphoid tissues and less frequent in non-lymphoid tissues.

The replicative form of PCV2 however was most frequently found in lung, lymph nodes, tonsils and liver, kidney and intestines. The cells with replication forms of the virus were mostly epithelial cells.

The susceptibility of intestinal epithelial cells for PCV2 infections has also been shown in in-vitro and in short-term in-vivo studies. PCV2 is able to replicate in intestinal epithelial cells.

Current microarray studies have shown that the infection in cell culture of intestinal epithelial cells significantly alters the gene expression of the cells. The up- or down-regulated genes are mostly involved in cell differentiation and cell structure processes. PCV2 infection also led to more apoptotic cells in cell culture studies with intestinal epithelial cells.

The clinical relevance of these findings as cause of diarrhoea or enteritis remains unclear.

Experimental triggering in the intestines by bacterial co-infection with E. coli in a model of post-weaning diarrhoea did not result in the expression of PMWS, nor in theses studies were enteritis symptoms aggravated in PCV2-infected animals.

October 2008

Further Reading

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