Diagnosis of PCVD's in pigs

For a definitive diagnosis of PCVD, clinical signs, post mortal lesions and the presence of PCV-2 within lesions need to all be taken into consideration.

Serology

Serology is only useful when paired sera are tested and sero-conversion is accompanied by an increase of PCV2 like clinical signs on the farm. When serology is used to screen different age groups, an indication of the time of infection can be given as most animals seroconvert 2 weeks post exposure.

Most pigs are infected with PCV-2 and/or comprise antibodies against PCV-2 for various reasons, thus the detection of antibodies alone is of little value. Differences are seen between IgM and IgG antibodies. IgM antibodies occur earlier indicating a recent infection. IgG antibodies occur later indicating an older infection.

ELISA tests are usually used. In moribund animals serological titers can be low as the affected immune system is no longer capable of producing antibodies.
Serology is used for monitoring and vaccination purposes.

Polymerase Chain Reaction (PCR)

PCR is the most sensitive method of detecting PCV-2 virus and is highly specific. PCR has proven to be of value in cases of PMWS diagnosis and especially the quantitative PCR when the hypothesis is true that the disease expression is largely influenced by the quantity of PCV-2 virus in the tissue.

It should however be kept in mind that different laboratories may use different techniques and that not all results can be compared.

Post mortem examinations

For the diagnosis of PCVD on a herd basis, it is suggested to perform autopsy on 5 pigs from a herd and that at least 1 of them should have all the following symptoms.

• Clinical signs including growth retardation and wasting, frequently with dyspnea and enlargement of inguinal lymph nodes, and occasionally with jaundice
• Presence of characteristic histopathological lesions in lymphoid tissues (lymphocyte depletion together with granulomatous inflammation, presence of PCV-2 inclusion bodies and multinucleate giant cells in a proportion of affected pigs)
• Detection of PCV-2 within the lesions in lymphoid tissues of affected pigs.

(Sorden 2000)

Wasting seen in a piglet affected by PCVD.

Severely enlarged lymph node with white foci from a pig affected by PCVD.