Key Messages

• Microscopic lesions were more severe and found in more tissues in pigs inoculated with both viruses instead of only with PCV2.
• PRRSV infection was found to affect the average daily gain of pigs.
• Pigs coinfected with PRRS had higher amounts of PCV2 nucleic acid and in more tissues than pigs only inoculated with PCV2.
• Also, a previous infection with PRRSV resulted in a higher PCV2 load in serum of PCV2 infected pigs.

PCV2 could also enhance replication of PRRSV, since a longer PRRSV viremia and a higher proportion of PRRS-viremic pigs were found when both viruses were inoculated.

Article Brief

The objective of the study was to reproduce PMWS in pigs by inoculating with PRRSV and PCV2. The enhancement of PCV2 replication by PRRSV was also investigated.

24 piglets (31 to 40 days old) were assigned to four groups:

1. controls
2. inoculated with PRRSV on day 0
3. inoculated with PCV2 on day 7
4. inoculated with PRRSV on day 0 and PCV2 on day 7.

Pigs were monitored during the study: body weight, rectal temperatures and blood samples were taken, and were euthanatised at day 32.

Only pigs (3 of 7) inoculated with both viruses had increased rectal temperature (above 40.5°C).

Average daily gain (ADG) was higher in control pigs (0.64kg per day), followed by PCV2 pigs (0.56kg per day), PRRSV (0.41kg per day), and both viruses (0.35kg per day). The growth retardation observed in this experiment was only significant in the PRRSV-inoculated pigs. The difference between control pigs and pigs inoculated only with PCV2 was not significant.

The microscopic lesions were more severe and detected in more tissues in pigs inoculated with both viruses than in pigs inoculated only with PCV2. Likewise, the amount of PCV2 nucleic acid detected was higher and found in more tissues in pigs inoculated with both viruses than in PCV2-inoculated pigs. In addition, a previous infection with PRRSV in PCV2 pigs resulted in a higher PCV2 load in serum.

Also, a longer PRRSV viremia and a higher proportion of viremic pigs were observed for pigs with both viruses, which indicate that PCV2 could also enhance replication of PRRSV.

The study showed that severe PMWS could be reproduced in pigs infected with PRRSV and PCV2. Also, it indicates that PRRSV can be a predisposing factor for developing the disease and it also promotes the replication of PCV2.

Reference

Rovira A., Balasch M., Segalés J., García L., Plana-Durán J., Rosell C., Ellerbrok H., Mankertz A. and Domingo M. 2002. Experimental inoculation of conventional pigs with Porcine reproductive and respiratory syndrome virus and porcine circovirus 2. Journal of Virology. 76:3232–3239.

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