The effects in breeding herds are reproductive failure and signs of respiratory disease. Weaned and finishing pigs suffer from respiratory disorders due to secondary infection, which are worsened by the immuno-modulatory properties of the PRRS virus (PRRSV).
For detailed information on PRRS in pigs also see the website www.porcilis-prrs.com.
Consequences of PRRS
The economic impact of PRRS in a finishing unit is substantial. In a breeding herd it is dramatic but in general only lasting for some month’s till the breeding herd reaches a stabile situation. However the reproductive problems may reoccur if the breeding herd become destabilised due to recycling of PRRSv from the finishing herd or excreting gilts.
Pathogenesis of PRRSV infection
The PRRS virus is transmitted by various means. The virus enters and replicates in macrophages. Disease may be subclinical or clinical. The syndrome presented, respiratory or reproductive, is dependent on the age of the pigs affected.
Stillborn and weak piglets at farrowing as a result of PRRS infection in the sow
In addition to reproductive failure, sows and gilts may show:
Neonatal piglets can display a variety of clinical signs. The most characteristic are dyspnea, tachypnea and death.
Growers and finishing pigs
PRRSV infection alone is often subclinical. It is however indirectly responsible for huge economic losses in finishing herds due to its major role in the multifactorial Porcine Respiratory Disease Complex (PRDC).
If clinical signs are present, they are usually respiratory:
Experimental challenge of SPF pigs with PRRSV alone usually produces no clinical signs.
Mechanism of interactions
The mechanism by which PRRSV interacts with other pathogens is still under investigation. However, it has been demonstrated experimentally that:
The role of PRRSV
It is still not possible to conclude which are the most important combinations of pathogens or to define the importance of PRRSV in the severity of respiratory disease in finishing pigs. This is difficult to prove experimentally due to pathogenicity of virus strains used, timing of infections, serological status of pigs used and the lack of predisposing or stress factors due to housing and/or management. Clinical experience in the field has shown that the occurence of new respiratory pathogens result in increasingly complex respiratory problems and improved performance has been observed in PRRSV-vaccinated herds.