As one of the most common agents causing the Porcine Respiratory Disease Complex Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is nowadays endemic in many swine producing countries and leads to severe economical losses (PESJAK et al. 1997, ROSSOW 1998). Furthermore PRRSV and SIV are the major primary viral pathogens causing respiratory diseases in pigs (CHOI et al. 2003).
The clinical signs vary widely and are complicated by bacterial coinfections. PRRSV infection of pregnant gilts or sows results in reproductive failures like late-term abortion, premature farrowing with stillborn fetuses, partially autolyzed fetuses and mummified fetuses. Nursery, growing and finishing pigs suffer from pneumonia, dyspnoe, fever, anorexia and lethargy. Gross lesions with PRRSV infection are tan mottled areas in the lung and enlarged lymph nodes. Microscopic lesions include interstitial pneumonia with expanded alveolar septa and hypertrophied and hyperplastic type 2 pneumocytes (ROSSOW 1998, ZIMMERMAN et al. 2006).