PRRS is caused by a virus that causes the host’s immune system to malfunction much in the same manner in which infectious agents can trigger the onset of autoimmune syndromes like Lupus or rheumatoid arthritis in humans. The damage caused by such a syndrome effects kidney function and damages vascular and epithelial integrity. Both may explain the greater susceptibility of PRRSV-infected piglets to opportunistic pathogens of swine and the malaise and morbidity of infected neonatal piglets. It is generally true that if the pathology caused by an infectious agent is understood, the development of counter measures and the development of effective vaccines will rest on firmer scientific principles and less on non-directed trial and error vaccination schemes.