Update on PRRSV immunology and viral genetics: From hopeless to hopeful

摘要

Scientific research and creative practice by swine veterinarians has transformed the prospects of PRRSV control and elimination from hopeless to hopeful. Herd closure, pioneered by veterinarians to eliminate PRRSV in sow herds, provides compelling evidence that the porcine immune response completely eliminates PRRSV from pigs. Thus, immunological control of PRRSV is possible and facilitates PRRSV elimination from commercial herds. Immune memory is expressed against future exposure, to both related and unrelated virus strains. Protective immunity is demonstrated for vaccination with live, attenuated strains, and for inoculation with virulent field strains. The degree of protection is variable, and may be influenced by animal age, viral strain, and other factors that are not understood at this time. PRRSV continues to evolve new strains, including highly virulent strains. A 1-18-2 strain appeared in 2007 and has caused widespread devastation in the north central USA. It is unrelated to the highly pathogenic Chinese PRRSV strain. It appears to be displacing resident viruses, including virulent viruses in the 184 family, suggesting that there might be poor cross-protection between these two types of viruses. However, the 1-18-2 virus also has been isolated from herds without clinical signs, suggesting good cross-protection against disease in some cases. An increasing body of research on highly pathogenic PRRSV is revising our understanding of PRRSV epidemiology. It is now clear that virulent virusesgrow to higher levels in pigs, are shed at higher levels, increase the environmental load, are transmitted by air in significant amounts, spread by air within an area, and may be more infectious. Nevertheless, advances in biosecurity and air filtration,combined with herd closure, demonstrate that PRRSV can be controlled effectively by good management practices, and that immunological protection reduces the harmful impact of outbreaks. Thus, the prospects for control of PRRS are bright.