Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of the, probably, most economically important disease for the pig industry worldwide. This disease, characterised by producing reproductive failure in sows and respiratory problems in growing pigs, appeared in the late 1980s in the United States and Canada. Since its appearance, strains capable of producing higher mortality rates as well as greater severity in clinical signs and lesions than classical strains have been identified. However, since the first reports of these “virulent” PRRSV outbreaks, no homogeneity and consensus in their description have been established. Moreover, to the authors’ knowledge, there is no published information related to the criteria that a PRRSV strain should fulfil to be considered as a “virulent” strain. In this review, we revise the terminology used and gather the information related to the main characteristics and differences in clinical signs, lesions, viral replication and tropism as well as immunological parameters between virulent and classical PRRSV strains and propose a first approximation to the criteria to define a virulent PRRSV strain.

猪繁殖与呼吸综合征病毒(PRRSV) 是全球养猪业最重要的经济疾病的病原体。这种疾病的特点是导致母猪繁殖失败和生长猪出现呼吸问题，出现在 1980 年代后期的美国和加拿大。自其出现以来，已经鉴定出能够产生比经典菌株更高的死亡率以及更严重的临床症状和病变的菌株。然而，自从这些“致命”PRRSV 爆发的第一次报告以来，在它们的描述中没有建立同质性和共识。此外，据作者所知，没有已发表的信息与 PRRSV 菌株应满足的标准相关才能被视为“毒力”菌株。在这次审查中，