Anses, French Agency for Food, Environmental and Occupational Health and Safety, Laboratory of Ploufragan-Plouzané, BP 53, F22440 Ploufragan, France.
Virus Res. 2012 Mar;164(1-2):78-89. doi: 10.1016/j.virusres.2011.12.002. Epub 2011 Dec 9.
PCV2 has been highly prevalent in the pig population for decades, prior to the emergence of associated clinical disease manifestations that severely affected the pig production worldwide in the late 90s. PCV2 can be further subdivided into several genotypes. From descriptive epidemiologic data, there is evidence of a global shift of the main PCV2 genotypes in different countries from PCV2a to PCV2b, which is generally associated with more severe disease. In addition, from analytic epidemiologic studies, the modified within-herd PCV2 dynamics of infection is strongly related to the increased incidence of clinical disorders associated with PCV2 infection. Because PCV2 is shed for a long time by an extremely large variety of routes, it easily spreads within the population both through horizontal and vertical transmission. Even if airborne transmission cannot be formally excluded, direct contact is certainly the most efficient infectious route due to the simultaneous exposure of susceptible pigs to contaminated respiratory, digestive, and urinary secretions since the probability of transmission is strongly limited by the distance between infectious and susceptible animals. Consequently, farm to farm transmission is restricted to the introduction of infected animals or infected animal products such as semen. More information would be required to assess the risk of other vehicles such as vaccines or feed ingredients since the probability of these products to be contaminated by PCV2 is unknown. However, owing to its transmission characteristics, PCV2 is able to be maintained within pig farms for years without any further need for re-introduction due to the population dynamics of modern pig operations, which continually renew the pool of the susceptible population through replacements and pig movements between compartments.
PCV2 在猪群中存在了几十年，在此之前，90 年代末与该病毒相关的临床疾病表现严重影响了全球的养猪业。PCV2 可以进一步细分为几种基因型。从描述性流行病学数据来看，有证据表明，不同国家的主要 PCV2 基因型从 PCV2a 向 PCV2b 发生了全球转移，这通常与更严重的疾病有关。此外，从分析性流行病学研究来看，感染的猪群内 PCV2 动力学的改变与与 PCV2 感染相关的临床疾病发病率的增加密切相关。由于 PCV2 通过极其多样化的途径持续大量排出，因此它很容易在猪群中通过水平和垂直传播进行传播。即使不能正式排除空气传播的可能性，但由于易感猪同时接触到受污染的呼吸道、消化道和泌尿道分泌物，直接接触肯定是最有效的感染途径，因为传播的可能性受到感染动物和易感动物之间距离的强烈限制。因此，农场之间的传播仅限于引入感染动物或受感染动物产品，如精液。由于对疫苗或饲料成分等其他媒介物的污染可能性未知，因此需要更多信息来评估这些媒介物的风险。然而，由于其传播特性，PCV2 能够在没有进一步引入的情况下在猪场中维持多年，这是由于现代养猪业的猪群动态所致，该动态通过更换和猪在不同隔间之间的移动不断更新易感猪群的群体。
