With the discovery of Porcine circovirus type 2d (PCV2d) in the USA in 2012 and subsequent genotype shift from the previously predominant PCV2b to PCV2d in the face of widespread PCV2a vaccination, concerns over PCV2 vaccine efficacy were raised. The objective of this study was to evaluate the efficacy of two similarly produced PCV2 vaccines, one containing the PCV2a capsid and the other one containing the PCV2b capsid, in the conventional pig model against PCV2d/porcine parvovirus 2 (PPV2) co-challenge. A co-challenge was added since there is evidence that PPV2 may exacerbate PCV2 infection and since PCV2 only rarely causes disease in experimentally infected pigs, hence vaccine efficacy can be difficult to assess. In brief, sixty 3-week-old-pigs from a PCV2 seropositive farm without evidence of active virus replication (no PCV2 viremia, low antibody titers with no evidence of increase after two consecutive bleedings) were blocked by PCV2 antibody titer and then randomly divided into three groups with 20 pigs each, a non-vaccinated group (challenge control), a PCV2a vaccinated group (VAC2a) and a PCV2b vaccinated group (VAC2b). Vaccinations were done at 4 and again at 6 weeks of age. At 8 weeks of age, all pigs were challenged with a PCV2d strain via intranasal and intramuscular routes of inoculation followed by intramuscular administration of PPV2 one day later. PCV2 vaccination, regardless of PCV2 genotype, resulted in significantly higher humoral and cellular immunity compared to non-vaccinated challenge control pigs as evidenced by increased numbers of interferon (IFN) γ secreting cells after PCV2d stimulation of peripheral blood mononuclear cells collected prior to challenge. Furthermore, PCV2a and PCV2b vaccinations both reduced PCV2d viremia and PCV2-associated pathological lesions. Under the study conditions, the PCV2a and PCV2b vaccine preparations each induced immune responses and clinical protection against a heterologous PCV2d/PPV2 co-challenge.

中文翻译：

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基于猪圆环病毒2a或2b型的实验疫苗可提供针对PCV2d /猪细小病毒2共同攻击的保护作用。

随着2012年在美国发现2d型猪圆环病毒（PCV2d）以及面对广泛的PCV2a疫苗接种，随后基因型从以前的主要PCV2b转变为PCV2d，引起了人们对PCV2疫苗功效的担忧。这项研究的目的是评估两种类似生产的PCV2疫苗在常规猪模型中针对PCV2d /猪细小病毒2（PPV2）共同攻击的功效，一种包含PCV2a衣壳，另一种包含PCV2b衣壳。加入了共同挑战，因为有证据表明PPV2可能加剧PCV2感染，并且由于PCV2仅很少在实验感染的猪中引起疾病​​，因此疫苗效力可能难以评估。简而言之，来自PCV2血清反应阳性农场的60只3周大的猪，没有活跃病毒复制的证据（没有PCV2病毒血症，低抗体滴度（连续两次出血后无增加的证据）被PCV​​2抗体滴度阻断，然后随机分为三组，每组20头猪，未接种组（攻击对照组），接种PCV2a的疫苗组（VAC2a）和一个PCV2b疫苗接种组（VAC2b）。在4周龄和6周龄再次接种疫苗。在8周龄时，所有猪都通过鼻内和肌内接种途径用PCV2d菌株攻击，然后一天后肌内施用PPV2。与未接种疫苗的攻击对照组猪相比，无论PCV2是何种基因型，PCV2疫苗接种均能显着提高体液和细胞免疫力，这一点可通过PCV2d刺激攻击前收集的外周血单核细胞后干扰素（IFN）γ分泌细胞数量的增加来证明。此外，PCV2a和PCV2b疫苗接种均减少了PCV2d病毒血症和与PCV2相关的病理性病变。在研究条件下，PCV2a和PCV2b疫苗制剂各自诱导针对异源PCV2d / PPV2共同攻击的免疫应答和临床保护。