Elanco Animal Health, Bergen, Norway.
VESO Aqualab, Vikan, Namsos, Norway.
Front Immunol. 2024 Mar 7;15:1342816. doi: 10.3389/fimmu.2024.1342816. eCollection 2024.
Salmonid alphavirus (SAV) causes pancreas disease (PD), which negatively impacts farmed Atlantic salmon. In this study, fish were vaccinated with a DNA-PD vaccine (DNA-PD) and an oil-adjuvanted, inactivated whole virus PD vaccine (Oil-PD). Controls were two non-PD vaccinated groups. Fish were kept in one tank and challenged by cohabitation with SAV genotype 2 in seawater. Protection against infection and mortality was assessed for 84 days (Efficacy study). Nineteen days post challenge (dpc), subgroups of fish from all treatment groups were transferred to separate tanks and cohabited with naïve fish (Transmission study 1) or fish vaccinated with a homologous vaccine (Transmission study 2), to evaluate virus transmission for 26 days (47 dpc). Viremia, heart RT-qPCR and histopathological scoring of key organs affected by PD were used to measure infection levels. RT-droplet digital PCR quantified shedding of SAV into water for transmission studies. The Efficacy study showed that PD associated growth-loss was significantly lower and clearance of SAV2 RNA significantly higher in the PD-DNA group compared to the other groups. The PD-DNA group had milder lesions in the heart and muscle. Cumulative mortality post challenge was low and not different between groups, but the DNA-PD group had delayed time-to-death. In Transmission study 1, the lowest water levels of SAV RNA were measured in the tanks containing the DNA-PD group at 21 and 34 dpc. Despite this, and irrespective of the treatment group, SAV2 was effectively transmitted to the naïve fish during 26-day cohabitation. At 47 dpc, the SAV RNA concentrations in the water were lower in all tanks compared to 34 dpc. In Transmission study 2, none of the DNA-PD immunized cohabitants residing with DNA-PD-vaccinated, pre-challenged fish got infected. In contrast, Oil-PD immunized cohabitants residing with Oil-PD-vaccinated, pre-challenged fish, showed infection levels similar to the naïve cohabitants in Transmission study 1. The results demonstrate that the DNA-PD vaccine may curb the spread of SAV infection as the DNA-PD vaccinated, SAV2 exposed fish, did not spread the infection to cohabiting DNA-PD vaccinated fish. This signifies that herd immunity may be achieved by the DNA-PD vaccine, a valuable tool to control the PD epizootic in farmed Atlantic salmon.
鲑鱼甲病毒 (SAV) 引起胰腺疾病 (PD)，对养殖大西洋鲑鱼产生负面影响。在这项研究中，鱼用 DNA-PD 疫苗 (DNA-PD) 和油佐剂灭活全病毒 PD 疫苗 (Oil-PD) 进行了疫苗接种。对照组是两个未接种 PD 的组。鱼被饲养在一个水箱中，并通过与海水中的 SAV 基因型 2 同居来进行挑战。在 84 天内评估了对感染和死亡率的保护（疗效研究）。挑战后 19 天（dpc），从所有治疗组中抽取的鱼亚组被转移到单独的水箱中，并与未接种疫苗的鱼（传播研究 1）或接种同源疫苗的鱼（传播研究 2）同居，以评估 26 天（47 dpc）的病毒传播情况。病毒血症、心脏 RT-qPCR 和 PD 影响的关键器官的组织病理学评分用于测量感染水平。RT-液滴数字 PCR 定量了 SAV 进入水中的脱落以进行传播研究。疗效研究表明，与其他组相比，PD-DNA 组的 PD 相关生长损失明显降低，SAV2 RNA 的清除率明显更高。PD-DNA 组的心脏和肌肉病变较轻。挑战后的累积死亡率较低，各组之间无差异，但 DNA-PD 组的死亡时间延迟。在传播研究 1 中，在 21 天和 34 天时，包含 DNA-PD 组的水箱中测量到的 SAV RNA 水平最低。尽管如此，并且与治疗组无关，SAV2 在 26 天的同居期间有效地传播给了未接种疫苗的鱼。在 47 dpc 时，与 34 dpc 相比，所有水箱中的 SAV RNA 浓度均较低。在传播研究 2 中，与 DNA-PD 疫苗接种、预先挑战的鱼一起居住的 DNA-PD 免疫的同居鱼没有感染。相比之下，与 Oil-PD 疫苗接种、预先挑战的鱼一起居住的 Oil-PD 免疫的同居鱼表现出与传播研究 1 中的未接种疫苗的同居鱼相似的感染水平。结果表明，DNA-PD 疫苗可能会抑制 SAV 感染的传播，因为暴露于 SAV2 的 DNA-PD 疫苗接种鱼并未将感染传播给同居的 DNA-PD 疫苗接种鱼。这表明，DNA-PD 疫苗可能实现群体免疫，这是控制养殖大西洋鲑鱼 PD 爆发的一种有价值的工具。
