Development of an Inactivated Vaccine from Attenuated Camelpox Virus Strain: Safety and Protection in Camels

This article describes the technology of preparing an inactivated vaccine from an attenuated strain of camelpox. The attenuated camelpox virus (CMLV) was grown in lamb kidney cells and in Vero cells. CMLV was accumulated to a significantly higher (p≤0.05) titer in lamb kidney cells (7.75±0.08 log TCID50/ml) than in Vero cells (4.00±0.14 log TCID50/ml). During virus inactivation, a concentration of 0.05% beta-propiolactone (BPL) completely inactivated the virus in 6 h at a temperature of 22 ± 1 °C, while a concentration of 0.2% formaldehyde inactivated the virus in 8 h. However, a viral antigen inactivated by BPL was used for vaccine preparation. The inactivated viral antigen was adsorbed with aluminum hydroxide gel, and as a result, an inactivated candidate vaccine was prepared. While the safety of the candidate vaccine was tested in camels and white mice, the protective efficacy of the vaccine was only tested in camels. In the safety evaluation of the inactivated vaccine, the vaccine did not cause any adverse effects in mice and camels. During the immunogenicity study in camels, antibody formation started (0.2 ± 0.16 log2) from the 21st day post-vaccination (DPV), the antibody titer peaked (1.33 ± 0.21 log2) at the 60th DPV and decreased at the 90th DPV (0.50 ± 0.22 log2). Furthermore, no antibodies were detected in vaccinated camels from 180 to 365 DPV. Vaccinated camels challenged with wild-type virus remained healthy even though they did not have antibodies, whereas at that time, unvaccinated camels were affected by camel pox during the challenge.

本研究详述了以减毒骆驼痘毒株为原料制备灭活疫苗的工艺方法。试验所用减毒骆驼痘病毒（Camelpox Virus, CMLV）分别在羔羊肾细胞与Vero细胞中增殖培养。结果显示，CMLV在羔羊肾细胞中的病毒滴度显著高于Vero细胞（p≤0.05），分别可达7.75±0.08 log TCID50/ml与4.00±0.14 log TCID50/ml。病毒灭活试验中，0.05%浓度的β-丙内酯（beta-propiolactone, BPL）在22±1℃条件下可于6小时内完全灭活病毒，而0.2%浓度的甲醛则需8小时方可完成病毒灭活。本研究最终选用BPL灭活的病毒抗原用于疫苗制备，将该灭活病毒抗原经氢氧化铝凝胶吸附后，即获得候选灭活疫苗。该候选疫苗的安全性评价在骆驼与小白鼠中开展，但其保护效力仅在骆驼群体中进行了检测。安全性评价结果表明，该候选灭活疫苗对小白鼠与骆驼均未引发任何不良反应。在骆驼的免疫原性研究中，免疫后第21天（Day Post-Vaccination, DPV）即可检出特异性抗体，抗体滴度为0.2±0.16 log2；于免疫后第60天抗体滴度达到峰值（1.33±0.21 log2），至第90天时滴度降至0.50±0.22 log2。此外，在免疫后180至365天期间，免疫骆驼体内未检出特异性抗体。即便此时免疫骆驼体内已无特异性抗体，用野生型骆驼痘病毒攻毒后仍可保持健康状态；而同期未免疫的骆驼在攻毒后均感染了骆驼痘。