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

Abstract

This article describes the preparation of 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 tested only in camels. In the safety evaluation of the inactivated vaccine, the vaccine was not observed to cause any adverse effects in mice and camels. During the immunogenicity study in camels, antibody formation started (0.2 ± 0.16 log2) at Day 21 post-vaccination (PV), and the antibody titer peaked (1.33 ± 0.21 log2) at Day 60 PV and decreased at Day 90 PV (0.50 ± 0.22 log2). Furthermore, no antibodies were detected in vaccinated camels from Days 180 to 365 PV. Camels that received vaccination and were subsequently exposed to wild-type virus evinced a healthy state despite lacking antibodies. In contrast, unvaccinated camels exhibited susceptibility to camelpox upon challenge.

Field Trials of Live and Inactivated Camelpox Vaccines in Kazakhstan

“…In this study, the immunogenicity of the inactivated vaccine was reproducible, as shown in a previous laboratory test [19]. Although the antibody response was very low, it showed 100% protection efficiency during a natural camelpox outbreak.…”

“…The transportation of animals from an infected area cannot occur under the veterinary laws of the Republic of Kazakhstan [ 33 ]. However, the protective properties of these vaccines have been previously demonstrated in experimental studies [ 18 , 19 ]. Another limitation of this study was the lack of a proper sampling design to collect samples for camelpox virus shedding and serology following the detection of clinical signs in control camels.…”

“…The CMLV KM-40 strain was cultivated on lamb kidney cells [ 19 ] using Dulbecco’s modified Eagle’s medium (DMEM) supplemented with 10% irradiated fetal calf serum. Lamb kidney cells were infected with the virus at a multiplicity of infection (MOI) of 0.01 TCID 50 /cell.…”

“…The inactivated vaccine antigen was adjuvanted with aluminum hydroxide at a concentration of 1.25 mg/mL. The finished vaccine was stored in 50 mL vials at 4 °C until needed [ 19 ].…”

“…It has been previously demonstrated that this live attenuated camelpox vaccine is safe by overdose inoculation, and it does not revert to virulence following three successive passages in camels [ 18 ]. In addition, the protective effectiveness of both the live attenuated, including the optimal dose to use, administered through scarification, and inactivated camelpox vaccines were evaluated using an experimental infection of camelpox in camels to test their efficacy [ 18 , 19 ].…”