Impact of ionizing radiation on the efficacy of the rift valley fever vaccine

The article presents the study of the impact of ionizing radiation on efficacy of vaccination of domestic animals against the Rift valley fever. Rift valley fever (RVF) is an acute viral disease that affects mainly ruminants, especially domestic animals, and infects humans. The fever is caused by the RVF virus (RVFV), that circulates in endemic areas between wild ruminants and haematophagous mosquitoes, that are both the reservoir and vector for the virus. The disease outbreaks occurred in African countries and South Arabia in the 21-st century caused significant economic losses in the livestock industry. Now doors to Europe, North America and South America continents are open to the epidemics. Some countries recognised the RFV virus as biological terror threat. At present time the occurrence of simultaneous viral disease outbreak and technological accident resulting in the uncontrolled release of hazardous materials, that have potential to harm humans, animals and environment may be possible. To ensure proper response to combined epidemic and radiological emergencies, effective measures should be developed in advance. The article presents the study of the impact of ionizing radiation on efficacy of vaccination of domestic animals against RVF. To estimate the impact, sheep susceptible to the RVF vaccine were vaccinated by intramascular injection of 1.0 cm3 of the live - attenuated 1974-VNIIVViM RVF vaccine at the dose of 104.0 TCID50, before and after the wholebody gamma-ray irradiation from 137Cs source. Exposure to the dose of 4.4 Gy (0.012 cGy/min) caused severe acute radiation sickness. Both control non-vaccinated and vaccinated animals were infected by intramuscular injection of 1 cm3 of the virulent Entebbe strain of RVFV at a dose of 104,0 MLD50. The survival of irradiated animals vaccinated 15, 30 and 40 days prior to exposure exceeds the survival of the non-vaccinated sheep by 45.7%. RVF vaccine increased resistance to radiation. To estimate immunity of vaccinated and non-vaccinated (control) sheep, the species were infected in 45 days after irradiation. The latent period for control animals lasted 1-3 days, in some hours after irradiation their body-temperature rose to 41-41.8 °С. They died in 1-2 days after the manifestation of the first signs of the disease. Lethality was 90%. The necropsy study showed pathognomonic signs of the RVF as signs of hepatitis: bloodstroke, focal or total necrosis of the hepatic parenchyma. Radioprotective effect of the RVF vaccine was studied in linear mice with splenic endo-colony method. It was found that the vaccine was able to stimulate proliferative activity of bone marrow stem cells.