Tick-borne encephalitis virus (TBEV) is a zoonotic flavivirus which is endemic in many European and Asian countries. Humans can get infected with TBEV usually via ticks, and possible symptoms of the infection range from fever to severe neurological complications such as encephalitis. Vaccines to protect against TBEV-induced disease are widely used and most of them consist of whole viruses, which are inactivated by formaldehyde. Although this production process is well established, it has several drawbacks, including the usage of hazardous chemicals, the long inactivation times required and the potential modification of antigens by formaldehyde. As an alternative to chemical treatment, low-energy electron irradiation (LEEI) is known to efficiently inactivate pathogens by predominantly damaging nucleic acids. In contrast to other methods of ionizing radiation, LEEI does not require substantial shielding constructions and can be used in standard laboratories. Here, we have analyzed the potential of LEEI to generate a TBEV vaccine and immunized mice with three doses of irradiated or chemically inactivated TBEV. LEEI-inactivated TBEV induced binding antibodies of higher titer compared to the formaldehyde-inactivated virus. This was also observed for the avidity of the antibodies measured after the second dose. After viral challenge, the mice immunized with LEEI- or formaldehyde-inactivated TBEV were completely protected from disease and had no detectable virus in the central nervous system. Taken together, the results indicate that LEEI could be an alternative to chemical inactivation for the production of a TBEV vaccine.

Low-energy electron irradiation is an emerging alternative technology for attenuated or complete pathogen inactivation with respect to medical, biotechnological, and pharmaceutical applications. Pathogen inactivation by ionizing radiation depends mainly on the absorbed electron dose. In low-energy electron irradiation processes, determination of the absorbed electron dose is challenging due to the limited, material-dependent penetration depth of the accelerated electrons into the matter. In general, there are established dosimetry systems to evaluate the absorbed dose under dry irradiation conditions. However, there is no system for precise dose monitoring of low-energy irradiation processes in liquids or suspensions so far. Therefore, in this study three different bacterial species were investigated as biological dose indicators, especially in the range of low doses (< 6.5 kGy) in aqueous solutions or suspensions. Escherichia coli, Bacillus subtilis, and Staphylococcus warneri were comparatively evaluated for their suitability as biological dose indicators. Thin homogeneous films of the respective bacterial suspensions were irradiated with increasing doses of low-energy accelerated electrons. The average absorbed dose was determined using a colorimetric dosimeter based on a tetrazolium salt solution. The maximum and minimum absorbed doses were measured with a referenced film dosimeter. Subsequently, the inactivation kinetics was determined in terms of inactivation curves and D10 values. Thus, the minimum inactivation dose of bacterial growth was assessed for E. coli and S. warneri. The effect of irradiation with low-energy accelerated electrons on the growth behavior and activity of the bacteria was studied in more detail using impedance spectroscopy. With increasing irradiation doses growth was delayed.

An expanding part of electron beam technology developed at Fraunhofer FEP tackles ecological and biotechnological challenges of highest relevance. Antimicrobial and fungicidal effects of electron beam are exploited in the chemical-free phytosanitary treatment of seeds. Chemical pollutants but also pathogens in gaseous effluents and waste water can be efficiently neutralized. Medical products such as tools, packaging and implants can be sterilized, disinfected, or even biologically advantageously functionalized. Viruses can be inactivated via electron beam to produce vaccines with an excellent antigen conservation leading to a high degree of immunization with good reproducibility, but without the usage of additional chemicals. Plasma synthesis in electron beam-sustained discharges allows for an exceptionally efficient energy transfer to non-reactive greenhouse gases like CO2 and CH4 and is a promising approach to the economical, scalable production of media for sustainable chemical energy storage (Power to X - PtX), driving the energy transition and reducing greenhouse gases. The publication gives an overview of the recent advances of electron beam technology at Fraunhofer FEP in these emerging fields of application.