Size Distribution of Inactivated Tick-Borne Encephalitis Virus Particles Revealed by a Comprehensive Physicochemical Approach

Tick-borne encephalitis virus (TBEV) is an enveloped RNA virus, a member of the genus Flavivirus (family Flaviviridae). Here, we provide a detailed analysis of the size and structure of the inactivated TBEV vaccine strain Sofjin-Chumakov. Four analytical methods were used to analyze individual TBEV particles—negative staining TEM, cryo-EM, atomic force microscopy (AFM), and nanoparticle tracking analysis (NTA). All methods confirmed that the particles were monodisperse and that their mean size was ~50 nm. Cryo-EM data allowed us to obtain a 3D electron density model of the virus with clearly distinguishable E protein molecules. STEM-EELS analysis detected phosphorus in the particles, which was interpreted as an indicator of RNA presence. Altogether, the described analytical procedures can be valuable for the characterization of inactivated vaccine virus samples.