Transmission electron micrograph of tick-borne encephalitis virus, one of the twenty-six flaviviruses which cause disease in humans. Tick- borne encephalitis covers a range of illnesses ranging from a severe paralytic encephalitis, which occurs in Siberia and is transmitted by Ixodes persulcatus, to a less paralytic encephalitis, which is found in central Europe and transmitted by Ixodes ricinus. Agricultural and forestry workers are most frequently affected, as the foci of infection are in and around forest areas, the vertebrate maintenance hosts being rodents and ground-living birds. Magnification: x270,000 at 147x196mm size.