EN
Preliminary results of the studies on the presence of tick-borne encephalitis virus, strain K₅ (Lachmajer, Kawecki, Wegner, 1957) in Leptopsylla segnis Schönherr are presented. The presence of the virus was demonstrated in fleas infected by biologic route, as well as the possibility of infecting normal mice in 1-3-day time using fleas fed on infected mice. However, the easiest way of infection consisted in oral administration of the suspension from the triturated infected fleas.