title: Study of the virulence of tick-borne encephalitis virus. XI. Genetic heterogeneity of the virus from naturally infectious Ixodes ricinus ticks.
mesh_terms: D000818:Animals; D002999:Clone Cells / Q000382:microbiology; D046508:Culture Techniques; D004669:Encephalitis Viruses, Tick-Borne / Q000302:isolation & purification*; D004675:Encephalitis, Tick-Borne / Q000401:mortality; D014644:Genetic Variation; D005827:Genetics, Microbial; D006358:Hot Temperature; D051379:Mice; D013987:Ticks / Q000032:analysis*; D013997:Time Factors; D014508:Urea; D014774:Virulence
chemical_list: D014508:Urea