The opposite temperature-sensitivity character (ts) in two attenuated flaviviruses, used for human immunization: 17D yellow fever and E5"14" (Langat) viruses. A reappraisal of thoughts.

For the reproduction of the man-attenuated E5"14" clone of the Langat virus (tick-borne encephalitis complex) in pig kidney epithelial cells, the temperature of 39 degrees C was shown as restrictive, whereas it was permissive for the 17D strain of yellow fever virus and three virulent strains of tick-borne encephalitis (western subtype) virus. The temperature of 36 degrees C permitted the reproduction of all viruses studied. The implication of genetic marker studies in the assessment of human neuropathogenicity of flaviviruses is discussed.