[Evaluation of arbovirus attenuation by changes in the histamine level in the blood of immunized animals].

Changes in the content of histamine in the blood of rabbits inoculated with pathogenic and attenuated strains of tick-borne encephalitis, eastern and Venezuelan equine encephalomyelitis viruses were studied. Pathogenic strains of the test viruses were found to produce much greater increases in histamine concentration in the blood of animals than attenuated strains. This index is suggested to be used for additional characterization of arbovirus attenuation.