Isolation of a Herpes Virus from Several Cases of Epidemic Encephalitis. ∗

Abstract

The principal reason that militates against acceptance of the one positive hypothesis of etiology in epidemic encephalitis, namely that it may be due to a neurotropic strain of Herpes virus, is the fact that this easily identifiable virus has been isolated in less than a dozen cases of the disease. The only positive isolations in this country are, so far as we know, those briefly referred to in connection with other work. 1 These first American isolations occurred in 3 successive cases of encephalitis after measles in children. The peculiar conditions explain, we believe, 2 of the reasons why more frequent success has not been obtained by others. In each instance the encephalitis occurred immediately after the exanthem, was clinically characteristic, and was histologically consistent with a diagnosis of epidemic encephalitis, but suspensions of these human brains failed to kill rabbits on intracerebral injection. Two of these 3 brains did, however, produce an herpetiform skin eruption in rabbits, proved to be due to a true Herpes virus of a strictly dermotropic type by the fact that immunization with each of these brains by intradermal inoculation in rabbits in several, but not in all instances, rendered these animals insusceptible to inoculation with a known Herpes virus. Another reason for failure is indicated by case number 3 in this series which failed on first inoculation to produce even dermal lesions but became active in this regard when the brain had been aged in glycerine for over a month. 2

In other words, failure to isolate Herpes virus from encephalitis may be due not only to the scant amount present but also to the fact that an erroneous assumption is made that the virus as obtained from a human case must be neurotropic instead of dermotropic for rabbits.