Five viruses of the California complex (California encephalitis, Tahyna, Trivittatus, Melao and Lumbo), all mouse-adapted strains, caused distinct cytopathic changes in HeLa cells. Adaptation to in vitro conditions was not necessary. HeLa cells proved to be as sensitive (Melao virus) as newborn mice, or only slightly less so, to minimal doses of the viruses. Specific antisera prevented the development of cytopathic effect.
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