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Abstract

Ilyenko, V. I., A. G. Panov, I. N. Prozorova, B. A. Osetrov and A. A. Smorodintsev (All-Union Research Inst. of Influenza, U.S.S.R. Ministry of Health, Leningrad, U.S.S.R.): Biologic and immunogenic properties of the m-pk/L attenuated strain of Japanese B encephalitis virus. Am J Epidemiol 95: 148–156, 1972.—In contrast to pathogenic laboratory strains of Japanese B encephalitis virus, a mutant strain m-pk/L proved to be nonpathogenic for white mice after oral or intraperitoneal inoculation and of reduced pathogenicity for rhesus monkeys. Experimental encephalitis was induced in monkeys only by the administration of large doses of the m-pk/L strain (5.0 log LD50), while lower doses failed to produce any clinical symptoms except occasional fever. The m-pk/L strain displayed great sensitivity to heat (negative T-50 marker).

Strain m-pk/L retained its properties without any variation in pathogenicity for mice and monkeys after 10–15 passages through tissue cultures and mouse brain.

Subcutaneous administration to 404 volunteers of live vaccine prepared from the m-pk/L strain containing 1.0–7.5 log LD50/1.0 ml of active virus produced no clinical symptoms.

Antigenic activity of the vaccine was studied in 528 volunteers. Effectiveness of immunization proved to depend upon the number of injections and the interval between them. A single injection of the vaccine resulted in antibody production in 53% of the cases, while two immunizations with a 1- to 2-month interval ensured antibody production in 80–90% of immunized volunteers, the induced immunity persisting for one year.

antigen-antibody reactions, encephalitis, Japanese B, vaccination, encephalitis
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© The Johns Hopkins University
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