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Development of Neutralizing Antibodies to the Viruses of Equine Encephalomyelitis (Western Strain) and St. Louis Encephalitis in the Blood and Cerebrospinal Fluid of Man and Animals, Together with Recovery of the St. Louis Virus from the Blood of Monkeys¹

From the George Williams Hooper Foundation, University of California Medical Center, San Francisco

Abstract

Neutralizing antibodies against the virus of western equine encephalomyelitis can be demonstrated in the cerebrospinal fluid of convalescent patients. Twenty-one or 26.2 per cent of 80 fluids tested were found to be positive. Twenty (31.2 per cent) of 64 sera from these 80 patients were also positive. All except 3 of the 20 gave positive reactions in both blood and spinal fluid. No neutralizing substances were demonstrated with fluids of negative sera. Antibodies were found in the fluids from 2 to 4 months after removal from the patients, and when taken at varying periods after 8 days from the onset.

Virus was recovered during the first few days from the blood and cisternal fluid of monkeys inoculated either intracutaneously or intracerebrally with the virus of equine encephalomyelitis alone (Br strain) and from the blood on the sixth, twelfth, twenty-fourth and seventy-second hours and fourth day of those inoculated by the same routes with the St. Louis virus alone.

Both viruses could be recovered at different intervals from the blood of those monkeys which received a mixture of the equine and St. Louis strains. Identification of the virus was determined by means of the neutralization test with known positive sera.

Antibodies to the western equine encephalomyelitic virus were demonstrated in the sera of 8 human cases taken prior to death and also in the serum of one experimental monkey. They were found at varying periods, ranging from 2 days after the onset of the equine disease to 9 months in 98 positive human sera tested. In 4 monkeys inoculated intracutaneously with the western equine virus, antibodies began to appear irregularly about the fifth or sixth day after injection and were more regularly present in 7 to 9 days, becoming progressively stronger through the fifth week. The neutralizing substances did not appear as early in the cerebrospinal fluid, but were found in small amounts by the eighth or ninth day, to become stronger by the tenth or eleventh. They either failed to appear or were only weakly positive in those animals running a fatal course after intracerebral inoculation of the equine virus.

Neutralizing substances were more difficult to demonstrate in the serum of the monkeys given the St. Louis virus intracutaneously. They appeared only occasionally after 14 days, but could be found within 9 to 14 days after intracerebral injection. The disease did not run a fatal course in these animals. In the mixed infection, with a single exception practically no antibodies developed against the St. Louis virus in either blood or spinal fluid following either route of inoculation.²

Footnotes

¹ Aided by a grant from the National Foundation for Infantile Paralysis, Inc.

² Since this paper went to press, articles by Philip, Cox and Fountain (Philip, C. B., Cox, H. R. and Fountain, J. W., Pub. Health Rep., 1941, 56, 1388 and by Cox, Philip and Kilpatrick (Cox, H. R., Philip, C. B. and Kilpatrick, J. W., Pub. Health Rep., 1941, 56, 1391) of the U. S. Public Health Service have corroborated the finding of neutralizing antibodies for the St. Louis virus in the serum of horses and have further shown that the latter may be susceptible to intracerebral inoculation of this strain.