Abstract
The 1937 outbreak of encephalitis in St. Louis afforded an excellent opportunity for further study of the disease. Despite the fact that the virus of encephalitis has never been demonstrated in nasal secretions procured from patients during the acute phase of the disease, 1 , 2 it is held by some workers that the mode of spread is by way of the upper part of the respiratory tract. It is well known that the disease is easily produced in mice by the instillation of mouse-brain virus directly into the nares. Furthermore, Armstrong 3 has reported that 30 to 60% of mice which had withstood an intranasal instillation of the virus may have become immune and would survive a subsequent intracerebral injection of an amount sufficient to kill normal controls.
In the present experiments nasopharyngeal washings from patients with the disease were given intranasally to mice on 2 successive days in order to attempt to demonstrate the presence of active virus. This route was used since material containing bacteria can be used as the inoculum, thus avoiding possible loss of virus by filtration or other means of removing the contaminating bacteria. Since none of the mice receiving intranasal instillation of nasopharyngeal washings developed recognizable symptoms of the disease, we attempted to determine whether any immunity was conferred by these instillations.
About 3 weeks after the last instillation, the mice were given an intracerebral inoculation of an amount of virus which was sufficient to kill all (20) control mice. Of the 40 test mice, 14 (35%) survived the injection. This observation encouraged us to make further trials. Accordingly, washings from 15 patients during the acute stage of the disease were instilled into the nares of a series of mice.
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