Attempts to reproduce amyotrophic lateral sclerosis in laboratory animals by inoculation of Schu virus isolated from a patient with apparent amyotrophic lateral sclerosis.

A virus isolated from the CSF of a patient who had amyotrophic lateral sclerosis for 7 years, and prolonged pleocytosis in the CSF, was adapted to suckling mouse brain by subsequent serial blind passages. This Schu virus belongs to the tick-borne encephalitis complex of the genus Flavivirus (Togaviridae). Suckling mouse brain homogenate of the 13th passage was used for transmission experiments in various species of laboratory animals. Golden hamsters infected subcutaneously fell ill after a number of months, lost weight, and had paresis of the legs. Histologically they had petechial hemorrhages in different parts of the CNS and inflammatory changes in the gray substance of the spinal cord. Pilot studies with repeated inoculations of small doses of different flavivirus strains suggest a course of the disease in experimental animals which resembles slow-virus infections insofar as no encephalitis is produced and degenerative changes of the anterior horn cells prevail over inflammatory signs in the spinal cord. After intracerebral application of Schu virus, cynomolgus monkeys developed the typical lesions of togavirus panencephalitis with epileptic seizures, ataxia, and paresis. After subcutaneous application, the virus seems to spread along peripheral nerves to anterior spinal roots and spinal cord, where mainly motor neurons of the anterior horn are damaged, and from there to the brain. The histological findings are such that one may assume the disease of the patient was due to the infection with the virus isolated from his CSF. Therefore, the hypothesis may be advanced that at least some of the cases diagnosed as amyotrophic lateral sclerosis are due to a togavirus infection.