Virus Isolated from Patients of Subacute Myelo-Optico-Neuropathy (SMON) in Japan

Abstract

In recent years, there have been many patients in Japan suffering from subacute myelo-optico-neuropathy (SMON) following abdominal disorders. At present, its etiology is not known, however, there are a few kinds of etiological hypotheses. One is that SMON may be a toxicosis caused by oral administration of chinoform, which have many contradictions in explaining the disease. Another is our viral etiological hypothesis, and the present report deals with isolation and some propertiesof the suspect virus present in stools and spinal fluid of SMON patients.
Virus was isolated, with a high frequency, in BAT-6 cell cultures accompanying a weak and incomplete cytopathic effect (CPE) from feces and spinal fluid of SMON patients living in different prefectures. Attempts to isolate the virus accompanying CPE in HeLa cells, primary monkey kidney cells, and human embryonic kidney cells were all unsuccessful. On the other hand, no virus was isolated in BAT-6 cells from control specimens except the case of aseptic meningitis. Antiserum prepared from the virus isolated from feces neutralized not only the CPE produced by other viruses from stool but also the CPE produced by all viruses from the spinal fluid of SMON patients.
Neutralizing antibody (NT) titers of 13 among 15 sera collected from SMON patients on different days after the onset of the disease were 5 to 10. In contrast, 10 sera collected from normal adults showed NT titer less than 5. Failure to detect high NT titers in patients sera may explain the subacute course and relapse of the disease. Furthermore, convalescent sera of two cases of aseptic meningitis showed NT titer of 160 to 320. The fact suggests that SMON may be a new viral infection following insufficient immunological state.
BAT-6 cells were found to be not susceptible to human enteroviruses so far tested, and the virus showed a characteristic host range in tissue culture. The virus was sensitive to ether, and 5-iodo-2'-deoxyuridine. Also, the virus was filtrable through a membrane filter with an average pore size of 220mμ, but the virus was unable to pass through a 100mμ pore filter. Studies on pathogenicity of the virus in mice are revealing that the virus seems to be a new neuropathic slow virus. Further investigations about the properties of the virus are now in progress.