MENINGOENCEPHALITIS AND PNEUMONITIS DUE TO WESTERN EQUINE VIRUS.

In a series of 20 cases here presented in a study of Western equine encephalitis, only ten were conclusively proven by serological or histopathological methods, while the other ten were presumptively cases of that disease. Involvement of the spinal cord was of relatively low incidence. In only one case of four in which autopsy was done could the Western equine virus be demonstrated in the cerebral tissues. There was a rather high incidence of involvement of the respiratory tree. A high proportion of patients had complaints referable to the respiratory tract. Physical signs denoting disease of both the upper and lower respiratory tract, x-ray evidence showing bronchial and pulmonary involvement, and autopsy evidence of bronchopneumonia were noted frequently. All patients had fever as well as symptoms and physical signs of central nervous system disease. Differential diagnosis posed many interesting and challenging problems. The clinical features were those of meningoencephalitis and never a "flu-like" syndrome, although in several of the cases diagnosis could not be made with certainty for several days, until meningeal signs developed, and usually the patients were treated with one or several antibiotics during that time. In all cases in which a neutralization test for the Western equine virus was done, the result was either positive or inconclusive. Results of complement fixation tests were significant in only six cases. In seven of 13 cases in which x-ray films of the chest were made, streaks of increased density were noted.