The epidemiology of St. Louis encephalitis: a review.

Abstract

In 1932, epidemic encephalitis, probably caused by St. Louis encephalitis (SLE) virus, was described in Paris, Illinois. The following summer, 1933, the classic epidemic occurred in St. Louis, Missouri, although cases occurred concurrently in other parts of Missouri and in Kansas, Illinois, and Ken­ tucky (1). The subsequent importance of SLE in the context of the broad picture of encephalitis in humans is illustrated by the recent compilation of cases of encephalitis reported to the National Communicable Disease Cen­ ter (2). Of 3 102 patients reported with encephalitis during 1966, 1059 (34 per cent) were classified as postinfectious, a broad category which included mumps, measles, varicella, herpes, influenza, and rubella. One hundred thirteen cases (3.6 per cent) were considered as possibly enteroviral, while 438 cases ( 14.1 per cent) were due to arboviruses. In the remaining 149 2 cases (48. 1 per cent), an etiology was not determined. Four arboviruses are presently recognized as numerically important causes of encephalitis in the United States: St. Louis encephalitis virus (SLE), Eastern equine encepha­ litis virus (EEE), Western equine encephalitis virus (WEE), and the Cali­ fornia encephalitis group of viruses. With few exceptions, for the last 12 years in the United States, SLE virus has been the most common cause of arboviral encephalitis in humans (Table I) (2) . The current upsurge in interest in the problem of St. Louis encephalitis in the United States results from the fact that, since 1962, five major urban epidemics (Tampa Bay area, Florida, 1962; Houston, Texas, 1964; Dela­ ware River Valley, New Jersey, and Pennsylvania, 1964; Dallas, Texas, 1966; and Corpus Christi, Texas, 1966) have occurred, each eventuating in ap­ proximately 100 or more laboratory documented cases (Table I I) (3-8). These epidemics were destructive not only in terms of human disease but also because they presented a serious disruption in the everyday activities of the population living in these metropolitan areas. Furthermore, no real alteration in the underlying causes related to the occurrence of these epi­ demics has taken place, with the result that SLE represents a present and possibly increasing threat to our society.