hypothesized N-linked glycosylation site of the envelope protein. Nevertheless, the latter can be due to selection in vitro (laboratory) rather than in vivo (host). In an independent study 14 out of 106 examined envelope gene sequences were found not to contain a specific codon at position 156 coding for this glycosylation site (Ser→Phe/Tyr). Another study estimated the evolutionary rate to be (95% confidence ). The virus seems to have evolved in northern Mexico and then spread northwards with migrating birds. Treatment There are no vaccines or any other treatments specifically for Saint Louis encephalitis virus, although one study showed that early use of interferon alfa-2b may decrease the severity of complications. Epidemiology In the United States an average of 128 cases of Saint Louis encephalitis are recorded annually. In temperate areas of the United States, Saint Louis encephalitis cases occur primarily in the late summer or early fall. In the southern United States where the climate is milder Saint Louis encephalitis can occur year-round. History The name of the virus goes back to 1933 when within five weeks in autumn an encephalitis epidemic of explosive proportions broke out in the vicinity of St. Louis, Missouri, and the neighboring St. Louis County. Over 1,000 cases were reported to the local health departments and the newly constituted National Institutes of Health of the United States was appealed to for epidemiological and investigative expertise. The previously unknown virus that caused the epidemic was isolated by the NIH team first in monkeys and then in white mice. References External links United States Centers for Disease Control and Prevention. Saint Louis encephalitis. The Encephalitis Society - A Global resource on Encephalitis Viral encephalitis Insect-borne diseases