CDC
Answers Your Questions About
St. Louis Encephalitis
Q. How do people get St. Louis encephalitis?
A. By the bite of a mosquito (primarily the Culex
species) that become infected with St. Louis encephalitis virus (a flavivirus
antigenically related to Japanese encephalitis virus).
Q. What is the basic transmission cycle?
A. Mosquitoes become infected by feeding on birds infected
with the St. Louis encephalitis virus. Infected mosquitoes then transmit the
St. Louis encephalitis virus to humans and animals during the feeding process.
The St. Louis encephalitis virus grows both in the infected mosquito and the
infected bird, but does not make either one sick. See Figure.
Q. Could you get the St. Louis encephalitis from another
person?
A. No, St. Louis encephalitis virus is NOT transmitted from
person-to-person. For example, you cannot get the virus from touching or
kissing a person who has the disease, or from a health care worker who has
treated someone with the disease.
Q. Could you get St. Louis encephalitis directly from birds
or from insects other than mosquitoes?
A. No. Only infected mosquitoes can transmit St. Louis
encephalitis virus.
Q. What are the symptoms of St. Louis encephalitis?
A. Mild infections occur without apparent symptoms other than
fever with headache. More severe infection is marked by headache, high fever,
neck stiffness, stupor, disorientation, coma, tremors, occasional convulsions
(especially in infants) and spastic (but rarely flaccid) paralysis.
Q. What is the incubation period for St. Louis
encephalitis?
A. Usually 5 to 15 days.
Q. What is the mortality rate of St. Louis encephalitis?
A. Case-fatality rates range from 3% to 30% (especially in the
aged).
Q. How many cases of St. Louis encephalitis occur in the
U.S.?
A. Since 1964 there have been 4,478 reported human cases of
St. Louis encephalitis, with an average of 128 cases reported annually.
Q. How is St. Louis encephalitis treated?
A. There is no specific therapy. Intensive supportive therapy
is indicated.
Q. Is the disease seasonal in its occurrence?
A. In temperate areas of the United States, St. Louis
encephalitis cases occur primarily in the late summer or early fall. In the
southern United States where the climate is milder St. Louis encephalitis can
occur year round.
Q. Who is at risk for getting St. Louis encephalitis?
A. All residents of areas where active cases have been
identified are at risk of getting St. Louis encephalitis.
Q. Where does St. Louis encephalitis occur?
A. See map:
St. Louis encephalitis outbreaks can occur throughout most of the
United
States. The last major epidemic of St. Louis encephalitis occurred in the
Midwest from 1974-1977. During that outbreak, over 2,500
cases in 35 states were reported to the CDC. Currently, outbreaks of St. Louis
encephalitis have been limited in size (usually <30 cases), although the
potential still exists for epidemic St. Louis encephalitis. The most recent
outbreak of St. Louis encephalitis occurred in New Orleans, Louisiana in 1999,
with 20 reported cases.
Q. Is there a vaccine against St. Louis encephalitis?
A. No.
Q. Where can I get more information on St. Louis
encephalitis?
A. See the CDC St. Louis Encephalitis Fact Sheet
(http://www.cdc.gov/ncidod/dvbid/arbo/slefact.htm)
and the CDC Arboviral Encephalitides Home Page (http://www.cdc.gov/ncidod/dvbid/arbor).
Return to top of page
|