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.

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?
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.

Japanese encephalitis virus is transmitted chiefly by the bites of mosquitoes in the Culex vishnui complex; the vector species depends on the specific geographic area. In China and many endemic areas in Asia, C. tritaeniorhyncus is the principal vector. This species feeds outdoors beginning at dusk and during evening hours until dawn; it has a wide host range, including domestic animals, birds, and humans. Larvae are found in flooded rice fields, marshes, and small stable collections of water around cultivated fields. In temperate zones, the vectors are present in greatest numbers from June through September and are inactive during winter months. Swine and certain species of wild birds function as viremic amplifying hosts in the transmission cycle.

Occurrence...

Habitats supporting the transmission cycle of Japanese encephalitis virus are principally in rural, agricultural locations. In many areas of Asia, however, the appropriate ecologic conditions for virus transmission occur near or occasionally within urban centers. Transmission is seasonal and occurs in the summer and autumn in the temperate regions of China, Japan, Korea, and eastern areas of Russia. Elsewhere, seasonal patterns of disease are more extended or vary with the rainy season and irrigation practices.
 

Risk for Travelers...

The risk to short-term travelers and those who confine their travel to urban centers is very low. Expatriates and travelers living for prolonged periods in rural areas where Japanese encephalitis is endemic or epidemic are at greatest risk. Travelers with extensive unprotected outdoor, evening, and nighttime exposure in rural areas, such as might be experienced while bicycling, camping, or engaging in certain occupational activities, might be at high risk even if their trip is brief.

INCIDENCE

• 639 confirmed cases in the U.S. since
     1964

SEQUELAE

COSTS

RISK GROUPS