ATLANTA — Japanese encephalitis was identified in four U.S. travelers who returned from Asia during 2003-2008.
The four are the only known cases of Japanese encephalitis among U.S. residents to have occurred since the licensure of a vaccine against the mosquito-borne infection in 1992.
All were civilian travelers or Asian expatriates, the Centers for Disease Control and Prevention reported (MMWR 2009;58:737-40).
Japanese encephalitis should be suspected in a patient with evidence of a neuroinvasive viral infection such as encephalitis, aseptic meningitis, or acute flaccid paralysis, who recently returned from a Japanese encephalitis-endemic country in Asia or the western Pacific.
Health care providers should contact their state or local health department or the CDC's Division of Vector-Borne Infectious Diseases at 970-221-6400 for assistance with diagnostic testing, the CDC said.
In June, the CDC's Advisory Committee on Immunization Practices recommended Japanese encephalitis vaccination for travelers who plan to spend a month or longer in endemic areas during transmission season.
The committee also advised that vaccination be considered for short-term (less than 1 month) travelers to endemic areas during transmission season if they will both travel outside of urban areas and engage in activities that increase the risk of exposure to mosquito bites.
The virus circulates in parts of China, India, Japan, and Southeast Asia, and all travelers to endemic countries should be advised of the risks of Japanese encephalitis disease and the importance of measures to reduce mosquito bites.
However, vaccination is not recommended for short-term travelers whose visit will be restricted to urban areas or whose visit will occur outside of a well-defined Japanese encephalitis virus transmission season, which varies by region, according to the ACIP. The CDC usually follows the recommendations of the committee.
Japanese encephalitis is the leading cause of encephalitis in Asia, with 35,000-50,000 cases annually, a case-fatality rate of 20%-30%, and a 30%-50% risk for significant sequelae among survivors.
There is no antiviral therapy, Dr. Marc Fischer, of the CDC's Arboviral Diseases Branch, said at the ACIP meeting.
One of the four Japanese encephalitis cases, a previously healthy unvaccinated 22-year-old student returning from a study-abroad program in Thailand, was initially reported in 2004. She recovered without apparent sequelae (MMWR 2005;54:123-5).
The other three cases had not been reported until now. All three patients were Asian immigrants or family members who traveled to Asia to visit friends or relatives and had not been vaccinated against Japanese encephalitis.
All recovered, but two had residual neurologic deficits, the CDC said.
In March 2009, the Food and Drug Administration licensed a new Japanese encephalitis vaccine, Intercell's Ixiaro (distributed by Novartis), for use in adults aged 17 years and older.
The only other Japanese encephalitis vaccine available in the United States, JE-Vax (Biken/Sanofi Pasteur), was associated with hypersensitivity reactions (20-600 cases per 100,000 vaccine recipients) as well as rare neurologic events (0.1-2 cases per 100,000 recipients).
JE-Vax is licensed for children and adults aged 1 year and older, but is no longer being produced. Sanofi Pasteur maintains a stockpile for children 1-16 years of age who meet the travel criteria, Dr. Fischer noted at the ACIP meeting.
More information about Japanese encephalitis (including seasonality) is available at the CDC Web site at www.cdc.gov/ncidod/dvbid/jencephalitis