Japanese Encephalitis Among Three U.S. Travelers Returning from Asia, 2003-2008

Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, is a leading cause of encephalitis in Asia. The risk for Japanese encephalitis (JE) for most travelers is low, but varies by travel destination, duration, season, and activities. As part of routine surveillance and diagnostic testing, state health officials or clinicians send specimens from patients with unexplained encephalitis to CDC. To characterize the epidemiologic and clinical features of JE cases, CDC reviewed all laboratory-confirmed cases that occurred during 1992 (when a JE vaccine was first licensed in the United States) to 2008. Four cases were identified, including one previously reported. This report describes the three previously unpublished cases. All were Asian immigrants or family members who traveled to Asia to live or to visit friends or relatives and had not been vaccinated for JE. The three patients experienced fever with mental status changes, but JE was recognized early in the clinical course of only one patient. All recovered, but two patients had residual neurologic deficits. Travelers to Asia might be at increased risk for JE because of rural itineraries and lack of perceived risk. To protect against JE, travelers should seek medical advice on protective measures, including possible JE vaccination, well in advance of departure for Asia. While in Asia, travelers should use personal protective measures to reduce the risk for mosquito bites. Health-care providers should assess the risk for JE in travelers to Asia and provide appropriate preventive or supportive treatment measures.