Abstract. The etiologic spectrum of acute encephalitis syndrome (AES) has not been well defined in Vietnam. Cohort and case-control studies were performed on all adult and pediatric AES patients admitted to the Neurology Service of Bach Mai Hospital between June 5 and August 3, 1995. Among pediatric AES patients, 31 (67%) of 46 had acute Japanese encephalitis (JE), compared with only two (6%) of 33 adult AES patients (P Ͻ 0.0001). For confirmed JE cases, serum specimens obtained 15-21 days after symptom onset had the highest mean anti-JE IgM signal-to-noise (P/N) ratios (8.08 ϩ 1.09 SE). A serosurvey of adult household members did not reveal any cases of recent subclinical JE infection, although 26% had evidence of past JE infection. The use of bed netting was nearly universal but did not appear to reduce the risk of AES or JE. Given the high incidence of JE, particularly among children, Vietnam seems well suited for the development of a targeted JE vaccination strategy.Japanese encephalitis (JE) virus, an arthropod-borne pathogen, is the most common documented cause of viral encephalitis in Asia, and potentially ranks only after human immunodeficiency virus as the most common cause of viral encephalitis in the world. 1 The JE virus is a member of the Flaviviridae family, is transmitted chiefly by mosquitoes of the Culex tritaeniorhynchus complex, and causes up to 50,000 cases annually in a broad geographic range extending from Japan and the People's Republic of China in the east to the Indian subcontinent in the West and to Oceania. 2 In Southeast Asia, the incidence of JE appears to be increasing, probably as a result of a steady rise in population density, deforestation, and increasing irrigation of agricultural areas. 3 Province-specific attack rates in northern Thailand are reported to be 10-20 per 100,000, making the incidence of the disease similar to that observed for poliomyelitis in the United States before the use of the Salk and Sabin vaccines. 4 The fatality rate for JE is generally high (5-30%), and approximately one-third of survivors suffer serious neurologic sequelae. [5][6][7] In addition, the social prognosis for handicapped survivors of JE is often poor in developing countries.Though viral encephalitis is a pressing public health problem in Vietnam, identification of the leading agents responsible for the acute encephalitis syndrome (AES) has been difficult. The development of the sandwich IgM ELISA test has greatly simplified the diagnosis of acute JE, but this test is generally not available in Vietnam. 8,9 From a perspective of disease surveillance and control, it is important to differentiate JE from other causes of AES, in part because JE is the only arbovirus encephalitis that can be prevented on a large scale by vaccination. We conducted the present study to determine the proportion of AES cases in children and adults that are due to JE, to investigate risk factors for acquisition of AES, and to assess the efficacy of household mosquito protection measures in the absence of a JE vaccin...

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Concerning the causes, the following were noted: (i) the rate of infectious diseases and trauma as causes of epilepsy was considerably higher in Vietnam than in developed countries; (ii) certain infectious diseases could be prevented if vaccinations and public health knowledge were improved; and (iii) the number of trauma cases, mainly due to traffic accidents, would likely be reduced if the traffic system was improved.