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International Notes Japanese Encephalitis: Report of a World Health Organization Working Group

Japanese encephalitis (JE) is a public health problem of increasing concern to countries in Southeast Asia and the Western Pacific because of the occurrence of thousands of cases over the past decade, with high case-fatality rates and expansion into new areas.

A World Health Organization (WHO) Working Group on the prevention and control of JE was convened in Tokyo, Japan, from December 19, to December 21, 1983, to review the current epidemiology; recommend ways of strengthening surveillance and control of the disease; and develop collaborative studies for vaccine development, production, control, and utilization.

Epidemiology: JE has changed epidemiologically during the past 10 years. The disease has recently been recognized in new areas and has recurred in previously endemic areas. In the Republic of Korea, after a decade of very low incidence, a resurgence was noted in 1982. Since 1978, JE has appeared as a new and major entity in the plains region of southern Nepal. It has been focally endemic in a few states of southern India for decades. In 1978, however, JE was recognized for the first time in Bihar, Uttar Pradesh, and West Bengal States in the north. This focus is contiguous to the affected area in Nepal.

Since 1966, JE has been uncommon in Japan, in part because of widespread vaccination of children 3-15 years of age and a decline in the vector population, Culex tritaeniorhynchus. In China, the disease is prevalent in all provinces except Xinjiang, Chenghai, and Tibet; over 10,000 cases are reported annually, with a case-fatality rate of approximately 10%. In Thailand, JE has become an increasingly reported disease over the past 10 years, primarily in the north and northeast regions. The attack rate and case-fatality rate were higher among children than adults. In Burma, fewer than 100 cases of JE are reported each year and confined mostly to children in tribal areas.

Vaccines: Formalin-inactivated vaccines have been manufactured and used in Japan and China for many years, and during the last decade, in the Republic of Korea. The Japanese and Korean vaccines are made in adult mouse brain; the Chinese vaccine, in primary hamster kidney tissue culture. Presently, the vaccines are evaluated in the countries of origin by different methods. A live, attenuated vaccine developed in China has undergone extensive field trials in humans and horses. The Working Group requested that WHO consider formulating requirements for JE vaccine and for establishing a reference standard preparation. The potency of candidate vaccines would be assessed in collaborative studies in terms of international (WHO) antigenic units. Field trials could be conducted under the auspices of WHO.

The Collaborating Centre for Arbovirus Reference and Research, Tokyo, will be the focal point for the above-mentioned studies, supported by the WHO network of Collaborating Centres. Reported by WHO Weekly Epidemiological Record 1984:59;21-2; Div of Vector-Borne Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Under an investigational new drug (IND) permit issued by the U.S. Food and Drug Administration's Bureau of Biologics, CDC is sponsoring the evaluation of an inactivated, highly purified mouse brain JE vaccine manufactured by Biken Laboratories, Osaka, Japan. This vaccine has been administered to 88 participants according to the manufacturer's recommendation in two doses at an interval of 7-10 days. By testing for presence of neutralizing antibody in sera obtained before vaccination and about 21 days after the second dose, a seroconversion to a titer of 8 or higher occurred in 72% of 68 seronegative participants. Before recommending a wider use of this vaccine for selected persons traveling to JE-endemic areas, an evaluation of a three-dose schedule (at 7-day intervals) will be done in an effort to induce a more satisfactory neutralizing antibody response.

For this stage of the IND evaluation, about 100 participants are being recruited by collaborators in five U.S. locations. Candidates to receive the vaccine are selected primarily from among persons who plan to visit JE-endemic areas for 3 weeks or more during the season of principal JE activity (June to October in temperate climates) and whose itineraries include activities--such as travel to rural areas--with increased risk of exposure to mosquito vectors.

The risk of any traveler developing JE is low, and short-term visits and tours confined to urban centers further decrease this low risk. Whether or not the traveler is vaccinated, precautions to guard against mosquito bites should be taken. These include: minimizing outdoor exposure at dusk and dawn and on overcast days; sleeping in screened quarters or under mosquito netting; wearing clothing leaving a minimum of bare skin; and using insect repellents on exposed skin surfaces. Preferable repellents are those containing over 30% active ingredient (N, N-diethyl-meta-toluamide commonly abbreviated "DEET").

Until the experimental vaccine is more widely available in the United States, long=term travelers at increased risk of acquiring JE who wish to be considered for vaccination should inquire from American Embassies in destination countries where JE is endemic as to how the vaccine can be obtained.

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