The Changing Risk of Japanese Encephalitis for Business Travelers

Abstract

Japanese Encephalitis is an often fatal and vaccine preventable disease. New vaccine recommendations are needed due to changes in travel and disease patterns.

Japanese Encephalitis (JE) is a flavivirus transmitted by Culex mosquitoes which breed in standing water, often in farms and rice paddies in most areas of Asia, year round in tropical areas and during the months of May through October in temperate areas. After the bite of a Culex mosquito and an incubation period of 5 to 15 days, illness usually begins with fever, headache, vomiting, and mental status changes leading to neurologic deficits including movement disorders. Of JE cases, 15% to 30% die, and 30% to 50% of survivors have significant neurologic sequelae.

Climate change and horticultural practices may be changing the epidemiology of JE. A review of JE cases in Taiwan showed a correlation with rainfall, temperature, and an earlier beginning of the transmission season. Irrigation projects and changes in pig farming practices may have changed vector habitats (Hsu, Yen, & Chen, 2008).

Economic and agricultural developments are blurring the boundaries of what is considered a rural area. Increased migration to cities has led to urbanization of rural areas, where the natural enzootic cycle exists. A significant shift in JE risk for business and occupational travelers is peri-urban exposure. Manufacturing and housing facilities are often located outside major cities in higher risk areas. The majority of more recent cases of JE among U.S. travelers have occurred after shorter stays in urban and peri-urban areas (Buhl & Lindquist, 2009).

In a study of travel medicine clinics with a database of 8,289 U.S. travelers, only 26.8% of higher risk travelers had received the JE vaccine. In some cases, travelers had insufficient time to be vaccinated prior to travel, the vaccine was not available, or a contraindication to the JE vaccine was identified. However, the majority of high-risk travelers were not vaccinated because clinicians deemed that the JE vaccine was “not indicated” (Deshpande, Rao, Jentes, Hills, & Fischer, 2014). Bunn (2014) reported general vaccination rates of 1% to 11% for at-risk travelers. These findings suggest that existing guidelines are not clear or too restrictive to adequately protect travelers.

JE is an unpredictable threat for travelers. Cases show that travelers visiting for a short time, even with little or no rural exposure and outside the established transmission season, have contracted JE. Preventive measures including human vaccination are the best protection, and all travelers should be assessed for the risk of contracting JE. The current JE recommendations require revision; revision is being considered by the Advisory Committee on Immunization Practices (ACIP).

A JE Vaccine Recommendations Working Group met in New Orleans in conjunction with the American Society of Tropical Medicine Hygiene (ASTMH) Annual Meeting in November 2014. Revised recommendations were agreed upon by consensus at this meeting and include the following: (a) a discussion of JE and availability of a safe and effective vaccine for all travelers to endemic areas of Asia; (b) travelers to rural or peri-urban areas in endemic countries, irrespective of duration of travel or itinerary, should be offered the vaccine; (c) all expatriates living in endemic countries or frequent travelers who may visit rural or peri-urban areas in endemic countries should be offered the vaccine; (d) travelers with uncertain itineraries or itineraries that may change should be offered the vaccine; and (e) the vaccine is not generally recommended if travel is restricted exclusively to urban areas.