Japanese encephalitis: a review of clinical guidelines and vaccine availability in Asia

Patricia BatchelorEmail author and
Kyle Petersen

Tropical Diseases, Travel Medicine and Vaccines20151:11

DOI: 10.1186/s40794-015-0013-6

Received: 9 June 2015

Accepted: 16 October 2015

Published: 9 November 2015

Abstract

Travelers to Asia are at risk for acquiring Japanese Encephalitis (JEV), an arbovirus with high rates of morbidity and mortality. Recent advances in vaccination resulting in vaccines with low rates of side effects have strengthened the rationale to vaccinate more travelers to this region, as reflected in many updated national guidelines for prevention of disease in travelers. Vaccines however still require a complex pre-travel schedule and are costly, often leading to a requirement or desire for a vaccination option in the destination country. We explore current national guidelines for prevention of Japanese Encephalitis and seek to provide information on availability of JEV vaccines in various Asian countries.

Introduction

Japanese encephalitis virus, a flavivirus transmitted by mosquitoes, is the leading cause of encephalitis in Asia [1]. The Japanese encephalitis (JE) cycle occurs between mosquitoes (mainly the species Culex tritaeniorrhynchus) and vertebrates. Swine and waterfowl play an important role as amplifying hosts [2]. Humans are a dead end host and as such there is no human-to-human transmission. This mosquito species preferentially breeds in rice paddies and is a dusk and evening feeder. Approximately 99 % of JE infections are asymptomatic; however, JE in symptomatic patients can be a devastating disease with a mortality of approximately 30 %. Following an incubation period of 4–14 days, symptomatic patients can present with high fever, chills, headache, myalgia and confusion. In children gastrointestinal complaints (pain and vomiting) can dominate initially and 75 % will experience seizures [1]. Up to 50 % of survivors will have persistent neurological deficits and this is particularly important in children as there may ensue a lifetime of handicap. Children and the elderly are more at risk of infection [3]. No treatment is available and thus apart from mosquito bite avoidance, vaccination is the only reliable method of prevention. Unfortunately in most countries a multiple injection series of vaccinations is required for pre-travel prevention. Many travellers fail to anticipate this and arrive at a clinic with inadequate time to achieve complete immunity prior to travel. However, as many patients who are at risk of Japanese Encephalitis have itineraries lasting several weeks to years, an opportunity to vaccinate the patient during travel exists that can mitigate the timing difficulties mentioned above. Hence, a comprehensive list of available vaccines by country and providers by city would be of value to many travel clinic providers, who could then counsel their patients on options for vaccination upon arrival to Asia. We will review the various current guidelines for vaccination and provide information about availability of various vaccines in Asia as an aid to the travel medicine provider.