Medicines for Japanese encephalitis

What it is

Japanese encephalitis (JE) is a viral infection spread by mosquitoes, which occurs in parts of Asia and the western Pacific. It is caused by a virus that is spread to people through the bite of infected mosquitoes (which pick up the virus from animals such as pigs and birds); it is not spread from person to person. JE occurs mainly in rural and agricultural areas of affected countries, particularly where there is rice farming and pig rearing, and the risk is higher in the wet season when mosquitoes are more active; the risk to most travellers is low, and is higher for those spending longer periods, or staying in rural areas, in affected regions during the transmission season. Most people infected with the JE virus have no symptoms or only a mild, flu-like illness. However, in a small proportion of infected people, JE causes a serious illness — encephalitis (inflammation of the brain) — which can be severe and life-threatening, and which is the reason JE is a concern. When it causes serious illness, the symptoms can include a high fever, headache, feeling and being sick, and then features of the brain being affected, such as confusion, drowsiness, seizures, weakness or paralysis, changes in behaviour, and, in severe cases, coma; the serious form can be fatal or leave lasting neurological effects in those who survive. There is no specific antiviral treatment for JE, so treatment of the serious form is supportive care in hospital. Because of this, prevention is very important, and there are two main ways to prevent JE for travellers to affected areas: a vaccine against Japanese encephalitis, which is recommended for certain travellers (based on the destination, duration, activities, and season, so travel health advice is important); and mosquito-bite prevention (as the virus is spread by mosquitoes) — using insect repellent, covering up, using mosquito nets, and other measures. The key messages are that Japanese encephalitis is a rare mosquito-borne viral infection in parts of Asia that can cause serious brain inflammation, that most infections are mild but a small proportion are serious, and that a vaccine (for certain travellers) and mosquito-bite prevention protect travellers to affected areas.

How it is treated

The approach to Japanese encephalitis centres on prevention for travellers to affected areas — through vaccination for certain travellers and mosquito-bite prevention — and supportive care for the rare serious cases, as there is no specific antiviral treatment. For most people, the practical relevance of JE is prevention when travelling to affected areas, and travel health advice is important to assess the risk and recommend appropriate measures: the risk depends on the destination, the length of stay, the areas visited (rural and agricultural areas carry more risk), the season (higher in the wet/transmission season), and planned activities, so travellers to affected regions should seek travel health advice (from a travel clinic, GP, or pharmacist) well before travelling. Two main preventive measures are used: the Japanese encephalitis vaccine, which is recommended for certain travellers — particularly those staying for longer periods, spending time in rural areas, or with higher-risk activities or itineraries in affected areas during the transmission season — and is given as a course before travel, so planning ahead is important; and mosquito-bite prevention, which is important for everyone in affected areas (and protects against other mosquito-borne infections too) — measures include using an effective insect repellent, covering up with clothing (especially around dawn and dusk when relevant mosquitoes may bite, and in the evening/night), sleeping under a mosquito net where appropriate, and staying in accommodation with screening or air conditioning where possible. There is no specific antiviral treatment for JE, so for the rare cases that develop the serious form (encephalitis), treatment is supportive care in hospital — managing the symptoms and complications, supporting the body’s functions (including breathing and other support in severe cases, in intensive care), controlling seizures, and providing rehabilitation and follow-up for any lasting effects in those who recover. Because the serious form can be severe, prompt medical attention for symptoms (particularly a feverish illness with confusion, drowsiness, seizures, or other neurological symptoms) after travel to an affected area is important. The reassuring messages are that Japanese encephalitis is rare and geographically limited, that the risk to most travellers is low (and higher for longer or rural stays in the transmission season), that most infections are mild, and that effective prevention — a vaccine for certain travellers and mosquito-bite prevention — protects travellers; so seeking travel health advice before visiting affected areas, and taking preventive measures, are the key points, along with seeking urgent care for a feverish illness with neurological symptoms after relevant travel.