Travel and Vaccinations

Japanese encephalitis virus belongs to the Flavivirus family. The virus is mainly transmitted between Culex mosquitoes and pigs or birds. However, humans can become infected after being bitten by a mosquito carrying the virus.

Japanese encephalitis virus is found in South, South-East Asia and the Western Pacific islands. In 2022 there were a number of cases in South Eastern Australia. It mainly occurs in rural areas, particularly around rice farming where there are many mosquitoes.

Only a few people develop symptoms, which range from fever, headache and vomiting to drowsiness and seizures. It can be fatal in some cases.

Download a copy of the Infectious Encephalitis. Guidelines for Travellers Factsheet

By Dr Hannah Brindle, Institute of Infection and Global Health, Liverpool, and peer- reviewed by Dr Lance Turtle, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool

With increasing numbers of people travelling worldwide, it is important to highlight the risk of infectious encephalitis and their preventive measures. The more common types or those for which there are prevention measures, are described below.

Infections transmitted by mosquitoes

Japanese encephalitis

What is it and how can I get it?

Japanese encephalitis virus belongs to the Flavivirus family. The virus is mainly transmitted between Culex mosquitoes and pigs or birds. However, humans can become infected after being bitten by a mosquito carrying the virus.

Where is it found?

Japanese encephalitis virus is found in South, South-East Asia and the Western Pacific islands. In 2022 there were a number of cases in South Eastern Australia. It mainly occurs in rural areas, particularly around rice farming where there are many mosquitoes.

What are the symptoms?

Only a few people develop symptoms, which range from fever, headache and vomiting to drowsiness and seizures. It can be fatal in some cases.

Can I prevent it?

If you are visiting South or South East Asia, visit your local travel clinic for up-to-date advice.

The Ixiaro vaccine is licensed in the UK. Two initial doses are normally given 28 days apart with a booster dose 12-24 months later for those still at risk. In those aged 18-64 years a fourth can be given 10 years for ongoing protection (UK Health Security Agency, 2018).

A rapid schedule administered at days 0 and 7 is also licensed for adults aged 18-64 years of age.

For children (from two months of age) and adults 65 years of age and older, although not

licensed for these age groups, the rapid schedule can be used in circumstances where there is genuinely insufficient time to complete the standard schedule prior to travel (Green Book, June 2018).

With both schedules, primary immunisation should ideally be completed at least one week prior to potential exposure to Japanese encephalitis virus.

West Nile virus belongs to the Flavivirus family. People usually become infected after being bitten by a mosquito which has fed on an infected bird.

West Nile virus first occurred in Uganda. However, since then it has been found in Africa, Europe, the Middle East, North America and West Asia.

Only around 20% of people who are infected with the virus develop symptoms. These often range from headache to fatigue and body ache. However, more severe symptoms including drowsiness, seizures and confusion can occur sometimes because of encephalitis or meningitis. Older people are more susceptible to encephalitis.

There is no vaccine against West Nile virus; however, you should exercise precaution against mosquito bites (please see Prevention of mosquito bites below).

Zika virus is also a Flavivirus, transmitted by the day-time biting Aedes mosquitoes. The virus can be transmitted to the foetus from the mother during pregnancy. Sexual transmission has also been reported.

A large outbreak of Zika virus occurred in South America in 2014. However, the virus has been reported in a number of other countries in Central America, the Caribbean, Asia, Africa and the USA.

Many people who are infected with a virus have no symptoms. However, of those who do report symptoms these may include fever, rash, headache, joint or muscle pain and red eyes (conjunctivitis). Although a few cases of encephalitis have been reported, the most common neurological complaint is Guillain-Barré syndrome (a weakness of the arms and legs). However, if infection occurs during pregnancy, this can result in a baby being born with microcephaly (a neurological birth defect).

At the time of writing there is no established vaccination against Zika virus. Pregnant women are advised to postpone non-essential travel to areas at high or moderate risk. Women who have travelled to areas at risk of Zika virus are advised to postpone pregnancy for at least eight weeks after leaving the area (or after experiencing symptoms on returning home) and six months after a male partner has returned from an area of risk. In all travellers and particularly in pregnant women, measures can be taken to prevent mosquito bites.

Rabies is caused by a virus which is carried in the saliva of infected animals commonly dogs, cats, bats and monkeys. Humans acquire the diseases when the infected saliva enters the blood. This may be via a bite, a scratch or a lick to an open wound or to other vulnerable areas including mouth and eyes.

Rabies is found throughout the world with only a few countries being free of rabies, including the UK. However, rates are higher in the developing world where fewer animals are vaccinated.

Symptoms may occur sometime after acquiring the virus. These include confusion and hydrophobia (fear of water).

It is advisable to keep your distance from animals whilst abroad especially stray dogs and cats. There is a vaccine available, which is recommended for those thought to be at increased risk of exposure to infected animals e.g., those working with animals or spending long periods in a country with well-known rabies risk. Three doses of the vaccine are required at least on days 0, 7 and 28 (or minimum of 0. 7 and 21) before travel with booster doses required as per the ongoing risk of exposure to animals.