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Japanese encephalitis

Japanese encephalitis is a potentially serious disease found mainly in Asia.

Please consult your doctor, pharmacist or a travel health clinic for further information.

Key facts

  • Japanese encephalitis (JE) is a rare disease in travellers, but can have serious consequences1
  • The disease is endemic in 25 countries in Asia and the Western Pacific, not just in Japan1
  • JE is caused by bites primarily from Culex mosquitoes which carry the JE virus1-3
  • JE causes inflammation of the brain, which can cause coma, paralysis and death1,2
  • Surviving JE sufferers may be left permanently disabled both physically and mentally1,3
  • There is currently no treatment for JE3
  • Three UK travellers were documented to have been infected with Japanese Encephalitis in 2014/155

What is JE?

Japanese encephalitis (JE) is a potentially serious disease2 which is caused by the virus Flavivirus, and is related to dengue, yellow fever, West Nile and Saint Louis viruses.1,4 JE is the main cause of viral encephalitis in many countries in Asia.2,4 JE virus is transmitted to humans through the bite of infected Culex species mosquitoes, particularly Culex tritaeniorhynchus. The virus is maintained in a cycle between mosquitoes and vertebrate hosts, primarily pigs and wading birds.6

Risk areas for JE1

map
Adapted from: Centers for Disease Control and Prevention. Yellow Book 2020. Chapter 4 Travel-Related Infectious Diseases. Japanese Encephalitis. June 2019.

Where does JE occur?

JE is endemic in 25 countries across Asia and the Western Pacific.1,2 Transmission of the virus through mosquitoes occurs mainly in rural agricultural areas, and there is an association with rice cultivation and flood irrigation. In temperate areas of Asia, transmission is seasonal and it is believed that JE disease is highest in the summer and autumn time. In the subtropics and the tropics, JE transmission occurs all year round and often peaks during the rainy season.1

Who is at risk of contracting JE?

Susceptible travellers to areas where JE is endemic are at risk of contracting JE.1 Travellers who are likely to spend time outdoors in rural or agricultural areas or participate in outdoor activities, such as camping, hiking, trekking, biking, fishing, hunting or farming are at risk. Staying in accommodation without air conditioning, screens or mosquito nets can also put travellers at risk.1,2,7

What are the symptoms and lasting effects of JE?

Most people infected with JE will not show any symptoms and will not develop the disease1. However, in a small number of cases, acute encephalitis is the most common clinical sign of the disease, observed between 5 and 15 days after infection.1 This shows itself as sudden onset of fever, headache and vomiting, which progresses to inflammation of the brain. The infected person’s mental state may deteriorate, there may be neurological changes, physical weakness and movement disorders, such as tremors and rigidity, and seizures can cause coma or paralysis.1-3 JE causes death in up to a third of cases.1 Among survivors of JE, one third to a half of all sufferers will have serious neurologic, cognitive, or psychiatric disabilities.1

How can JE be treated?

There is currently no specific treatment for JE.1,3

How can you prevent Japanese encephalitis?

Precautions to avoid mosquito bites can help protect you from JE.1,3 Consult your GP, pharmacist or a travel health clinic to learn about others ways to protect yourself against JE.

Useful links

References

  1. Centers for Disease Control and Prevention. Yellow Book 2020. Chapter 4 Travel-Related Infectious Diseases. Japanese Encephalitis. June 2019. Available online: cdc.gov (Last accessed March 2023)
  2. Centers for Disease Control and Prevention. Japanese Encephalitis. Frequently Asked Questions. May 2019. Available online: cdc.gov (Last accessed March 2023)
  3. PATH. Landmark protection for Asia’s children. Available online: path.org (Last accessed March 2023)
  4. Word Health Organisation. Japanese Encephalitis. Fact sheet. May 2019. Available online: who.int (Last accessed March 2023)
  5. Turtle L, et al. ‘More than devastating’-patient experiences and neurological sequelae of Japanese encephalitis. J Travel Med. 2019;26(7)
  6. Centers for Disease Control and Prevention. Japanese Encephalitis. Transmission. February 2019. Available online: cdc.gov (Last accessed March 2023)
  7. Centers for Disease Control and Prevention. Japanese Encephalitis Vaccine. February 2023. Available online: cdc.gov (Last accessed March 2023)

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