As parents, our instinct is to protect our children from every possible danger, including diseases that may not be common but can have life-changing consequences. One such illness is Japanese Encephalitis (JE), a mosquito-borne viral infection that causes inflammation of the brain. It was first reported in Japan in 1871 and remains a public health concern across Asia today.
What is Japanese Encephalitis?
JE is caused by the Japanese Encephalitis virus (JEV), a flavivirus related to dengue, yellow fever, and West Nile viruses¹. It spreads through the bite of an infected Culex mosquito, which carries the virus from animals such as pigs and water birds to humans².
The World Health Organization (WHO) notes that JE cannot spread from person to person, as humans are considered “dead-end hosts”³. However, the impact of the disease can be devastating: JE affects around 69,000 people annually, with a fatality rate of up to 30 %, and 30–50 % of survivors experience long-term neurological or psychiatric complications⁴⁵.
How Serious Is Japanese Encephalitis?
According to pediatric neurologist Dr. Janette Calzada,
“The mortality rate of Japanese Encephalitis is high. It’s like the rule of thirds. There are one-third who will survive and be okay, one-third who will survive but have disabilities, and then one-third who will not do well.”
JE remains the most common cause of viral encephalitis in Asia⁶. Children under 15 years old are most at risk, especially those living near rice fields, piggeries, or flood-prone areas where mosquitoes thrive.
In the Philippines, Japanese Encephalitis continues to be a serious health concern. Between 2014 and 2023, cases fluctuated from 69 to 361 each year⁷. The fatality rate can reach 21.1 %, and up to 45 % of patients may develop long-term neurological problems⁸. Outbreaks have been reported in Western Visayas, particularly in Iloilo, where the virus tends to surge during the rainy months of June to October⁹.
Neighboring countries like Australia and South Korea have also recorded an increase in JE cases in recent years¹⁰, showing that the disease remains a regional threat.
photo: dreamstime
Symptoms of Japanese Encephalitis
JE is sometimes called “brain fever” because it inflames the brain and often starts with fever and headache. Many people infected with the virus do not show symptoms, but when they do, the illness can progress quickly¹¹.
Common symptoms include high fever, vomiting, severe headache, stiff neck, seizures, and light sensitivity.
In infants, a bulging skull and stiff neck are warning signs, while older children may experience lethargy, weakness on one side of the body (hemiparesis), abnormal postures, and dystonia.
Adults may show confusion, disorientation, or behavioral changes as the disease affects brain function¹¹.
If your child develops these symptoms, especially during mosquito season, seek medical help immediately. Early diagnosis and supportive care can make a difference.
In infants, the main symptoms are a stiff neck and a bulging skull. In children 2 years of age and older, severe headache, lethargy, confusion, hemiparesis (weakness on one side of the body), opisthotonus (“arching” of the body, as in tetanus), dystonia (abnormal muscle tone causing muscle spasms in the affected part of the body), and sensitivity to light. Vomiting and dizziness may also occur.
For older adults, mental disturbances are the more common symptoms.
Treatment and Diagnosis of Japanese Encephalitis
There is currently no specific antiviral treatment for Japanese Encephalitis. Diagnosis involves a detailed physical examination, imaging tests such as MRI, and laboratory confirmation¹¹.
Doctors focus on relieving symptoms and preventing complications through:
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Pain and fever management
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Reducing brain swelling or intracranial pressure
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Intravenous fluids for hydration
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Anticonvulsants for seizures
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Feeding and respiratory support
- Using lumbar support
Patients recovering from JE may require rehabilitation to manage neurological effects such as movement problems, speech issues, or learning difficulties.
How can Japanese Encephalitis be prevented?
While treatment options are limited, Japanese Encephalitis is largely preventable.
Vaccination
The WHO recommends that children living in or traveling to endemic countries, including the Philippines, receive the JE vaccine as part of national immunization programs¹¹. Additional sources show the vaccine schedule and guidelines for travelers¹²¹³.
Avoiding mosquito bites
Protect yourself and your children by:
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Applying mosquito repellent with picaridin or oil of lemon eucalyptus, or using products recommended by the Centers for Disease Control and Prevention (CDC)².
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Dressing children in long sleeves and pants.
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Using mosquito nets, especially when sleeping outdoors or in unscreened rooms.
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Eliminating stagnant water near your home to prevent mosquito breeding.
When using mosquito nets, always tuck the edges under the mattress, check for holes, and keep them away from open flames. Choose dense, white nets with about 156 holes per square inch for best protection.
Japanese Encephalitis may not be as common as dengue, but its consequences can be far more severe. With high fatality rates and lifelong complications among survivors, awareness and prevention are key.
Protect your loved ones through vaccination, mosquito control, and early recognition of symptoms, especially if you live in or plan to travel to endemic areas. A simple mosquito bite should never take away a healthy future.
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Turtle, L., & Solomon, T. (2018). Japanese encephalitis — the prospects for new treatments. Nature Reviews Neurology, 14, 298–313.
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Centers for Disease Control and Prevention. (2024). Preventing Japanese Encephalitis. https://www.cdc.gov/japanese-encephalitis/prevention/?CDC_AAref_Val=https%3A%2F%2Fwww.cdc.gov%2Fjapaneseencephalitis%2Fprevention%2Findex.html
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World Health Organization. (2023). Japanese encephalitis – number of reported cases. https://www.who.int/data/gho/data/indicators/indicator-details/GHO/japanese-encephalitis—number-of-reported-cases
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Wang, H., & Liang, G. (2015). Epidemiology of Japanese Encephalitis: Past, Present & Future Prospect. Therapeutics and Clinical Risk Management, 11, 435–448.
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Lopez, A. L., et al. (2015). Epidemiology of Japanese Encephalitis in the Philippines: A Systematic Review. PLoS Neglected Tropical Diseases, 9(3), e0003630.
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Lopez, A. L., Raguindin, P. F., & Aldaba, J. G. (2021). Epidemiology of Japanese Encephalitis in the Philippines prior to routine immunization. International Journal of Infectious Diseases, 102, 344–351.
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Department of Health (Philippines). (2024). JE Surveillance Reports, 2014–2023.
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Lopez, A. L., et al. (2015). Epidemiology of Japanese Encephalitis in the Philippines: A Systematic Review.
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Manila Bulletin. (2023, June 23). 25 Japanese Encephalitis cases logged in Western Visayas.
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McGuinness, S. L., Lau, C. L., & Leder, K. (2023). The evolving Japanese encephalitis situation in Australia and implications for travel medicine. Journal of Travel Medicine, 30(2).
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Medical News Today. (2018, August 28). What’s to know about Japanese encephalitis? https://www.medicalnewstoday.com/articles/181418
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Mayo Clinic. (2025, March 1). Japanese encephalitis virus vaccine (intramuscular route) – Side effects & uses. https://www.mayoclinic.org/drugs-supplements/japanese-encephalitis-virus-vaccine-intramuscular-route/description/drg-20072758
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World Health Organization. (2024). Immunization against Japanese Encephalitis: WHO Position Paper.
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