Japanese encephalitis is a viral brain infection that often presents a deceptive clinical picture, with the majority of infected individuals exhibiting no symptoms at all.
In fact, up to 99% of people infected with the Japanese encephalitis virus (JEV) show no symptoms or only mild flu-like signs. But when the virus reaches the brain, symptoms can worsen quickly and become life-threatening. Knowing the symptoms of Japanese encephalitis helps people act early and get medical help in time.
The symptoms of Japanese encephalitis range from mild to severe. In some, the disease starts with general signs and quickly turns into a brain infection. The virus can cause seizures, coma, and death if not treated properly.
The Incubation Period and Asymptomatic Cases
After a mosquito bite, the incubation period lasts 5 to 15 days. During this time, the virus multiplies in the body without causing symptoms. Most people remain unaware of the infection. In some, however, the virus crosses into the brain, leading to clinical illness.
In more than 99% of cases, people experience only mild symptoms such as:
- Fever
- Headache
- Fatigue
- Nausea or vomiting
- A general feeling of being unwell
These mild symptoms often resemble the common flu and usually go away on their own. Still, vulnerable people—especially children and those with weak immune systems—face a higher risk of complications.
Prodromal Phase: Early Symptoms of Japanese Encephalitis
In the small number of people who develop symptoms, Japanese encephalitis begins with a prodromal phase lasting 2 to 5 days. Early warning signs include:
- Sudden high fever above 39°C
- Severe headache
- Muscle aches and general pain
- Nausea and vomiting
- Abdominal discomfort
- Weakness and fatigue
- Cough or respiratory symptoms (less often)
These signs can be mistaken for malaria, dengue, or the flu. However, Japanese encephalitis becomes clearer when neurological signs develop shortly afterward.
Acute Encephalitic Phase
Once the virus enters the brain, it triggers the acute encephalitic phase. This happens in about 1 in 250 infected people. Symptoms may appear within hours or days after the fever begins. Key signs during this stage include:
a. Changes in Mental Status
- Confusion and disorientation
- Difficulty following commands
- Hallucinations and delirium
- Loss of consciousness or coma
b. Neurological Symptoms
- Seizures (especially in children)
- Stiff neck
- Muscle weakness or spastic paralysis
- Tremors or jerky movements
- Trouble with balance and coordination (ataxia)
- Sensitivity to light (photophobia)
Some patients may show Parkinson-like features such as facial stiffness, tremors, or slow movements.
c. Speech and Behavior Changes
People may speak slowly, mumble, or stop speaking altogether. Children may become aggressive, irritable, or withdrawn.
Recovery and Late Symptoms of Japanese Encephalitis
If the patient survives the acute phase, symptoms may ease over a few weeks. However, full recovery is rare. Many people live with long-term effects such as:
- Ongoing fatigue
- Difficulty thinking clearly
- Depression or anxiety
- Trouble sleeping
- Seizures needing long-term treatment
- Muscle weakness or poor coordination
As many as 30–50% of survivors develop permanent disabilities. Recovery often needs months of physical, speech, or mental health therapy.
Symptoms in Children vs Adults
Children are more likely to show early warning signs such as:
- High fever
- Vomiting
- Convulsions
Adults may instead display mood changes or confusion first. Sadly, children also face a greater chance of lasting brain damage, especially when treatment is delayed.
Unusual Presentations of Japanese Encephalitis
Some people may have rare or unexpected symptoms, which can delay diagnosis. These include:
- Flaccid paralysis (similar to polio)
- Involuntary movements like dystonia or chorea
- Sudden mental illness such as psychosis or mania
- Brainstem problems that affect breathing
Doctors in high-risk areas must stay alert to these rare forms—especially during mosquito season.
Why Knowing the Symptoms of Japanese Encephalitis Matters
There is no specific medicine to cure Japanese encephalitis. Treatment focuses on easing symptoms and preventing complications. This is why recognising early signs—especially neurological ones—is so important. Prompt medical care can save lives and limit brain damage.
Raising awareness also helps. Families should know that symptoms like fever with confusion, seizures, or stiff neck mean urgent care is needed—especially in young children.
Conclusion
The symptoms of Japanese encephalitis range from mild or invisible to sudden and severe brain inflammation. Understanding this range helps with early detection and life-saving care.
In areas where the disease is common, doctors should always consider Japanese encephalitis when patients show signs of brain infection—especially during mosquito season. Education, fast action, and vaccines are key to reducing the harm caused by this serious but preventable illness.
