Inflammation of the brain, usually from infection or an immune reaction, needing prompt diagnosis and treatment.

Overview of encephalitis

Encephalitis is a condition in which the brain becomes swollen or inflamed. It may happen due to viral or bacterial infections or when the body’s immune system mistakenly attacks healthy brain tissue. Certain viruses that cause encephalitis can spread through mosquito or tick bites.

Causes of encephalitis

In nearly half of encephalitis cases, the exact cause is unknown. The condition is mainly classified into two types:

• Infectious encephalitis: This occurs when an infection directly affects the brain, most commonly due to viruses. The infection may involve one part of the brain or spread more widely. In rare cases, bacteria, fungi or parasites may also cause encephalitis.
• Autoimmune encephalitis: This happens when the body’s immune system mistakenly attacks healthy brain cells or produces antibodies against the brain. Sometimes it may be linked to tumors or triggered by an infection, although in many cases the exact trigger is not identified.

Viruses that may lead to encephalitis include:

• Herpes simplex virus (HSV)
• Other herpes viruses such as Epstein–Barr virus and varicella-zoster virus (chickenpox and shingles)
• Enteroviruses
• Mosquito-borne viruses
• Tick-borne viruses
• Rabies virus

Signs and symptoms

Symptoms of encephalitis can be mild at the beginning but can become severe within hours or days. In some cases, symptoms develop slowly over weeks or months.

Early symptoms: The first signs may feel similar to the flu and can include:

• Fever
• Headache
• Nausea or vomiting
• Muscle and joint pain

Some people may also develop a rash or blisters on the skin. However, these early symptoms are not always present.

Serious symptoms: As the brain becomes affected, more severe symptoms can appear, such as:

• Confusion or disorientation
• Excessive sleepiness
• Seizures (fits)
• Changes in behaviour or personality
• Difficulty speaking
• Weakness or difficulty moving parts of the body
• Seeing or hearing things that are not real (hallucinations)
• Loss of sensation in certain areas
• Uncontrolled eye movements
• Vision problems
• Loss of consciousness

Some patients may also develop symptoms similar to meningitis, including severe headache, neck stiffness, sensitivity to bright light and a rash that does not fade when pressed with a glass.

Risk factors

Anyone can develop encephalitis, but certain factors may increase the risk:

• Age: Young children and older adults are more likely to develop severe forms of encephalitis. Some autoimmune types are more common in children and young adults, while others are seen more often in older adults
• Weak immune system: People with conditions such as human immunodeficiency virus (HIV), those taking immune-suppressing medicines or individuals with weakened immunity are at higher risk
• Geographical location: Infections spread by mosquitoes or ticks are more common in certain regions
• Season: Mosquito- and tick-borne infections tend to occur more frequently during warmer months
• Autoimmune diseases: People with existing autoimmune conditions (the body’s immune system mistakenly attacks its own healthy cells) may have a higher chance of developing autoimmune encephalitis
• Smoking: Smoking increases the risk of lung cancer, which may trigger certain immune-related conditions linked to encephalitis

Complications due to encephalitis

People with mild encephalitis often recover within a few weeks without lasting health problems. However, severe inflammation can damage the brain and may sometimes lead to coma or even death.

Some complications may continue for months or become permanent. These can include:

• Constant tiredness
• Muscle weakness or poor coordination
• Changes in personality or behaviour
• Memory difficulties
• Hearing or vision problems
• Difficulty speaking

Diagnosis

Doctors diagnose encephalitis through a physical examination, medical history and tests to look for infection or brain inflammation. They may ask about recent infections, insect or animal bites, travel history, medical conditions and medicines. Early diagnosis is important because symptoms can worsen quickly and may lead to serious complications.

Common diagnostic tests include:

• Neurological examination: Checks movement, sensation, balance, speech, memory, vision and behaviour
• Blood and cerebrospinal fluid tests: Help identify infections, inflammation or autoimmune causes
• Lumbar puncture (spinal tap): A small sample of fluid from the lower back is tested for bacteria, viruses, blood or inflammation
• Brain imaging, including computed tomography (CT) or magnetic resonance imaging (MRI) scan: Detects brain swelling, bleeding or other abnormalities and helps rule out conditions like stroke or tumours
• Electroencephalogram (EEG): Measures electrical activity in the brain to detect abnormal brain waves or seizures

Treatment

Treatment for encephalitis focuses on managing the underlying cause and relieving symptoms. Most patients are treated in the hospital so doctors can closely monitor their condition and respond quickly if symptoms worsen.

Common treatments include:

• Antiseizure medicines: Used to control seizures
• Antiviral medicines: Medicines such as Acyclovir may be given for viral encephalitis
• Breathing support: Severe cases may require oxygen or a ventilator to help with breathing
• Corticosteroids: Help reduce brain swelling and pressure
• Intravenous (IV) fluids: Prevent dehydration and provide supportive care
• Tube feeding (enteral nutrition): Used if a patient is unconscious or unable to eat
• Immune therapies: Treatments such as immune globulin (a treatment that gives healthy antibodies to help control the immune system) or plasmapheresis (a procedure that filters harmful antibodies out of the blood) may be used for autoimmune encephalitis
• Physical therapy: Helps improve balance, movement and strength
• Speech therapy: Supports patients with speech or communication difficulties
• Mental health support: Counseling or psychological support may help with memory, behaviour or emotional changes after encephalitis

Recovery

Mild encephalitis often lasts for a short time and many people recover completely. However, severe cases can still be life-threatening despite advances in diagnosis and treatment. Some people who recover from severe encephalitis may continue to have long-term problems such as tiredness, irritability, difficulty concentrating, seizures, hearing loss, memory problems or vision loss. Recovery can take several months or even years.

Rehabilitation services can help patients regain skills and adapt to daily life after encephalitis. Support may include:

• Neuropsychologists: Help with memory, thinking, and emotional changes
• Occupational therapists: Assist with daily activities and practical coping strategies
• Physiotherapists: Help improve movement, strength, and balance
• Speech and language therapists: Support communication and swallowing difficulties

Before leaving the hospital, doctors and healthcare professionals assess the patient’s physical and emotional needs and prepare a personalized care plan, often involving close family members or caregivers.

Prevention of encephalitis

Viral infections and insect-borne viruses are common causes of encephalitis. The risk can be reduced by keeping vaccinations up to date and protecting yourself from mosquito bites.

Ways to prevent mosquito bites include:

• Wear protective clothing: Use lightweight full-sleeved shirts, long pants, and hats when outdoors
• Use insect repellents: Choose repellents containing DEET and follow the instructions carefully
• Remove standing water: Mosquitoes breed in stagnant water found in flowerpots, buckets, or open containers
• Use window screens and fans: Screens help keep mosquitoes outside, while fans make it harder for them to land on you

When to contact a doctor?

If you have encephalitis, speak with your doctor about warning signs that may indicate your condition is worsening. Seek emergency medical care immediately if you develop confusion, sudden personality changes, difficulty speaking, weakness or trouble moving your arms or legs.

Frequently Asked Questions