Encephalitis is an inflammatory condition in which the brain becomes irritated and swollen—most often due to viral or bacterial infection, and in some cases, due to an overactive immune response that mistakenly targets healthy brain cells. Although rare, it more commonly affects young children, older adults, and people with weakened immune systems.

Early symptoms may resemble a flu-like illness, including fever, fatigue, and headaches. Symptoms begin mildly but can progress quickly within one to two weeks after infection. The severity and pattern of symptoms vary from person to person. Severe cases can escalate rapidly and lead to life-threatening complications, making timely medical care essential.

Common Symptoms

Because encephalitis often begins with an infection, its early symptoms resemble those of a cold or flu. This overlap can make early diagnosis difficult, and many cases may go undetected.

Mild cases often last one to two weeks, with symptoms peaking in the first two weeks (the acute phase). More severe cases can persist for months and may require a longer recovery period.

Early symptoms may include:

  • Fever

  • Fatigue

  • Headaches

  • Body aches

  • Lethargy

  • Loss of appetite

  • Vomiting

As the illness progresses, symptoms may fluctuate—some days feeling improved, other days worsening.

Neurologic Symptoms

When the brain and spinal cord become inflamed, neurological symptoms may develop. Inflammation affects neuron function, disrupting communication pathways within the brain.

Neurological signs may include:

  • Difficulty with memory

  • Seizures or involuntary movements

  • Poor balance or clumsiness

  • Difficulty speaking

  • Vision impairment, double vision, or vision loss

  • Stiffness, tremors, or muscle rigidity

  • Loss of sensation in certain body areas

Psychiatric Symptoms

Because encephalitis impacts brain function, psychological symptoms are also common. People may experience:

  • Hallucinations

  • Paranoia

  • Aggressive or unpredictable behavior

  • Anxiety or panic episodes

  • Difficulty sleeping

  • Compulsive or repetitive behaviors

Symptoms By Sex

Encephalitis affects people of all sexes equally when caused by infection. However, autoimmune encephalitis shows some differences:

  • People assigned female at birth are more likely to develop NMDA receptor encephalitis, involving antibodies that disrupt communication between brain cells.

  • People assigned male at birth are more likely to develop CASPR2 encephalitis, involving antibodies that affect nerve signaling.

Research continues to better understand sex-based differences.

Symptoms In Children

Children can develop encephalitis from viral infections. In infants and newborns, herpes infections are a common cause. Symptoms may be harder to recognize, as they resemble other childhood illnesses.

Warning signs in infants include:

  • A bulging soft spot on the head

  • Sudden or severe vomiting

  • Poor feeding

  • Body stiffness

  • Crying that worsens when held

Immediate medical evaluation is crucial because encephalitis can be more severe in young children.

Is Encephalitis Contagious?

Encephalitis itself is not contagious. However, the infections that lead to encephalitis—such as herpes or West Nile virus—can spread through:

  • Contact with infected saliva

  • Inhaling droplets from someone who is sick

  • Contaminated food or drinks

  • Kissing or sharing utensils

  • Using shared toothbrushes

  • Insect bites from mosquitoes or ticks

Good hygiene, proper food safety, vaccinations, and avoiding contact with infected individuals help lower the risk of developing infections that may lead to encephalitis.

When To See A Healthcare Provider

Symptoms of encephalitis can worsen quickly within one or two weeks, even if they start mildly. Because the condition can escalate rapidly, prompt evaluation is essential.

Seek immediate medical attention if you experience:

  • Loss of consciousness

  • Muscle weakness or paralysis

  • Seizures

  • Severe or persistent headaches

  • Poor responsiveness

  • Sudden cognitive decline, such as confusion or memory loss

Questions To Ask A Provider

If you visit a healthcare provider for possible encephalitis, consider asking:

  • Could my symptoms be caused by another infection?

  • How long might these symptoms last?

  • Will I need any tests for an accurate diagnosis?

  • What treatments can help improve my symptoms?

  • What happens if my symptoms don’t improve with treatment?