Encephalitis: Causes, Types, Symptoms, Diagnosis, Treatment, Prognosis, Prevention and Complications

It is defined as a pathological state of brain parenchymal dysfunction.

It also refers to inflammation of the brain parenchyma associated with neurological dysfunction such as altered consciousness, seizures, personality changes, cranial nerve palsies, speech problems, and motor and sensory deficits.

It is the result of direct inflammation of the brain tissue, as opposed to inflammation of the meninges ( meningitis ), and can be the result of infectious or non-infectious causes.

Most cases are caused by a viral infection or by the immune system mistakenly attacking brain tissue.

This disorder is serious, complex, and potentially fatal with infectious and non-infectious causes.


Encephalitis can develop as a result of a direct infection of the brain by a virus, bacteria, or fungus, or when the immune system responds to a previous infection; the immune system mistakenly attacks brain tissue.

The most common cause of encephalitis is due to a viral infection.

Encephalitis is more likely to affect children, older adults, people with weakened immune systems, and people who live in areas where mosquitoes and ticks that spread specific viruses are common.

The brain becomes inflamed as a result of the body’s attempt to fight the virus.

In more than 50 percent of encephalitis cases, the exact cause of the disease is not known. Encephalitis can be life-threatening, but this is rare.

Mortality depends on a number of factors, including the severity of the disease and the age of the patient.

Younger patients tend to recover without many health problems, while older patients have a higher risk of complications and mortality.


According to the causes that cause encephalitis, they are divided into primary encephalitis and secondary encephalitis.

When there is a direct viral infection of the brain or spinal cord, it is called primary encephalitis.

Secondary encephalitis refers to an infection that started in another part of the body and then spread to the brain.

Primary (infectious) encephalitis

It can be divided into three main categories of viruses:

  • Common viruses, such as the herpes simplex virus and the Epstein-Barr virus.
  • Childhood viruses, including measles and mumps.
  • Arboviruses that are spread by mosquitoes, ticks and other insects, thus Japanese encephalitis is transmitted by mosquitoes, West Nile encephalitis and tick-borne encephalitis.

Secondary encephalitis

Secondary or postinfectious encephalitis is when the immune system responds to a previous infection and mistakenly attacks the brain.

It is caused by a complication of a viral infection. Symptoms begin to appear days or even weeks after the initial infection.

The patient’s immune system treats healthy brain cells as foreign organisms and attacks them.

The risk factors are:

  • Be under 1 year old or over 65 years old.
  • Present immunodeficiency.
  • Vaccination
  • Exposure to infected contacts.


The patient usually has a fever, headache, and photophobia (excessive sensitivity to light).

There may also be general weakness and seizures.

Less common symptoms that patients may experience are: nuchal stiffness (stiff neck), which can lead to a misdiagnosis of meningitis. There may be stiffness in the limbs, slow movements, and clumsiness.

The patient may also be sleepy and have a cough.

In the most severe cases, the person may experience severe headaches, nausea, vomiting, confusion, disorientation, memory loss, speech problems, hearing problems, hallucinations, as well as seizures and possibly coma.

In some cases, the patient can become aggressive.

Signs and Symptoms in Babies

Initially, encephalitis is more difficult to detect in young children and babies.

Parents or caregivers should watch out for vomiting, a bulging fontanelle (the soft area at the top center of the head), incessant crying that does not improve when the baby is held and comforted, and stiffness in the body.


Diagnosing encephalitis can be challenging.

The diagnosis of encephalitis is based on a medical history (including recent exposure to insects, travel, personality changes, and contact with animals or unusual illnesses).

Clinicians identifying classic adult symptoms such as fever, headache, confusion and occasionally seizures, irritability, poor appetite, rash, altered mental status, focal neurological deficit, cough, gastrointestinal infection, biphasic disease.

The patient is usually seen to be confused and sleepy.

A neurological exam is done to assess mental status, detect neurological problems such as motor dysfunction and seizures, and help determine which area of ​​the brain is affected.

If the neck is stiff, caused by irritation of the meninges (membranes that cover the brain and spinal cord), the doctor may consider a diagnosis of meningitis or meningoencephalitis.

A lumbar puncture, which takes a sample of cerebrospinal fluid from the spine, may reveal higher than normal levels of protein and white blood cells.

A lumbar puncture is done to detect signs of infection in the cerebrospinal fluid and to help establish a diagnosis.

In this procedure, a needle is inserted between two lower vertebrae in the spine (lumbar), cerebrospinal fluid is collected, and the fluid is tested for elevated white blood cell counts, blood, and the presence of viruses.

However, this test is not always conclusive, in some cases, the results may return to normal even though the patient has encephalitis.

A CT scan can be helpful in detecting changes in the structure of the brain.

It can also rule out other causes, such as a stroke, aneurysm, or tumor.

However, an MRI is the best imaging option for encephalitis, it can identify classic brain changes that suggest encephalitis.

CT and MRI scans produce computerized images of the brain that are used to detect abnormalities such as swelling (edema) and bleeding.

MRI is able to detect abnormalities earlier in the course of infection.

An EEG that monitors the electrical activity of the brain can show sharp waves in one or both temporal lobes in patients with encephalitis.

The wave patterns may suggest a seizure disorder or a specific viral infection, such as herpes virus.

Your doctor may order a blood test if a West Nile virus infection is thought to be the cause.

Blood and urine tests are used to isolate and identify viruses.

Enzyme-linked immunosorbent assays can identify viruses that cause encephalitis soon after infection.

The polymerase chain reaction can identify small amounts of viral DNA.

An enteroviral culture in the stool can also be requested.


Treatment for encephalitis focuses on relieving symptoms. Treatment for encephalitis depends on the cause.

Some cases of viral encephalitis can be treated successfully if the medicine is started as soon as possible.

If herpes simplex encephalitis is suspected, antiviral medications are often given.

There are only a limited number of specific, reliably proven antiviral agents that can help.

Of which the most common are acyclovir (Zovirax) and ribavirin (Virazol).

These can be given right away to improve the chances of recovery and prevent complications.

Side effects of these medications include nausea, vomiting, and headache.

Treatment for viral encephalitis also includes palliative care.

Its success is limited for most infections, except when the condition is due to herpes simplex.

Corticosteroids may be given to reduce inflammation of the brain, especially in post-infectious (secondary) encephalitis.

If the patient has severe symptoms, they may need mechanical ventilation to help them breathe and other supportive treatment.

Anticonvulsants are sometimes given to patients who have seizures.

Sedatives can be effective for seizures, restlessness, and irritability.

For patients with mild symptoms, the best treatment is rest, plenty of fluids, and Tylenol (acetaminophen) for fever and headaches.

There is no cure for arboviral encephalitis, and the goal of treatment is to relieve symptoms.

Palliative care may include IV fluids to prevent dehydration, antibiotics to prevent secondary infections, and other medications to prevent complications.

Diuretics (eg, furosemide, mannitol) may be given to reduce intracranial pressure, and benzodiazepines such as lorazepam may be given to prevent seizures.

Prognosis of encephalitis

The outlook depends on the type of encephalitis, the patient’s age, general health, and the state of the immune system.

Rabies encephalitis, eastern equine encephalitis, Japanese encephalitis, and untreated viral encephalitis caused by herpes viruses carry a high risk of serious neurological damage and even death.

The prognosis is worse in very young patients, elderly patients, and patients with compromised immune systems.

Acute disseminated encephalitis caused by rabies infection is often fatal.

Rabies is transmitted through the bite of an infected animal and there is no cure once symptoms have developed.

Prevention of encephalitis

Staying up-to-date with vaccinations is the most effective way to reduce your risk of developing encephalitis.

These include vaccines against measles, mumps, and rubella, and if the virus exists in those areas, Japanese encephalitis and tick-borne encephalitis.

In areas known to have mosquitoes that carry viruses that cause encephalitis, people should take steps to reduce the risk of being bitten.

This may include wearing appropriate clothing, avoiding mosquito-infested areas, avoiding going outside at specific times during the day when mosquitoes are high, keeping the home free of mosquitoes, and making sure there is no standing water around the home. .

In areas where arbovirus encephalitis is prevalent, insecticide spraying can be used to control outbreaks.


Most patients who have encephalitis continue to have at least one complication, especially elderly patients, those who had coma symptoms, and people who did not receive treatment at an early stage.

Complications can include:

  • Memory loss, especially among those with herpes simplex encephalitis.
  • Behavioral or personality changes, such as mood swings, bouts of frustration and anger, and anxiety.
  • Neurological sequelae such as motor problems.
  • Drowsiness and loss of consciousness, and even coma.
  • Epilepsy .
  • Aphasia: speech and language problems.
  • Seizures
  • Hydrocephalus