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Encephalitis is an acute inflammation of the brain. The majority of cases are caused by either a viral infection or the immune system mistakenly attacking brain tissue.

In the United States, encephalitis is responsible for an estimated 19,000 hospitalizations, 230,000 hospital days, and $650 million in hospitalization costs.

Around 15 percent of encephalitis cases occur in the HIV-infected population.

In this article, we will look at the symptoms, causes, treatments, and complications of encephalitis.

Fast facts on encephalitis

Here are some key points about encephalitis. More detail and supporting information is in the main article.

  • Early symptoms are fever, photophobia, and headache
  • Encephalitis is rarely life-threatening
  • Encephalitis most often affects children, older adults, and those with compromised immune systems
  • Only a handful of antiviral medications can help treat encephalitis
  • Complications of encephalitis can include epilepsy and memory loss

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Encephalitis is an acute inflammation of the brain.

Encephalitis is an acute inflammation (swelling) of the brain usually resulting from either a viral infection or due to the body's own immune system mistakenly attacking brain tissue.

In medicine, "acute" means it comes on abruptly and develops rapidly; it usually requires urgent care.

The most common cause is a viral infection. The brain becomes inflamed as a result of the body's attempt to fight off the virus.

Encephalitis occurs in 1 in every 1,000 cases of measles.

Encephalitis generally begins with fever and headache. The symptoms rapidly worsen, and there may be seizures (fits), confusion, drowsiness, and loss of consciousness, and even coma.

Encephalitis can be life-threatening, but this is rare. Mortality depends on a number of factors, including the severity of the disease and age.

Younger patients tend to recover without many ongoing health issues, whereas older patients are at higher risk for complications and mortality.

When there is direct viral infection of the brain or spinal cord, it is called primary encephalitis. Secondary encephalitis refers to an infection which started off elsewhere in the body and then spread to the brain.

Different types of encephalitis have different causes.

  • Japanese encephalitis is spread by mosquitoes
  • Tick-borne encephalitis is spread by ticks
  • Rabies can be spread through a bite from a mammal

There is also primary or secondary encephalitis.

Primary or infectious encephalitis can result if a fungus, virus, or bacterium infects the brain.

Secondary, or post-infectious, encephalitis is when the immune system responds to a previous infection and mistakenly attacks the brain.

The patient typically has a fever, headache, and photophobia (excessive sensitivity to light). There may also be general weakness and seizures.

Less common symptoms

The individual may also experience nuchal rigidity (neck stiffness), which can lead to a misdiagnosis of meningitis. There may be stiffness of the limbs, slow movements, and clumsiness. The patient may also be drowsy and have a cough.

More serious cases

In more serious cases, the person may experience very 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 infants

Initially, encephalitis is harder to detect in young children and babies. Parents or guardians should look out for vomiting, a bulging fontanel (the soft area on the top center of the head), incessant crying that does not get better when the baby is picked up and comforted, and body stiffness.

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

Primary (infectious) encephalitis can be split into three main categories of viruses:

  1. Common viruses, including HSV (herpes simplex virus) and EBV (Epstein-Barr virus)
  2. Childhood viruses, including measles and mumps
  3. Arboviruses (spread by mosquitoes, ticks, and other insects), including Japanese encephalitis, West Nile encephalitis, and tick-borne encephalitis

Secondary encephalitis: could be caused by a complication of a viral infection. Symptoms start 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. We still do not know why the immune system malfunctions in this way.

In more than 50 percent of encephalitis cases, the exact cause of the illness is not tracked down.

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

Treatment for encephalitis focuses on alleviating symptoms. There are only a limited number of reliably tested specific antiviral agents that can help, one of which is acyclovir; success is limited for most infections except when the condition is due to herpes simplex.

Corticosteroids may be administered to reduce the brain's inflammation, especially in cases of 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 (paracetamol) for fever and headaches. Tylenol is available to purchase online.

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Diagnosis of encephalitis can be challenging.

Doctors who identify the classic symptoms in adults - fever, headache, confusion, and occasionally seizures, or irritability, poor appetite, and fever in young children - may order further diagnostic tests.

A neurological examination generally finds that the patient is confused and drowsy.

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, might reveal higher-than-normal levels of protein and white blood cells.

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

A CT scan may be useful in detecting changes in brain structure. It can also rule out other causes, such as stroke, an aneurysm, or a tumor. However, an MRI is the best imaging option for encephalitis; it can identify the classic brain changes that suggest encephalitis.

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

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

The majority of patients who have encephalitis go on to have at least one complication, especially elderly patients, those who had symptoms of coma, and individuals who did not receive treatment at an early stage.

Complications may include:

  • Loss of memory - especially among those who had herpes simplex virus encephalitis
  • Behavioral or personality changes - such as mood swings, bouts of frustration and anger, and anxiety
  • Epilepsy
  • Aphasia - language and speech problems

Keeping up-to-date with vaccines is the most effective way of reducing the risk of developing encephalitis. These include vaccines for measles, mumps, rubella, and if the virus exists in those areas, Japanese encephalitis and tick-borne encephalitis.

In areas known to have mosquitoes that carry encephalitis-causing viruses, individuals should take measures 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 there are large numbers of mosquitoes about, keeping the home mosquito-free, using mosquito repellent, and making sure there is no stagnant water around the home.