Encephalitis is inflammation (swelling) of the brain. It can happen when an infection or medical condition that affects the brain activates your immune system. The inflammation can cause a wide range of symptoms. In extreme cases, it can lead to brain damage, stroke, or even death.

There are different types of encephalitis, based on what the cause is. The two main types are infectious encephalitis and autoimmune encephalitis.

Infectious encephalitis is usually caused by a virus. In fact, viruses are the most common cause of encephalitis. Some of the different viruses that cause it include:

• Herpes viruses, including herpes simplex (HSV), the Epstein-Barr virus (which causes infectious mononucleosis) and the varicella-zoster virus (which causes chickenpox).
• Viruses you can get if you are bitten by an infected tick, such as tick-borne encephalitis (TBE virus) and Powassan virus.
• Viruses you can get if you are bitten by an infected mosquito, such as eastern equine encephalitis virus, West Nile virus, and La Crosse virus.
• Enteroviruses, which are a common group of viruses that mostly cause mild illness or respiratory infection. These infections usually happen in the summer and fall.

Bacteria, fungi, and parasites can also cause infectious encephalitis. But this is not common.

Autoimmune encephalitis happens when your immune system mistakenly attacks healthy brain cells. It can be triggered by conditions such as certain cancers, benign tumors, and infections. Sometimes the cause is not known.

Anyone can get encephalitis, but you are more likely to get it if you:

• Have a weakened immune system, for example from having HIV or taking certain medicines. These could include medicines taken after an organ transplant, certain chemotherapy medicines, and specialized treatments for certain autoimmune diseases.
• Are a young child or older adult.
• Live in areas where there are ticks and mosquitoes that carry viruses that can cause encephalitis.

The symptoms of encephalitis can vary a lot, depending on how severe it is. Many people do not have any symptoms. Others may have mild flu-like symptoms such as fever, fatigue, headache, or body aches. If encephalitis becomes more serious, it can cause:

• Severe headache
• Stiff neck
• Vomiting
• Seizures
• Behavior changes
• Drowsiness
• Muscle weakness
• Partial paralysis in your arms and legs
• Coma

Encephalitis can be dangerous in infants. Their symptoms may include:

• Fever
• Lethargy (weakness or drowsiness)
• Poor feeding
• Vomiting
• Body stiffness
• Unusual irritability or crying
• A full or bulging fontanel (the soft spot on the top of the head)

If you or your child is having symptoms of encephalitis, it's important to get medical care right away.

To find out if you have encephalitis, your health care provider:

• Will do a physical exam
• Will take your medical history, which includes asking about your symptoms
• May do a neurologic exam
• May order imaging tests, such as a brain CT scan or MRI
• May order an EEG (electroencephalography), which use small electric sensors to measure your brain activity
• May order blood and cerebrospinal fluid (CSF) tests

Most people with encephalitis will need treatment in the hospital. Depending on the cause, treatments may include antiviral medicines, antibiotics, corticosteroids, and other medicines.

For some types of encephalitis, there is no medicine to treat it. But rest, nutrition, and fluids can help your body fight the infection and relieve symptoms.

Some people may need physical, speech, and occupational therapy once the illness is under control.

There are steps you can take to help prevent encephalitis that is caused by infections:

• Use good hygiene, including washing your hands often with soap and water.
• Don't share food, drinks, utensils, and glasses with other people.
• Get vaccines for viruses that can cause encephalitis.
• Avoid mosquito and tick bites, for example by:
  • Wearing insect repellent with DEET or another U.S. Environmental Protection Agency (EPA)-registered insect repellent. Make sure to follow the instructions for using the repellant.
  • Wearing clothes that cover your arms, legs and feet.
  • Treating your clothing and gear with products containing 0.5% permethrin before you go in grassy or woody areas.

NIH: National Institute of Neurological Disorders and Stroke

Eosinophils are a type of white blood cell. They help fight off infections and play a role in your body's immune response. They can also build up and cause inflammation.

Normally your blood doesn't have a large number of eosinophils. Your body may produce more of them in response to:

• Allergic disorders
• Skin conditions
• Parasitic and fungal infections
• Autoimmune diseases
• Some cancers
• Bone marrow disorders

In some conditions, the eosinophils can move outside the bloodstream and build up in organs and tissues. This can happen in many different parts of the body, including the esophagus, heart, lungs, blood, and intestines. Treatment of eosinophilic disorders can vary, depending on the cause and which part of the body is affected. Steroids are often part of the treatment.

Erectile dysfunction (ED) is a common type of male sexual dysfunction. It is when a man has trouble getting or keeping an erection. ED becomes more common as you get older. But it's not a natural part of aging.

Some people have trouble speaking with their doctors about sex. But if you have ED, you should tell your doctor. ED can be a sign of health problems. It may mean your blood vessels are clogged. It may mean you have nerve damage from diabetes. If you don't see your doctor, these problems will go untreated.

Your doctor can offer several new treatments for ED. For many men, the answer is as simple as taking a pill. Getting more exercise, losing weight, or stopping smoking may also help.

NIH: National Institute of Diabetes and Digestive and Kidney Diseases

Your family history includes health information about you and your close relatives. Families have many factors in common, including their genes, environment, and lifestyle. Looking at these factors can help you figure out whether you have a higher risk for certain health problems, such as heart disease, stroke, and cancer.

Having a family member with a disease raises your risk, but it does not mean that you will definitely get it. Knowing that you are at risk gives you a chance to reduce that risk by following a healthier lifestyle and getting tested as needed.

You can get started by talking to your relatives about their health. Draw a family tree and add the health information. Having copies of medical records and death certificates is also helpful.

Centers for Disease Control and Prevention

A fever is a body temperature that is higher than normal. A normal temperature can vary from person to person, but it is usually around 98.6 °F (37 °C). A fever is not a disease. It is usually a sign that your body is trying to fight an illness or infection.

Infections cause most fevers. You get a fever because your body is trying to kill the virus or bacteria that caused the infection. Most of those bacteria and viruses do well when your body is at your normal temperature. But if you have a fever, it is harder for them to survive. Fever also activates your body's immune system.

Other causes of fevers include:

• Medicines, including some antibiotics, blood pressure medicines, and anti-seizure medicines
• Heat illness
• Cancers
• Autoimmune diseases
• Some childhood vaccines

Treatment depends on the cause of your fever. If the fever is very high, your health care provider may recommend taking an over-the-counter medicine such as acetaminophen or ibuprofen. Adults can also take aspirin, but children with fevers should not take aspirin. It is also important to drink enough liquids, to prevent dehydration.