Encephalitis needs urgent treatment and most cases will be admitted to a hospital intensive care unit (ICU).

Treatment depends on the type of encephalitis you have, but aims to:

• stop and reverse the process of infection
• control immediate complications caused by fever, such as seizures or dehydration
• prevent long-term complications developing

An oxygen mask will be used to help with breathing. Feeding tubes will provide nutrition and help keep the body hydrated.

Encephalitis is a very serious condition and recovery can take months. There is also a significant risk of developing complications of encephalitis, such as memory loss, behavioural changes or even death.

Infectious encephalitis

In the UK, a medicine called aciclovir (sometimes spelt acyclovir) is the most widely used treatment for infectious encephalitis. However, it is only effective in treating cases caused by the herpes simplex virus or varicella zoster virus.

The earlier aciclovir is used, the more successful it is. Therefore, treatment with aciclovir is usually started while the condition is being diagnosed. If tests reveal encephalitis is being caused by something else, alternative treatments will be considered.

Aciclovir works by directly attacking the DNA inside viral cells, which stops the virus from reproducing and spreading further into the brain. It is given directly via a tube into a vein (intravenously), usually three times a day for two to three weeks.

Common side effects of aciclovir include:

• headache
• nausea (feeling sick)
• vomiting
• diarrhoea

Less common side effects include:

• liver damage
• hallucinations (seeing things that are not real)
• a decrease in the number of white blood cells that are produced by the bone marrow, which can make you more vulnerable to infection

In rare cases where a bacterial or fungal infection causes encephalitis, treatment usually consists of antibiotics or antifungal medicines.

Post-infectious encephalitis

Post-infectious encephalitis is usually treated with injections of high-dose corticosteroids. This may last several days, depending on the severity of the condition.

Corticosteroids work by calming the immune system (the body's natural defence against infection and illness). This reduces the levels of inflammation inside the brain.

Some people's symptoms may improve a few hours after treatment. But in most cases it will take a few days before symptoms start to improve.

Side effects of corticosteroids include:

• nausea and vomiting
• indigestion
• skin irritation at the site of the injection
• rapid mood changes, such as feeling very happy one moment and very depressed the next

If your symptoms fail to respond to treatment with corticosteroids, an additional medication called immunoglobulin therapy may be used. This comes from a blood donation and contains specific antibodies that help to regulate the immune system.

If your symptoms do not improve, a therapy called plasmapheresis may be considered. Plasmapheresis involves gradually passing your blood through a machine to remove the parts that contain antibodies before it is returned to your body.

Autoimmune encephalitis

Autoimmune encephalitis can be treated with corticosteroids, immunoglobulin therapy and plasmapharesis. An additional medication known as an immunosuppressant may also be recommended. 

Immunosuppressants suppress your immune system, which should prevent your immune system from attacking healthy tissue.

Ciclosporin is a widely used immunosuppressant in the treatment of autoimmune encephalitis.

Common side effects of ciclosporin include:

• numbness or tingling
• loss of appetite
• nausea and vomiting
• high blood pressure
• tremor (uncontrollable shaking or trembling)
• muscle pains or cramps
• increased body hair growth

Chronic encephalitis

There is currently no cure for the subacute sclerosing panencephalitis (SSPE) type of chronic encephalitis. Anti-viral medication can slow its progression, but this condition inevitably proves fatal within one to two years of receiving a diagnosis.

The recommended treatment for progressive multifocal leukoencephalopathy (PML) type of chronic encephalitis usually depends on what is causing the immune system to weaken.

If the immune system is weakened due to a treatment such as chemotherapy or taking immunosuppressants, this treatment may be temporarily withdrawn.

If your immune system is weakened due to a HIV infection, a type of medication known as highly active antiretroviral therapy may be effective. For more information, see treating HIV.

HIV medication can also effectively treat chronic progressive HIV encephalitis if used early. If it is left untreated, it is fatal.