IT'S rare, but potentially fatal.

Encephalitis simply means inflammation of the brain. A relatively rare condition, it affects between 4 and 6,000 individuals every year in the UK, though the estimated worldwide incidence is potentially hundreds of thousands.

The most common cause of encephalitis is a viral infection, such as herpes simplex (that which causes cold sores), measles, varicella (colloquially known as chicken pox) and rubella (German measles).

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Viruses not common to the UK include rabies (found in infected animals), Japanese and West Nile as well as tick and mosquito borne viruses.

Although many will acquire viruses such as chicken pox and herpes simplex, thankfully only a tiny proportion will suffer encephalitis.

Sometimes autoimmune encephalitis is triggered without prior exposure to a virus.

Bacteria and fungi are rarer causes of encephalitis, however in half of cases no definite culprit is identified.

Although autoimmune encephalitis may have a more protracted and perhaps less obvious presentation, it is vital that anyone with any worrying neurological symptom is promptly brought for urgent medical attention, as timely intervention has a significant impact on outcome including survival.

The outcome for encephalitis is very varied and mortality can be between 10 and 30 per cent. For those who survive, they and their family will have to live with an acquired brain injury (ABI). For some, disability will be mild, with full or almost near complete recovery. Unfortunately for others there may be significant issues that affect both physical and psychological wellbeing. The brain recovers at a much slower rate than other body tissues and part of rehabilitation focusses on working within these new limitations. Like any significant illness, it has the potential to affect not just the individual but also their loved ones.

Prevention or reducing your chances of suffering encephalitis starts with something as easy as robust hand hygiene. It is recommended that you have the Measles Mumps and Rubella (MMR) vaccination.

If you are travelling abroad, make sure you are appropriately immunised. To reduce your chances of being bitten by a tick, use an insect repellent, and remove immediately if bitten.

World Encephalitis Day is a week today.