What is viral encephalitis? How up to 60% of cases of rare brain infection that causes flu-like symptoms and was suffered by late Pogues singer Shane MacGowan go undiagnosed

Shane MacGowan, the singer and songwriter of the pioneering Celtic punk band The Pogues, has died aged 65.

The legendary Irish rocker, who was behind the iconic Christmas carol Fairytale of New York, died at 3am today with his wife Victoria Mary Clarke and family by his side.

The singer was diagnosed with viral encephalitis – a life-threatening condition that leads to swelling of the brain – last year and had been in intensive care for months. His condition was worsened by shingles that spread to his eye.

In recent years, he was also confined to a wheelchair and assisted by his wife and a caregiver at home, as he was plagued by ill health related to his years of alcohol and substance abuse.

The cause of encephalitis, when the brain swells, is not always known.

However, viral infections – such as measles, chickenpox and herpes – can cause the condition. In rarer cases, bacterial infections can also be the cause.

In the vast majority of cases, infections do not cause encephalitis.

According to the Brain & Spine Foundation, the condition only affects 4,000 Britons every year.

The inflammation can affect one or more different parts of the brain and ranges from mild to severe.

Early signs of the condition include flu-like symptoms, such as fever and headache.

More serious symptoms develop over hours, days, or weeks, such as confusion, seizures, personality changes, difficulty speaking, and loss of consciousness.

However, up to 60 percent of cases go undiagnosed.

Research shows that although thousands of cases are reported worldwide each year, more can occur as symptoms can be mild to non-existent in most individuals.

The NHS says encephalitis needs ‘urgent’ treatment.

People suspected of having encephalitis should receive immediate medical treatment in the hospital, where they may need to stay for months.

The disease can progress rapidly and can cause severe, irreversible neurological damage.

The singer was diagnosed with viral encephalitis – a life-threatening condition that leads to swelling of the brain – last year and had been in intensive care for several months. His death came just days after he returned home after being discharged from hospital, with his wife Victoria sharing a photo of him in his hospital bed.

His wife Victoria Mary Clarke regularly posted updates about her husband’s well-being on social media

Treatment depends on the underlying cause. But antiviral drugs, such as acyclovir and ganciclovir, steroid injections and antibiotics can be used.

Anticonvulsants and painkillers may also be offered to reduce discomfort, while corticosteroids can help reduce swelling of the brain. Those with the condition may also need breathing support, such as oxygen through a face mask or a ventilator.

While some may make a full recovery, many people will suffer from long-term problems caused by damage to their brain.

These include memory loss, personality and behavioral changes, and problems with attention, concentration, planning, and problem solving.

Anyone can be affected by the disease, but the very young and elderly are most at risk.

Although it is not always possible to prevent encephalitis, the NHS recommends using the MMR vaccine. It also recommends getting travel-related shots before going on holiday, such as the Vaccine against Japanese encephalitis before it goes to parts of Asia.