Sarita had developed fever and sore throat for two days. She had taken some throat lozenges which failed to respond. It then got worse with each passing day. She was then hospitalised and started having seizures. The seizures got worse and became more frequent and prolonged. When she started losing consciousness, the treating doctors transferred her to the intensive care unit where she remained for several weeks. Her family were told there was very little hope for her complete recovery because she had viral encephalitis.

Ramu had developed fever, headache and generalised body aches, for which he remained in bed for a whole day. He recovered the next day after consuming medicines for fever. However, after a week, he began to feel ill again. He began to develop headache and confusion. He even failed to recognise his classmates. In the afternoon, his classmates found him, unconscious, on the floor of his classroom during lunch break. They carried him to the school van and rushed him to the nearby hospital.

At the emergency, his heart stopped beating and was resuscitated and put in a ventilator. After doing a brain scan and testing the fluid around the brain, he was diagnosed with viral encephalitis. Eventually, after three weeks, he was out of the hospital feeling weak and barely able to walk, confused, unable to remember his past and recognise his relatives.

These are a few real stories reflecting the burden of millions of people affected by herpes simplex encephalitis every year. Although Japanese encephalitis virus is the most important causative agent, herpes simplex, dengue, Nipah and Enterovirus encephalitis are now being increasingly reported in Nepal.

Herpes simplex encephalitis is the most common cause of sporadic episodes of encephalitis in the world. Around 70 per cent of the people are affected by it. It is caused by the herpes simplex virus (HSV). In most of the people, it travels from the nose or mouth to the nerves in the back of the nose and comes down to cause cold sores around the lips.

In an unfortunate small number of people, it travels instead in the opposite direction and into the brain through the olfactory or trigeminal nerves, causing encephalitis. It causes bleeding, swelling and altered function of the brain, also known as inflammation, involving typically the temporal lobes.

The affected people, during the initial period, may just have flu like illness, such as fever, headache, body aches or generalised weakness. They could then recover spontaneously.

Some may progress to become more ill, confused, muddled or demonstrate strange behaviour. They may also have features of mental illness. Some may further progress to become drowsy, develop seizures, paralysis, difficulty with speech and fall unconscious. This then suggests that they have serious infection of the brain by the virus and require immediate medical treatment. Hence, what looks like a bout of flu could be an early feature of life-threatening encephalitis.

The diagnosis of encephalitis is confirmed by conducting a brain scan (MRI/CT Scan/diffusion weighted imaging) and lumbar puncture. Lumbar puncture is conducted by popping in a needle in between the bones of the vertebrae in the back and withdrawing cerebrospinal fluid which is present around the brain and spinal cord.

This fluid can then be tested to look for blood cells for evidence of bleeding, inflammatory cells as marker of inflammation, viral culture and polymerase chain reaction for confirmation of HSV. Brain scan is abnormal and helps in localising the site of bleeding, inflammation and swelling of the brain.

Early recognition and treatment are necessary to achieve complete recovery from the disease. If untreated, around three quarters of the affected people die. However, it could be significantly reduced to only a quarter, if they receive treatment early.

Herpes simplex encephalitis can be treated by administering an anti-virus drug called acyclovir for three weeks. During recovery, typically, affected people may continue to feel unwell for the first few days. When later, after acyclovir stops viral replication and swelling of the brain, they begin to feel and function as normal.

However, in those who are treated late, there may be excessive inflammation and swelling of the brain causing residual physical, neurological and mental problems, such as loss of short-term memory, learning difficulties, abnormal behaviours and difficulty in walking, depending on the area of the brain most affected by the virus.

Reducing such undesirable outcomes is the focus of interest to most of the researchers in the field today. Many are also exploring the role of anti-inflammatory medicines such as dexamethasone in reducing the swelling of the brain and improving the outcome. Thankfully as a result of many researches and innovations in the diagnosis and treatment of this dreadful illness, such unfavourable outcomes are decreasing.

Professor Dr Ajit is with the National Academy of Medical Sciences, Kanti Children's Hospital, and Dr Amod is with B & B Hospital, Gwarko, Lalitpur