Viral Encephalitis

A recent news on 16 April 2015 shocking the community in Malaysia as a standard 5 student died with suspected H1N1 infection. However, State Education, Science, Technology, Green Technology, and Innovations committee chairman Datuk Md Yunos Husin said this was confirmed by a report issued by the Pantai Hospital that the student died of viral encephalitis, not H1N1.

Students wearing mask

What is Viral encephalitis?

Encephalitis is a general term that means inflammation of the brain. Encephalitis can occur two different ways: From direct infection of the brain, or from a previous infection that causes your immune system to attack your brain. Direct infection can be caused by many different agents, including bacteria, fungi, and viruses. 

This article will explore only viral causes of encephalitis. There are many encephalitis-causing viruses, so only causes, symptoms, and treatment related to the most common viruses will be discussed.

Encephalitis - inflammation of the brain

The symptoms of viral encephalitis include:

• High temperature
• Headache
• Sensitivity to light (photophobia)
• General malaise
• Stiff neck
• Stiff back
• Vomiting
• Changes to personality
• Confusion
• Memory loss (amnesia)
• Seizures
• Paralysis
• Coma.

General Causes

Encephalitis can result from certain viral infections passed between humans, or from contact with infected animals or insects.

Encephalitis can develop 5 to 10 days after some childhood illnesses (for example, chickenpox, measles, mumps, rubella, and polio). Fortunately, it is not common to get encephalitis after a viral illness. On rare occasions, encephalitis can occur weeks, months, or years after the initial viral infection. Vaccine programs have markedly reduced some of these diseases in the developed world.

Chickenpox

There are many viruses transmitted between humans that can lead to encephalitis. Viruses from the herpes group are familiar examples. Chickenpox, cytomegalovirus, and Epstein-Barr virus (the cause of infectious mononucleosis) are herpes viruses. All herpes viruses may cause encephalitis occasionally, but herpes simplex virus 1 is the most common culprit.

The herpes simplex virus 1 causes herpes simplex encephalitis.

Herpes simplex viruses occur throughout the world. About 90% of adults age 50 or older have been exposed to herpes simplex virus 1 at some time during their lifetime. Herpes simplex virus 1 is most commonly known for causing cold sores (fever blisters) on the lips or around the mouth area. The most common cause of non-epidemic (not affecting a large number of people at once) encephalitis in developed countries is the herpes simplex virus. About 30% of herpes encephalitis infections result from initial contact with the virus. However, 70% of encephalitis cases occur years after the first infection. This happens when virus particles that have been dormant in the brain since the initial infection become active. While it is not known what causes the herpes simplex virus to reactivate, it is thought that a weakened or suppressed immune system may play a role.

Ticks or mosquitoes spread certain encephalitis-causing viruses to people.

Insect-transmitted viruses are the most common cause of epidemic viral encephalitis in the world. Viruses that can be transmitted to humans from mosquitoes or ticks are called arboviruses. Mosquitoes and ticks acquire these viruses from feeding on an infected host. Depending on the specific virus, birds, horses, small animals, or rodents can act as hosts. After the mosquito bites an infected host, the virus multiplies inside the mosquito. When it feeds or bites again, the mosquito can transmit the virus to the person or animal it bites. 

Tick borne encephalitis

Infection and the immune system response

Once the viruses have gained access to the bloodstream, they multiply and head to the spinal cord and brain (central nervous system). Access to the brain is by blood or nerves. After breaching the blood–brain barrier, the viruses slip inside brain cells. This disrupts, damages and ultimately ruptures the infected brain cells. 

Certain viruses have a preference for different areas of the brain. For example, the herpes simplex virus likes to target the temporal lobes located over each ear. The cells of the immune system rush to the brain and start attacking the viruses. This causes the characteristic brain swelling (cerebral oedema). Both the infection and the attempts of the body to fight the infection are responsible for the symptoms of viral encephalitis.

Mosquito plays a role in spreading encephalitis

Complications

Babies, older people and people with reduced immunity are at increased risk of developing complications of viral encephalitis. Some of these complications include:

• Low blood pressure (hypotension)
• Low oxygen levels in the blood (hypoxaemia)
• Bleeding inside the brain (intracerebral haemorrhage)
• Brain damage
• Death.

Swelling of brain cause brain damage

Treatments

Unlike bacteria, viruses are difficult to treat. Antiviral medications only work on a limited number of viruses. Treatment aims to reduce the severity of the symptoms and can include:

• Hospitalization
• Antiviral medication, given intravenously, if the virus is known to be drug-sensitive (such as the herpes simplex virus)
• Intravenous administration of carbohydrate solutions to help reduce brain swelling
• Drugs, including cortico-steroids to reduce brain swelling
• Pain-killing drugs
• Drugs to prevent vomiting
• Anti-convulsive drugs
• Drugs to reduce fever, such as paracetamol
• Fluids to prevent dehydration, but not too much as this can worsen cerebral oedema (swelling of the brain).

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