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Know More About Encephalitis And Can It Be Contagious?

Viruses are the most common and important cause of encephalitis.

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Infectious and non-infectious disorders affecting the brain can activate the immune system, resulting in inflammation, which is called encephalitis. This can produce a variety of symptoms, such as fever, headache, vomiting, seizures, and altered behaviour or confusion. In serious cases, these can cause brain damage, stroke, or even death.

Infectious causes of encephalitis include bacteria, viruses, fungi, and parasites. In some individuals, environmental exposure, recent travel, or an immunocompromised state (such as HIV, diabetes, steroids, chemotherapy treatment) are important risk factors. Non-infectious causes include autoimmune/rheumatological diseases, certain medications, etc.

Viruses are the most common and important cause of encephalitis. Etiology of viral encephalitis in the tropical countries of Asia and the Indian subcontinent is different from those of the Western and developed world. Although Japanese encephalitis virus (JEV) is a key etiological agent for acute encephalitic syndrome (AES) in India, many recent studies suggest that enteroviruses, rhabdoviruses, measles virus, mumps virus, varicella-zoster (chickenpox) virus, herpes simplex virus type 1 and 2, also account for outbreaks of viral encephalitis. Dengue, which is a common arboviral infection seen in the monsoons can also present with encephalitis. Nipah virus encephalitis is a reemerging infection, with cases being reported from  Kerala. Rabies, which occurs after the animal bite (dog bite most commonly) can also present with encephalitis.

Since the cause of encephalitis is not immediately known and often may remain undiagnosed, such cases are often termed as an acute encephalitis syndrome (AES).

Encephalopathy, on the other hand,  means brain disease, disorder, or damage and essentially causes brain swelling. It can occur due to injury, chemicals and toxins, hypoxia, metabolic causes like hypoglycaemia (low blood sugar), hyponatremia (low sodium), high blood pressure, endocrine causes (affection of thyroid), vitamin B1 deficiency BUT not due to infections. So, encephalitis may be accompanied by fever, headache vomiting of a few days duration but encephalopathy may be more acute in onset. All the causes of viral encephalitis often have no specific treatment ( some do have) and supportive therapy is the mainstay and the course is prolonged. Encephalopathy, however, if treated immediately (eg. glucose administration in case of hypoglycaemia) can result in the reversibility of the condition.

The cases reported from Bihar have mainly occurred in children (even JEV mainly affects children under 15 years), was sudden in onset (the children being alright the night before), in summer months (where the temperature and humidity have been high), leading to dehydration which causes hyponatremia), on empty stomach (presence of hypoglycaemia) and after consumption of lychees (unripe) which contain a toxin called methylene cyclopropyl glycine (MCPG) which can cause hypoglycaemia. So these cases are likely to be a metabolic encephalopathy (hypoglycaemia, hyponatremia). However, the presence of an infectious agent in the lychee fruit cannot be ruled out. Also, JE is common in these areas. So there is a possibility of some of these cases being JE.

The infectivity or contagiousness in encephalitis depends on the underlying cause. Herpes viruses can be transmitted sexually, a varicella-zoster virus which causes chickenpox is contagious. Nipah virus is a virus that is spread from person to person through contact with infectious body fluids from another person such as nasal or respiratory droplets, urine, or blood. However, some of these such as JEV and DENV that are transmitted through the bite of infected insects are not considered contagious from person to person. These are preventable if adequate precautions are taken. There are other causes of encephalitis such as autoimmune problems or chemical encephalitis that are not contagious.

The prognosis depends on the infectious agent involved, the severity of the illness, and the rapidity with which the treatment is instituted.   In most cases, people with very mild symptoms can make a full recovery, although the process may be slow.  In more severe cases, there can be residual neurological deficits such as hearing and/or speech loss, blindness, permanent brain and nerve damage, behavioural changes, memory loss, etc.  Treatment and management may be prolonged in these situations.

Disclaimer: The views expressed in the article above are those of the authors' and do not necessarily represent or reflect the views of this publishing house. Unless otherwise noted, the author is writing in his/her personal capacity. They are not intended and should not be thought to represent official ideas, attitudes, or policies of any agency or institution.

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Dr. Mala Kaneria

The author is Consultant Infectious Diseases, Jaslok Hospital and Research Centre

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