Encephalitis

Encephalitis

Encephalitis is an inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue. Further symptoms include seizures or convulsions, tremors, hallucinations, stroke, and memory problems.

• In 2013, encephalitis was estimated to have resulted in 77,000 deaths, down from 92,000 in 1990.

There are a variety of causes:

1) Viral

• Viral encephalitis can occur either as a direct effect of an acute infection, or as one of the sequelae of a latent infection.
  • The most common causes of acute viral encephalitis are rabies virus, HPV infection, poliovirus, and measles virus.
  • Herpes simplex (the virus causing cold sores) remains the most common virus involved in encephalitis in the United States and throughout the world. These viruses are usually transmitted from person to person.
  • In the United States, there are five main encephalitis-causing viruses spread by mosquitoes: West Nile, Eastern equine encephalitis (EEE), Western equine encephalitis (WEE), La Crosse, and St. Louis encephalitis. Two types of Powassan viruses, an infrequent cause of encephalitis, are transmitted by at least two types of ticks.
  • Venezuelan equine encephalitis is found in South America. It can be a rare cause of encephalitis in the southwestern United States, particularly Texas. The infection is very mild, and nervous system damage is rare.
  • Japanese encephalitis virus is the most common arbovirus in the world (virus transmitted by blood-sucking mosquitoes or ticks) and is responsible for 50,000 cases and 15,000 deaths per year worldwide. Most of China, Southeast Asia, and the Indian subcontinent are affected.

2) Bacterial and other

• It can be caused by a bacterial infection, such as bacterial meningitis.
• It may be a complication of a current infectious disease such as syphilis (secondary encephalitis).
• Certain parasitic or protozoal infestations, such as toxoplasmosis, malaria, or primary amoebic meningoencephalitis, can also cause encephalitis in people with compromised immune systems.
  • Lyme disease and/or Bartonella henselae may also cause encephalitis.
  • Other bacterial pathogens, like Mycoplasma and those causing rickettsial disease, cause inflammation of the meninges and consequently encephalitis.
  • A non-infectious cause includes acute disseminated encephalitis which is demyelinated.

3) Limbic encephalitis

4) Autoimmune encephalitis

5) Encephalitis lethargica

In more serious cases, a person may grow lethargic, or become angry and irritable, and eventually fall into a coma. Such cases have a high death rate. Encephalitis can be particularly severe in elderly people and in babies, who are more likely to suffer permanent brain damage than adults.

Some kinds of encephalitis are caused by arboviruses, which are viruses that are spread from animals to humans by insects.

In the United States these include:

• St. Louis encephalitis, a virus found in birds. The most common form of encephalitis, with about 200 cases reported in an average year, mostly in midwestern and eastern states. Of cases severe enough to diagnose, about 5 to 15 percent are fatal, with the elderly at greatest risk.
• LaCrosse encephalitis, found in chipmunks and squirrels. It averages 75 cases reported a year, mostly in midwestern states in children younger than age 16. It is rarely fatal.
• Eastern equine encephalitis, found in horses. The most severe, it can kill as many as one third of those who get it, but usually only a handful of cases occur each year, in southeastern states.
• Western equine encephalitis, also found in horses. Despite its name, it can occur in any part of the country, although there have been no recent reports. It is rarely fatal, but it sometimes causes permanent brain damage in babies.

Other regional forms of encephalitis include:

• In Asia, by contrast, Japanese encephalitis virus is common, with more than 45,000 cases reported each year in the region, usually in rural and agricultural areas. It is fatal in less than 10 percent of cases, but can be more dangerous in children. A vaccine to prevent it is widely used in Japan, China, India, Korea, and Thailand. The Japanese encephalitis virus is related to the St. Louis one and infects mostly pigs, ducks, and wading birds.
• Venezuelan equine encephalitis. Causes occasional epidemics in Central and South America. Usually mild.
• Russian spring-summer encephalitis. Spread by ticks, with death rates as high as 25 percent in some outbreaks. A vaccine is available in Russia and Europe.
• West Nile encephalitis. A milder relation of Japanese and St. Louis encephalitis, it occurs in Africa, Asia, and Europe. A strain similar to the West Nile virus was first detected in the Western Hemisphere in New York City during the summer of 1999.
• Murray Valley encephalitis. Found in parts of Australia and New Guinea, it is also related to St. Louis and Japanese encephalitis. It is rarely fatal.

Additional Reading Links:

• Wikipedia - Encephalitis
• Mayo Clinic Encephalitis
• eMedicine Health Encephalitis
• National Institute of Neurological Disorders Meningitis & Encephalitis Information
• Acute Encephalitis by Richard T Johnson
• Japanese Encephalitis Morbidity, Mortality, and Disability
• Human Diseases - Encephalitis
• The New York Times - Encephalitis In-Depth Report

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