Skip directly to search Skip directly to A to Z list Skip directly to site content
CDC Home

Announcements: World Encephalitis Day — February 22, 2014

Encephalitis, inflammation of the brain, is caused by several different infectious and noninfectious entities. Encephalitis can be an uncommon complication of a common infection, such as infection with a herpes virus or with any of several vaccine-preventable disease viruses, or a predictable presentation of a rare pathogen, such as the ameba, Naegleria fowleri.

The epidemiology of encephalitis is influenced by many factors, including vaccine availability, global travel, and environmental alterations, such as climate change (1). Some encephalitis etiologies, such as the measles, mumps, rubella, and varicella viruses, have been virtually eliminated in certain settings through vaccination. However, other encephalitis pathogens have emerged or reemerged, including West Nile virus, Nipah virus, European tickborne encephalitis virus, enterovirus 71, and the ameba, Balamuthia mandrillaris.

Determining the cause of encephalitis can be difficult in part because of its nonspecific clinical presentation and the large number of causative agents. Despite exhaustive testing, an etiology is only identified in 40%–80% of cases (2). Moreover, autoimmune and infectious encephalitides are clinically indistinguishable (3).

The overall case-fatality rate of encephalitis is 5%–30%, but individual outcomes are highly dependent on the underlying cause and host factors, and survivors are often left permanently disabled. For instance, rabies is almost universally fatal, whereas encephalitis from enterovirus infection generally has better outcomes. Encephalitis also has substantial health-care costs given its severity as well as complexity of diagnosis and treatment (2).

Despite these challenges, progress is being made. World Encephalitis Day will be observed on February 22, 2014, to draw attention to encephalitis and invigorate global prevention efforts (4–6).


  1. Tyler KL. Emerging viral infections of the central nervous system: part 1. Arch Neurol 2009;66:939–48.
  2. Vora NM, Holman RC, Mehal JM, Steiner CA, Blanton J, Sejvar J. Burden of encephalitis-associated hospitalizations in the United States, 1998—2010. Neurology 2014;82:443–51.
  3. Bloch KC, Glaser C. Diagnostic approaches for patients with suspected encephalitis. Curr Infect Dis Rep 2007;9:315–22.
  4. The Encephalitis Society. World Encephalitis Day. North Yorkshire, United Kingdom: The Encephalitis Society; 2014. Available at
  5. The Encephalitis Society. About the Encephalitis Society. North Yorkshire, United Kingdom: The Encephalitis Society; 2014. Available at
  6. International Encephalitis Consortium. Reducing the global impact of encephalitis. Richmond, CA: International Encephalitis Consortium; 2014. Available at

Use of trade names and commercial sources is for identification only and does not imply endorsement by the U.S. Department of Health and Human Services.

References to non-CDC sites on the Internet are provided as a service to MMWR readers and do not constitute or imply endorsement of these organizations or their programs by CDC or the U.S. Department of Health and Human Services. CDC is not responsible for the content of pages found at these sites. URL addresses listed in MMWR were current as of the date of publication.

All MMWR HTML versions of articles are electronic conversions from typeset documents. This conversion might result in character translation or format errors in the HTML version. Users are referred to the electronic PDF version ( and/or the original MMWR paper copy for printable versions of official text, figures, and tables. An original paper copy of this issue can be obtained from the Superintendent of Documents, U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800. Contact GPO for current prices.

**Questions or messages regarding errors in formatting should be addressed to The U.S. Government's Official Web PortalDepartment of Health and Human Services
Centers for Disease Control and Prevention   1600 Clifton Road Atlanta, GA 30329-4027, USA
800-CDC-INFO (800-232-4636) TTY: (888) 232-6348 - Contact CDC–INFO
A-Z Index
  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #