Topic Overview

Viruses and bacteria carried by mosquitoes and sometimes ticks are some of the most common causes of encephalitis throughout the world. Most people who are bitten by infected mosquitoes do not develop any symptoms or develop only a mild flu-like illness. For those who do develop encephalitis, symptoms may develop within a few days or up to 2 weeks after the mosquito bite occurred, depending on which virus the mosquito was carrying.

Encephalitis caused by mosquito-borne viruses is spread by the bite of an infected mosquito. It also may be transmitted through blood transfusions and breastfeeding. There is no proof that it can be passed from one person to another through casual contact or from an animal to a person.

The mosquito-borne viruses that cause encephalitis cannot be destroyed with antiviral or other medicines. Treatment for these types of encephalitis focuses on reducing symptoms and providing supportive care while the body heals.

If you have signs of encephalitis caused by bacteria, your doctor will prescribe antibiotics.

Types of encephalitis include:

  • West Nile encephalitis. West Nile encephalitis happens mostly in North and Central America, Africa, parts of Asia, the Middle East, and southern Europe. It is more common in older adults and people with an impaired immune system.
  • St. Louis encephalitis. St. Louis encephalitis happens mostly in North America, Central America, and South America. It is more common in older adults.
  • La Crosse encephalitis. La Crosse encephalitis happens mostly in midwestern and eastern North America. It is more common in school-aged children.
  • California encephalitis. California encephalitis happens mostly in midwestern and northeastern North America. It is more common in children.
  • Japanese encephalitis. Japanese encephalitis happens mostly in Japan, China, Korea, Taiwan, Southeast Asia, India, Nepal, and northern Australia. It is more common in children. A vaccine against this type of encephalitis is available.
  • Eastern equine encephalitis. Eastern equine encephalitis happens mostly in North America. It usually gets to Canada with birds migrating from the southern United States to northern Canada. It is more common in older adults and children.
  • Venezuelan equine encephalitis. Venezuelan equine encephalitis happens mostly in Florida and the southwestern United States, Central America, and South America. It is rare in Canada.
  • Western equine encephalitis. Western equine encephalitis happens mostly in North America (especially in the prairie provinces in Canada and states west of the Mississippi in the United States), Central America, and South America. It is more common in older adults and children.
  • Powassan encephalitis. Powassan encephalitis happens mostly in North America (especially in Canada and New England in the United States) and Asia. This type of viral encephalitis is caused by a tick bite.

Most cases of mosquito-borne encephalitis occur during the warmest months of the year, when mosquitoes are most active. In areas that are warm year-round, people may get encephalitis throughout the year.

Rocky Mountain spotted fever can cause encephalitis in some cases. It happens mostly in North, Central, and South America. In Canada it occurs mostly in the west. This type of bacterial encephalitis is caused by a tick bite.

Related Information

References

Other Works Consulted

  • Jubelt B (2010). Viral infections and postviral syndromes. In LP Rowland, TA Pedley, eds., Merritt's Neurology, 12th ed., pp. 156-185. Philadelphia: Lippincott Williams and Wilkins.
  • Ropper AH, et al. (2014). Viral infections of the nervous system, chronic meningitis, and prion diseases. In Adams and Victor's Principles of Neurology, 10th ed., pp. 743-777. New York: McGraw-Hill Education.

Credits

ByHealthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Anne C. Poinier, MD - Internal Medicine
Adam Husney, MD - Family Medicine
Specialist Medical Reviewer W. David Colby IV, MSc, MD, FRCPC - Infectious Disease
Christine Hahn, MD - Epidemiology

Current as ofMarch 3, 2017