Mosquito-Borne Encephalitis

Viruses cause disease around the world

Some types of mosquitoes carry viruses which can cause potentially severe illness in humans. If you live in the United States, you've probably heard of West Nile virus. But that disease is caused by just one of several mosquito-borne viruses which occur around the world. (In fact, West Nile usually occurs in Africa, West Asia, and the Middle East.)

The diseases
Some of the encephalitis diseases caused by mosquito-borne viruses are:

• La Crosse encephalitis
  Occurs in: United States (Midwest, mid-Atlantic, southeastern)
  Symptoms: fever, headache, nausea, vomiting, lethargy
  Severe disease: most common in children under age 16, consists of seizures, coma, paralysis, brain damage
  Death rate: less than 1% of cases
• Eastern equine encephalitis
  Occurs in: United States (eastern, Gulf Coast, Midwest)
  Symptoms: fever, muscle pains, headache
  Severe disease: seizures, coma, brain damage
  Death rate: as high as 1/3 of all cases
• Japanese encephalitis
  Occurs in: throughout Asia
  Symptoms: fever, headache, vomiting
  Severe disease: encephalitis, brain damage
  Death rate: 10-30% of cases (A vaccine is available for this disease.)
• St. Louis encephalitis
  Occurs in: lower 48 states of United States
  Symptoms: fever, headache
  Severe disease: meningoencephalitis
  Death rate: 5-15% of cases
• Venezuelan equine encephalitis
  Occurs in: Central and South America
  Symptoms: flu-like symptoms
  Severe disease: encephalitis
• Western encephalitis
  Occurs in: western United States and Canada
  Symptoms: usually mild, but may have fever, headache, nausea, vomiting, malaise
  Severe disease: altered mental status, meningitis, brain damage Death rate: about 3% of cases
• West Nile virus
  Occurs in: Africa, West Asia, Europe, Middle East, United States
  Symptoms: fever, headache
  Severe disease: encephalitis
  Death rate: low

How to protect yourself
1. Personal protective measures

• stay out of mosquito-infested areas such as swamps
  
• mosquitoes are active in the early evening, so avoid being outdoors then
  
• wear long pants (not shorts) and long-sleeved shirts in wooded areas or near lakes and ponds
  
• wear mosquito repellent
  
• make sure your yard doesn't have standing water in buckets, pools, wheelbarrows, jars, etc., where mosquitoes can breed

2. Public health measures

• spray insecticide where mosquitoes breed, such as lakes, ponds, roadside ditches, etc.
  
• educate people about eliminating standing water and protecting themselves when outdoors
  
• monitor the mosquito population and test for viruses

Source:
Centers for Disease Control and Prevention, Division of Vector-Borne Infectious Diseases, Arboviral Encephalitides.