Medical Health Encyclopedia

Symptom Onset

7-10 days following infection.

Incidence and Mortality Rates

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Although over 4500 cases have been reported since 1964, the average number of cases has been declining with a yearly average of only 11 cases between 1995 and 2000. Mortality rate of between 3 - 30%, with about 5% of survivors suffering complications afterward.

La Crosse Encephalitis

Virus Family

Bunyaviridae (genus Bunyavirus)

U.S. Geographic Areas

Occurs most frequently in upper Midwestern, southeastern (Appalachia), and mid-Atlantic states. Most cases have occurred in Ohio and Wisconsin. Unlike other encephalitis viruses which originate in birds, La Crosse encephalitis is transmitted to mosquitoes from infected chipmunks and squirrels.

Symptom Onset

5-10 days following infection.

Incidence and Mortality Rates

An average of 70-100 cases reported per year. Mortality rates are less than 1%. More common and severe in children under age 16.

West Nile Encephalitis

Virus Family

Flaviviridae (genus Flavivirus).

U.S. Geographic Areas

Cases have been reported throughout the mainland United States. In 2004, majority of West Nile encephalitis cases occurred in California, Arizona, Texas, and Louisiana.

Incidence and Mortality Rates

In 2005, 2819 cases of WNV were reported to the CDC, and 105 people died. (The average age of those who died was 57 years.) Of all the reported cases, more than half (53%) were due to West Nile fever. Forty-two percent of those who contracted WNV had more severe conditions, such as meningitis and encephalitis. However, most cases of West Nile virus do not produce symptoms, and are not reported, so these numbers paint a more worrisome picture than actually exists. In fact, experts think that less than 1% of people infected with WNV go on to develop severe neurological disease.