La Crosse Encephalitis 2003

Table 1. La Crosse Encephalitis Cases by Race and Sex, Indiana, 2003

  2003 1999-2003
Cases Rate* Cases
Total 3 0.05 14
Race
   White 3 0.06 9
   Black 0 0 1
   Other 0 0 1
   Not Reported 0 - 3
Sex
   Male 2 0.07 10
   Female 1 0.03 4
   Not Reported 0 - 0

*Rate per 100,000 population based on the U.S. Census Bureau’s population data as of July 1, 2003

La Crosse encephalitis virus is endemic in Indiana. The disease is found primarily in the eastern United States where hardwood forests exist. The disease is maintained in nature in a cycle between the tree-hole mosquito, Ochlerotatus triseriatus, and small woodland mammals such as squirrels and chipmunks.

During the five-year period 1999-2003, 14 cases of La Crosse encephalitis were reported in Indiana with 3 reported cases in 2003. Figure 1 shows the number of reported cases per year from 1999-2003. Cases ranged in age from 7-10 years, with over half of the cases in the 5-9 years age group (Figure 2). Cases were diagnosed in nine counties; however, no county reported five or more cases.

Clinically recognized infections occur mainly in children under 16 years of age. Symptoms include headache, fever, nausea, vomiting, drowsiness, and disorientation. Severe cases may result in seizures or coma. Cases are rarely fatal but may result in learning disabilities in recovered individuals. It has been estimated that for every symptomatic case there are 1,500 asymptomatic cases.

You can learn more about La Crosse encephalitis by visiting the following Web site:
http://www.cdc.gov/ncidod/dvbid/arbor/lacfact.htm