Banner Bar
NPS Arrowhead National Park Service
US Department of the Interior
Office of Public Health 1201 Eye Street, NW
Room 1131
Washington, DC 20005

Phone: 202-513-7215
Fax: 202-371-1349
Banner Bar
Office of Public Health -Viral encephalitides Factsheet
Points Of Contact
(202) 513-7217
Assistant to Director for Science
(202) 513-7097
(505) 248-7806
Assistant to Director for Field Operations
(202) 513-7056
National Capitol Region
Northeast Region
(215) 597-5371
Southeast Region
(404) 507-5730
Mid-West Region
(402) 661-1718
Intermountain Region
(505) 988-6040
Pacific West Region
(510) 817-1375
Alaska Region
(206) 220-4270

Eastern, Lacrosse, St. Louis & Western encaphalitis

Encephalitis is an inflammation of the brain, which can be caused by viruses transmitted through the bite of an infected mosquito. Susceptibility to clinical disease is highest in infancy and old age. With an incubation period between 5 and 15 days, mild cases result in a febrile headache while severe cases present with acute onset of high fever and headache, but most infections are asymptomatic. Case fatality rates range from 0.3% to 60% with Eastern Equine exhibiting the highest.

Each disease is caused by a specific virus, occurs in specific geographic regions, transmitted by specific species of mosquitoes and may follow certain cyclic patterns based on multiple environmental factors.

Risk Reduction

Effective risk reduction for mosquito-borne diseases within the NPS requires all employees and visitors to be knowledgeable and proactive in taking necessary steps to minimize exposure. Primary risk reduction practices include eliminating man-made mosquito-breeding habitat, avoiding activities when mosquitoes are most active, and wearing long sleeved shirts and pants. Many species of mosquito breed in stagnant water, therefore, it is critical that containers such as tires, buckets, birdbaths, gutters and miscellaneous debris are either removed or not holding water. The use of an insect repellant containing DEET, picaridin or oil of lemon eucalyptus (p-menthane or PMD) are effective against mosquitoes and should be used during periods of high mosquito activity. DEET should be used with caution on children – DEET is not recommended for the very young. Products containing oil of lemon eucalyptus should not be used on the very young.


Health Information, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Department of Health and Human Services.

If you have any questions, please contact your nearest Regional Point of Contact, park sanitarian or call WASO Public Health for more information.

Return to Vectorborne and Zoonotic Infectious Agents Page