Disease Information
Arthropod-borne viruses, i.e., arboviruses, are viruses that are maintained in nature through biological transmission between susceptible vertebrate hosts by blood feeding arthropods (mosquitoes, psychodids, ceratopogonids, and ticks). There are four main virus agents of encephalitis in the United States: eastern equine encephalitis (EEE), western equine encephalitis (WEE), St. Louis encephalitis (SLE) and La Crosse (LAC) encephalitis, all of which are transmitted by mosquitoes. Another virus, Powassan, is a minor cause of encephalitis in the northern United States, and is transmitted by ticks. Most cases of arboviral encephalitis occur from June through September, when arthropods are most active.
The majority of human infections are asymptomatic or may result in a nonspecific flu-like syndrome. Onset may be insidious or sudden with fever, headache, myalgias, malaise and occasionally prostration. Infection may, however, lead to encephalitis, with a fatal outcome or permanent neurologic sequelae. Fortunately, only a small proportion of infected persons progress to frank encephalitis.
Disease Reporting
What is required?
Health Care Providers and Clinical Laboratories
Health care providers and clinical labs are
required by law to report cases and suspect cases of arboviral encephalitis to local health departments within
one working day.
For Tribal and Local Public Health Authorities
For reportable diseases lacking Oregon-specific investigative guidelines or case report forms, please contact the epidemiologist on call for assistance at 971-673-1111.
See Also