Medical Health Encyclopedia

Tick-borne encephalitis (TBE) is commonly found in many countries throughout Europe, Asia, and the former Soviet republic, but it is reported only rarely in the U.S. Powassan encephalitis is the main tick-borne encephalitis found in the United States and Canada. Cases of tick-borne encephalitis have also been reported from Rocky Mountain spotted fever, but this is a bacterial (not viral) infection.

Enteroviruses

Enteroviruses account for between 10 - 20% of viral encephalitis cases. For example, the group A coxsackievirus has been detected in infants and children with encephalitis and is among the important viruses in the class. (It should be noted that the enteroviruses are nearly as common as cold viruses and are rarely serious.) Enteroviruses can be spread through food or water contaminated by trace amounts of fecal material and through sneezing and coughing.

Herpes Viruses

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The herpesvirus group includes a number of common infections, including herpes simplex, varicella-zoster (the cause of chicken pox and shingles), cytomegalovirus, herpesvirus 6, and Epstein-Barr (EB) virus (the cause of mononucleosis). About 2,100 people are hospitalized each year from herpes-associated encephalitis. These viruses share certain features, including the capacity to cause an infection and then to go into hiding. They can lie dormant for periods of time as short as months or as long as a lifetime. In a few cases, when the viruses reactivate, they cause encephalitis. In fact, some evidence suggests that varicella-zoster, cytomegalovirus, and Epstein-Barr (EB) virus may be more common causes of encephalitis than previously thought. In most cases, however, encephalitis from these viruses occurs in people with impaired immune systems, such as people with HIV or organ transplant patients.