What Is Encephalitis? 

Encephalitis (pronounced: in-seh-fuh-lye-tus)  is typically caused by three different groups of viruses. The herpes viruses  is one group,  and includes chickenpox, EBV (Epstein-Barr virus —  the virus  that causes mono),  and herpes simplex (the virus that causes cold sores). The second group  is made up  of viruses  and other germs that are transmitted by insects. Viruses like West Nile virus, which  is transmitted through  a mosquito bite, and  the germs that cause Lyme disease and Rocky Mountain spotted fever, which are transmitted thorough tick bites, can also cause encephalitis. The third group  is made up  of viruses that cause childhood infections that used to be common. These  include measles, mumps,  and German measles. Because lots  of countries immunize against these diseases, it's rarer today that a person will develop encephalitis  as a result of an illness like measles or mumps. 

Some cases of encephalitis  are mild and symptoms only last  for a short time.  However, it  is possible  to develop a severe case  of encephalitis that can be serious  and possibly even life threatening. When  a person has encephalitis, his or her brain becomes inflamed — inflammation means swelling  and irritation. 

Is It Contagious? 

Infection with  many different viruses can lead  to encephalitis. So how contagious  the infection  is depends on which virus caused it. Viruses like West Nile  are only transmitted through  the bite  of infected insects; it's not possible  to catch them from other people. But viruses like EBV are passed from person  to person.
Even if  a person catches  a virus  that can cause encephalitis, that does  not mean  that person will automatically develop  the condition. In fact,  very few  of the people  who are infected with these viruses actually develop encephalitis.