Once in the brain, the virus and the host's inflammatory response disrupt neural function, leading to illness and complications, many of which frequently are neurological in nature, such as impaired motor skills and altered behavior.
Prognosis is good for most individuals who are infected by an encephalitic virus but is poor among those who develop severe symptoms, including viral encephalitis.
Long-term complications of viral encephalitis typically relate to neurological damage, such as experiencing seizures, memory loss, and intellectual impairment.
Many cases of viral encephalitis are not identified either because of lack of testing or mild illness, and serological surveys indicate that asymptomatic infections are common.
[12] An example of person-to-person transmission is the herpes simplex virus, which is transmitted by means of intimate physical contact.
Specific examples include:[1] The brain histology of viral encephalitis shows dead neurons with nuclear dissolution and elevated eosinophil count, called hypereosinophilia, within cells' cytoplasm when viewed with an optical microscope.
Computed tomography (CT) or magnetic resonance imaging (MRI) help identify increased intracranial pressure and the risk of uncal herniation before performing an LP.
Electroencephalography (EEG) is abnormal in more than 80% of viral encephalitis cases, including those who are experiencing seizures, and may need to be monitored continuously to identify non-convulsive status.
[1][4] Test results specific to certain viruses include:[1] A broad differential diagnosis can be performed that looks at many potential causes of the encephalitis, infectious and noninfectious.
Individuals may require intensive care for frequent neurological exams or respiratory support, and treatment for electrolyte disturbance, autonomic disregulation, and renal and hepatic dysfunction, as well as for seizures and non-compulsive status epilepticus.
[1][4] A very specific exception is herpes simplex virus (HSV) encephalitis, which can be treated with acyclovir for 2 to 3 weeks if it is provided early enough.
Acyclovir significant decreases morbidity and mortality of HSV encephalitis and limits the long-term behavioral and cognitive impairments that occur with illness.
Elevated ICP can be relieved with steroids and mannitol, though there is limited data of the efficacy of such treatment with regards to viral encephalitis.
Mortality rates vary for those who do not receive treatment, for example being about 70% for herpes encephalitis[13] but low for the La Crosse virus.
Individuals who remain symptomatic after initial infection may have difficulty concentrating, behavior or speech disorders, or memory loss.
However, individuals who have unilateral mesial temporal lobe seizures after viral encephalitis have good results following neurosurgery.
For example, arbovirus infections are seasonal and cause viral encephalitis at the highest rate during the summer and early fall when mosquitos are most active.