In rural areas, arboviruses that are carried by mosquitoes or ticks , or that are accidentally ingested, are the most common cause. In urban areas, enteroviruses are most common, including Coxsackievirus, poliovirus, and echovirus. Once the virus has entered the blood stream, it can localize in the brain causing inflammation of the brain cells and surrounding membranes. White blood cells invade the brain tissue as they try to fight off the infection. Encephalitis is uncommon.
Animal vaccination is important to prevent encephalitis that occurs because of the rabies virus.
Various symptoms resembling gastroenteritis or meningitis may be present, or symptoms may mimic subdural hematoma or brain abscess . An examination may show signs of meningeal irritation or increased intracranial pressure , or other neurologic symptoms such as muscle weakness or changes in sensation. Viral cultures of CSF or blood that reveal any type of virus will confirm the diagnosis of encephalitis, however, viral cultures are rarely useful. More often the health care provider also relies on serology tests to provide evidence of viral infection. EEG test results are abnormal.