[Acute encephalitis].

Acute encephalitis can be due to many causes, although most are viral, and is a medical emergency. A significant percentage remains without a definitive diagnosis due to the large number of etiologic agents. The single most frequent cause of sporadic encephalitis around the world is herpes simplex virus type 1, although in certain locations diverse local agents should be considered such as West Nile virus or tick-borne encephalitis, among others. Patients with encephalitis require intense care measures with special emphasis on respiratory problems secondary to a depressed level of consciousness, seizures, and intracranial hypertension due to cerebral edema. Herpes encephalitis has an incidence of 4 cases per million inhabitants. Clinical presentation, together with electroencephalography, magnetic resonance imaging and cerebrospinal fluid (CSF) findings are critical to establish a diagnosis. Polymerase chain reaction (PCR) in CSF is highly sensitive and specific (> 95%), but the results can be negative during the first 3 days of the disease. The treatment of choice is currently acyclovir 10 mg/kg/8 h for 10-21 days. Whenever resistance is suspected, foscarnet is an alternative. The family of arboviruses represents another important etiologic group of encephalities. These are zoonotic diseases transmitted by mosquitoes or ticks and include alphaviruses, bunyaviruses (Toscana virus and others) and flaviviruses. The West Nile virus belongs to the latter group. There is no specific therapy and diagnosis is based on serology and PCR depending on the suspected virus.