Encephalitis

CASES/YEAR

200,000 (US); 4,000,000 (Global)

CATEGORY

Localized Infections

AGENT TYPE

Mixed

OTHER NAMES

Acute viral encephalitis; Viral infection of the brain parenchyma;

ACUITY

Acute-Severe

INCUBATION

Estimated: days to weeks;

INITIAL SYMPTOMS

Headache and fever with altered mental status, often with seizures and focal neurological deficits; [Merck Manual, p. 1850-1]

PRECAUTIONS

See specific etiological agents.

COMMENTS

Encephalitis is caused by viral infection of the brain parenchyma, either primary or secondary (postinfectious). The best examples of primary encephalitis as a late consequence of a viral infection are HIV encephalopathy, subacute sclerosing panencephalitis (reactivation of measles virus), and progressive multifocal leukoencephalopathy (reactivation of JC virus). [Merck Manual, p. 1851] Aseptic meningitis and encephalitis are caused by the same organisms. Sporadic cases of encephalitis are usually caused by the herpes-viruses (HSV, VZV, and EBV). Epidemic cases of encephalitis are usually caused by arboviruses (West Nile virus in the US). In CSF analysis, PCR tests are rapid and reliable for HSV, EBV, VZV, CMV, HHV-6 and enteroviruses. West Nile virus IgM antibodies are also diagnostic. [Harrisons, p. 1058-9] Any history of travel, sexual contact, animal contact, or ticks/insect bites? MRI is normal early; may show temporal lobe changes characteristic of HSV infection; treat empirically with acyclovir while awaiting test results. Other treatable viral causes are VZV, B virus, HHV6, and CMV. [ABX Guide] Parkinsonism, choreoathetosis, opisthotonus and other movement disorders occur in about 25% of patients with Japanese encephalitis and other flavivirus infections. [PPID, p. 1244] Lumbar puncture is indicated unless severely increased intracranial pressure. The typical CSF pattern is the same in both viral meningitis and encephalitis. [Harrison ID, p. 346] Cranial nerve palsies occur infrequently in viral encephalitis relative to several nonviral CNS infections (Lyme disease, syphilis, tuberculosis, and fungal infection) in which they are common. [PPID, p. 1230] See "Viral encephalitides, mosquito-borne."

DIAGNOSTIC

MRI and CSF analysis (including PCR for HSV); CT is less sensitive, but rapidly available and helpful prior to LP; CSF: Lymphocytic pleocytosis; Protein mildly elevated; Glucose normal; [Merck Manual, p. 1852-3]

SCOPE

Global

SIGNS & SYMPTOMS

• >fever
• >myalgia
• E dysphagia
• E pharyngitis
• G abdominal pain
• G diarrhea
• G nausea, vomiting
• N confusion, delirium
• N headache
• N lethargy
• N muscle weakness
• N opisthotonus
• N paresthesia
• N seizure
• N stiff neck
• R cough
• S rash (exanthem)
• *cranial neuropathy
• *encephalitis
• *meningitis
• *paralysis
• *stupor, coma

ANTIMICROBIC

Yes

VACCINE

No

ENTRY

Inhalation, Ingestion, Needle (Includes Drug Abuse), Scalpel or Transfusion, Skin or Mucous Membranes (Includes Conjunctiva), Animal Bite, Swimming, Sexual Contact

VECTOR

Fleas, Biting Flies, Lice, Mites, Mosquitoes, Ticks

SOURCE

Person-to-Person, Human Fecal-Oral, Fecally Contaminated Soil, Animal Excreta, Animal Tissue, Soil or Dust (Ingesting or Inhaling), Eating Contaminated Food, Eating Contaminated or Infected Meat, Eating Infected or Toxin-Containing Fish, Eating Contaminated Mollusks or Crustacean, Eating Unpasteurized Milk or Cheese, Eating Contaminated Produce, Waterborne (Ingesting, Inhaling, or Swimming)

RESERVOIR

Birds and Poultry, Cattle, Goats and Sheep, Cats, Deer, Elk and Antelope, Dogs, Fish and Shellfish, Horses, Monkeys, Rabbits, Rodents, Swine, Human, Wild Animals

RISK FACTORS

• AIDS patients
• Cancer patients

DRUG LINK

Merck Manual: Encephalitis

REFERENCES FOR CASES/YEAR

1. (US) Estimated 20,000 cases per year, but number is likely to be much larger; [Harrison ID, p. 346] Use correction factor of 10 for reported diseases: 20,000 X 10 = 200,000;
2. (Global) 20 X US cases/yr;