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Hsv encephalitis.jpg
Coronal T2-weighted MR image shows high signal in the temporal lobes including hippocampal formations and parahippocampal gyrae, insulae, and right inferior frontal gyrus. A brain biopsy was performed and the histology was consistent with encephalitis. PCR was repeated on the biopsy specimen and was positive for HSV
Specialty Neurology, infectious disease
Frequency 4.3 million (2015)[1]
Deaths 150,000 (2015)[2]

Encephalitis is a sudden onset inflammation of the brain.[3] Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue. Further symptoms include seizures or convulsions, tremors, hallucinations, stroke, and memory problems.[4]

In 2015, encephalitis was estimated to have affected 4.3 million people and resulted in 150,000 deaths worldwide.[2][1] The word is from Ancient Greek ἐγκέφαλος, enképhalos "brain",[5] composed of ἐν, en, "in" and κεφαλή, kephalé, "head", and the medical suffix -itis "inflammation".[6]

Signs and symptoms[edit]

Adult patients with encephalitis present with acute onset of fever, headache, confusion, and sometimes seizures. Younger children or infants may present irritability, poor appetite and fever.[7] Neurological examinations usually reveal a drowsy or confused patient. Stiff neck, due to the irritation of the meninges covering the brain, indicates that the patient has either meningitis or meningoencephalitis.[8]


Rabies virus


Viral encephalitis can occur either as a direct effect of an acute infection, or as one of the sequelae of a latent infection, the most common causes of acute viral encephalitis are rabies virus, HSV infection, poliovirus, and measles virus.[9]

Other possible viral causes are arbovirus (St. Louis encephalitis, West Nile encephalitis virus), bunyavirus (La Crosse strain), arenavirus (lymphocytic choriomeningitis virus) and reovirus (Colorado tick virus).[10] The Powassan virus is a rare cause of encephalitis.

Bacterial and other[edit]


It can be caused by a bacterial infection, such as bacterial meningitis,[11] or may be a complication of a current infectious disease syphilis (secondary encephalitis).[12]

Certain parasitic or protozoal infestations, such as toxoplasmosis, malaria, or primary amoebic meningoencephalitis, can also cause encephalitis in people with compromised immune systems. Lyme disease or Bartonella henselae may also cause encephalitis.[citation needed]

Other bacterial pathogens, like Mycoplasma and those causing rickettsial disease, cause inflammation of the meninges and consequently encephalitis. A non-infectious cause includes acute disseminated encephalitis which is demyelinated.[13]

Limbic encephalitis[edit]

Limbic encephalitis refers to inflammatory disease confined to the limbic system of the brain, the clinical presentation often includes disorientation, disinhibition, memory loss, seizures, and behavioral anomalies. MRI imaging reveals T2 hyperintensity in the structures of the medial temporal lobes, and in some cases, other limbic structures, some cases of limbic encephalitis are of autoimmune origin.[14]

Autoimmune encephalitis[edit]

Autoimmune encephalitis signs can include catatonia, psychosis, abnormal movements, and autonomic dysregulation. Antibody-mediated anti-N-methyl-D-aspartate-receptor encephalitis and Rasmussen encephalitis are examples of autoimmune encephalitis.[15]

Encephalitis lethargica[edit]

Encephalitis lethargica is identified by high fever, headache, delayed physical response, and lethargy. Individuals can exhibit upper body weakness, muscular pains, and tremors, though the cause of encephalitis lethargica is not currently known, from 1917 to 1928, an epidemic of encephalitis lethargica occurred worldwide.[16]


Spinal tap on a newborn

Diagnosing encephalitis is done via a variety of tests:[17]

  • Brain scan, done by MRI, can determine inflammation and differentiate from other possible causes.
  • EEG, in monitoring brain activity, encephalitis will produce abnormal signal.
  • Lumbar puncture (spinal tap), this helps determine via a test using the cerebral-spinal fluid, obtained from the lumbar region.
  • Blood test
  • Urine analysis


Treatment (which is based on supportive care) is as follows:[18]


Vaccination is available against tick-borne[19] and Japanese encephalitis[20] and should be considered for at-risk individuals. Post-infectious encephalomyelitis complicating smallpox vaccination is avoidable, for all intents and purposes, as smallpox is nearly eradicated.[21] Contraindication to Pertussis immunization should be observed in patients with encephalitis.[22]


Encephalitis deaths per million persons in 2012

The number of new cases a year of acute encephalitis in Western countries is 7.4 cases per 100,000 population per year. In tropical countries, the incidence is 6.34 per 100,000 per year.[23] In 2015, encephalitis was estimated to have affected 4.3 million people and resulted in 150,000 deaths worldwide.[2][1] Herpes simplex encephalitis has an incidence of 2–4 per million population per year.[24]

See also[edit]


  1. ^ a b c GBD 2015 Disease and Injury Incidence and Prevalence Collaborators (8 October 2016). "Global, regional, and national incidence, prevalence, and years lived with disability for 310 diseases and injuries, 1990–2015: a systematic analysis for the Global Burden of Disease Study 2015". Lancet. 388 (10053): 1545–1602. PMC 5055577Freely accessible. PMID 27733282. doi:10.1016/S0140-6736(16)31678-6. 
  2. ^ a b c GBD 2015 Mortality and Causes of Death Collaborators (8 October 2016). "Global, regional, and national life expectancy, all-cause mortality, and cause-specific mortality for 249 causes of death, 1980–2015: a systematic analysis for the Global Burden of Disease Study 2015.". Lancet. 388 (10053): 1459–1544. PMC 5388903Freely accessible. PMID 27733281. doi:10.1016/S0140-6736(16)31012-1. 
  3. ^ "encephalitis". 
  4. ^ "Meningitis and Encephalitis Fact Sheet: National Institute of Neurological Disorders and Stroke (NINDS)". www.ninds.nih.gov. Retrieved 2015-08-05. 
  5. ^ "Woodhouse's English-Greek Dictionary" (in German). The University of Chicago Library. Retrieved 2013-01-10. 
  6. ^ The word seems to have had a meaning of “lithic imitation of the human brain” at first, according to the Trésor de la langue française informatisé (cf. the article on “encéphalite”). The first use in the medical sense is attested from the early 19th century in French (J. Capuron, Nouveau dictionnaire de médecine, chirurgie…, 1806), and from 1843 in English respectively (cf. the article “encephalitis” in the Online Etymology Dictionary). Retrieved 11 March 2017.
  7. ^ "Symptoms of encephalitis". NHS. Retrieved 5 January 2015. 
  8. ^ Shmaefsky, Brian; Babcock, Hilary (2010-01-01). Meningitis. Infobase Publishing. ISBN 9781438132167. 
  9. ^ Fisher, D. L.; Defres, S.; Solomon, T. (2015). "Measles-induced encephalitis". QJM. 108 (3): 177–182. PMID 24865261. doi:10.1093/qjmed/hcu113. 
  10. ^ Kennedy, P. G. E. (2004-03-01). "Viral Encephalitis: Causes, Differential Diagnosis, and Management". Journal of Neurology, Neurosurgery & Psychiatry. 75 (Suppl 1): i10–5. PMC 1765650Freely accessible. PMID 14978145. doi:10.1136/jnnp.2003.034280. 
  11. ^ Ashar, Bimal H.; Miller, Redonda G.; Sisson, Stephen D. (2012-01-01). Johns Hopkins Internal Medicine Board Review: Certification and Recertification. Elsevier Health Sciences. ISBN 1455706922. 
  12. ^ Hama, Kiwa; Ishiguchi, Hiroshi; Tuji, Tomikimi; Miwa, Hideto; Kondo, Tomoyoshi (2008-01-01). "Neurosyphilis with Mesiotemporal Magnetic Resonance Imaging Abnormalities". Internal Medicine. 47 (20): 1813–7. PMID 18854635. doi:10.2169/internalmedicine.47.0983. 
  13. ^ "Encephalitis: Practice Essentials, Background, Pathophysiology". 
  14. ^ Larner, A. J. (2013-05-02). Neuropsychological Neurology: The Neurocognitive Impairments of Neurological Disorders. Cambridge University Press. ISBN 9781107607606. 
  15. ^ Armangue, Thaís; Petit-Pedrol, Mar; Dalmau, Josep (2012-11-01). "Autoimmune Encephalitis in Children". Journal of child neurology. 27 (11): 1460–9. PMC 3705178Freely accessible. PMID 22935553. doi:10.1177/0883073812448838. 
  16. ^ encephalitis_lethargica at NINDS
  17. ^ "Encephalitis: Diagnosis". NHS Choices. Retrieved 2015-08-05. 
  18. ^ MedlinePlus Encyclopedia Encephalitis
  19. ^ "Tick-borne Encephalitis: Vaccine". International travel and health. World Health Organization. Retrieved 2 April 2013. 
  20. ^ "Japanese encephalitis". Immunization, Vaccines and Biologicals. World Health Organization. Retrieved 2 April 2013. 
  21. ^ "CDC Media Statement on Newly Discovered Smallpox Specimens". www.cdc.gov. Retrieved 2016-05-19. 
  22. ^ "Contraindications and Precautions to Commonly Used Vaccines in Adults". Vaccines. Center for Disease Control. Retrieved 2015-08-05. 
  23. ^ Jmor F, Emsley HC, et al. (October 2008). "The incidence of acute encephalitis syndrome in Western industrialised and tropical countries". Virology Journal. 5 (134): 134. PMC 2583971Freely accessible. PMID 18973679. doi:10.1186/1743-422X-5-134. 
  24. ^ Rozenberg, F; Deback C; Agut H (June 2011). "Herpes simplex encephalitis: from virus to therapy". Infectious Disorders Drug Targets. 11 (3): 235–250. PMID 21488834. doi:10.2174/187152611795768088. 

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