Japanese encephalitis overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Anthony Gallo, B.S. [2]
Overview
Japanese encephalitis (JE) virus is the leading cause of vaccine-preventable encephalitis in Asia and the western Pacific. For most travelers to Asia, the risk for JE is very low but varies based on destination, duration of travel, season, and activities. JE virus is maintained in a cycle involving mosquitoes and vertebrate hosts, mainly pigs and wading birds. Humans can be infected when bitten by an infected mosquito. Most human infections are asymptomatic or result in only mild symptoms. However, a small percentage of infected persons develop inflammation of the brain (encephalitis), with symptoms including sudden onset of headache, high fever, disorientation, coma, tremors and convulsions. About 1 in 4 cases are fatal. There is no specific treatment for JE. Patient management focuses on supportive care and management of complications. Steps to prevent JE include using personal protective measures to prevent mosquito bites and vaccination.
Historical Perspective
Japanese encephalitis was first discovered in 1871 following a large number of recurring outbreaks in the summer months. In 1930, the first vaccine was developed to prevent Japanese encephalitis; today, there are approximately 15 vaccines available.[1]
Classification
Japanese encephalitis virus is a Group IV positive-sense ssRNA virus within the Flaviridae family of viruses, and the genus Flavivirus. Japanese encephalitis virus is closely related to yellow fever virus, dengue virus, west nile virus, and St. Louis encephalitis virus.[2] Japanese encephalitis is also known as an arbovirus, or an arthropod-borne virus.
Pathophysiology
Causes
Differentiating Japanese encephalitis from Other Diseases
Epidemiology and Demographics
Risk Factors
Natural History, Complications, and Prognosis
Diagnosis
History and Symptoms
Less than 1% of people infected with Japanese encephalitis (JE) virus develop clinical illness. Mild infections occur without apparent symptoms other than fever with headache. More severe infection is marked by quick onset headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, occasional convulsions (especially in infants) and spastic (but rarely flaccid) paralysis.
Physical Examination
Signs of Japanese encephalitis which develop during the acute encephalitic stage include neck rigidity, cachexia, hemiparesis, convulsions and a raised body temperature between 38 and 41 degrees Celsius. The classical description of Japanese encephalitis includes a Parkinsonian syndrome with masklike facies, tremor, cogwheel rigidity, and choreoathetoid movements. Acute flaccid paralysis, with clinical and pathological features similar to those of poliomyelitis, has also been associated with JE.
Laboratory Findings
Diagnosis of Japanese encephalitis is based on a combination of clinical signs and symptoms and specialized laboratory tests of blood or cerebrospinal fluid. It is diagnosed by detection of antibodies in serum and CSF (cerebrospinal fluid) by IgM capture ELISA. Clinical laboratory findings might include a moderate leukocytosis, mild anemia, and hyponatremia. Cerebrospinal fluid (CSF) typically has a mild to moderate pleocytosis with a lymphocytic predominance, slightly elevated protein, and normal ratio of CSF to plasma glucose. Because humans have low or undetectable levels of viremia by the time distinctive clinical symptoms are recognized, virus isolation and nucleic acid amplification tests are insensitive and should not be used for ruling out a diagnosis of JE.
CT
MRI
Magnetic resonance imaging (MRI) of the brain is better than computed tomography (CT) for detecting Japanese encephalitis virus-associated abnormalities such as changes in the thalamus, basal ganglia, midbrain, pons, and medulla. Thalamic lesions are the most commonly described abnormality; although these can be highly specific for JE in the appropriate clinical context, they are not a very sensitive marker of JE.
Other Diagnostic Studies
EEG abnormalities in Japanese encephalitis may include theta and delta coma, burst suppression, epileptiform activity, and occasionally alpha coma.
Treatment
Medical Therapy
No specific treatments have been found to benefit patients with Japanese encephalitis, but hospitalization for supportive care and close observation is generally required. Treatment is symptomatic. Rest, fluids, and use of pain relievers and medication to reduce fever may relieve some symptoms.
Primary Prevention
The control of Japanese encephalitis is based essentially on three interventions: mosquito control, avoiding human exposure to mosquitoes and immunization. Mosquito control has been very difficult to achieve in rural settings and avoidance of exposure is difficult as Culex mosquitoes bite during day time. Immunization is the only effective method for sustainable control. Routine immunization of school-age children is currently in use in Korea, Japan, China, Thailand and Taiwan. The introduction of the JE vaccine into the Expanded Program of Immunization has helped curb the disease in countries like Thailand, Vietnam, Sri Lanka and China.[3]
Secondary Prevention
References
- ↑ Paulke-Korinek M, Kollaritsch H (2008). "Japanese encephalitis and vaccines: past and future prospects". Wien Klin Wochenschr. 120 (19-20 Suppl 4): 15–9. doi:10.1007/s00508-008-1071-9. PMID 19066766.
- ↑ Flavivirus. SIB Swiss Institute of Bioinformatics (2015). http://viralzone.expasy.org/viralzone/all_by_species/24.html Accessed on April 12, 2016
- ↑ Tauber E, Dewasthaly S (2008). "Japanese encephalitis vaccines--needs, flaws and achievements". Biol Chem. 389 (5): 547–50. PMID 18953721.