Tick-borne encephalitis natural history, complications and prognosis
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Ilan Dock, B.S.
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Tick-borne encephalitis Microchapters |
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Diagnosis |
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Treatment |
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Overview
Natural history
- Two thirds of infected individuals are asymptomatic and will not display any clinical manifestations.
- Incubation period will last an average of 8 days. However incubation periods have been shown to range from 4-28 days.
- Characteristic biphasic course:
- Early phase:
- Disease will begin with the onset of nonspecific febrile illness accompanied by a headache, myalgia, and fatigue.
- The early phase of the biphasic course will commonly occur over the course of several days.
- Following common symptoms of the early infection phase, patient may display an afebrile and relatively asymptomatic period.
- Nearly two-thirds of patients have been reported to have recovered without any further illness, following the completion of the first phase.
- Late phase:
- As the disease progresses the onset of a second phase may result in central nervous system involvement including aseptic meningitis, encephalitis, or myelitis.
- Further findings within the progression of tick borne-encephilitis include meningeal signs, altered mental status, cognitive dysfunction, ataxia, rigidity, seizures, tremors, cranial nerve palsies, and limb paresis.
Complications
- The majority of complications associated with tick-borne encephilitis are commonly developed during the second phase. Complication may include:
- Aseptic meningitis
- Encephalitis
- Myelitis
- Meningeal signs
- Altered mental status
- Cognitive dysfunction
- Ataxia
- Rigidity
- Seizures
- Tremors
- Cranial nerve palsies
- Limb paresis
Progressive form and Amyotrophic Lateral Sclerosis
The TBE virus is a slow virus; it can take decades to become fulminant. This is termed Progressive Form of the TBE Virus (PFTBE). In 1983 in Russia a follow-up study was done of patients with acute TBE 2-22 years later. 68% developed PFTBE, the "overwhelming majority" of these developing ALS, Amyotrophic Lateral Sclerosis. The first isolation of a TBE virus connected with ALS was in 1975 when 70% of the ALS cases in Hamburg, Germany were found to have contact with this virus. In 1978, ALS was reproduced in laboratory animals by inoculation of the Schu virus, a TBE flavivirus, taken from the CSF of a patient with ALS. In regard to the sexual and vertical transmission of the TBE virus, it is thought provoking that conjugal and familial ALS have both been documented.
Prognosis
- The prognosis is usually good for two-thirds of individuals diagnosed with tick-borne encephilitis. These patient will remain asymptomatic for the duration of the infection.
- More severe cases have been associated with ages about 50 years as well as young children. Though severity in young children is less often reported than in elderly populations.
- Prognosis also depends on subtype. European subtypes are commonly associated with lesser to mild symptoms while Far Eastern subtypes are associated with more severe cases and a case fatality ratio of 20-40%.
- In humans, the disease is lethal in approximately 1.2% of cases and leaves 15-20% of its survivors with permanent neurological damage.