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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Overview
Tick-borne encephalitis commonly presents itself as a biphasic infection. Following an incubation period of 7 to 14 days, a patient will experience an early phase including non-specific flu like symptoms. [1] Once early phase symptoms reside, a remission phase occurs in which a patient experiences lessened severity of symptoms or appears entirely asymptomatic. Infection will conclude at this point within nearly two-thirds of patients. However, a second phase will onset within the remaining one-third. This phase includes the infection of the central nervous system. Progression of the disease at this point will present itself as aseptic meningitis, encephalitis, or myelitis. Complications are commonly associated with this later phase, including the aforementioned meningitis and encephalitis as well as long term cognitive dysfunction and limb paresis. The prognosis is usually good for the majority of infected patients. Many patients will appear to be asymptomatic during the course of infection. For individuals displaying signs and symptoms, the clinical manifestations will typically reside after the first wave of non-specific flu like symptoms. However as mentioned earlier, a second phase can occur. The prognosis for patients undergoing this course of infection is still fairly good. Yet, patients experience an infection of the central nervous system are more prone to long term complications.
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.
- ↑ Signs and Symptoms Centers for Disease Control and Prevention. http://www.cdc.gov/vhf/tbe/symptoms/index.html Accessed February 9, 2016