Tick-Borne Encephalitis: Symptoms, Types, Causes and Treatment

Tick-borne encephalitis (TBE) is a growing public health concern across Europe and Asia, impacting thousands of people annually. Despite being vaccine-preventable, the incidence is rising and the clinical spectrum is wide—from mild, flu-like illness to severe, life-changing neurological complications. In this article, we’ll take a deep dive into the symptoms, types, causes, and treatments for tick-borne encephalitis, drawing on the latest scientific research and expert consensus.

Symptoms of Tick-Borne Encephalitis

Tick-borne encephalitis presents with a wide array of symptoms, making it a challenging disease to diagnose early. Symptoms can range from non-specific fever to severe neurological impairment. Understanding the symptomatology is crucial for early recognition and effective medical intervention.

Phase	Main Symptoms	Severity Range	Sources
Initial	Fever, headache, fatigue, muscle pain	Mild to moderate	1 2 3 4 12
Neurological	Meningitis, meningoencephalitis, paralysis	Moderate to severe	1 2 4 7 12
Sequelae	Cognitive issues, paresis, tremor, fatigue	Mild to permanent	1 2 4 12

Table 1: Key Symptoms

The Biphasic Course

A hallmark of classic TBE is its biphasic (two-phase) presentation, but variations are common:

• First Phase: Resembles a generic viral illness, with fever, fatigue, headache, muscle aches, and sometimes gastrointestinal symptoms. This phase often lasts several days and may resolve completely before the next phase begins.
• Second Phase: Characterized by central nervous system involvement, including symptoms such as stiff neck, severe headache, confusion, photophobia, vomiting, and neurological deficits (e.g., limb weakness, tremors, cranial nerve palsies) 1 2 4 12.

Neurological Manifestations

The second phase can progress to several neurological syndromes:

• Meningitis: Inflammation of the membranes covering the brain and spinal cord; presents with headache, neck stiffness, and photophobia.
• Meningoencephalitis: Involvement of both the brain and its covering membranes; symptoms include altered consciousness, seizures, confusion, and sometimes behavioral changes.
• Meningomyelitis: Extension into the spinal cord, potentially causing paralysis 2 4 7 12.
• Cranial Nerve Palsies and Paresis: Some patients develop paralysis affecting facial muscles or limbs 2.
• Chronic/Progressive and Abortive Forms: Rarely, TBE may present as a chronic progressive disease or abortive (mild, self-limited) illness 1 7 12.

Long-Term Sequelae

Up to 50% of survivors may develop post-encephalitic syndrome, with symptoms such as:

• Persistent fatigue
• Cognitive impairment (memory, attention deficits)
• Paresthesia (abnormal sensations)
• Tremors
• Limb weakness or paralysis 1 2 4 12

Men and older adults are at higher risk for severe outcomes and long-term sequelae 1 2 4.

Types of Tick-Borne Encephalitis

TBE is not a single, uniform disease. It encompasses several types, distinguished by viral subtype, geography, and clinical presentation. Understanding the distinctions between types is important for grasping the disease’s variable severity and risk.

Type/Subtype	Geographic Distribution	Clinical Severity	Sources
European (TBEV-Eu)	Central/Eastern Europe	Mild to moderate	4 7 8 10 12 13
Far Eastern (TBEV-FE)	Far Eastern Russia, China, Japan	Often severe	4 7 8 9 12 13
Siberian (TBEV-Sib)	Siberia, Northern Asia	Mild/chronic forms	4 7 8 9 12 13
Baikalian (TBEV-Bkl)	Siberia (Lake Baikal region)	To be determined	7 8
Himalayan (TBEV-Him)	Qinghai-Tibet Plateau, China	Unknown	6 7

Table 2: Main Types and Subtypes of TBE

Major Subtypes Explained

• European Subtype (TBEV-Eu):
  Common in Central and Eastern Europe. Typically causes a biphasic illness; the acute phase is milder and long-term outcomes are generally better. Mortality is less than 2% 4 7 12 13.

• Far Eastern Subtype (TBEV-FE):
  Found in the Russian Far East, China, and Japan. More likely to cause severe and sometimes fatal disease, with prominent neurological involvement. Chronic or hemorrhagic forms can occur 7 9 12 13.

• Siberian Subtype (TBEV-Sib):
  Prevalent in Siberia and parts of Northern Asia. Often causes milder acute disease but is notable for chronic, progressive forms in some patients 7 8 9 12 13.

Recently Described and Emerging Subtypes

• Baikalian (TBEV-Bkl):
  Identified in Siberia’s Lake Baikal region, now considered a distinct genetic lineage 7 8.

• Himalayan (TBEV-Him):
  Discovered in wild rodents on the Qinghai-Tibet Plateau, China. Its impact on humans is still under study 6 7.

Clinical Variants

• Abortive TBE:
  A mild, short-lived form resembling a nonspecific viral illness 1 12.
• Chronic Progressive TBE:
  Rare, mostly associated with Siberian and Far Eastern subtypes; manifests as slowly worsening neurological deficits 7 12.

Causes of Tick-Borne Encephalitis

TBE is a zoonotic infection—passed from animals to humans—primarily via tick bites. The complexity of its ecology and transmission patterns underscores the importance of prevention and surveillance.

Agent/Vector	Transmission Route	Risk Factors	Sources
TBE Virus	Tick bite (Ixodes spp.)	Outdoor activity, endemic regions	4 11 12 13
Ixodes ricinus	Bite	Europe, central Asia	4 11 13
Ixodes persulcatus	Bite	Russia, Asia	4 11 13
Rare: Unpasteurized dairy	Oral	Unpasteurized milk products	12

Table 3: Main Causes and Transmission Factors

The Causative Agent: TBE Virus

• Tick-Borne Encephalitis Virus (TBEV):
  A member of the Flavivirus genus, TBEV is the primary cause of TBE in humans. There are several subtypes, as described in the previous section 4 7 11 13.

Vectors and Reservoirs

• Main Vectors:
  • Ixodes ricinus (castor bean tick): Prevalent in Europe and parts of Asia.
  • Ixodes persulcatus (taiga tick): Found in Russia and northern Asia 4 11 13.
• Reservoir Hosts:
  Small mammals (e.g., rodents), birds, and wild vertebrates maintain the virus in nature 11 13.

Modes of Transmission

• Tick Bite:
  The vast majority of cases result from the bite of an infected tick. The risk is highest during periods of peak tick activity—spring through autumn 4 11 12.
• Unpasteurized Dairy Products:
  Rarely, TBEV can be transmitted by consuming unpasteurized milk or cheese from infected animals (mainly goats, sheep, or cows) 12.
• Person-to-person Transmission:
  There is no evidence of direct human-to-human transmission.

Risk Factors

• Spending time in grassy, wooded, or rural areas in endemic regions.
• Occupational or recreational exposure (e.g., forestry workers, hikers).
• Not being vaccinated, especially in regions with a high incidence of TBE 4 12 16.

Treatment of Tick-Borne Encephalitis

Currently, there is no specific antiviral treatment for TBE, making supportive care and prevention through vaccination the mainstays of management. Research into new therapies is ongoing.

Approach	Description	Efficacy/Availability	Sources
Supportive care	Hospitalization, symptom management	Mainstay	4 12 14 16
ICU/ventilation	For severe/neurological cases	As needed	4 16
Antivirals	Experimental (e.g., nucleoside inhibitors)	In research phase	15 18
Immunoglobulin	IVIG trials, some benefit in severe cases	Not standard, region-specific	7 17
Vaccination	Highly effective prevention	Available in Europe, Asia	4 12 14 16

Table 4: Main Treatment and Prevention Strategies

Supportive Care

• Hospitalization:
  Most patients with neurological symptoms require admission. Care includes monitoring and treating fever, pain, and complications like seizures or respiratory distress 4 12 14 16.
• Intensive Care:
  Severe cases may need mechanical ventilation, especially if brainstem involvement or paralysis occurs 4 16.

Investigational Therapies

• Antiviral Agents:
  No approved antiviral drugs exist for TBE. However, laboratory research is exploring nucleoside analogues (e.g., 7-deaza-2′-CMA) and protease inhibitors targeting the TBEV viral machinery, with some compounds showing promise in preclinical studies 15 18.
• Immunoglobulin Therapy:
  High-dose intravenous immunoglobulin (IVIG) containing TBEV-specific antibodies has shown protective effects in animal studies and is used in some countries (e.g., Russia, Kazakhstan) for post-exposure prophylaxis or severe cases. Its use is limited elsewhere due to concerns about safety and efficacy 7 17.

Vaccination

• Prevention is Key:
  Vaccination is the most effective preventive measure. Multiple vaccines are available in Europe and parts of Asia, offering robust protection for people living in or traveling to endemic areas 4 12 14 16.
• Who Should Be Vaccinated?
  • Residents of, or travelers to, endemic areas
  • Occupationally exposed individuals
  • Anyone engaging in outdoor activities in regions with TBE risk 4 12 16

Other Measures

• Tick Bite Prevention:
  • Use of repellents and protective clothing
  • Prompt tick removal
  • Avoiding unpasteurized dairy products in endemic regions 12

Conclusion

Tick-borne encephalitis is a complex, potentially life-altering disease with a rising incidence worldwide. Here’s a summary of key points:

• Symptoms:

  • Range from mild, flu-like illness to severe neurological deficits; biphasic course is characteristic, but variants exist.
  • Up to half of survivors may experience long-term sequelae 1 2 4 12.

• Types:

  • Caused by several subtypes of TBEV (European, Far Eastern, Siberian, and recently described Baikalian and Himalayan subtypes), each with differing geographic distributions and clinical outcomes 4 6 7 8.

• Causes:

  • Transmitted primarily via Ixodes tick bites; small mammals serve as reservoirs. Rarely, unpasteurized dairy products can transmit the virus 4 11 12 13.

• Treatment:

  • No specific antiviral therapy exists; supportive care is the mainstay.
  • Vaccination is highly effective and strongly recommended for individuals at risk 4 12 14 16.

• Emerging Research:

  • New antiviral drugs and immunotherapies are under investigation, but prevention through vaccination remains paramount 7 15 17 18.

Staying informed, practicing tick avoidance, and considering vaccination are the best strategies to protect yourself and your loved ones from TBE.