Tick-Borne Encephalitis (TBE): Symptoms, Vaccine & Prevention

What Is Tick-Borne Encephalitis (TBE)?

Tick-borne encephalitis (TBE) is a serious viral infection caused by the TBE virus (TBEV), transmitted primarily through the bite of infected ticks. The virus can cause inflammation of the brain (encephalitis) and the protective membranes surrounding the brain and spinal cord (meningitis), leading to potentially severe neurological complications.

TBE is one of the most important tick-borne infections in Europe and Asia, with approximately 10,000 to 15,000 clinical cases reported annually across endemic regions. The disease is caused by a flavivirus closely related to other mosquito and tick-borne viruses, including those responsible for dengue fever, yellow fever, and Japanese encephalitis. Three main subtypes of the TBE virus exist: European (Western), Siberian, and Far Eastern, each with somewhat different clinical characteristics and geographic distributions.

The European subtype, transmitted mainly by the tick species Ixodes ricinus, causes a milder form of the disease compared to the Far Eastern subtype transmitted by Ixodes persulcatus. However, all subtypes can lead to serious neurological complications and long-term health consequences. Understanding TBE is particularly important for travelers, outdoor workers, and residents of endemic areas, as the disease is entirely preventable through vaccination.

Unlike many infectious diseases that have decreased with improved public health measures, TBE incidence has been increasing in recent decades. Climate change, changes in land use, increased outdoor recreational activities, and improved surveillance and diagnostic capabilities have all contributed to rising case numbers. The geographic range of TBE has also been expanding, with new endemic foci being identified in previously unaffected areas.

How TBE Differs from Lyme Disease

While both TBE and Lyme disease are transmitted by ticks, they are fundamentally different infections requiring different approaches to prevention and treatment. Lyme disease is caused by bacteria (Borrelia species) and can be treated effectively with antibiotics if diagnosed early. TBE, being viral, cannot be treated with antibiotics and has no specific antiviral therapy available.

Another crucial difference lies in transmission timing. Lyme disease bacteria require approximately 24-48 hours of tick attachment for transmission, making prompt tick removal an effective preventive measure. In contrast, TBE virus resides in the tick's salivary glands and can be transmitted within minutes of the tick beginning to feed. This rapid transmission makes vaccination the cornerstone of TBE prevention rather than relying solely on tick avoidance and removal.

What Are the Symptoms of TBE?

TBE symptoms typically occur in two phases: an initial flu-like phase with fever, headache, muscle pain, and fatigue lasting about one week, followed by a symptom-free interval of 1-3 weeks. In approximately one-third of cases, a second phase develops with high fever, severe headache, neck stiffness, confusion, and potentially paralysis.

The clinical presentation of TBE follows a characteristic biphasic pattern in most symptomatic cases, though it's important to note that many infections remain asymptomatic or cause only very mild illness. When symptoms do occur, the disease progression can be divided into distinct phases, each with its own set of clinical manifestations and implications for patient management.

First Phase: Viremic Stage

The first phase of TBE typically begins 4 to 28 days after an infected tick bite, with most people developing symptoms within 7 to 14 days. During this phase, the virus circulates in the bloodstream (viremia), causing non-specific flu-like symptoms that may be easily mistaken for a common viral illness. The initial symptoms usually include:

• Fever: Usually moderate, ranging from 38-39°C (100.4-102.2°F)
• Headache: Often described as dull and persistent
• Muscle pain (myalgia): Generalized aching throughout the body
• Fatigue and malaise: General feeling of unwellness and exhaustion
• Loss of appetite: Reduced desire to eat
• Nausea: Some patients experience mild gastrointestinal symptoms

This first phase typically lasts between 2 to 7 days, after which symptoms resolve and most patients feel they are recovering. Approximately two-thirds of infected individuals will recover completely at this stage without developing further complications. However, for the remaining one-third, a more serious phase of the illness lies ahead.

Symptom-Free Interval

Following the initial phase, patients experience an apparent recovery period lasting anywhere from 1 to 21 days, with most symptom-free intervals lasting about one week. During this time, patients feel well and may assume they have recovered from a minor viral illness. This asymptomatic period occurs while the virus crosses the blood-brain barrier and begins to affect the central nervous system.

Second Phase: Neurological Stage

The second phase of TBE represents the most serious manifestation of the disease and occurs in approximately 20-30% of symptomatic patients. This phase begins abruptly with the return of high fever and the development of neurological symptoms indicating central nervous system involvement. The severity of neurological disease varies widely, from mild meningitis to severe encephalitis with life-threatening complications.

Common symptoms during the neurological phase include:

• High fever: Often exceeding 39°C (102.2°F)
• Severe headache: Intense and unrelenting
• Neck stiffness (meningismus): Classic sign of meningeal inflammation
• Photophobia: Painful sensitivity to light
• Phonophobia: Painful sensitivity to sound
• Nausea and vomiting: Often severe
• Confusion and altered consciousness: Ranging from mild disorientation to coma
• Seizures: Occur in some cases
• Paralysis: Particularly affecting the shoulders and upper arms
• Tremors: Involuntary shaking movements
• Ataxia: Problems with coordination and balance

TBE Symptoms in Children

Children who become infected with TBE generally experience milder illness compared to adults. The immune system response in children typically controls the infection more effectively, resulting in fewer cases progressing to the neurological phase. When neurological involvement does occur in children, it is usually limited to meningitis rather than the more severe encephalitis seen in adults.

However, children are not immune to serious complications, and any child showing symptoms of neurological involvement should receive prompt medical attention. Parents in endemic areas should be vigilant about checking children for ticks after outdoor activities and consider TBE vaccination for children who are frequently exposed to tick habitats.

What Causes TBE and How Is It Transmitted?

TBE is caused by the tick-borne encephalitis virus (TBEV), a flavivirus transmitted primarily through the bite of infected ticks. The virus can also rarely be transmitted through consumption of unpasteurized dairy products from infected animals. The virus is present in the tick's saliva and can be transmitted within minutes of attachment.

Understanding the transmission cycle of TBE is essential for implementing effective prevention strategies. The TBE virus maintains itself in nature through a complex cycle involving ticks, small mammals, and other vertebrate hosts. Humans are incidental hosts who do not play a role in maintaining the viral cycle but can become infected when bitten by an infected tick.

The Tick Vector

Two main tick species are responsible for transmitting TBE to humans. In Europe, the primary vector is Ixodes ricinus, commonly known as the castor bean tick or sheep tick. This species is found throughout Europe and into parts of North Africa and Western Asia. In Russia and parts of Asia, Ixodes persulcatus, the taiga tick, serves as the main vector. Both species can remain infected with TBEV throughout their life stages and pass the virus to their offspring (transovarial transmission).

Ticks become infected when they feed on viremic animals, particularly small rodents that serve as the primary reservoir hosts. The virus then persists in the tick through its various life stages - larva, nymph, and adult - making any stage capable of transmitting infection to humans. However, nymphs and adult female ticks are most commonly implicated in human infections because of their larger size, longer feeding times, and greater likelihood of encountering humans.

Rapid Transmission Time

One of the most important characteristics of TBE transmission that distinguishes it from Lyme disease is the speed at which the virus can be transferred. Unlike Lyme disease, which requires prolonged tick attachment for bacterial transmission, TBEV is present in the tick's salivary glands and begins to be transmitted almost immediately when the tick starts feeding. Studies suggest that virus transmission can occur within the first few minutes of tick attachment, making the traditional advice of "check for ticks within 24 hours" insufficient for TBE prevention.

This rapid transmission has significant implications for prevention strategies. While prompt tick removal remains important for reducing the risk of Lyme disease and other tick-borne infections, it cannot be relied upon as the primary means of TBE prevention. This is why vaccination is so strongly recommended for anyone with regular exposure to tick habitats in endemic areas.

Alternative Transmission Routes

While tick bites account for the vast majority of TBE cases, the virus can also be transmitted through consumption of unpasteurized dairy products, particularly raw milk and cheese from infected goats, sheep, or cows. This alimentary transmission route is more common in certain regions where raw dairy consumption is culturally prevalent. Outbreaks linked to contaminated dairy products have been documented in several European countries.

Laboratory-acquired infections have been reported among researchers working with live virus, and theoretical transmission through blood transfusion or organ transplantation is possible, though no confirmed cases have been documented. Person-to-person transmission does not occur under normal circumstances.

Where Is TBE Found Geographically?

TBE is endemic across a vast region extending from Western Europe to Japan, including Central and Eastern Europe, Scandinavia, Russia, China, and other parts of Asia. High-risk areas include forested and rural regions where tick populations thrive, particularly during spring through autumn when ticks are most active.

The geographic distribution of TBE spans approximately 27 countries in Europe and extends across Russia into Asia. The endemic area has been gradually expanding over recent decades, with new foci of transmission being identified in previously unaffected regions. Understanding where TBE is present helps guide vaccination recommendations and travel health advice.

European Endemic Areas

In Europe, TBE is found in a broad arc extending from France and Switzerland in the west through Central Europe to Scandinavia in the north and the Baltic states and Russia in the east. The countries with the highest incidence rates include:

• Baltic States: Lithuania, Latvia, and Estonia have some of the highest TBE incidence rates in Europe
• Czech Republic: Historically high endemic activity
• Slovenia: High incidence, particularly in central and northeastern regions
• Austria: Once had high rates before widespread vaccination programs
• Germany: Southern regions, particularly Bavaria and Baden-Württemberg
• Poland: Northeastern regions have highest risk
• Sweden: Coastal areas around Stockholm and Uppsala, spreading northward
• Finland: Åland Islands and coastal regions
• Switzerland: Northeastern and central cantons

Russian and Asian Endemic Areas

Russia has the largest TBE-endemic area in the world, extending from the European part through Siberia to the Far East. The Siberian and Far Eastern regions are affected by different viral subtypes (Siberian and Far Eastern) that can cause more severe disease with higher mortality rates than the European subtype. Other Asian countries with documented TBE activity include China, Mongolia, Japan, and South Korea.

Seasonal Risk Patterns

TBE transmission follows the activity patterns of tick vectors, which are closely tied to environmental conditions. In most endemic areas, the primary transmission season extends from March/April through October/November, with peak activity during late spring and early autumn. However, unusually warm weather can extend tick activity into winter months, and climate change has been associated with earlier spring emergence and later autumn activity of ticks.

The risk of TBE transmission varies not only by geographic region but also by specific habitat. Ticks are most abundant in deciduous and mixed forests, areas with thick underbrush, tall grass, and leaf litter. Forestry workers, hunters, mushroom and berry foragers, hikers, and campers face elevated exposure risks.

How Can I Protect Myself with TBE Vaccination?

TBE vaccination is the most effective way to prevent tick-borne encephalitis, providing over 95% protection after completing the primary series. The standard vaccination schedule consists of 3 doses given over 5-12 months, with booster doses recommended every 3-5 years depending on age and ongoing risk.

Vaccination against TBE is the cornerstone of disease prevention and is highly recommended for anyone living in or traveling to endemic areas where they may be exposed to ticks. The vaccines available are based on inactivated (killed) virus and have an excellent safety profile with demonstrated high efficacy. Multiple vaccines are available depending on geographic location, including FSME-IMMUN and Encepur in Europe and TBE-Moscow and EnceVir in Russia.

Standard Vaccination Schedule

For most adults under age 50, the primary vaccination series consists of three doses administered over a period of 5-12 months:

• First dose: Given at the initial visit
• Second dose: Administered 1-3 months after the first dose
• Third dose: Given 5-12 months after the second dose

Following the primary series, the first booster dose is typically recommended 3 years later, with subsequent boosters every 5 years for people under 50 and every 3 years for those over 50. The more frequent boosters for older adults account for the age-related decline in immune response.

Accelerated Vaccination Schedules

For individuals who need faster protection, such as travelers with limited time before departure, accelerated schedules are available. These typically involve giving doses at shorter intervals (such as days 0, 7, and 21) to achieve protective immunity more quickly. While accelerated schedules provide earlier protection, standard schedules may produce more durable immunity, so a regular booster schedule should still be followed.

Vaccination for Special Groups

People aged 50 years and older, as well as those with immunocompromising conditions, may need a modified vaccination schedule with four doses in the first year to achieve adequate protection. This is because immune responses to vaccines can be less robust in these populations. Consultation with a healthcare provider is recommended to determine the optimal vaccination approach.

Children can be vaccinated against TBE from one year of age, using pediatric vaccine formulations. The vaccination schedule for children is similar to that for adults, and the vaccine is generally well-tolerated in pediatric populations. Vaccination is recommended for children who live in or will travel to endemic areas where they may be exposed to ticks.

Vaccine Side Effects

TBE vaccines are generally well-tolerated, with most side effects being mild and self-limiting. Common reactions include pain, redness, and swelling at the injection site, as well as mild systemic symptoms such as headache, fatigue, muscle pain, and low-grade fever. These symptoms typically resolve within a few days without treatment.

Serious adverse events are rare. As with any vaccine, allergic reactions including anaphylaxis can occur but are extremely uncommon. Individuals with known severe allergies to any vaccine component should discuss this with their healthcare provider before vaccination.

What Other Ways Can I Prevent TBE?

While vaccination is the most effective prevention, additional protective measures include wearing long clothing when in tick habitats, using tick repellents containing DEET or permethrin, performing thorough tick checks after outdoor activities, and avoiding consumption of unpasteurized dairy products in endemic areas.

Although vaccination provides the most reliable protection against TBE, comprehensive prevention involves multiple strategies that reduce the risk of tick bites. These measures are particularly important for individuals who cannot be vaccinated or who are awaiting completion of their vaccination series. However, it's crucial to remember that tick avoidance measures alone are not sufficient for TBE prevention due to the rapid transmission of the virus.

Personal Protective Measures

When spending time in areas where ticks are present, several behavioral and clothing-based measures can reduce the likelihood of tick bites:

• Wear appropriate clothing: Long-sleeved shirts, long pants tucked into socks or boots, and closed-toe shoes provide a physical barrier against ticks. Light-colored clothing makes it easier to spot ticks.
• Use tick repellents: Products containing DEET (20-30%) applied to exposed skin, or permethrin applied to clothing, can deter ticks. Permethrin-treated clothing remains effective through multiple washes.
• Stay on trails: Avoid walking through tall grass, brush, and leaf litter where ticks are most abundant.
• Create tick-safe zones: In endemic areas, keeping lawns mowed, removing leaf litter, and creating gravel or wood chip barriers between lawns and wooded areas can reduce tick populations near homes.

Tick Checks and Removal

After spending time outdoors in tick habitats, thorough tick checks should be performed on yourself, children, and pets. Pay particular attention to warm, hidden areas such as behind the ears, in the hairline, armpits, groin, behind the knees, and around the waist. Showering within two hours of coming indoors can help wash off unattached ticks.

If a tick is found attached, it should be removed promptly using fine-tipped tweezers. Grasp the tick as close to the skin surface as possible and pull upward with steady, even pressure. Avoid twisting or jerking, which can cause the mouthparts to break off and remain in the skin. After removal, clean the bite area with rubbing alcohol or soap and water.

While prompt tick removal significantly reduces the risk of Lyme disease transmission, remember that TBE virus can be transmitted much more rapidly. A tick removed within hours of attachment may have already transmitted TBE virus if it was infected. This underscores why vaccination remains the primary prevention strategy for TBE.

Dietary Precautions

In some endemic areas, particularly in Central and Eastern Europe, TBE can be transmitted through consumption of unpasteurized dairy products from infected animals. To avoid this route of transmission:

• Only consume pasteurized milk and dairy products
• Avoid raw milk cheeses from endemic areas, especially during tick season
• Be cautious of homemade or artisanal dairy products when traveling in endemic regions

How Is TBE Diagnosed?

TBE is diagnosed through a combination of clinical symptoms, exposure history, and laboratory testing. Blood tests detect specific antibodies (IgM and IgG) against TBE virus, while cerebrospinal fluid analysis may be performed in patients with neurological symptoms to confirm central nervous system involvement.

Diagnosing TBE requires a high index of clinical suspicion, particularly during the first phase of illness when symptoms are non-specific. Healthcare providers must consider TBE in any patient presenting with compatible symptoms who has potential exposure to ticks in endemic areas, even if a specific tick bite was not noticed—many patients never observe the tick that transmitted infection.

Clinical Assessment

The diagnosis of TBE begins with a thorough clinical evaluation including detailed history of potential tick exposure, travel to endemic areas, and consumption of unpasteurized dairy products. The characteristic biphasic illness pattern, when present, can be highly suggestive of TBE. Physical examination during the neurological phase may reveal signs of meningeal irritation (neck stiffness, Kernig's sign, Brudzinski's sign) and neurological deficits.

Laboratory Diagnosis

Serological testing forms the cornerstone of TBE laboratory diagnosis. The most commonly used tests detect:

• IgM antibodies: Indicate recent or acute infection; typically detectable at symptom onset or shortly thereafter
• IgG antibodies: Indicate current or past infection; rise later and persist longer than IgM

In patients with neurological symptoms, a lumbar puncture (spinal tap) may be performed to analyze cerebrospinal fluid (CSF). Typical findings in TBE meningoencephalitis include elevated white blood cell count (pleocytosis) with lymphocyte predominance, elevated protein levels, and normal glucose levels. Detection of TBE-specific antibodies in CSF, particularly an elevated CSF/serum antibody ratio, confirms central nervous system infection.

PCR (polymerase chain reaction) testing to detect viral genetic material can be performed but is only useful during the initial viremic phase; by the time neurological symptoms develop, the virus is typically no longer detectable in blood or CSF.

How Is TBE Treated?

There is no specific antiviral treatment for TBE. Management is entirely supportive, focusing on symptom relief and prevention of complications. Patients with severe neurological involvement may require hospitalization for intensive monitoring, treatment of brain swelling, and management of respiratory complications.

The absence of specific antiviral therapy for TBE underscores the critical importance of prevention through vaccination. Once infection occurs, the body's immune system must clear the virus on its own, with medical care aimed at supporting the patient through the illness and managing complications as they arise.

Supportive Care

For patients with mild TBE limited to the first phase or with uncomplicated meningitis, treatment typically includes:

• Rest: Adequate rest supports immune function and recovery
• Hydration: Maintaining fluid intake, particularly if vomiting is present
• Pain management: Acetaminophen or ibuprofen for fever and headache
• Anti-nausea medications: To control vomiting if needed

Hospital Care for Severe Cases

Patients who develop encephalitis or severe meningoencephalitis typically require hospital admission, often to an intensive care unit. Hospital-based management may include:

• Intravenous fluids: To maintain hydration and electrolyte balance
• Treatment of cerebral edema: Corticosteroids and other measures to reduce brain swelling
• Seizure management: Anticonvulsant medications if seizures occur
• Respiratory support: Mechanical ventilation if breathing is compromised
• Prevention of secondary complications: Including blood clot prevention and nutritional support

Rehabilitation

Patients who survive severe TBE may require extensive rehabilitation to address neurological deficits. Depending on the nature and extent of complications, rehabilitation may involve physical therapy, occupational therapy, speech therapy, and cognitive rehabilitation. The recovery process can take months to years, and some patients may have permanent neurological sequelae.

What Is the Prognosis and Long-Term Outlook?

Most TBE patients recover fully, particularly those with mild illness or isolated meningitis. However, 30-60% of patients with encephalitis experience long-term neurological symptoms including memory problems, concentration difficulties, and motor impairments. Mortality rates vary from less than 2% for European TBE to 20-40% for Far Eastern TBE.

The prognosis of TBE depends on several factors including the viral subtype, patient age, severity of initial illness, and whether significant encephalitis develops. Understanding the potential outcomes helps patients and families prepare for what may be a prolonged recovery process.

Recovery from Mild Illness

Patients who experience only the first phase of TBE or who develop meningitis without significant brain parenchymal involvement generally have excellent outcomes. Complete recovery is the norm for these patients, typically occurring within weeks to a few months. These individuals do not usually experience significant long-term neurological complications.

Long-Term Effects of Encephalitis

For patients who develop encephalitis, the outlook is more variable and concerning. Studies have shown that between 30% and 60% of patients with encephalitic TBE experience persistent symptoms that may last for years or be permanent. Common long-term sequelae include:

• Cognitive difficulties: Problems with memory, concentration, and executive function
• Chronic fatigue: Persistent exhaustion that limits daily activities
• Headaches: Chronic or recurrent headaches
• Sleep disturbances: Insomnia or altered sleep patterns
• Balance and coordination problems: Difficulty with fine motor skills and gait
• Psychological symptoms: Depression, anxiety, and personality changes
• Paralysis: In severe cases, permanent weakness or paralysis of limbs

Mortality

Death from TBE is relatively uncommon with the European subtype, with fatality rates generally below 2%. However, the Far Eastern subtype carries a much higher mortality rate, ranging from 20% to 40% in some reports. Siberian TBE has intermediate severity. Deaths typically occur due to severe encephalitis with respiratory failure or due to complications in elderly patients or those with underlying health conditions.

Recovery from TBE provides lifelong immunity against the disease—once you have had TBE, you cannot get it again. This natural immunity, while providing future protection, comes at the potential cost of significant acute illness and possible long-term complications, which is why vaccination to prevent infection in the first place remains strongly recommended.

TBE in Pregnancy and Children

TBE infection during pregnancy does not appear to cause harm to the fetus based on available evidence. Children who contract TBE typically experience milder illness than adults, though neurological complications can still occur. Vaccination is available for children from 1 year of age and is recommended for those in endemic areas.

TBE During Pregnancy

There is limited data on TBE during pregnancy, but the available evidence is reassuring. Unlike some viral infections such as Zika or rubella, TBE does not appear to cross the placenta and cause fetal infection or birth defects. Pregnant women who contract TBE are managed similarly to non-pregnant patients, with supportive care as the mainstay of treatment.

Regarding prevention, pregnant women in endemic areas face a difficult decision about vaccination. While the TBE vaccine is an inactivated vaccine with no theoretical risk of fetal infection, it has not been formally studied in pregnant women. Healthcare providers generally advise that vaccination can be considered during pregnancy if the risk of TBE exposure is substantial and outweighs the theoretical risks of vaccination.

TBE in Children

Children who become infected with TBE generally experience milder disease than adults. The first phase may present as a mild febrile illness that resolves without the biphasic pattern seen in adults. When progression to the neurological phase does occur in children, it is more often limited to meningitis rather than encephalitis, and severe outcomes are less common.

Despite the generally milder course, TBE can still cause significant illness in children, including hospitalization and rarely, long-term neurological effects. For this reason, vaccination is recommended for children living in or traveling to endemic areas. The vaccine is licensed for children from one year of age and is well-tolerated in this age group.