Tick-Borne Encephalitis (TBE): Symptoms, Causes & Treatment

What Is Tick-Borne Encephalitis (TBE)?

Tick-borne encephalitis (TBE) is a viral infection that affects the central nervous system, including the brain and its protective membranes. It is primarily transmitted through the bite of infected Ixodes ticks and occurs in endemic areas across Europe and Asia, with approximately 10,000-12,000 cases reported annually.

Tick-borne encephalitis is caused by the TBE virus, a member of the Flaviviridae family closely related to other mosquito and tick-borne viruses such as dengue, yellow fever, and Japanese encephalitis. The virus exists in three main subtypes: European, Siberian, and Far Eastern, each with slightly different characteristics and geographic distributions. Understanding these subtypes is important because they can cause disease of varying severity.

The European subtype, found predominantly in Central and Western Europe, typically causes less severe disease with a case fatality rate of approximately 1-2%. In contrast, the Far Eastern subtype, prevalent in Russia and parts of Asia, can cause more severe illness with fatality rates reaching 20-40% in some outbreaks. The Siberian subtype falls somewhere in between and is notable for potentially causing chronic or progressive disease in some patients.

TBE has been recognized as a significant public health concern for decades, with the first clinical descriptions dating back to the 1930s in Russia. Since then, the endemic area has been steadily expanding, likely due to a combination of factors including climate change, changes in land use, increased outdoor recreational activities, and improved surveillance and diagnosis. Countries that were previously considered TBE-free are now reporting cases, making this an emerging infectious disease of growing importance.

How TBE Virus Affects the Body

When an infected tick bites a human, the TBE virus enters the bloodstream through the tick's saliva. The virus has a particular affinity for nerve tissue, which explains why it predominantly affects the central nervous system. After initial replication at the bite site and in regional lymph nodes, the virus spreads through the bloodstream (viremia) to various organs.

In most cases, the immune system successfully controls the infection during this initial phase, and many people experience no symptoms or only mild illness. However, in approximately 20-30% of symptomatic cases, the virus crosses the blood-brain barrier and infects the central nervous system, leading to the characteristic neurological manifestations of TBE including meningitis (inflammation of the brain's protective membranes), encephalitis (inflammation of the brain tissue itself), or myelitis (inflammation of the spinal cord).

What Are the Symptoms of Tick-Borne Encephalitis?

TBE symptoms typically appear in two phases. The first phase (7-14 days after tick bite) includes flu-like symptoms: fever, fatigue, headache, and muscle pain lasting 2-7 days. After a symptom-free interval of about one week, the second neurological phase may develop with high fever, severe headache, neck stiffness, and potentially confusion, paralysis, or seizures.

Understanding the symptom progression of TBE is crucial for recognizing the disease and seeking appropriate medical care. The characteristic biphasic (two-phase) pattern occurs in approximately 70-75% of patients who develop clinical disease. However, it's important to note that the majority of TBE infections (estimated at 70-98%) are asymptomatic or cause only very mild symptoms that are easily mistaken for other common illnesses.

The variability in disease presentation depends on several factors including the viral subtype involved, the amount of virus transmitted during the tick bite, the individual's age and immune status, and possibly genetic factors. Older adults, immunocompromised individuals, and those with certain underlying health conditions tend to experience more severe disease and have a higher risk of long-term complications.

First Phase Symptoms

The first phase of TBE typically begins 7 to 14 days after the tick bite, although the incubation period can range from 2 to 28 days. This phase is characterized by non-specific symptoms that are difficult to distinguish from many other viral infections, which is why TBE is often not suspected at this stage. The symptoms usually last 2 to 7 days before resolving spontaneously.

During this initial phase, patients commonly experience fever (usually 38-39°C/100.4-102.2°F), generalized fatigue and malaise, headache that may be moderate to severe, muscle aches and pains (myalgia), joint pain (arthralgia), and general weakness. Some patients also report loss of appetite, nausea, and occasionally mild upper respiratory symptoms. Laboratory tests during this phase may show decreased white blood cell counts and mildly elevated liver enzymes.

Symptom-Free Interval

Following the first phase, approximately 70-75% of patients experience a symptom-free interval lasting typically 1 to 20 days (average about 7 days). During this period, patients feel completely recovered and may assume they had a simple viral illness. This asymptomatic period can be particularly deceptive, as patients may resume normal activities unaware that the virus may be spreading to their central nervous system.

Second Phase Symptoms (Neurological Phase)

The second phase of TBE occurs in approximately 20-30% of patients who experienced symptomatic first-phase illness. This neurological phase represents the most serious manifestation of TBE and can take several forms depending on which part of the central nervous system is affected. The onset is typically sudden, with high fever returning along with new and more alarming symptoms.

The mildest form of neurological TBE is meningitis, characterized by severe headache, neck stiffness (nuchal rigidity), sensitivity to light (photophobia), nausea and vomiting, and fever. While serious, isolated meningitis generally has a good prognosis with most patients recovering fully, although the recovery period may take several weeks.

Meningoencephalitis, where both the meninges and brain tissue are affected, is more severe. In addition to meningitis symptoms, patients may experience confusion and altered consciousness, memory problems and difficulty concentrating, drowsiness progressing to stupor, tremors and movement disorders, and behavioral changes. This form of TBE can lead to significant long-term cognitive and neurological problems.

What Causes Tick-Borne Encephalitis?

TBE is caused by the tick-borne encephalitis virus (TBEV), transmitted primarily through the bite of infected Ixodes ricinus (European) or Ixodes persulcatus (Asian) ticks. The virus is maintained in nature through a cycle involving ticks and small mammal hosts. Infection can also occur through consumption of unpasteurized dairy products from infected animals.

The TBE virus belongs to the family Flaviviridae and is closely related to other important human pathogens including dengue virus, yellow fever virus, Japanese encephalitis virus, and West Nile virus. Like these relatives, TBE virus is an enveloped RNA virus with a single-stranded positive-sense genome. Understanding the virus's biology helps explain both how it causes disease and why certain prevention strategies are effective.

Tick transmission occurs when an infected tick attaches to human skin and feeds on blood. The virus is present in the tick's salivary glands and is transmitted during the feeding process, which typically requires the tick to be attached for several hours. However, TBE virus can be transmitted more quickly than some other tick-borne pathogens because it is present in the saliva from the beginning of feeding, rather than needing to migrate from the tick's gut.

The Tick Vector

The primary vectors for TBE virus are hard-bodied ticks of the genus Ixodes. In Europe, Ixodes ricinus (the castor bean tick or sheep tick) is the main vector, while in Asia, Ixodes persulcatus (the taiga tick) predominates. These ticks have a complex three-stage life cycle - larva, nymph, and adult - and can acquire and transmit the virus at any of these stages.

Ticks become infected by feeding on viremic animals (those with virus circulating in their blood) or through a unique process called co-feeding transmission, where uninfected ticks feeding near infected ticks on the same host can acquire the virus even if the host animal does not have detectable viremia. This co-feeding mechanism is particularly important for maintaining the virus in nature.

Ixodes ticks are found in temperate forest environments, particularly in areas with dense undergrowth and leaf litter. They thrive in humid conditions and are most active during spring and early summer (April to June) and again in autumn (September to November), although they can be encountered whenever temperatures are above approximately 5-7°C (41-45°F). Climate change has extended tick activity seasons in many areas.

Risk Factors for TBE Infection

Several factors increase the risk of acquiring TBE infection. Geographic location is paramount - living in or traveling to endemic areas significantly increases exposure risk. Within endemic areas, rural and forested environments pose higher risks than urban settings, although ticks can be found in city parks and gardens in endemic regions.

Occupational and recreational activities that involve time spent in tick habitats increase exposure risk. These include forestry work, farming and agriculture, hiking and camping, hunting, berry and mushroom picking, gardening in rural areas, and military training in forested areas. The risk is particularly high during peak tick activity seasons.

Individual factors also influence both the likelihood of infection and disease severity. Age is an important factor, with older adults (especially those over 50) at higher risk for severe neurological disease and long-term complications. Immunocompromised individuals may also experience more severe disease. Importantly, lack of vaccination is the single most significant modifiable risk factor.

How Is TBE Diagnosed?

TBE is diagnosed through a combination of clinical assessment, exposure history, and laboratory testing. Blood tests detect specific IgM and IgG antibodies against TBE virus. Cerebrospinal fluid analysis through lumbar puncture confirms central nervous system involvement. Diagnosis can be challenging during the first phase when symptoms are non-specific.

Accurate diagnosis of TBE requires a high index of clinical suspicion, particularly in patients presenting with neurological symptoms and a history of potential tick exposure in endemic areas. The diagnostic process typically involves several steps, beginning with a thorough clinical assessment and exposure history.

During the initial evaluation, healthcare providers will ask about recent tick bites (although many patients do not recall being bitten), time spent in TBE-endemic areas, outdoor activities that might have exposed the patient to ticks, consumption of unpasteurized dairy products, and the timing and progression of symptoms. The characteristic biphasic illness pattern, if present, is a helpful diagnostic clue.

Laboratory Testing

Serological testing (blood tests that detect antibodies) is the primary method for confirming TBE infection. The tests look for two types of antibodies against the TBE virus: IgM antibodies, which appear early in infection and indicate recent or current infection, and IgG antibodies, which appear later and persist longer, indicating past infection or vaccination.

TBE-specific IgM antibodies are typically detectable in blood by the time neurological symptoms appear and usually peak within 1-2 weeks of symptom onset. IgG antibodies appear slightly later but rise to higher levels and persist for years. A diagnosis of acute TBE is typically made when IgM antibodies are detected in serum, or when there is a significant rise in IgG antibody levels between acute and convalescent samples taken 2-4 weeks apart.

Cerebrospinal fluid (CSF) analysis, obtained through a lumbar puncture (spinal tap), is important for evaluating patients with suspected central nervous system involvement. In TBE, CSF typically shows elevated white blood cell count (pleocytosis) with a predominance of lymphocytes, mildly elevated protein levels, and normal glucose levels. TBE-specific antibodies may also be detected in CSF, which helps confirm central nervous system infection.

Differential Diagnosis

Several other conditions can cause similar symptoms to TBE and must be considered in the diagnostic evaluation. These include other tick-borne infections such as Lyme neuroborreliosis, bacterial meningitis (which requires urgent antibiotic treatment), other viral encephalitides (herpes simplex, enteroviruses, West Nile virus), and non-infectious causes of meningitis or encephalitis. Appropriate testing helps distinguish between these conditions and guides treatment.

How Is Tick-Borne Encephalitis Treated?

There is no specific antiviral treatment for TBE. Management is primarily supportive, focusing on symptom relief and preventing complications. This includes rest, adequate hydration, pain and fever management, and hospitalization with intensive care for severe neurological cases. Prevention through vaccination is therefore crucial.

The absence of specific antiviral therapy for TBE underscores the critical importance of prevention through vaccination. Once infection has occurred, treatment focuses on supporting the patient through the acute illness, managing symptoms, and preventing secondary complications. The approach to treatment depends on the severity of the disease.

For patients with mild first-phase illness, treatment is typically conservative and includes bed rest during the acute febrile period, adequate fluid intake to prevent dehydration, analgesics and antipyretics for pain and fever control (such as acetaminophen/paracetamol or ibuprofen), and monitoring for progression to neurological disease. Most patients with only first-phase symptoms recover fully without complications.

Hospital Care for Severe Cases

Patients who develop neurological symptoms typically require hospitalization for monitoring and supportive care. The goals of hospital treatment include careful monitoring of neurological status and vital signs, management of increased intracranial pressure if present, prevention and treatment of secondary complications such as pneumonia or urinary tract infections, nutritional support and fluid management, and physical therapy to maintain mobility and prevent complications of immobility.

Severe cases, particularly those with encephalitis or significant brain involvement, may require intensive care unit admission. Potential interventions in intensive care include mechanical ventilation if respiratory function is compromised, treatment of seizures with anti-epileptic medications, management of autonomic instability, and careful monitoring and treatment of cerebral edema.

Corticosteroids have been used in some cases of TBE, based on the theory that they might reduce inflammation in the brain. However, their benefit has not been proven in clinical trials, and they are not routinely recommended. Other experimental treatments have been investigated, but none has shown clear efficacy in clinical studies.

Rehabilitation and Recovery

Recovery from TBE, particularly from cases involving neurological symptoms, can be prolonged. Many patients experience a post-encephalitic syndrome characterized by persistent fatigue, headaches, difficulty concentrating and memory problems, sleep disturbances, mood changes and depression, and balance and coordination difficulties. These symptoms may persist for months to years and can significantly impact quality of life.

Rehabilitation may involve physical therapy to address motor deficits and improve strength and coordination, occupational therapy to help with daily living activities, cognitive rehabilitation for memory and concentration problems, speech therapy if communication or swallowing is affected, and psychological support for mood disturbances and adjustment to long-term disability.

Is There a Vaccine for TBE?

Yes, highly effective TBE vaccines are available and provide 95-99% protection after completing the full vaccination series. The standard schedule involves three doses: two doses given 1-3 months apart, followed by a third dose 5-12 months later. Booster doses are recommended every 3-5 years. Vaccination is strongly recommended for all individuals living in or traveling to endemic areas.

TBE vaccination is one of the most successful examples of prevention for a potentially serious infectious disease. Multiple safe and effective vaccines are available, and countries with high vaccination coverage have seen dramatic reductions in TBE incidence. The vaccines contain inactivated (killed) TBE virus and stimulate the immune system to produce protective antibodies without causing disease.

Several TBE vaccines are available internationally, including FSME-IMMUN (marketed as TicoVac in some countries), Encepur, and vaccines produced in Russia (TBE-Moscow, EnceVir). While there are some differences between these vaccines, they are generally considered interchangeable for completing a vaccination series. All licensed vaccines have excellent safety profiles and high efficacy.

TBE Vaccination Schedule

The standard (conventional) vaccination schedule involves three primary doses. The first dose can be given at any time but is ideally started before tick season begins. The second dose is given 1 to 3 months after the first dose. The third dose is given 5 to 12 months after the second dose. This three-dose primary series provides long-lasting immunity in most individuals.

For individuals who need rapid protection (such as travelers departing soon for endemic areas), an accelerated schedule is available. Under this schedule, the second dose is given 2 weeks after the first dose, and the third dose is given 5-12 months after the second dose. While this provides faster protection, completing the third dose is essential for long-term immunity.

Booster doses are recommended to maintain immunity over time. The timing of boosters varies by vaccine product and patient age, but general guidelines suggest a first booster 3 years after completing the primary series, then subsequent boosters every 3-5 years depending on age and ongoing risk. Individuals over 60 may need more frequent boosters as immune responses tend to wane more quickly with age.

Who Should Get Vaccinated?

Vaccination is recommended for individuals who live in TBE-endemic areas, travelers who will spend time in endemic areas especially if planning outdoor activities, people whose occupations put them at risk (forestry workers, farmers, military personnel), and laboratory workers who may be exposed to TBE virus. The vaccine can be given to children from 1 year of age, although specific recommendations vary by country.

How Can You Prevent Tick Bites and TBE?

Prevention of TBE involves both vaccination (95-99% effective) and personal protective measures to avoid tick bites. Key strategies include wearing protective clothing, using insect repellent containing DEET or icaridin, staying on marked trails, performing thorough tick checks after outdoor activities, and removing any attached ticks promptly and correctly.

While vaccination provides the best protection against TBE, taking measures to prevent tick bites reduces the risk of both TBE and other tick-borne diseases such as Lyme borreliosis, for which no vaccine is currently available in most countries. A comprehensive approach combining vaccination with tick bite prevention offers the most complete protection.

Understanding tick behavior helps in avoiding bites. Ticks do not jump or fly; they wait on vegetation with their front legs extended, ready to grasp onto passing hosts (a behavior called "questing"). They are typically found in areas with tall grass, brush, and leaf litter, particularly at forest edges and in areas where vegetation provides shade and humidity. Ticks are most active when temperatures are above 5-7°C (41-45°F) and are most commonly encountered from spring through autumn.

Protective Clothing and Repellents

When spending time in tick-endemic areas, wearing appropriate clothing can significantly reduce the risk of tick bites. Long pants tucked into socks or boots create a barrier against ticks climbing up legs. Long-sleeved shirts with buttoned or tight cuffs protect arms. Light-colored clothing makes it easier to spot ticks before they reach skin. Closed-toe shoes or boots are preferable to sandals.

Insect repellents provide additional protection. Products containing DEET (20-30% concentration) are effective against ticks when applied to exposed skin according to product instructions. Icaridin (also known as picaridin) is an effective alternative for those who prefer not to use DEET. Permethrin-treated clothing provides excellent protection and remains effective through multiple washings; it should be applied only to clothing, not directly to skin.

Tick Checks and Proper Removal

After spending time in areas where ticks may be present, performing a thorough tick check is essential. Check the entire body, paying particular attention to the scalp and hairline, behind and around the ears, armpits, belly button, groin and genital area, behind the knees, and between the toes. Showering within two hours of coming indoors may help remove unattached ticks and provides an opportunity to do a tick check.

If you find an attached tick, prompt removal is important. While TBE virus can be transmitted quickly (unlike some other tick-borne pathogens), removing ticks as soon as possible is still beneficial. The correct method is to use fine-tipped tweezers to grasp the tick as close to the skin surface as possible, pull upward with steady, even pressure without twisting or jerking, clean the bite area with rubbing alcohol or soap and water, and dispose of the tick by flushing it down the toilet or placing it in alcohol.

Where Is TBE Endemic?

TBE is endemic across much of Europe and Asia, from France and the UK in the west to Japan in the east. High-risk areas include Central Europe (Austria, Germany, Czech Republic), Baltic states (Estonia, Latvia, Lithuania), Scandinavian countries (Sweden, Finland), Russia, and parts of China and Japan. The endemic area has been expanding in recent decades.

The geographic distribution of TBE is determined by the presence of infected tick populations, which in turn depends on environmental factors suitable for tick survival and the presence of animal hosts that maintain the virus in nature. Understanding the endemic areas is crucial for assessing personal risk and making informed decisions about vaccination.

In Europe, TBE occurs in a band stretching from France through Central and Eastern Europe to Russia. The highest incidence is typically reported from the Baltic states (Estonia, Latvia, Lithuania), Slovenia, Czech Republic, and parts of Russia. Germany, Austria, Poland, and Switzerland also report significant case numbers. The endemic area in Europe has been expanding northward and to higher altitudes, likely due to climate change affecting tick habitats.

TBE by Region

In Central Europe, countries including Austria, Germany, Switzerland, Czech Republic, Slovakia, Hungary, and Slovenia have well-established endemic areas. Austria has achieved dramatic reductions in TBE incidence through high vaccination coverage (approximately 85% of the population), demonstrating the effectiveness of vaccination programs.

The Baltic states (Estonia, Latvia, Lithuania) report among the highest TBE incidence rates in Europe. These countries have extensive forested areas with high tick density and historically had lower vaccination coverage, although this has been improving.

In Scandinavia, Sweden and Finland have endemic areas particularly along coastlines and archipelagos. The endemic area in Sweden has been expanding northward in recent years. Norway and Denmark have limited endemic areas but report occasional cases, primarily in returning travelers.

Russia has the highest absolute number of TBE cases globally, with endemic areas extending from western Russia through Siberia to the Pacific coast. The Siberian and Far Eastern TBE subtypes found in Russia can cause more severe disease than the European subtype.

In Asia, TBE occurs in parts of China (particularly northeastern provinces), Japan, South Korea, and Mongolia. The Far Eastern subtype predominates in these regions.

What Is the Prognosis for TBE?

The prognosis for TBE varies widely depending on disease severity. The majority of infections cause no symptoms or mild illness with full recovery. Among those who develop neurological disease, approximately 35-58% recover fully, 40-45% experience long-term neurological sequelae, and the case fatality rate is 1-2% for the European subtype (higher for Far Eastern subtype).

Understanding the potential outcomes of TBE helps put the disease in perspective and underscores the importance of prevention. While many infections are asymptomatic or mild, the potential for serious and lasting complications makes TBE a significant health concern in endemic areas.

For the majority of people infected with TBE virus, the outcome is favorable. Most infections (estimated 70-98%) cause no symptoms at all or only mild, non-specific symptoms that resolve completely. Among those who develop symptomatic first-phase illness, most recover fully before any neurological involvement occurs.

Outcomes in Neurological Disease

The prognosis becomes more guarded when the disease progresses to the neurological phase. Among patients with central nervous system involvement, outcomes vary based on the specific manifestation. Patients with isolated meningitis (inflammation of the meninges without brain involvement) generally have a good prognosis, with most recovering fully over several weeks, though some may experience prolonged fatigue and headaches.

Meningoencephalitis (involvement of both meninges and brain tissue) has a more variable outcome. While many patients recover, a significant proportion experience long-term cognitive and neurological problems. Studies suggest that 30-40% of patients with TBE encephalitis experience persistent symptoms or deficits at long-term follow-up.

Encephalomyelitis (involvement of brain and spinal cord) and myelitis (spinal cord involvement alone) have the worst prognosis among TBE manifestations. Paralysis from spinal cord involvement may be permanent in some cases, leading to significant disability.

Long-Term Complications

Post-encephalitic syndrome is a recognized consequence of TBE that can significantly impact quality of life. Symptoms that may persist for months to years include cognitive impairment affecting memory, concentration, and executive function, chronic fatigue that is often debilitating, persistent headaches, balance and coordination problems, shoulder girdle weakness (particularly associated with TBE), mood disorders including depression and anxiety, and sleep disturbances.

The risk of severe disease and long-term complications increases with age, with adults over 50 having significantly worse outcomes than younger patients. This is one reason why vaccination is particularly important for older adults who may be exposed to TBE.