Tick-borne encephalitis: Symptoms, Prevention by vaccination

The tick is one of the most well-known vectors of infectious diseases in the world. One of them is tick-borne encephalitis.

Overall, for Europe, the estimated risk is roughly 1 case per 10,000 human-months of woodland activity. Source: Tick-borne encephalitis - Wikipedia

Tick-borne encephalitis is a viral disease affecting the nervous system. 

The cause is the spherical Flavivirus with a single-stranded ribonucleic acid (RNA) that carries the genetic information of the virus. The capsid, i.e. the shell, of the virus is encased in a lipid envelope.

Thanks to the presence of proteins on the shell, it was possible to create an effective vaccine against this virus.

Based on the differences of these proteins, there are three subtypes of the virus: the European, the Siberian, and the Far Eastern.

The global endemic range of tick-borne encephalitis ranges from the south of Scandinavia through Slovenia, Croatia towards Eastern Europe.

In the past, infected ticks were found mainly in the warm lowlands. Nowadays, with the change in climatic conditions, ticks are moving to higher altitudes, increasing the risk of infection in these, formerly colder, areas.

In Europe, 0.5 - 5% of ticks are infected, depending on the season and altitude.

This viral disease is named after its vector, Ixodes ricinus, i.e. the castor bean tick. The Far Eastern subtype of the virus can also be transmitted by Ixodes persulcatus, i.e. the taiga tick.

The virus survives in the salivary glands of the tick. When a tick attaches itself to a person, the virus enters the body through the saliva. A few minutes is enough for the tick to transmit the virus and infect the host.

The host is infected within a few minutes.

Small rodents such as rats, mice, voles, etc. are natural reservoirs of infection. Larger mammals such as cows, goats, sheep, foxes, wild boars and humans are usually only incidental hosts.

The virus can also enter the mammary glands and milk of infected cattle and livestock.

Consumption of undercooked sheep or goat milk or dairy products from sheep or goat milk is a less common route of human infection. It is more of a local and familial occurrence.

The virus first circulates in the human host's bloodstream, multiplies for 2-3 days and produces mild flu-like symptoms.
Later, in the second stage, the virus can invade the central nervous system.
That is when the characteristic symptoms of meningitis, meningoencephalitis or meningoencephalomyelitis appear.

The two phases of viral penetration into the human body manifest in two characteristic phases.

The first phase is characterized by flu-like symptoms.

Manifestations of the first phase:

• headache,
• fever,
• fatigue
• joint pain,
• vomiting,
• dizziness,
• sometimes nasal discharge and full sinuses are associated.

A transitional period of dormancy occurs after the first phase and lasts between 2 and 10 days.

The second stage is manifested based on the site of involvement of the central nervous system.

Meningitis

About 50 - 55% of the disease appears as meningitis.

The symptoms are moderate:

• headache,
• nausea,
• vomiting,
• signs of meningeal irritation - most often a symptom of neck stiffness, making the patient is unable to bend his/her head to the chest.

Meningoencephalitis

30-35% of patients develop meningoencephalitis.

It has pronounced/severe symptoms:

• quantitative disturbance of consciousness - drowsiness, unconsciousness, coma
• qualitative disturbance of consciousness - confusion, haste, apathy, disinterest
• tremors of the limbs,
• tongue tremor,
• impaired balance and gait,
• paresis (paralysis) of the oculomotor nerves - double vision, photophobia,
• paresis of the facial nerve - falling off the corner of the mouth and eye,
• memory impairment,
• insomnia, 

Meningoencephalomyelitis

Of the total number of patients, about 10% suffer from the myelitic form.

It affects the anterior horns of the spinal cord.

It is characterized by limb paresis, i.e. motor and sensory weakness in the hands and feet.

It mainly affects the proximal muscle groups, i.e. the muscles in the shoulder and thigh. Unlike poliomyelitis, polio also occurs several days after the fever has subsided.

But it leaves lasting and serious consequences.

Brainstem involvement

The most severe form of tick-borne encephalitis is when it attacks the brain region with vital functions, i.e. the brain stem and the medulla oblongata.

In that case,  the patient has a high risk of cardiac arrest, malignant arrhythmias and choking.

If these centres are suspected to be affected, the patient must be immediately transferred to the intensive care unit, connected to artificial pulmonary ventilation or temporary cardiac pacing.

A major complication are cerebral edema and secondary bacterial superinfection.

Elderly patients are the most likely to be at risk.

This form of encephalitis can be fatal for elderly patients.

The European and Siberian subtypes of the virus have a mortality rate of 1-3%, whereas the Far Eastern subtype has a mortality rate of up to 20%.

Postencephalitic syndrome

Unfortunately, even if the acute stage of the disease and its symptoms retreats, the problems do not.

Patients that have overcome meningoencephalitis and meningoencephalomyelitis will suffer from long-lasting problems.

They experience a range of neuropsychiatric symptoms:

• headache,
• impaired concentration,
• memory impairment,
• emotional lability,
• insomnia,
• fatigue and inefficiency,
• dizziness

Up to 58% of patients describe these symptoms as interfering significantly with their quality of life.

They may last for several months, but rarely they are expressed permanently.

Diagnosis is based mainly on the medical history and characteristic clinical course of the disease.

The most important aspect of history taking is information on a recent tick bite. If the patient has not noticed the tick, knowing which places the patient has been to, especially if the are is endemic, will also help.

The riskiest activities are picking mushrooms and herbs, running in the woods, cycling, picnicking, mowing tall grass etc.

The blood  test in phase 2 of the disease is looking for increased sedimentation, increased number of leukocytes, and elevated liver enzyme levels.

If the doctor suspects tick-borne encephalitis, there will be an additional blood serology for viral antibodies. At this advanced stage of the disease, the result will be positive, with both IgM and IgG antibody titres (levels) elevated.

If the person is positive for meningeal symptoms, it is necessary to perform a diagnostic lumbar puncture. This is done by collecting cerebrospinal fluid and its laboratory examination in order to obtain valuable information about the type of infection affecting the central nervous systems.

Tick-borne meningoencephalitis as a viral infection has different cerebrospinal fluid findings than a bacterial purulent infection.

Specifically, we are looking for increased cell counts, protein, glucose, increase in lactate, and abnormally increased leukocytes and polymorphonuclear cells.

Examining the cerebrospinal fluid for evidence of antibodies to the virus is meaningless. In the first stage of the disease, the result will be negative, and in the second stage it will be positive even with a simple venepuncture, i.e. venous blood sampling.

Of the medical imaging techniques, a brain MRI (magnetic resonance imaging) is a great benefit. It visualizes the brain, in which the thalamic area will be significantly saturated.

Differential diagnosis

Ddifferential diagnosis focuses on excluding other types of neuroinfections.

The most important task to do is to exclude purulent processes affecting the central nervous system, e.g. brain abscess, or purulent (i.e. with pus) meningitis, caused by bacteria. In these diseases, prompt administration of appropriate antibiotics is crucial. However, they are ineffective in viral infections, which is also the case in tick-borne encephalitis.

If the cerebrospinal fluid clearly suggests serous (non-purulent) meningitis without any indication of a tick bite, the doctor looks for other neurotropic viruses that affect the nervous system. The most common causes are herpes viruses and enteroviruses.

Bacterial microorganisms can also be transmitted to a humans via a tick bite. They cause diseases affecting the central nervous system, e.g. Lyme disease, anaplasmosis and tularemia (also known as rabbit fever).

The clinical course may strikingly resemble a demyelinating (Sclerosis multiplex), oncological or vascular disease such as a stroke. Imaging, CT or MRI of the brain or spinal cord will help rule out some of these.

About 70% of cases of tick-borne encephalitis take their course asymptomatically, i.e. without symptoms.

The incubation period (i.e. the time between the entry of the virus into the body and the first symptoms) for vector-borne infection is between 2 and 28 days, usually 1 to 2 weeks.

The incubation period is shorter in the case of alimentary infection from milk and milk products, which is about 4 to 6 days.

The first stage of the disease is rarely recognized by the patient or the doctor. The patient will see the doctor due to flu symptoms.

Suffers from headache, fever, fatigue, joint pain, vomiting, dizziness, sometimes nasal discharge and full sinuses are added.

This period lasts roughly 2 to 7 days.

A blood test shows whether there is a reduced number of leukocytes and platelets or an increase of hepatic enzymes. However, at this early stage of the disease, the test for antibodies to tick-borne encephalitis virus is usually false negative and the disease is not diagnosed.

After the initial symptoms subside, there is a temporary period of calm that lasts for 2 to 10 days.

If there is no outbreak of symptoms in the second phase, the form of infection is called abortive.

After this period of quiescence, the virus multiplies in the central nervous system and, depending on which part is affected and what symptoms accompany the disease, there can be several forms of phase 2.

Learn more: 
How to remove a tick correctly and safely in 6 important steps

Prevention

Prevention of tick-borne encephalitis involves several measures.

1. Identify endemic areas

An endemic area is a place with a high prevalence of tick infestation infected with the virus. Identifying and avoiding these areas effectively reduces the incidence of tick-borne encephalitis.

2. Consume sufficiently pasteurised milk and milk products

This is the best prevention of alimentary transmission of tick-borne encephalitis, especially from sheep and goat milk.

If you are buying from a private breeder, it is always advisable to boil the milk. The virus is inactivated at 65 °C in 10 minutes.

3. Protect against tick bites by wearing appropriate clothing

When you're exploring an area in nature, make sure your ankles and calves are covered by long trousers, knee-high socks or tick-repellent hiking socks. 

Long sleeves or gloves should be worn during activities that involve having your hands touching the vegetation or the undergrowth.

The tick waits for its host hanging from the blades of grass and gets caught on the skin as it passes through this dense undergrowth. It then crawls around the body for a few minutes looking for a suitable area to bite. As a rule, they are areas where the skin is thin and rich with blood.

The most common places include the knee pit (hough), in the groin area, in the genital area, in the armpits and behind the ears.

4. Use repellents

The most effective repellents can be found in the pharmacy.

Although manufacturers claim repellents are effective 6 to 8 hours, that does not apply to all types of insects. If you are using them against ticks, the repellents will protect you 3 to 4 hours, so you will need to apply it regularly.

You can also apply the repellent on your clothes.

5. Get vaccinated

The most effective and readily available method of prevention is getting a vaccine against tick-borne encephalitis.

Vaccination is most beneficial for populations living or working in endemic areas with the highest tick infestation and activity. These are mainly forestry workers, hunters, rescuers, etc.

However, vaccination is also suitable for tourists and safe to administer to children.

In certain EU countries, several vaccines are available and registered against tick-borne encephalitis. In order to get them at the local pharmacy you will need a prescription. The vaccine is prescribed by a GP who then administers the vaccine.

The vaccine is not covered by health insurance companies and must be purchased in full by the patient.

The vaccination schedule consists of three administrations.

The first dose is followed by a second dose to be given 1 to 3 months after the initial dose.
The patient receives the third dose 9 to 12 months after the second one.
The vaccination is complete and the patient is fully immunized.

In a situation where tick-borne encephalitis vaccination is scheduled, it is most appropriate to start the initial administration of the vaccine in the winter months. This is because of the time needed for the body to build up immunity. With this time margin, there is a greater chance that by the summer months, which is the tick season, you will already be protected.

If, however, the basic vaccination is started in the summer months, the second dose of the vaccine should be given two weeks after the first dose as there is a greater chance of a rapid rise in protective antibody levels.

Antibodies that protect against infection are produced in about 10 to 14 days after the second dose.

Immunisation after the basic vaccination, i.e. the three doses, lasts for at least three years. After this period, a single dose of vaccine is required.

In general, the vaccine is suitable for any person who is interested in immunisation.

Vaccination is contraindicated in ongoing infectious diseases, fever, and autoimmune processes. The vaccine should also not be given to people who are allergic or hypersensitive to egg white.

If you get bitten by a tick in an endemic area and you are not vaccinated, you should be given a specific immunoglobulin. Such immunization is called passive because an preformed antibody is injected into the person's body so that the organism does not have to actively produce it itself.

Such protection against infection is only effective within 96 hours of exposure.

Tick-borne encephalitis in children

The course of the disease in children has similarities and differences.

The 2-phase progression is identical.

The first one is characterised by a flu-like syndrome with fever, headache, joint pain and other non-specific symptoms.

If after the first phase the symptoms spontaneously subside, the infection has taken an abortive form.

The second phase, as in adults, proceeds as a neurological one, i.e. the symptoms result from the involvement of the central nervous system. However, symptoms are milder, polio is uncommon and deaths are rather rare.

In children under 4 years of age, the disease can be completely asymptomatic. If symptoms do appear, febrile convulsions are a frequent along with high temperatures. In the encephalitic form, confusion and other mental disturbances may occur. They are more difficult to assess in toddlers.

In older children, symptoms such as headache, muscle and joint pain, sore throat, and a runny nose are common. Fever above 39.5 °C is present in 75% of pediatric patients and more than half vomit.

Prominent meningeal symptoms are more common than in adults. The meningitic form of the disease is more common in children, while the encephalitic course is most common in adults.

Treatment is symptomatic, including analgesics and antipyretics which are calculated based on the weight of the child.

Antiedematous therapy with mannitol is necessary only in half of the cases. Corticosteroids can be administered with regard to the age and weight of the patient; realistically, only about one-third of those infected require it.

Children can get the tick-borne encephalitis vaccine.

However, they are more likely to experience post-vaccination reactions.

They include the following typical symptoms:

• elevated temperature,
• febrile convulsions,
• sleepiness,
• lack of appetite,
• headache,
• fatigue,
• general weakness,
• muscle and joint pain

As a rule, they last only a day and occur more often if the vaccination takes place in the winter months, i.e. in January and February.