Tick-borne encephalitis

TBE is a growing public health problem in Europe and globally, advises Professor Michael Kunze.

Tick-borne encephalitis (TBE) is a rapidly growing public health problem in Europe and other parts of the world. Based on statistical modelling, it has been estimated that the likelihood for an unvaccinated tourist to acquire TBE in a highly endemic region, mainly central Europe, is similar to the risk of acquiring typhoid fever in India.1

Tick feeding on the eyelid

The risk of acquiring TBE in an endemic area such as Austria is 1:10,000, compared with 1:3,000-1:25,000 for an unvaccinated tourist contracting typhoid in an endemic region.

At least 10,000 cases of TBE are referred to hospitals each year, although the incidence of TBE may not be recognised fully. The reason is that TBE produces clinical features similar to those of many other types of meningitis and/or encephalitis.

Long-term sequelae
TBE is a viral disease that attacks the nervous system and may cause illnesses ranging from mild to severe, with permanent consequences such as concentration problems, paralysis and depression.

According to WHO estimates, between 35 and 58 per cent of TBE patients are left with long-term neurological sequelae, such as paralysis, and around 2 per cent of patients die of the disease.

Until recently, TBE was believed to be a rather limited problem in a few well-defined endemic areas; however, this notion has now been revised.

Endemic regions
The disease is now endemic in 27 countries across Europe, from Scandinavia down to the Mediterranean and includes popular Alpine regions and emerging tourist destinations in eastern Europe. TBE is a notifiable disease in 16 European countries (Austria, the Czech Republic, Estonia, Finland, Germany, Greece, Hungary, Latvia, Lithuania, Norway, Poland, Russia, Slovakia, Slovenia, Sweden, and Switzerland).

Climate change and global warming have also had an influence on the geographical distribution of ticks.

Not only have ticks infected with the TBE virus spread to previously unaffected regions, 2008 also marked the first time these infected ticks have been detected at more than 1,500 metres above sea level.2

As a result, hikers, trekkers and mountain bikers are among outdoor enthusiasts now at risk of exposure to TBE.

The frequency of illness is subject to seasonal fluctuations and arises from the extent of tick activity. Mild winters and humid springs promote the numbers of ticks and the risk of infection can begin as early as February and last until November depending on the region.

Vaccination schedule

Conventional primary immunisation:

First vaccination - The first dose should be given on an elected date in the cold season, to be effective by the beginning of the tick activity.

Second vaccination - 1-3 months after the first vaccination

Third vaccination - 5-12 months after the second vaccination

Booster doses:

  • First booster dose should be given 3 years after the primary immunisation series;
  • Sequential booster doses should be given according to national recommendations.

Clinical features
The illness progresses in two phases; in up to 20 per cent of the cases the first phase is not perceived by patients. The first phase of the illness occurs after an incubation period of six to 14 days; this is when the virus enters the bloodstream.

Patients complain of general symptoms such as fever (usually under 39 degsC), headaches, overall weakness, fatigue, GI problems, cough and sniffles.

After an often symptom-free interval of between two and up to a maximum of eight days, symptoms indicating progression to the nervous system may appear. This second phase occurs as the virus crosses the blood-brain barrier.

Another temperature inc-rease (usually over 39 degsC) ensues, with typical additional symptoms of aggravated headaches, neck stiffness, impaired consciousness, delirium, cranial nerve paralysis, coordination problems and paralysis of the arms and legs.

Ultimately, paralysis of the respiratory musculature can occur. Intensive treatment, including artificial respiration, is then essential. There is no specific treatment for TBE and therapy is symptomatic.

Vaccination
TBE can be prevented by vaccination. Field trials have shown up to 99 per cent effectiveness.2 Children over 1 year can be vaccinated.

Research has shown that about one in three infections with the TBE virus will lead to overt TBE requiring hospitalisation. Some 80 per cent of patients will have to undergo rehabilitation, and between 30 and 40 per cent will suffer permanent neurological sequelae, such as psychological disturbances, co-ordination problems or paralysis.

  • Professor Kunze is director of the Institute for Social Medicine, Medical University, Vienna and chair of the International Scientific Working Group on Tick-Borne Encephalitis (ISW-TBE)

REFERENCES

1. Rendi-Wagner P. Risk and prevention of tick-borne encephalitis in travelers. J Travel Med 2004; 11(5): 307-12.

2. Heinz F X, Holzmann H, Essl A, Kundi M. Field effectiveness of vaccination against tick-borne encephalitis. Vaccine 2007; 25(43): 7,559-67.

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