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Author(s): Federal Office of Public Health (FOPH)
Editorial office: WSL, Switzerland
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How dangerous are tick bites?

Ticks are one of the less pleasant reminders of a trip to the forest. Here you can find information about ticks and about the illnesses TBEV and Lyme disease.

Zecken
Fig. 1 - The common tick (Ixodes ricinus) in various stages. Larva (small), adult female tick (large) and Nymph (lower left). Click on the picture to enlarge.
Photo: www.isw-tbe.info
 
Stechapparat (Rostrum) der Zecke
Fig. 2 - Tick probosis (rostrum)
Photo: www.isw-tbe.info

Out of the more than 800 known species of ticks the common tick (Ixodes ricinus) is for us the most important (Fig. 1). Ticks can be found all over Switzerland up to an altitude of around 1500m. The preferred habitats of these spider related creatures are mildly damp places in deciduous and mixed forests with an abundance of undergrowth (grasses, shrubs, bushes), in particular overgrown edges of forests, forest clearings and paths, also hedgerows and land with tall growing grasses and bushes. Ticks are rarely to be found in well looked after family gardens, town parks, which are not near forests and pure coniferous forests.

Ticks sit on low growing plants (up to max. 1.5m), wait for a passing host and then let themselves be brushed off onto the host. Ticks do not fall from trees! The danger of being bitten in winter is very low, in spring (February to the middle of June) and in autumn (middle of August to October) much higher. These periods can vary from year to year depending on climatic conditions. Hosts for ticks, depending on their stage of development, are small rodents, birds or larger wild animals such as hares, deer, domestic animals (cats and dogs) and in some cases humans.

For a tick to develop it has to suck blood at least once in every phase – as a larva, a nymph and as an adult. With larva this blood sucking process lasts for two to three days, with an adult tick from seven to eleven days. During this time the weight of these 0.5 to 6 mm large creatures can increase a hundredfold. Ticks have a proboscis, a so-called rostrum with which they drill into the skin (Fig. 2). With the help of several small teeth, which are used as barbed hooks, they hang on tightly to the skin and are very difficult to remove. With the bite they give off an anaesthetizing substance, which is why it is often not noticed.

Wood ticks pass on germs

In Switzerland wood ticks can pass on several germs to humans, a bacterium (Borrelia burgdorferi) and a virus (the tick-borne encephalitis virus (TBEV))

All over Switzerland 5-30% (up to 50%) of ticks are infected with the bacterium Borrelia burgdorferi. An estimated 3’000 people yearly contract the so-called Lyme disease caused by this bacterium. Lyme disease can be treated with antibiotics.

Ticks, which carry the tick-born encephalitis virus, are only to be found in certain areas, so called natural herds (endemic areas) (Fig. 3). Affected are the following cantons Zurich, Thurgau, Schaffhausen, Sankt Gallen, Graubunden, Aargau, Lucerne, Zug, Niedwalden, Obwalden, Uri, Solothurn, Bern, Freibourg, Vaud and the Principality of Liechtenstein. In these endemic areas around 1% (0.5-3%) of ticks carry the virus. There are at present no known areas with TBE invested ticks above an altitude of ca. 1000 m.

In 2005 the cases of TBE drastically increased with 200 cases, compared to an average of 100 per year during the preceding 5 years. There is a well-tolerated and efficient vaccination against tick-borne encephalitis.

Tick-borne encephalitis (TBE)

The tick-borne encephalitis (TBE) typically manifests itself in two phases of illness. In the first phase around 7 to 14 days after the insect bite certain people show flu like symptoms such as headaches, fever, fatigue, or painful joints. The symptoms disappear after a few days and a connection with the tick bite is seldom made. For most patients the illness is now over and they will most probably be immune for the rest of their life. For approximately 5-15% of patients after a symptom free phase there follows a second phase of illness with an attack on the central nervous system.

The symptoms of this form of meningitis are bad headaches, aversion to light, dizziness, lack of concentration, difficulties of speech, sight and difficulty in walking. These symptoms can last for weeks even months. Certain patients can experience paralysis of arms, legs or facial nerves, which can lead to permanent disabilities. Approximately 1% of the patients die from this disease. With children it usually takes its course harmlessly without any lasting damage. There is no special therapy. The treatment aims at alleviating the symptoms.

Bekannte Endemiegebiete der Zeckenenzephalitis (FSME)

Fig. 3  - Known endemic areas (natural herds) of Tick-borne encephalitis in Switzerland.

Lyme disease has a diversity of symptoms. Apart from the skin, the nervous system and the loco motor system the heart can also be affected. There are 3 stages to the illness. The first symptom is often a local inflammation of the skin, the so-called Erythema migrans, a circular rash. Several days after the bite a rash appears, which spreads out and becomes circular in appearance. This symptom only appears with around 30% of patients and is often located at the back of the knee, on the stomach, or on the shoulders. At the same time flu symptoms may occur. The first phase of the illness usually heals by itself within days to weeks. However a treatment with antibiotics is necessary to prevent the virus from spreading to other organs.

After weeks or months for some of patients the second phase of the illness takes place, with the nervous system (dura mater, brain, facial nerves), the skin (swelling, etc) and rarely the heart (cardiac dysrythmia) being affected. If these symptoms are not recognised straight away and treated with antibiotics, irreversible damage can be done (i.e. arthritis, adermotrophia, changes in personality) (Phase III). The diagnosis of Lyme disease can be very difficult; laboratory tests do not help much in the first phase of the illness.

What measures of protection can be taken against tick bites?

General measures:

Tight fitting clothing and keeping out of undergrowth are a good way of avoiding tick bites. Also the proper usage of tick repellent can offer affective protection. This can be sprayed onto the skin as well as onto clothes. As tick bites being painless are often not noticed it is advisable to check for ticks on the body and clothes after long walks. Ticks prefer warm, damp, and thin parts of the skin, like the back of the knee or the inside of the thigh, on the groin, throat, neck, or in the armpits; ticks are often found in children’s hair.

Vaccination against tick-borne encephalitis:

Vaccination is advisable for people who live in areas with natural herds (endemic areas, see Fig. 3) or who spend time there (generally from the age of 6). A vaccination is not necessary for people who have no risk of exposure. For complete immunity three doses of vaccine are required (two doses within a month and a third after five to twelve months). A booster vaccination is required after ten years. The vaccination can have slight short lasting side effects, pain at the penetration point, headaches, fever or pains in the joints; serious complications are very rare. For children under six years a vaccination is not necessary because a serious illness at this age is very rare. The special situation of pre school forest play groups must be evaluated locally and individually. The cost of the vaccination is covered by basic health insurance.

What to do when a tick bites.

so entfernen Sie Zecken richtig
Fig. 4 - How to remove a tick properly.
Photo: www.isw-tbe.info

The tick must be taken off as quickly as possible; the best way is to take hold of it, using fine-tipped tweezers, directly above the skin and to pull firmly. (Fig.4). The bite must then be disinfected. If symptoms develop after a tick bite a doctor should be consulted.

If symptoms of a borreliose i.e. an erythema migrans (circular rash) appear then treatment with antibiotics is necessary to prevent an escalation of the illness and other organs from being affected (see above). A preventative treatment after a tick bite when no symptoms are present is not recommended.

    Translation: Dawn Meister, Stallikon

Note

Contact

  • Bundesamt für Gesundheit BAG
    Abteilung übertragbare Krankheiten
    e-mail: epi @ bag.admin.ch
    www.bag.admin.ch