What is a tick?
A tick is an arthropod parasite that bites humans (and animals) to gorge itself on blood. During this process, if the tick is infected, it can transmit the bacterium Borrelia burgdorferi, the cause of Lyme disease. Many tick species exist in Europe; the one that can transmit Lyme disease is the common sheep tick (Ixodes ricinus). Fortunately not all ticks that can carry Borrelia are actually infected with it. Ticks occur in undergrowth and high grass in woods, dunes, roadside verges and gardens.
How does the tick become infected?
The tick begins life as a larva that develops into a nymph and then an adult, needing a new host for each stage. When a nymph or adult tick has fed on an infected host at an earlier stage, it becomes infected, and can transmit Borrelia at a subsequent blood meal on a new host. After the bite, some bacteria move from the tick’s gut to its salivary glands and so reach the host’s skin, a process taking about 24 hours. Nymphs are thought to be the most important source for humans: they are tiny (just over 1 mm) and the bite is usually painless, so an attached nymph is often discovered late — which matters, because the chance of transmission is small if the tick is removed within 24 hours. Often the bite is not even noticed: half of all Lyme patients cannot remember being bitten.
What is Lyme disease?
Lyme disease is caused by Borrelia burgdorferi spread by the tick. Not everyone infected actually becomes ill. The disease is divided into three stages, each with its own possible complaints: early Lyme disease (skin signs: erythema migrans, lymphocytoma cutis); early disseminated Lyme disease within a year (multiple erythema migrans, neuroborreliosis, Lyme arthritis, Lyme carditis, hepatitis, uveitis, myositis); and late Lyme disease (acrodermatitis chronica atrophicans, chronic neuroborreliosis, chronic arthritis). This article focuses on the skin signs.
Skin signs of Lyme disease
Erythema migrans. A red, often itchy spot develops at the bite site. A red spot appears almost always, even without Borrelia infection; if it disappears within a week, infection is unlikely, but if the redness expands over several days — and certainly if a red ring-shaped patch forms — infection is very likely. Erythema migrans is the most common symptom, developing in about 80% of infected people. The characteristic ring can appear within a few days but is sometimes only visible after several months (on average about 17 days after the bite). It sometimes causes itch or mild burning. In this first stage, 23–50% of people also have headache, muscle pain, fatigue or fever.
Lymphocytoma cutis. A red-purple swelling of the skin, on average a few centimetres in size. Although it can occur anywhere, the earlobe (especially in children) and the area around the nipple are favourite sites. It is much rarer than erythema migrans, occurring in only 2–3% of infected people.
Acrodermatitis chronica atrophicans. This late stage causes skin changes that sometimes appear only years after infection (in about 3% of infected people). The skin first becomes red-purple and then, over months to years, atrophic — very thin and without elasticity — usually on the lower legs, especially around the ankles and shin. Skin sensation is often altered, and there can be fatigue or malaise.
Laboratory investigation
When Lyme disease is suspected, blood can be examined for antibodies against Borrelia. This test has limitations: depending on the timing, on average only about 50% of infected people are found to have antibodies, though the chance of a positive test rises with longer-standing infection. Because of the test’s limited value, the doctor will always treat on clinical suspicion regardless of the result, and usually does not wait for the result.
Treatment of Lyme disease
The skin signs are very treatable with antibiotics. For adults doxycycline is the preferred agent; for children, amoxicillin. The duration depends on the stage but is usually between 10 and 30 days.
How do I prevent tick bites and infection?
- Wear good covering clothing for recreation in woods, fields or dunes, especially from March to November.
- Check the whole skin for ticks on returning home.
- Remove ticks with special tweezers developed for this.
- Remove ticks as quickly as possible, which reduces the chance of transmission.
- Keep an eye on the bite site for at least 8 weeks.
- Consult your doctor if a red skin change develops around the bite.
When to see a doctor
See a doctor if a red, expanding or ring-shaped patch develops around a tick bite, or if you develop fever, joint, nerve or heart symptoms after a bite — early antibiotic treatment is effective.