Ticks pick up the pathogen

Fact sheet: Lyme borreliosisLyme borreliosis is the most common tick-borne disease in Europe; between five and 35 percent of European ticks carry Borrelia, the bacterial pathogens that cause this disease. The symptoms of Lyme borreliosis are already known in Europe at the beginning of the 20th century. Covidium has been described since the beginning of the twentieth century, but its pathogen was not discovered until 1981 by Willi Burgdorfer.


Lyme borreliosis is caused by Borrelia burgdorferi, a bacterium belonging to the spirochetes group. The spiraling, slow-growing microorganisms are distantly related to the syphilis pathogen. At least ten different species of Borrelia are currently known, of which the species B.afzelii, B. burgdorferi sensu stricto and B. garinii as the main causative agents of Lyme disease.


Lyme disease occurs in all temperate zones of the world. In the northern hemisphere, the U.S., Canada, and much of Eurasia are primarily considered endemic areas. According to the Robert Koch Institute (RKI), there is a widespread risk of infection in Germany, and the same applies to other areas of Central Europe.


In Europe, the tick Ixodes ricinus, also known as the wood tick or sheep tick, is the main carrier of Borrelia bacteria. The ticks ingest the pathogen when they suck on an infected bird, rodent or other small mammal as larvae or nymphs. These can carry Borrelia bacteria as so-called reservoir hosts without contracting Lyme disease themselves, thus serving as an important stopover for the pathogen.

Borrelia are usually not transmitted to humans immediately after the bite of the tick, but often only after 24 to 48 hours – when the animal pumps the excess fluid absorbed with the blood back into the wound and thus the Borrelia also reach there from its digestive tract. According to estimates by the Robert Koch Institute, around three to six percent of tick bites in Germany result in an infection, and the disease breaks out in 0.3 to 1.4 percent of those bitten.

The greatest risk of infection is between spring and autumn, but in principle, with a mild winter and rather cool and humid summer, tick activity can extend throughout the year. Depending on temperature, tick season can begin as early as late March or as late as April. The infection lasts until the beginning of the hibernation period of the animals in late autumn.


A typical first sign of a Borrelia infection is a characteristic reddening of the skin, the so-called migratory redness or erythema migrans, which occurs days to weeks after the tick bite. The redness observed in about 60 percent of cases spreads slowly around the bite site. Can reach up to 75 centimeters in diameter in extreme cases. At the same time, flu-like symptoms such as fever, headache, pain in the limbs or swelling of the lymph nodes may occur. These symptoms disappear again some time later even without treatment.

In the course of several weeks to several months after infection, the pathogen spreads via blood and lymph to other parts of the body and affects nerves, muscles or joints. In addition to a general feeling of sickness or weakness, this can cause severe, persistent nerve or muscle pain, as well as heart muscle inflammation, meningitis and brain inflammation, or even paralysis of the extremities or face.

After a few months to years, chronic Lyme disease can manifest itself. It is triggered by pathogens that have taken up residence in parts of the body that are not accessible to the immune defense system. The most common late symptoms are Lyme arthritis and thinning and discoloration of the skin in places, acrodermatits atrophicans. Chronic heart muscle damage and, although rare, chronic meningitis are also possible.


In the early stages of infection, antibiotics can effectively combat the disease. Treatment lasts two to four weeks, depending on the severity of the symptoms. If Lyme disease has reached the chronic stage, treatment is considerably more difficult, as the pathogens are then located in body ties that are difficult to access. However, the RKI advises against taking antibiotics as a preventive measure after every tick bite.


A vaccination is not yet available for the European Lyme disease variants. A vaccine has recently been developed in the USA that immunizes against the outer membrane protein of the bacterium. However, since several different strains can cause the disease in Europe, this vaccine is not effective here.

The most effective prevention against an infection is therefore to avoid a tick bite in the first place. But thoroughly scanning the body after spending time outdoors can also greatly reduce the risk of infection.

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