All ticks carry Lyme disease

Lyme disease: transmission & frequency

transmission

Lyme borrelia are transmitted to humans by ticks via the proboscis during the sucking process. In Germany, Ixodes ricinus, also known as the "common wood tick", is the type of tick that occurs predominantly as a carrier. Transmission by other blood-sucking insects such as horseflies, flies, mosquitoes and fleas has rarely been reported. Infections are particularly common in the warm season from April to October, when the ticks lurk in forests, grass (mostly larvae), low bushes (nymphs) or bushes (adult ticks) to suckle their blood.Ticks have a predilection for rough things and stick to them firmly when they can make contact with it (e.g. the fur of the game passing by), but they are not always picky and also pass over to people walking by.

The ticks, which belong to the group of arachnids, ingest the pathogen during blood meals on wild animals (e.g. rodents, red deer) without becoming ill themselves. Ticks go through three stages of development: larva (3 pairs of legs), nymphs and adult ticks (4 pairs of legs each). As a rule, the tick only bites once at each stage, with female adult ticks in particular swelling to a multiple of their "sober" body size. Since the probability of ingestion increases with each blood meal, larvae are the least common and adult ticks are the most common carriers of Borrelia.

The probability of transmission by ticks containing Borrelia is primarily related to the duration of the sucking act: If this is less than 24 hours, the risk of transmission is low, but if it lasts longer it increases to 10-25%. The sober tick harbors Borrelia in the intestine, which are coated with a certain surface protein (OspA). Only during the act of sucking does the blood contact change this surface protein from OspA to OspC. Only OspC-positive Borrelia migrate through the intestinal wall into the tick's salivary glands and can then infect the host. This process takes a certain amount of time (at least 36 hours in the USA, probably shorter in Europe).

frequency

Lyme disease is the most common tick-borne infectious disease in the northern hemisphere. In Germany there is no nationwide reporting requirement. In the last few years, however, a reporting requirement for certain manifestations has been introduced in some federal states (erythema migrans, arthritis, neuroborreliosis). The number of reported newly diagnosed diseases per year fluctuated between 15 and 50 per 100,000 inhabitants, depending on the region. According to this, the number of new cases is estimated at 40,000-80,000 per year. In prospective studies, in certain regions there were sometimes significantly higher numbers with up to 150 new cases per 100,000 population per year. Extrapolated to Germany, that would mean 80,000 to over 200,000 cases per year.

By no means every infection leads to an illness in humans. Usually, however, antibodies are formed that remain detectable in the long term (possibly for life). When examining blood samples from the last nationwide health survey, specific antibodies were detectable in 9.4% of adults. There was a clear increase with age from around 6% for 18-40 year olds to 20% for> 70 year olds. Antibodies were detectable significantly more frequently in men, in the rural population and in southern Germany.

Depending on the region and stage of development, 5-35% of Ixodes ticks in Germany are infected with Borrelia, with adult ticks being infected with an average of 20%, nymphs 10% and larvae only about 1%. Probably nymphs are particularly important vectors, as they are hardly noticed due to their small size. Although I.ricinus has a very broad host range (e.g. mice, birds, lizards, roe deer and red deer, foxes, rabbits and domestic animals such as cattle, sheep, dogs and cats), mice represent the main reservoir of pathogens.

According to current knowledge, 1.5–6% of those affected in Germany are likely to have an infection (including clinically inconspicuous cases) after a tick bite and 0.3–1.4% with an actual disease. In the majority this occurs as so-called wandering redness (erythema migrans), in about 10% of the diseases, however, untreated it can lead to more serious complications, secondary diseases and long-term damage.