Ixodes ricinus

The most common tick species in Central Europe, Ixodes ricinus, is also the main carrier of B. burgdorferi s.l. In the USA and Eurasia, Ixodes scapularis and Ixodes persulcatus are the most important vectors of the pathogen. Due to its high adaptability and resistance to changing environmental conditions, Ixodes ricinus has been widely distributed geographically in recent decades. In Germany, coniferous forests, deciduous forests and mixed forests provide suitable habitats. The required relative humidity is at least 70-80 %. From an altitude of 1,500 metres, ticks are hardly ever found.

Ixodes ricinus is a carrier of the following diseases:

• Lyme borreliosis
• Early summer meningoencephalitis
• endemic relapsing fever
• Babesiosis
• Honest.
• S.a. ticks, tick bite, tick granuloma, erythema chronicum migrans, acrodermatitis chronica atrophicans, Q fever, tularaemia, lymphadenosis cutis benigna.

Host search activity: The host search activity takes place at different vegetation levels depending on the stage of development. Larvae remain limited to vegetation near the ground. Nymphs and adult ticks ascend to a height of about 150 cm in search of a suitable host. Here they remain at the top of leaves or blades of grass. With the help of the Haller organ, which is located in a sensory pit on both sides of the first pair of legs, mechanical, thermal and chemical stimuli can be absorbed.

If a host is located due to the perception of an increased carbon dioxide or ammonia concentration, ground vibrations or temperature increases, the tick clings to the host while passing it or falls onto it. Afterwards, it looks for a suitable bite site (in the animal often finely hairy or hairless body regions) with comparatively thin skin. The skin is scratched at this point with the paired chelicers. Afterwards, she drills the puncture organ (hypostome) into the wound. At the same time, it injects anaesthetic and anti-inflammatory components into the stab wound with the saliva it releases, so that tick bites are often not noticed by the host (Rufli T et al. 1981). It can take up to 12 hours from the infestation of the host to the actual stinging. The duration of the sucking act varies and depends on the developmental stage of the tick. Nymphs suck for 4-6 days; adult ticks suck for 6-8 days. Adult female ticks can suck 100 to 200 times their body weight.

Transmission of Borrelia: During the sucking act on an infected host, Borrelia are absorbed with the body fluid. The pathogens multiply in the midgut of the tick. Later the Borrelia bacteria migrate via the haemolymph into the salivary gland (Piesman et al. 2001).

The next stage of development of the tick transfers the Borrelia bacteria to a new host during the sucking process. In order to be able to enter the host tissue with the tick saliva, the Borrelia bacteria first migrate into the salivary gland via the lymphatic system (Piesman J et al. 2001). The pathogen is also transmitted via regurgitation of the tick's midgut secretions into the stab wound.

Reservoir hosts: Ixodes ricinus has a very low host specificity, parasitizing over 300 reptile, avian and mammalian species. The 3 developmental stages of the tick are clustered around different host groups according to their range of action: larvae are often found on small mammals that are closer to the ground. In Central Europe, these are mainly various types of mice. Nymphs are found on somewhat larger mammals such as squirrels, martens, hedgehogs and birds. Like adult ticks, nymphs also parasitize on various larger wild animals (roe deer and red deer). Humans and domestic animals are also infested.

According to the Robert Koch Institute, it can be assumed that there is a risk of infection in all parts of Germany, but there are no comprehensive epidemiological studies. The prevalence of B. burgdorferi in ticks in Germany is estimated at 5 - 35 %. On average about 20 % of adult ticks, about 10 % of nymphs and up to 1 % of larvae are infected with Borrelia bacteria. (Source: Robert Koch Institute 2013).

1. Piesman J et al (2001) Use of Quantitative PCR to Measure Density of Borrelia burgdorferi in the Midgut and Salivary Glands of Feeding Tick Vectors. J Clin Microbiol 39: 4145-4148.
2. Rufli T et al (1981) Dermatological entomology: Ixodidae, ticks. Switzerland Round Med 70: 362-385.
3. http://www.rki.de/DE/Content/Infekt/EpidBull/Merkblaetter/Ratgeber_LymeBorreliose.html?nn=23 74512#doc2398672bodyText2.