The Vector (Ixodes Ricinus)
Throughout the world 850 tick species have been described. Eight members of the family of hard ticks have become notorious as carriers of disease agents in our climate. Ixodes ricinus, the common castor-bean tick, is the most important and most common tick species in Europe and, thus, mainly responsible for the spread of TBE virus (Western subtype) in Europe. The Far-Eastern subtype of TBE virus is found mainly beyond the Ural mountains; its vector is primarily Ixodes persulcatus.
The scientific name “Ixodes ricinus” is derived from the replete tick’s close resemblance to a ricinus seed or castor bean. A fasting adult female is 3–4mm in size, while male ticks are about 2.5mm long. The body, which is variously covered with hairs as well as warts and rings, is vastly extensible in the female and often takes on a light grey color after blood feeding. The female can take in up to 100–200 times its own body weight in blood, thus increasing its volume approximately 120 fold.
lxodes ricinus is equipped with piercing and sucking mouthparts (chelicerae and hypopharynx). The saliva of blood-feeding ticks contains numerous bioactive components with a broad spectrum of pharmacologic properties, among them anti-coagulants, enzymes and inhibitors, local anesthetics and anti-inflammatory compounds, toxins and other secretions such as cement for anchoring the mouth-parts in the host’s skin.
By use of sense organs the tick can react to thermic, chemical, and physical stimuli such as vibrations or changes in temperature caused by a passing host. Probably also the CO2 and butyric acid discharged by the host play a role in this process.