Ticks

Ticks are the main vectors of pathogens relevant for animals and humans in Central Europe. The ticks occurring in Germany belong to two families that differ quite significantly from each other, the hard ticks (Ixodidae) and the soft ticks (Argasidae). Only one type of human medical importance exists from the latter family in Germany, the pigeon tick, Argas reflexus. Its bite and saliva can cause serious irritation and allergic reactions, including anaphylactic shock. It is relatively rare in Stuttgart, Mannheim, Karlsruhe and other large cities, however, it is a relatively common parasite of feral pigeons. In Germany, 17 species of hard ticks have been recorded, eight of them in Baden-Württemberg.

All known species of Ixodidae in Germany have a three-host life cycle (see Figure). The female lays its eggs on the ground under organic matter. The number of eggs depends on the tick species: a female of Ixodes ricinus lays about 1,000-2,500 eggs, while female Dermacentor reticulatus lay between 2,000 and 5,000 eggs. Depending on temperature and humidity, it takes a number of weeks until the larvae hatch. The larva has to find a host, usually a small mammal or a bird, to suck blood and other body fluids until it is fully engorged. The duration of the blood meal extends over several days, after which the engorged larva drops to the ground where they moult within a few weeks to develop into a nymph. The nymph finds a new host, feeds on its blood, falls off and moults either into a male or a female. The females require a blood meal in order to ensure egg production. The entire development cycle can be completed within one year (D. reticulatus) or needs several years (I. ricinus).

Ticks spend only a small part of their lives on their respective host animals, with most of their lives, up to 99 %, being spend developing to the next stage and waiting for hosts. This means that during this period development depends on local environmental conditions such as temperature and humidity. For tick species such as I. ricinus, D. marginatus and D. reticulatus both the habitat in forests and grasslands, as well as microhabitat, belong to this environment. For I. hexagonus (hedgehog tick) and Rhipicephalus sanguineus (brown dog tick) which are strongly attached to their hosts’ nests, or in Central Europe to human dwellings, the microclimate plays the most important role.

Developmental cycle of Ixodes ricinus (Picture: Nina Littwin)