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Chapter 3: Transmission / Natural cycle

other lower vegetation to wait for a host near mediators of pain, itching and inflammation,
by passing. particularly the host’s own histamine,
serotonin, and bradykinin. 7,25
Ixodes ricinus adults can climb as high as 1.5 m
19
on brushy vegetation. The immature stages Ixodid ticks feed gradually because they must
are found lower, up to 70 cm for larvae (O. first produce new cuticle to accommodate the
17
Kahl, personal communication) and less than 1 massive blood meal. Typical attachment
19
m for nymphs. Ticks are able to sense a host periods range from as few as 2 days for larvae
with their Haller’s organ, which is located on to as long as 13 days for females. 3,14
the tarsi I. Haller’s organ possesses chemo-,
mechano-, and thermoreceptors that also An I. ricinus can reach approximately 450 mg
ensures (together with the receptors on the at the end of feeding from approximately 2
21
palps) selection of a suitable feeding site on mg at the beginning of feeding.
the host body. The most important stimuli are
carbon dioxide (CO 2), vibration produced by Drop-off
the moving potential hosts, and host tempera-
The controlled timing of drop-off from the
ture. For some species, visual images, smell,
and even noise also can stimulate the tick. 14,20- host offers important ecological advantages.
22 For non-nidicolous ticks, such drop-off

rhythms are synchronized with host behave-
Feeding behavior ioral patterns. This tends to disperse fed ticks
in optimal habitats where they can develop
Feeding behavior, even on preferred hosts, is and reproduce. Photoperiod appears to be the
not a uniform process. An ixodid tick may dominant abiotic exogenous factor affecting
crawl on the host for several hours in search drop-off patterns. The daily light:dark cycle
of a suitable feeding site. After attachment, induces a regular rhythm of feeding and
many ixodid ticks secrete cement during the dropping off. Detachment may occur while the
first 1–2 days to secure themselves at the hosts are inactive in their nests or burrows or,
22
wound site. Subsequently, the feeding tick alternatively, it may be coordinated with the
14
begins salivating into the developing period of maximum host activity.
hematoma and sucking blood; salivation and
7
blood sucking are repeated alternately. Host specificity
Saliva not only plays an important role in the
23
feeding tick’s osmoregulation but also a Tick species can be either opportunistic or
specific with respect to the hosts they choose
variety of pharmacological effects. There is an
to feed on; both I. ricinus and I. persulcatus
extensive array of antihemostatic, anti-
inflammatory, and immunomodulatory pro- are opportunistic species, especially the
teins and lipids in the tick saliva that suppress immatures. For I. ricinus, more than 300
the host’s ability to reject the feeding tick. 7,23– species of vertebrate hosts have been
14,27
26 recorded. Larvae and nymphs of I. ricinus
Anticoagulant effects, inhibiting factor Xa,
were first shown in I. ricinus in 1898-1899. 22,23 feed readily on lizards, birds, and small
In addition, many tick species produce mammals, as well as on larger hosts including
proteins that inhibit thrombin directly or deer. Adults feed on medium-sized and large
mammals, especially ungulates, as well as
inhibit the conversion of prothrombin to 14
humans, as do the immature ticks. I.
thrombin by inhibiting factor V. Other
persulcatus is more restricted to mammal
proteins prevent platelet aggregation or bind, 28
antagonize or degrade important host hosts.

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