Ticks are blood-feeding external parasites (Figure 82-1).
Ticks are a significant infectious disease problem in the United
States as well as worldwide. They have been implicated as vectors
in the transmission of a large number of diseases including Lyme
disease, ehrlichiosis, babesiosis, Rocky Mountain spotted fever,
tularemia, and tick borne relapsing fever. Disease transmission
is postulated to occur when stomach contents and saliva from the
tick are introduced into the host during the blood-feeding process.
There is significance in how long a tick has been attached and how
quickly a feeding tick can be removed. Early removal is felt to
greatly limit the transmission of disease. Current entomological
thinking suggests that the tick must be attached for at least 24 hours
in order to transmit B. burgdorferri, the
spirochete responsible for Lyme disease.1
There are two main families of ticks.2 Hard body ticks
belong to the Ixodidae family. Soft body ticks belong to the Argasidae
family. Hard body ticks are responsible for the transmission of
the majority of human diseases and will be the focus of this chapter.
Hard ticks pass through four life cycle stages from birth (egg,
larva, nymph, and adult). They require a blood meal in order to
progress into the next stage of their development.
The bite of a tick is painless and often not noticed until the
tick is seen attached to the skin. Ticks are often encountered in
the late spring, summer, and early fall. Ticks are more prevalent
in rural and wooded areas. They like to feed in dark (covered) and
moist areas of the body such as the axilla, groin, or scalp.
Ticks have specialized mouthparts that make their removal difficult
(Figure 82-2).2 They screw their mouthparts into the skin
in a clockwise direction. Mouthparts include the palps, the chelicerae,
and the hypostome. The chelicerae are used to cut through the epidermis
and allow passage of the hypostome, through which the feeding takes
place. Ticks attach themselves to their host by inserting the rod-like
hypostome into the skin. The hypostome has many backward pointing
sharp projections on it that prevent it from being pulled out. The
tick secretes a cement-like material around the hypostome to secure
its attachment to the host while it feeds. The tick releases its
mouthparts from the host after the meal is complete. It can take
hours to days for a tick to finish its blood meal.
The specialized mouthparts of the tick.
Any tick found attached to the skin should be removed. Transmission
of bacteria, spirochetes, viruses, or other infectious agents is
directly related to length of time of attachment. It is felt that ticks
attached less ...