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Ectoparasites 221

infections to humans. Some species of ticks are efficient complaints of arthritis of the large joints, along with
vectors of more than one infectious agent. An example myalgia and malaise, and in some instances neurologic
of this is found in the North American species of tick, and cardiac problems. The Borrelia are parasitic organ-
Dermacenter andersoni vector, which is an efficient isms responsible for several diseases (including relapsing
purveyor of both Rocky Mountain spotted fever and fever) transmitted by ticks and the human body louse.
tularemia. Other important pathogens are rickettsial or- Prophylactic treatment before exposure with antibiot-
ganisms, an obligate intracellular parasite that is spread ics has not halted the development of the disease to any
by vectors such as fleas, ticks, mites, and lice. great extent. Australian paralysis ticks cause paralysis in
Lyme disease is caused by a spirochete (Borrelia), humans but upon removing the tick, paralysis often be-
which is spread by a tick vector called Ixodes dammini. comes worse rather than improving. A number of tick
A number of tick species may embed themselves into the species are capable of transmitting many diseases around
skin of humans and animals, from which diseases may the world, and avoiding the bites of these vectors is of
be transmitted from these vectors (Figure 10-11). The utmost importance in preventing disease.
disease affects multiple organs and entire systems of
the human body and after recovery often leaves residual Fleas

Fleas are small, wingless, bloodsucking insects that act
as vectors for the spread of such diseases as tularemia,
Source: Centers for Disease Control and Prevention (CDC) that infest mostly warm-blooded animals including
typhus (rickettsial disease spread by lice, fleas, or mites),
and brucellosis (a bacterial disease). Fleas are parasites

humans. Various species infect certain animals, with
humans being chiefly infected by the bites from a human
flea Pulex irritans (Figure 10-12). Throughout his-
tory, rats that flourish in large cities have harbored fleas
capable of transmitting diseases to humans. The most

FIGURE 10-10 Dorsal view of a female yellow prominent occurrence of a serious epidemic that killed
dog tick, Amblyomma aureolatum, vector of Rocky
Mountain spotted fever in Brazil

Source: Centers for Disease Control and Prevention (CDC) Source: Centers for Disease Control and Prevention (CDC)

FIGURE 10-11 Dorsal view of an unidentified male FIGURE 10-12 Humans may contract plague,
Dermacentor sp. tick found upon a cat Y. pestis, when bitten by a rodent flea