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248 CHAPTER 11

Rhipicephalus sanguineus: The brown dog tick is a furniture (Figure 11-24). This species is a vector of a dog
species that is a worldwide pest of dogs and occurs in the disease known as “canine ehrlichiosis.”
southern United States. It is not native to the midwestern
states and the northeastern and western states but has Can the Brown Dog Tick Transmit
been repeatedly introduced into these states by infested a Disease-Causing Agent of
dogs being brought there. Adults are small and almost
uniformly brown with short mouthparts. Domestic dogs Humans in the United States?
are the primary host for the developmental forms of The brown dog tick has not been known to transmit a
larvae, nymphs, and adults, all of which conceal them-
disease-causing agent of humans in the United States.
selves in places near where dogs sleep, and will aggres- However, a recent outbreak of spotted fever in Ari-
sively pursue their prey. This is a tick species known to
zona appears to have been associated with the brown
inhabit homes and they are capable of reproducing in- dog tick, based on a research publication by Demma
doors and tend to secrete themselves in homes and dog
et. al., in 2005, “Rocky Mountain Spotted Fever from
kennels that have source of heat including animal heat. an Unexpected Tick Vector in Arizona,” an article that
A female can lay about 4000 eggs before she dies. Larvae,
was published in the New England Journal of Medicine.
nymphs, and adults of the brown dog tick rarely bite The authors found that homes of several patients were
humans, but infestations in kennels and homes occur all
infested with brown dog tick larvae, nymphs, and adults,
too frequently. These ticks may overwinter in houses and many of which were infected with Rickettsia rickettsii,
are sometimes seen crawling up walls, curtains, and on
the bacterium that causes spotted fever. But remember
that to date, no definite transmissions of tick-borne dis-
ease by the brown dog tick has occurred.

MACROSCOPIC DIAGNOSTIC
FEATURE (REQUIRES
MAGNIFYING GLASS IN

SOME CASES)

General Classification—Tick
Source: Centers for Disease Control and Prevention (CDC) Stage found on host)
Organism
Ixodes scapularis
Specimen Required Organism (often
Adult
Color & Appearance Dark brown to black
3 mm in length
Size
Shape
Elongated oval
Motility
Fall from vegetation
onto host, or crawl
over the body of the
host after contact
FIGURE 11-24 Male brown dog tick, Rhipicephalus with vegetation
sanguineus, a hard tick, from dorsal view