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230 CHAPTER 11

Source: Centers for Disease Control and Prevention (CDC)

FIGURE 11-3 White-tailed deer, Odocoileus
virginianus, responsible for tick populations and
transmission of disease Source: Centers for Disease Control and Prevention (CDC)

pathogenicity are met, the contraction of a disease may
result when bitten by a tick.
A related species, Ixodes pacificus, is found in the
western portion of the United States and is responsible
for the majority of Rocky Mountain spotted fever cases
FIGURE 11-4 Dorsal view of female lone star tick,
in that region. Livestock, rather than deer, are the adult
Amblyomma americanum, with characteristic star
host of this species of tick found in the western states
marking on dorsal surface
(Figure 11-3). Immature stages or nymphs of the Ixodes
scapularis tick also feed on smaller mammals or birds
until they are ready to infest deer or livestock. The female the Ixodidae family (Figure 11-4). These female ticks
tick as an adult must have a blood meal for several days have a white marking on their back resembling a star
before reaching the point where she can be productive in and are responsible for the transmission of Southern
laying eggs. Tick–associated Rash Illness. The causative organism
A considerable number of species of ticks are for this disease is the Borrelia species, the same genus
spread throughout the United States and around the as the organism that causes Lyme disease. These species
world, and are responsible for spreading diseases will be considered when discussing specific diseases
worldwide. Discussions of these numerous species is transmitted by each of them later in this section.
beyond the scope of this publication, but those com- It should again be stressed that a tick must gener-
monly associated with infectious diseases in the United ally remain imbedded in the skin of its victim for at least
States are discussed in this publication. A significant 18 to 24 hours in order to transmit a pathogen to a hu-
number of these species are also primarily important man or other animal. Therefore it is important to remove
because they impact agricultural endeavors rather than the tick when it is still roaming about the body before it
spreading pathogens to humans. Many of these para- becomes embedded in the skin. Removal of the feeding
sitic ticks attack cattle, sheep, goats, and horses, caus- tick must be performed carefully in order to avoid decap-
ing death and illness among these animals and thereby itating the tick and leaving the head in the skin, result-
extracting a great economic toll. Ticks are divided into ing in infections of various pathogens. Although almost
two general and basic groups called “hard” ticks and a thousand species of ticks exist, around 80 species of
“soft” ticks. Ixodidae (hard ticks) and perhaps 10 species of soft
Another “hard” tick of the Ixodes genus is the ticks are currently found in the United States. In addi-
lone star tick (Amblyomma americanum), a member of tion to the lone star tick and the deer tick, two species of