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Organisms Borne by Ticks and Other Vectors 235

heart damage may occur. Mucous membranes may inhabit tall grasses along with the ticks. In the United
become inflamed, particularly the tissues around the States the majority of vector-borne cases of diseases may
eyes, a condition called conjunctivitis. be attributed to the causative agent for Lyme disease.
■ Stage Three The name for the disease is derived from an area
of the northeastern United States, specifically from
The third and final stage, called late, persistent infec-
Old Lyme, Connecticut, where it was first described,
tions, results in permanent damage to the joints of the although it most likely existed prior to this time. The
body and the entire nervous system. Clinical signs
Lyme disease spirochete, B. burgdorferi, employs the
will include swelling and inflammation of the joints, traditional pattern of other parasites where the vector is
causing considerable pain. Numbness and tingling
the deer tick (I. dammini) and the white-footed mouse
of the hands and feet and sometimes in the back will serves as the reservoir host. White-tailed deer are not
occur. Extreme feelings of tiredness are commonly
directly involved in this method of transmission but they
experienced. These symptoms, due to damage to are crucial in maintaining a large tick population as the
the tissues of the body, may not occur for months or
primary host for the adult stage. Other rodents and at
years following the initial infection. When the condi- least one species of bird are also known to serve as hosts
tion has become chronic the signs and symptoms are
in the United States and to transmit disease organisms to
extremely serious with a grave prognosis.
the vectors, the I. dammini tick.
Nymphal stages of ticks transmit the majority of
the disease agents through the injection of spirochetes Rocky Mountain Spotted Fever
contained in the saliva of the tick and into the victim,
but some cases are known to have occurred from bites Why the name “Rocky Mountain spotted fever” was as-
involving the adult stage of a particular species of tick. cribed to the infection of the organism whose scientific
Lyme disease cases are more significant in some pock- name is Rickettsia rickettsii has apparently been lost to
ets of geography than in others with small areas of high history, because it appears to be a misnomer. As early as
prevalence. Lyme disease spirochetes may be found in the 1930s, it became clear that this disease occurred in
roughly two-fifths of nymphal ticks in endemic areas many areas of the United States other than the Rocky
and in almost all species of rodents, such as rats and Mountain region. In the 1980s the disease gained a
ground-welling squirrels as well as other species of ro- great deal of publicity and it can now be shown that this
dents, found in areas where the disease is prevalent disease is broadly distributed through almost all of the
(Figure 11-10). These small ground-dwelling animals states, and even extends into Canada and to the south
are particularly vulnerable to tick bites as they also through Central America and parts of South America.
Transmission of Rocky Mountain spotted fever from
ticks mostly occurs when the tick vectors are most active
and during warm weather when people tend to spend
Source: Centers for Disease Control and Prevention (CDC) disease, are two of the most frequently reported rick-
more time outdoors.
Rocky Mountain spotted fever, along with Lyme

ettsial illnesses in the United States and are also among
the most lethal diseases transmitted by ticks. Because it
has been diagnosed on both of the American continents,
there is an increasing potential for even more widespread
outbreaks. Some synonyms for Rocky Mountain spot-

as well as a number of names used exclusively in certain
regions and countries of Mexico and of South America.
Rocky Mountain spotted fever, caused by a species of
FIGURE 11-10 Rodents, which also include prairie ted fever used in other countries include “tick typhus”
dogs, ground squirrels, mice, and other mammals, can bacteria called R. rickettsii, is spread to humans by the
transmit tick-borne illnesses, including Lyme disease Ixodid (hard) tick. This is a species involved in the