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Organisms Borne by Ticks and Other Vectors 249

SUMMARY

Ticks operate as both parasites and as vectors of para- as are I. scapularis and I. pacificus, is that of the lone star
sites. In this way the tick is able to gain nutrients from the tick, Amblyomma americanum, also a member of the
host and to infect its benefactor with bacterial, rickettsia, Ixodidae family. This species is blamed for the transmis-
and viral diseases. Some of the organisms transmitted sion of Southern Tick–associated Rash Illness (STARI),
must live inside blood cells in order to complete part of by a Borrelia organism, the same genus that causes Lyme
their life cycle. Some of these bacterial diseases are not disease.
between parasitic and basic bacterial infections. Many diseases of the United States and the world
Ticks are blood-feeding parasites that are often are responsible for spreading diseases over wide areas of
found predominantly at the edges of woods, in tall grass the world. Other than the lone star tick and the deer tick,
and shrubs, where they await the opportunity to attach there are two species of dog ticks of importance in North
themselves to a passing warm-blooded animal host. America: Dermacentor variabilis, commonly called the
Ticks can be found in most wooded or forested regions American dog tick or the eastern wood tick, and the
throughout the world and are most common in areas Rhipicephalus sanguineus, or the brown dog tick.
where there are deer trails or human pathways. In these A veritable multitude of diseases that are tick borne
areas, a tick attaches itself to its host by inserting its sharp are covered in the chapter. Lyme disease is a disorder
mandibles called chelicerae and a hollow feeding tube that involves multiple systems of the body, with chronic
called a hypostome into the skin of its host. Ticks are and serious permanent problems if not treated at the
also quite proficient at transmitting parasites and other right time. Some other countries, particularly several
organisms into the bodies of their hosts while they are that are located in Europe, also suffer Lyme-like diseases
feeding on the host’s blood. transmitted by species of ticks other than those found in
Because ticks do not have wings and are unable the United States.
to jump, as they have somewhat short legs that are not Rocky Mountain spotted fever (RMSF), a rickett-
adapted for jumping, physical contact, or close contact sial disease, is another disorder that is named for a par-
is the only method of infestation for ticks. Ticks often ticular region of the country but is now found in many
fall onto their hosts from vegetation but some actually areas of the United States and even extends into Canada
stalk the host on foot. Ticks often take several days to and Latin and South America. And despite effective
complete a blood meal, and the attachment must last for treatment, the mortality rate stands at approximately
roughly a day in order to pass infective organisms on to 5 percent, even with the progress in treatment. RMSF is
their hosts. sometimes transmitted through breaks in the skin, be-
Ticks require hosts to support the maturation of cause the organisms are spread throughout the infected
the organisms. The significant species of ticks in the tick’s body.
United States that transmit most of the tick-borne dis- Babesiosis is called the “malaria of the Northeast.”
eases are as follows. White-tailed deer in the eastern Babesiosis is a parasitic disease caused by the genus
United States carry the Ixodes scapularis tick, which may Babesia, and like malaria, is also caused by a protozoan.
be found as “seed ticks” on the deer, and the tick popula- However, a chief difference is that babeosis does not
tion is directly proportional to the white-tailed deer. The have an extracellular phase in its life cycle, as does the
Ixodes pacificus ticks from the western portion of the causative organism for malaria. Babesiosis is a somewhat
United States are responsible for the majority of Rocky rare infection of the blood caused by a parasite that lives
Mountain spotted fever cases in that area, as are the in some species of ticks. Another similar disease is that
Ixodes scapularis for Lyme disease in the eastern parts it is intracellular caused by the genus Trypanosomiasis is
of the country. also attributed to a blood parasite, also a protozoan, but
Immature stages of the Ixodes scapularis tick also is caused by a true bug rather than by ticks or mosqui-
feed on small mammals or birds until they are ready to toes, as are babesiosis and malaria, respectively. Other
infest a deer, and are capable of laying up to 2000 eggs species of Babesia have been reported in other countries
following a blood meal of several days. Another hard tick, and the disease may be self-limiting without treatment,