Page 270 - parasitology for medical and clinical laboratoryprofessionals

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except in the immunocompromised and somewhat seri- particular region of the country. The American dog tick,
ously ill victims. A number of animals also fall victim to Dermacentor variabilis, is found throughout the eastern
babesiosis, at a greater rate than their human counter- United States, in Colorado, and the Pacific Northwest.
parts. The learner should note that babesiosis may be Adults are characterized by creamy-grey markings on the
so mild as to be self-limiting with no long-term damage scutum and by short mouthparts. Larvae and nymphs
to the victim. feed on small mammals and are seldom seen by people.
The term ehrlichiosis also applies to tick-borne Adults appear in the spring and early summer, where
illnesses, and is used to describe any of several bacte- they feed on mammals such as deer, other wild animals,
rial diseases that affect both animals and humans. These livestock, pets, and humans. This species of female tick
diseases are caused by the organisms chiefly of the genus may deposit over 6000 eggs before she dies. Tick paraly-
Ehrlichia, of which there are four species that cause sis has also occurred from bites by these ticks.
human disease. All of these four Ehrlichia species are The lone star tick, Amblyomma americanum,
capable of infecting two types of white blood cells called occurs across the southeastern and south-central United
monocytes and granulocytes. States, most commonly in moist woodlands. Adult fe-
Southern Tick–associated Rash Illness (STARI) males are characterized by a pearly white spot at the tip
is a Lyme-type disease transmitted by the lone star of the scutum and long mouthparts. A range of hosts are
tick, Amblyomma americanum, and causes a rash with a source of blood, such as ground-dwelling birds, small
malaise, fatigue, fever, headache, and muscle and joint mammals, and larger mammals such as deer, livestock,
pains. Diagnosis is based on a circular and expanding and pets. The long, barbed hypostome of female adults
“bulls eye” rash at the site of infection called erythema inflicts a deep feeding wound, and embedded females
chronicum migrans and is similar to the rash in Lyme engorging themselves have been tied to tick paralysis.
disease, and the causative is again the same as or similar This species is also capable of transmitting spotted fever,
to by Borrelia burgdorferi, the same organism that causes ehrlichiosis, and Southern Tick–associated Rash Illness
Lyme disease. Another spirochete, Borrelia lonestari has (STARI).
been isolated from one patient. But unlike Lyme disease, The black-legged tick, Ixodes scapularis, occurs
STARI is not been linked to arthritic, neurological, or throughout the eastern United States, and may be
chronic symptoms. abundant in moist woodlands with thick ground cover.
Tularemia, also called “rabbit fever,” “deer fly fever,” Adults, somewhat smaller than Amblyomma and Derma-
or “Ohara’s fever,” is a potentially deadly disease and centor ticks, are a deep mahogany color, with the female
occurs naturally in the United States, caused by a type of being tear drop–shaped and with long mouthparts. The
bacterial called Gram-negative coccobacillus. The disease larvae feed mostly on mice, and are abundant through
is contracted variously by ticks, other blood- sucking the summer and into September. Adults feed readily on
insects, direct contact with infected animals, poorly deer, important to the reproductive spread of the black-
cooked meat, or contaminated water. Water-dwelling legged tick.
rodents such as beavers and muskrats, as well as ground- The brown dog tick has not yet been shown to
dwelling animals may harbor the disease. Tularemia is a pass disease-causing agents to humans in the United
highly contagious disease caused by a bacterial infection States. But a relatively recent outbreak of spotted fever in
by an organism called Francisella tularensis with several Arizona may be associated with the brown dog tick. The
subspecies of varying levels of virulence. authors found that the homes of several patients were in-
Tick identification may be necessary to help in iden- fested with brown dog tick larvae, nymphs, and adults,
tifying the disease present. Images of the various ticks are many of which were infected with Rickettsia rickettsii,
helpful as well as knowing the likely tick inhabitants of a the bacterium that causes spotted fever.