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242 CHAPTER 11

How Is Ehrlichiosis Contracted? Endemic Areas of the
United States
In the United States, Ehrlichiae organisms are trans-
mitted via two different genera of hard ticks. As stated Most cases of ehrlichiosis are reported within the
previously, the specific vector responsible for any of these geographic distribution of the three vector ticks, namely
tick-borne illnesses is based upon geographic location. Amblyomma americanum, Ixodes scapularis, and
There are two known vectors of the bacterial species I. pacificus. Occasional cases may occur from areas out-
capable of causing ehrlichiosis in the United States. The side the normal distribution of the tick vector. But in most
lone star tick (Amblyomma americanum), the blacklegged of these instances the cases have been traced to persons
tick (Ixodes scapularis), and the western blacklegged tick who have recently traveled to areas where the tick-borne
(Ixodes pacificus) are both known vectors of ehrlichiosis diseases are endemic. Therefore, it is reasonable that
in the United States. The bacterial species of the caus- these individuals were unknowingly bitten by an infected
ative agent for ehrlichiosis may vary between the two ma- tick and did not develop symptoms until after returning
jor genera of Anaplasma and Ehrlichia. to their home areas. Therefore, travel to an area that is
Thirty states within the United States have reported considered endemic for ehrlichiosis within the past 2 to
the disease, whereas most of the southern states are 3 weeks prior to developing symptoms should alert the
responsible for the majority of the cases, as the climate physician that there is a possibility of a tick-borne illness,
supports a large tick population. On the European con- including that of ehrlichiosis.
tinent, Ixodes ricinus is the primary tick vector respon-
sible for transmitting the disease. An Ixodid, or hard Diagnosis and Treatment for
tick, A. americanum is found through the eastern and Ehrlichiosis
south-central states and can transmit a number of disease
agents including ehrlichiosis that affects humans, dogs, Ehrlichiosis is a febrile illness with significant systemic
goats, and white-tailed deer. Representatives from all symptoms including severe headaches, chills, muscle pain,
three of its life stages may aggressively bite people in the and sometimes a rash along with other assorted subjec-
southern United States. The lone star ticks are capable tive symptoms dependent upon the severity of the infec-
of transmitting Ehrlichia chaffeensis and E. ewingii, both tion and the victim’s general health. Laboratory findings
of which cause the disease. may include anemia, a decreased white blood cell count
where certain types of white cells are specifically affected
Symptoms of Ehrlichiosis and which include a lymphocyte count and a blood plate-
let count. Biochemistry levels with plasma electrolyte im-
Non-specific symptoms similar to those of influenza balances (sodium, potassium, and chloride) may reveal
are the predominant characteristics of the symptoms of low sodium values perhaps related to nausea along with
ehrlichiosis. The complaints by patients requesting medi- elevated liver enzymes that would indicate a degree of
cal treatment and who are diagnosed with ehrlichiosis will liver damage. Examinations of cerebral spinal fluid (CSF)
often resemble symptoms of a number of other infectious may reveal an increased white blood cell level as well as
and some non-infectious diseases. These clinical features an increased total protein level, values that are commonly
generally include fever, general malaise, fatigue, leukopenia found during infections. The antibiotic doxycycline is
(low white blood cell count), thrombocytopenia (low the most effective, whereas antibiotic susceptibility tests
platelet count), headache, and muscular aches and pains. appear to show resistance of some strains of the organism
Other signs and symptoms may include nausea, vomiting, to a powerful antibiotic called chloramphenicol.
diarrhea, cough, joint pains, confusion, and occasionally
a rash. Symptoms typically appear after an incubation Southern Tick–Associated Rash
period of 5 to 10 days following the tick bite. It is possible Illness (STARI)
that some individuals who are infected with an ehrlichial
agent will not become ill enough to be aware of a disease A rash similar to that of Lyme disease has been de-
state or they may develop only mild and innocuous symp- scribed in humans following bites of the lone star tick,
toms that are spontaneously resolved. Amblyomma americanum. The rash may be accompanied