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occur anywhere on the body and is less commonly seen on the palms and/or
soles. Vasculitis is less prominent, and leukopenia, anemia, and hepatitis are more
common in ehrlichiosis than in RMSF.
As for RMSF, doxycycline is the drug of choice for therapy in patients of all
ages and at the same dose of 4 mg/kg/day in divided doses (maximum 100 mg
twice a day). Therapy is continued until the patient is afebrile for at least 2 to 3
days and for a minimum total course of 5 to 10 days. Clinical improvement is
usually apparent within 3 days, and if not, an alternative diagnosis should be
sought. Disease may be more severe or even fatal in untreated patients. Early
initiation of therapy minimizes morbidity and mortality.
Dengue Fever
Dengue fever is caused by four dengue viruses transmitted by Aedes mosquitos
and is seen in tropical and subtropical areas of almost all continents (including
areas of Puerto Rico and the Caribbean basin and now in Florida). Many cases are
asymptomatic. In symptomatic cases, initial constitutional symptoms include
sudden onset of high fever, severe headache, myalgia, arthralgia, and abdominal
pain. During the course of fever that lasts 2 to 7 days, back and leg pain may be
severe, hence, the disease’s nickname “break bone fever.” The development of a
hemorrhagic vasculitis, most common in patients younger than 15 years, leads to
the more concerning subtype called dengue hemorrhagic fever. The term dengue
shock syndrome is used in even more severe cases when increased vascular
permeability leads to shock. Encephalopathy, hepatitis, myocardiopathy, intestinal
bleeding, and pneumonia are other complications.
Two distinct rashes may be seen, which coincide with the disease’s biphasic
fever pattern. The first rash is a generalized, transient, macular rash that blanches
under pressure and is seen within the first 24 to 48 hours of the onset of systemic
symptoms. The second rash coincides with or occurs 1 to 2 days after
defervescence and is generalized morbilliform, sparing the palms and soles.
Diagnosis is based on clinical suspicion and potential exposure based on the
virus’s geographic distribution. Serologic testing is available as is viral isolation
and measurement of serum immunoglobulin antibodies in paired serum

specimens obtained 4 weeks apart. Treatment is supportive, and may require
aggressive fluid management and pain control. Intravenous immunoglobulin
and/or plasma exchange may be of benefit in severe cases.

Causes of Other Widespread Rashes Associated With Fever
Non–life-threatening illnesses associated with fever and widespread rash include
coxsackievirus infections, erythema infectiosum, scarlet fever, and early varicella.