96
The treatment of choice for tularemia has been streptomycin, but recent shortages
of this drug have forced reliance on other agents. Prospective, controlled data
about these drugs do not exist. Gentamicin at a dosage of 5.4 to 7.5mg/kg/day
intravenously in divided doses every 8 hours (mean, 6 mg/kg/day) for seven to
fourteen days, depending upon clinical response, has been effective. Tetracycline
and its derivatives have been shown to be effective, but are generally reserved for
less severe infections.
H. Colorado Tick Fever: Colorado tick fever is the most common human arbovirus
infection. It is transmitted exclusively by female wood ticks (Dermacentor
andersoni) in North America, and its distribution roughly approximates that of
this vector. The virus has been isolated from humans and from ticks in California,
Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, South Dakota, Utah,
Washington, and Wyoming, and also in Canada's southern Alberta and British
Columbia. This infection continues to be under recognized and underreported.
People with recreational or occupational exposure to ticks in the period April
through June have a higher incidence of infection. After an incubation period of
less than one to nineteen days (average, about four days), the onset is usually
abrupt and is characterized by high fever, chills, joint and muscle pains, severe
headache, ocular pain, conjunctival injection, nausea, and occasional vomiting.
The spleen and liver may be palpable. A transitory petechial or maculopapular
rash is seen in a few individuals.
No specific signs or symptoms, physical findings, or laboratory abnormalities
define Colorado tick fever, but the diagnosis is strongly suggested if the illness is
interrupted by an afebrile, symptom-free interval that lasts two to three days. Fifty
percent of the individuals with clinical illness manifest this interval.
Colorado tick fever is rarely a life-threatening illness, but can cause severe
discomfort, and symptoms may last for some weeks. A few individuals have a
more severe illness that produces extended prostration, anorexia, continuing
fatigue, and convalescence for several more weeks. Children may have
hemorrhagic manifestations ranging from a more pronounced rash to
disseminated intravascular coagulopathy and gastrointestinal bleeding.
The diagnosis is confirmed by serologic testing. No specific therapy or vaccine is
available.
I. Tick Paralysis: Tick paralysis has been recognized since 1912 and involves
humans and animals. This disorder is found world wide, but occurs most often in
North America and Australia. The Pacific Northwest and Rocky Mountain areas
account for most cases. At least forty-three species of tick have been reported to
cause tick paralysis, but the dog tick, D variabilis, and the wood tick, D andersoni
are the most common vectors.
Tick paralysis occurs during the spring and summer when ticks are feeding.
Children are affected more often than adults, and girls are affected twice as often
as boys, possibly because their long hair hides the tick. Men are affected more
