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Rocky Mountain spotted fever

Definition

Rocky Mountain spotted fever is an infectious disease caused by Rickettsia rickettsii transmitted to humans by the bite of a tick.

Causes, incidence, and risk factors

In the western U.S., the causative agent, R. rickettsii, is transmitted by the wood tick, and in the eastern U.S., by the dog tick. Other ticks transmit the infection in the southern U.S. and in Central and South America.

Contrary to the name "Rocky Mountain," most recent cases have been reported in the eastern United States: North and South Carolina, Virginia, Maryland, Georgia, Tennessee, and Oklahoma. Most cases occur in the spring and summer with about 1,000 cases reported per year. Most of the reported cases have been in children.

The risk factors include recent hiking or exposure to ticks in an area where the disease is known to occur.

Symptoms

fever
chills
incubation period of 2 to 14 days
severe headache
muscle pain
mental confusion
rash, first appearing on wrists and ankles, then spreading to most of the body, usually starts a few days after fever starts; up to 20% of people do not get a rash

Additional symptoms that may be associated with this disease:

excessive thirst
nausea and vomiting
hallucinations
diarrhea
loss of appetite
abnormal sensitivity to light

Signs and tests

low platelets
low red blood cell count in 30% of patients
possible renal failure, elevated creatinine
possible clotting problems, elevated PT and PTT
blood in the urine and protein in the urine
antibody titer by complement fixation or immunofluorescence that indicates the presence of infection
skin biopsy at the site of the rash may show the Rickettsia rickettsii

Treatment

The objective of treatment is careful removal of the tick from the skin and antibiotics to eliminate the infection. Doxycycline or tetracycline are frequently used. Chloramphenicol may be used in pregnant women.

Note: oral tetracycline and doxycycline is usually not prescribed for children until after all the permanent teeth have erupted because it can permanently discolor teeth that are still forming. For this disease, it may be used for short periods of time when it is felt that the risks outweigh the benefits.

Expectations (prognosis)

Treatment usually cures the infection. Complications are rare but can include paralysis, hearing loss, and nerve damage. The death rate is 5 to 7% and usually reflects a delay in seeking treatment.

Complications

pneumonitis
respiratory or cardiac failure
meningitis
brain damage
clotting problems
kidney failure
shock

Calling your health care provider

Call your health care provider if symptoms develop after exposure to ticks or known tick bite. The complications of untreated Rocky Mountain spotted fever can be life threatening.

Prevention

When walking or hiking in tick-infested areas, tuck long pants into socks to protect the legs, and wear shoes and long-sleeved shirts. Ticks will show up on white or light colors better than dark colors, making them easier to remove from clothing.

Remove ticks immediately by using a tweezers, pulling carefully and steadily. Insect repellent may be helpful. Because less than 1% of ticks carry this infection, antibiotics are not usually given after a tick bite if there is no evidence of disease.

There is no vaccine against this disease.