Rocky Mountain spotted fever

Definition

Rocky Mountain spotted fever is an infectious disease brought on by a specific type of bacteria carried by ticks.

Alternative Names

Spotted fever

Causes, incidence, and risk factors

Rocky Mountain spotted fever is caused by Rickettsia rickettsii (R. Rickettsii), which is carried by ticks. The bacteria spread to humans through a tick bite.

In the western United States, the bacteria are carried by the wood tick, and in the eastern U.S. it is carried by the dog tick. However, other ticks spread 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, including 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.

Risk factors include recent hiking or exposure to ticks in an area where the disease is known to occur. The bacteria is unlikely to be transmitted to a person by a tick that is attached for less than 20 hours.

Symptoms

Symptoms usually develop about 2 to 14 days after the tick bite. They may include:

• Chills
• Fever
• Severe headache
• Muscle pain
• Mental confusion
• Rash -- usually starts a few days after the fever; first appears on wrists and ankles as spots that are 1 - 5 mm in diameter, then spreads to most of the body. About one-third of infected people do not get a rash at all.

Additional symptoms that may be associated with this disease:

• Abnormal sensitivity to light
• Diarrhea
• Excessive thirst
• Hallucinations
• Loss of appetite
• Nausea
• Vomiting

Signs and tests

Tests that may be done include:

• Antibody titer by complement fixation or immunofluorescence
• Kidney function tests
• Platelet count
• Partial thromboplastin time (PTT)
• Prothrombin time (PT)
• Red blood cell count
• Skin biopsy taken from the rash to check for R. rickettsii
• Urinalysis to check for blood in the urine or protein in the urine

Treatment

Treatment involves careful removal of the tick from the skin and antibiotics to eliminate the infection. Doxycycline or tetracycline are frequently used for both confirmed and suspected cases. Chloramphenicol may be used in pregnant women.

Note: There is concern that tetracycline and doxycycline may stain the teeth of children whose permanent teeth have not yet formed. Tooth discoloration, however, is very unusual when a child takes these medicines for 14 days or less. Therefore these medicines are first line treatment, even for children.

Expectations (prognosis)

Treatment usually cures the infection. Complications are rare but can include paralysis, hearing loss, nerve damage, and, rarely, death.

Complications

• Brain damage
• Clotting problems
• Heart failure
• Kidney failure
• Lung failure
• Meningitis
• Pneumonitis (lung inflammation)
• 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 see and 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.

References

Raoult D. Rickettsioses. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier. 2007: chap 348.