Rocky Mountain Spotted Fever (RMSF) (cont.)

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What causes Rocky Mountain spotted fever?

RMSF is caused by Rickettsia rickettsii, a bacterium that is transmitted to humans via the bite of an infected tick. In the United States, these ticks include the Rocky Mountain wood tick (Dermacentor andersoni), American dog tick (Dermacentor variabilis), and brown dog tick (Rhipicephalus sanguineus).

The tick needs to bite humans and then attach itself for at least six to 10 hours for the transmission of the bacterium to occur, although transmission does not occur for up to 24 hours in some cases.

What are Rocky Mountain spotted fever risk factors?

Being outdoors in areas where the ticks carrying Rickettsia rickettsii are prevalent is the major risk factor for acquiring the disease.

Although the name of the disease includes the Rocky Mountains, it is somewhat of a misnomer as RMSF is most commonly reported in the southeastern part of the United States (though the Rocky Mountain region was one of the first areas where the disease was identified).

The incidence of RMSF increases when ticks are most active and people spend more time outdoors, which commonly occurs during the summer months.

What are Rocky Mountain spotted fever symptoms and signs?

The signs and symptoms of RMSF can appear within the first few days after the tick bite, or they can be delayed by up to two weeks.

RMSF typically begins with headaches, a high fever, and muscle aches. Some individuals may also develop abdominal pain, nausea, and vomiting. It is frequently followed by a rash (usually two to five days after the onset of fever) that appears around the ankles, forearms, and wrists. The rash consists of small, non-itchy, flat pink spots that then spread to the individual's chest and back and then down the remainder of the extremity. The rash can sometimes involve the palms and soles. In some cases (about 10% of the time), no rash develops, which makes diagnosing RMSF much more difficult. In about 35%-60% of patients with RMSF, a spotty rash that is red or purple (petechiae) may develop around the sixth day or later after the onset of symptoms. The appearance of this type of rash indicates that the disease has become more severe.

The damage to the lining of small blood vessels causes them to become leaky, with bleeding or clot formation leading to the following potential complications:

  • Kidneys: Kidney failure may occur due to damage of the small blood vessels in the kidney.
  • Extremities: Due to damage to the smallest blood vessels in the fingers or toes, blood flow can be disrupted, leading to gangrene, with amputation sometimes being necessary.
  • Brain: Headaches, lethargy, confusion, and even seizures can occur due to damage to the blood vessels in the brain.
  • Heart and lungs: Inflammation of heart tissue (myocarditis) or respiratory failure can lead to death.
  • Eyes: Damage to the eyes may occur, often due to inflammation of the vascular structures of the eye (uveitis or retinal vasculitis).
Medically Reviewed by a Doctor on 12/8/2014

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