Rocky Mountain Spotted Fever

What is Rocky Mountain spotted fever?

Rocky Mountain spotted fever is a potentially severe illness caused by tiny bacteria called Rickettsia rickettsii, which are transmitted through the bite of an infected tick. In the eastern United States and in California, the infected tick is usually Dermacentor variabilis, the American dog tick. In most of the western United States, the tick is more likely to be Dermacentor andersoni, the Rocky Mountain wood tick. Humans typically become infected in the spring and early summer.

Once someone is bitten by an infected tick, Rocky Mountain spotted fever bacteria can spread throughout the bloodstream and lymphatic system. The tick must remain attached and be actively feeding to transmit the bacteria. Not everybody who is bitten by an infected tick develops Rocky Mountain spotted fever. It is not clear why some people get the disease and others do not.

Once in the body, the bacteria attack and severely damage the linings of blood vessels. The injured vessels leak a watery fluid, which causes swelling. The blood vessels also can lose blood, which causes potentially life-threatening hemorrhages (serious bleeding). As damaged blood vessels continue to leak, blood pressure can decrease. If this happens, blood flow to the kidneys can decrease, causing kidney damage and, possibly, kidney failure.

Rocky Mountain spotted fever bacteria also may attack the brain directly, causing symptoms of encephalitis (brain infection) or meningoencephalitis (infection of the brain and its surrounding membranes). Rocky Mountain spotted fever also can cause jaundice (yellowing of the skin and eyes) as a result of liver injury. In the lungs, Rocky Mountain spotted fever can lead to an accumulation of fluid in the lungs (pulmonary edema) and severe breathing difficulties.

According to the U.S. Centers for Disease Control and Prevention (CDC), about 1,200 cases of Rocky Mountain spotted fever are diagnosed each year in the United States. While persons of any age can be infected, some studies suggest that children ages 5 to 9 are more likely to be infected than any other age group.

Symptoms of Rocky Mountain spotted fever

Typically, symptoms begin two to 14 days after a tick bite, with an average of one week. During the first three days of symptoms, an infected person usually has a fever of more than 102° Fahrenheit and a severe headache. Muscle aches, nausea and vomiting are common. Between the third and fifth day of fever, most people develop a rash, which usually begins on the wrists and ankles, then spreads to the arms, legs and trunk. In about two-thirds of patients, the rash also involves the palms of the hands and the soles of the feet. On day six or later, the areas of rash may show tiny broken blood vessels and small hemorrhages under the skin.

Other symptoms of Rocky Mountain spotted fever include:

lungs: rapid breathing, severe shortness of breath, bluish tint to fingernails and lips
liver and gastrointestinal tract: abdominal pain, nausea, vomiting, diarrhea and jaundice
brain: confusion, lethargy, difficulty walking, extreme drowsiness, seizures and coma.

Diagnosing Rocky Mountain spotted fever

The classic features that may lead your doctor to suspect Rocky Mountain spotted fever are high fever, rash, headache, and a history of tick exposure, such as walking in a tick-infested area, within 14 days of developing the symptoms of Rocky Mountain spotted fever. Only about 60% of patients recall being bitten by a tick.

The early symptoms of Rocky Mountain spotted fever are not specific, and diagnostic tests often are negative early in the disease. Therefore, if your doctor suspects that you have Rocky Mountain spotted fever, he or she generally will begin treatment immediately, even if your blood tests are negative. Early treatment is essential to help you avoid severe complications.

Your doctor may recommend removing a small piece of skin from the area of the rash so it can be examined in a laboratory. This procedure is called a biopsy. The biopsy sample can be tested in the laboratory with chemicals to confirm the presence of Rocky Mountain spotted fever bacteria.

Standard antibody blood tests can confirm the diagnosis, but it usually takes a week or more for the body to produce the antibodies that indicate infection. As a result, treatment decisions usually must be made before definitive test results are available.

Some labs offer a more rapid test (called PCR) that is helpful if positive as an indication of infection. But a negative result does not reliably rule out infection. Because PCR testing for Rocky Mountain spotted fever is not yet widely available, it is not routinely used for diagnosis.

Expected duration of Rocky Mountain spotted fever

Symptoms of Rocky Mountain spotted fever begin two to 14 days after a bite by an infected tick. Most cases of Rocky Mountain spotted fever respond to appropriate antibiotic treatment within a week. Once symptoms develop, a person can die within two weeks without proper treatment.

Preventing Rocky Mountain spotted fever

Because there is no vaccine against Rocky Mountain spotted fever, the most effective way to prevent the illness is to avoid tick bites. This could include avoiding wooded areas or fields where ticks are found. If you do walk in tick-infested areas, follow these precautions:

Wear light-colored clothing, which allows you to promptly identify a clinging tick.
Wear long-sleeved shirts and pants that are snug around the wrists and ankles.
While you are outdoors, check yourself for ticks every two hours.
Use an approved tick repellent.
If you find a tick latched onto your body, remove it immediately with tweezers, then wash your hands thoroughly.

Treating Rocky Mountain spotted fever

Rocky Mountain spotted fever is effectively treated with one of the tetracycline drugs, usually doxycycline (sold as a generic). Chloramphenicol (Chloromycetin) is another antibiotic that attacks the bacteria, but it appears to be less effective than doxycycline and is only recommended when doxycycline cannot be given due to allergy or other reaction.

When to call a professional

Call your doctor immediately if you develop fever, headaches and nausea, with or without a rash, after you have been bitten by a tick. Even if you don't remember being bitten, call your doctor if you develop these symptoms and you have walked recently in tick-infested areas.

Prognosis

Before effective antibiotics were available, 20% to 25% of people with Rocky Mountain spotted fever died. Now, however, less than 1% of patients die from this illness.