What Is Rocky Mountain Spotted Fever?

Rocky Mountain spotted fever (RMSF) is the most severe tick-borne rickettsial illness in the United States. This disease is caused by infection with the bacterial organism Rickettsia rickettsii. RMSF was first diagnosed in 1896 in Idaho and was first named "black measles" but then was termed Rocky Mountain spotted fever. In 1906, Howard Ricketts showed that ticks were vectors (carriers) and in 1909 showed evidence that bacteria (later named after him) caused the disease.

How Do People Get Rocky Mountain Spotted Fever?

The organism that causes Rocky Mountain spotted fever is transmitted by the bite of an infected tick. The American dog tick (Dermacentor variabilis) and Rocky Mountain wood tick (Dermacentor andersoni) are the primary arthropods (vectors) which transmit Rocky Mountain spotted fever bacteria in the United States. The brown dog tick Rhipicephalus sanguineus has also been implicated as a vector, as well as the tick Amblyomma cajennense in countries south of the United States.

What Are the Symptoms and Signs of Rocky Mountain Spotted Fever?

Patients infected with R. rickettsii usually visit a physician in their first week of illness, following an incubation period of about five to 10 days after a tick bite. The early clinical presentation of Rocky Mountain spotted fever is often nonspecific and may resemble many other infectious and noninfectious diseases. Initial symptoms may include fever, nausea, vomiting, muscle pain, lack of appetite, and severe headache. Later signs and symptoms include rash, abdominal pain, joint pain, and diarrhea. Three important components of the clinical presentation are fever, rash, and a previous tick bite, although one or more of these components may not be present when the patient is first seen for medical care. Rocky Mountain spotted fever can be a severe illness, and the majority of patients are hospitalized.

Where Do Most Cases of Rocky Mountain Spotted Fever Occur in the U.S.?

Rocky Mountain spotted fever is a seasonal disease and occurs throughout the United States during the months of April through September. Over half of the cases occur in the South Atlantic region of the United States (Delaware, Maryland, Washington D.C., Virginia, West Virginia, North Carolina, South Carolina, Georgia, and Florida). The highest incidence rates have been found in North Carolina and Oklahoma. Although this disease was first discovered and recognized in the Rocky Mountain area, relatively few cases are reported from that area today. Additionally, almost every area in the world (except Antarctica) has reported the disease syndrome similar to RMSF. In the U.S., the fatality rate is about 2%; before effective treatments were available, reported fatality rates varied from 30%-70%. The age groups at highest risk for infection with RMSF are children under 10 years of age, although any age group can be infected.

How Is Rocky Mountain Spotted Fever Diagnosed?

The diagnosis of RMSF is usually made clinically when a patient's history of their problem includes a fever and a rash (usually on the wrists and ankles first, then to the palms and soles of the feet) that occurs a few days after a tick bite. Treatment should not be delayed while waiting for a definitive diagnosis as the disease may advance rapidly. A laboratory test is done in some patients with a presumptive diagnosis of RMSF. It is a biopsy of the skin rash stained specifically to show R. rickettsii in the patient's cells. Another test involves a direct immunofluoresence staining of R. rickettsii in skin-tissue samples; such tests can confirm the diagnosis in about 70% of cases and, in some laboratories, can be done the same day the specimen is collected.

How Is Rocky Mountain Spotted Fever Treated?

Rocky Mountain spotted fever is best treated by using a tetracycline (Achromycin) antibiotic, usually doxycycline (Vibramycin). This medication should be given in doses of 100 mg every 12 hours for adults or 4 mg/kg body weight per day in two divided doses for children under 45 kg (100 lbs.). Patients are treated for at least three days after the fever subsides and until there is unequivocal evidence of clinical improvement. Standard duration of treatment is five to 10 days. Because laboratory confirmation is generally not available during acute illness, treatment is initiated based on clinical and epidemiological information.

Can a Person Get Rocky Mountain Spotted Fever More Than Once?

Infection with R. rickettsii is thought to provide long-lasting immunity against reinfection. However, prior illness with Rocky Mountain spotted fever should not deter people from practicing good tick-preventive measures or visiting a physician if signs and symptoms consistent with Rocky Mountain spotted fever occur, especially following a tick bite, as other diseases may also be transmitted by ticks.

How Can Rocky Mountain Spotted Fever Be Prevented?

Limiting exposure to ticks reduces the likelihood of infection with Rocky Mountain spotted fever. In people exposed to tick-infested habitats, prompt, careful inspection and removal of crawling or attached ticks is an important method of preventing disease. It may take extended attachment time before organisms are transmitted from the tick to the host. It is unreasonable to assume that a person can completely eliminate activities that may result in tick exposure. Therefore, the following preventative measures (see following slides) should emphasize personal protection when exposed to natural areas where ticks are present.

Prevention Tip #1: Proper Clothing

Wear light-colored clothing which allows you to see ticks that are crawling on your clothing.

Prevention Tip #2: Keep Ticks Out

Tuck your pant legs into your socks so that ticks cannot crawl up the inside of your pant legs.

Prevention Tip #3: Apply Repellents

Apply repellents to discourage tick attachment. Repellents containing permethrin can be sprayed on boots and clothing and will last for several days. Repellents containing DEET (n, n-diethyl-m-toluamide) can be applied to the skin but will last only a few hours before reapplication is necessary. Use DEET with caution on children. Application of large amounts of DEET on children has been associated with adverse reactions.

Prevention Tip #4: Self-Check

Conduct a body check upon return from potentially tick-infested areas by searching your entire body for ticks. Use a handheld or full-length mirror to view all parts of your body. Remove any tick you find on your body.

Prevention Tip #5: Check Children and Pets

Parents should check their children for ticks, especially in the hair, when returning from potentially tick-infested areas. Ticks may also be carried into the household on clothing and pets and only attach later, so both should be examined carefully to exclude ticks.

How to Remove a Tick: Step 1

Use fine-tipped tweezers or notched tick extractor, and protect your fingers with a tissue, paper towel, or latex gloves. People should avoid removing ticks with bare hands.

How to Remove a Tick: Step 2

Grasp the tick as close to the skin surface as possible and pull upward with steady, even pressure. Do not twist or jerk the tick; this may cause the mouthparts to break off and remain in the skin. (If this happens, remove mouthparts with tweezers. Consult your health-care provider if illness occurs.)

How to Remove a Tick: Step 3

After removing the tick, thoroughly disinfect the bite site and wash your hands with soap and water.

How to Remove a Tick: Step 4

Do not squeeze, crush, or puncture the body of the tick because its fluids may contain infectious organisms. Skin accidentally exposed to tick fluids can be disinfected with iodine scrub, rubbing alcohol, or water containing detergents.

How to Remove a Tick: Step 5

Save the tick for identification in case you become ill. This may help your doctor to make an accurate diagnosis. Place the tick in a sealable container or plastic bag and put it in your freezer. Write the date of the bite on a piece of paper with a pencil and place it in the bag.

Do Folklore Remedies Work?

No. Folklore remedies, such as the use of petroleum jelly or hot matches, do little to encourage a tick to detach from skin. In fact, they may make matters worse by irritating the tick and stimulating it to release additional saliva or regurgitate gut contents, increasing the chances of transmitting the pathogen. These methods of tick removal should be avoided.

How Can Ticks Be Controlled?

Strategies to reduce vector tick densities through area-wide application of acaricides (chemicals that will kill ticks and mites) and control of tick habitats (for example, leaf litter and brush) have been effective in small-scale trials. New methods being developed include applying acaricides to animal hosts by using baited tubes, boxes, and feeding stations in areas where infected ticks are endemic. Biological control with fungi, parasitic nematodes, and parasitic wasps may play supportive roles in integrated tick-control efforts. Community-based integrated tick management strategies may prove to be an effective public-health response to reduce the incidence of tick-borne infections. However, limiting exposure to ticks is presently the most effective method of prevention of tick-transmitted diseases.

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