Rocky Mountain spotted fever (RMSF) is the most deadly tickborne disease in the world. A bacterium called Rickettsia rickettsii causes this disease.

The bacterium is found only in North and South America.

Before antibiotics, RMSF in certain locations had a mortality rate of 70 percent. RMSF is now easier to treat and has a mortality rate of 0.3 percent following treatment.

Woman sneezing into a tissue.Share on Pinterest
Symptoms of RMSF commonly represent flu.

The symptoms of RMSF are similar to those of common illnesses such as the flu. If RMSF is not treated within 5 days of symptom onset, there is a rapid increase in the chances of severe complications and death.

Many people with RMSF do not remember or even notice being bitten by a tick. They do not, as a result, associate the symptoms with the bite in good time to reduce complications.

Signs and symptoms of RMSF do not manifest immediately after being bitten by a tick. The incubation period of the disease, or the time between the tick bite and first symptoms, is typically 5 to 7 days. However, symptoms may begin as soon as 2 days after infection, or take as long as 14 days to show.

Signs of RMSF include:

  • fever
  • digestive problems, such as nausea, diarrhea, vomiting, or lack of appetite
  • severe abdominal pain
  • headache, particularly at the front of the head
  • muscle aches
  • a dry cough, sore throat, or both
  • chest pain that feels worse when coughing, sneezing, or inhaling (known as pleuritic chest pain)
  • red eyes resembling a pink eye infection

Another common symptom is a rash that begins on the wrists and ankles and may spread to feet, palms of hands, arms, legs, and torso. It typically begins with small, flat, pink spots that do not itch. Later, the spots may darken to a red or purple color. The darkening of the rash is a sign of advanced disease.

Anyone bitten by an infected tick can get RMSF, and it can cause death even in young or previously healthy people.

The American dog tick (Dermacentor variabilis), Rocky Mountain wood tick (Dermacentor andersoni), and brown dog tick (Rhipicephalus sanguineus) have all been shown to spread RMSF in the United States.

The states that are most commonly affected by RMSF are North Carolina, Oklahoma, Arkansas, Tennessee, and Missouri, though cases have been reported in nearly all of the contiguous U.S.

People who have high exposure to dogs have a higher chance of getting RMSF, according to the CDC, because dog ticks so often carry R. rickettsia.

An outbreak of RMSF was seen recently in Eastern Arizona, with 140 cases over a 7-year period and a 10 percent mortality rate. Experts identified the brown dog tick as the culprit for the infections and nearly all of the infections were reported in areas that had a high number of free-roaming dogs.

People who live near wooded areas or who spend time in areas with tall grass, brush, or woods are also at greater risk of getting bitten by a tick and contracting RMSF or other tickborne diseases.

Share on Pinterest
Diagnosis and confirmation of RMSF is carried out by laboratory tests.

Doxycycline is an antibiotic in the tetracycline family that effectively treats RMSF if given within the first 5 days of a person experiencing symptoms.

RMSF can kill if a course of treatment is not started within this timeframe. Studies have demonstrated other antibiotics not to be effective, and other medicinal options have been shown to worsen the illness.

RMSF's distinctive rash sometimes appears at a very late stage of the infection, days or occasionally weeks after a person should have started a course of antibiotics. In some cases, the rash does not appear at all.

A doctor may therefore decide to treat a patient for RMSF if they have other symptoms and suspect that a tick may have bitten them.

Some other tickborne illnesses, including ehrlichiosis and anaplasmosis, have symptoms that are similar to RMSF and also respond well to doxycycline, so this approach can treat several different illnesses.

R. rickettsii does not always show in blood tests unless the patient has a severe, late-stage infection of RMSF. Laboratory tests can confirm the presence of antibodies to RMSF, but these do not appear until between 7 and 10 days after the onset of symptoms.

Sometimes a sample (or biopsy) of the rash can show the presence of RMSF, but these tests are accurate only 70 percent of the time.

Because of these delays and possible false negative results, treatment is typically done on suspicion alone, without a laboratory diagnosis of RMSF. Do not wait for the presentation of the rash or the laboratory results.

Antibiotics are not recommended after every tick bite, as this has not been proven to prevent RMSF or other tickborne illnesses. Instead, people who have been bitten by a tick should look for signs of illness and see a doctor immediately if they feel sick.

There is no vaccine for RMSF, but a person can prevent infection by avoiding tick bites and removing ticks as soon as possible.

People can avoid tick bites by:

  • Using an insect repellent containing at least 20 percent DEET on the skin when outdoors. Follow the product's instructions and avoid the eyes, hands, and mouth area, especially on children.
  • Using permethrin insecticide, which kills ticks and lasts through several washes, on clothing and gear.
  • Treating pets for ticks, especially dogs. Dogs can easily contract RMSF and they may carry the ticks that spread it to humans. Ask a veterinarian about safe and effective tick prevention products for pets.
  • Staying in the center of trails when walking in tall grass, woods, or brush.

Enjoying the outdoors is possible as long as a person takes active steps to find ticks and quickly remove them. After being outdoors, the following is recommended:

  • Check thoroughly for ticks on skin. Prime areas for ticks to hide include the scalp, ears, hairline, underarms, groin, and belly button. Check pets' ears, underarms, groin, and paws.
  • Shower within 2 hours of coming inside. This can wash away ticks that are not attached. Wash all clothing and dry on high heat for 1 hour to kill ticks.
  • Remove any attached ticks right away. The sooner a tick is removed, the less of a chance of getting a tickborne disease. Use tweezers to grasp the tick as close to the skin as possible. Pull it straight out slowly and clean the area with a skin disinfectant. Seek medical attention if the tick is not completely removed. Do not apply Vaseline or heat to the tick body to remove it.
  • Watch for any signs of illness in the following days and weeks, especially fever and flu-like symptoms. Seek medical help if these signs appear.

Rocky Mountain spotted fever can cause long-term health problems and death, especially in severe cases or if a patient does not commence doxycycline treatment soon after the first signs of illness.

A severe infection of RMSF can cause bleeding or clotting in the blood vessels, which can damage organs, including the brain. Damaged blood vessels can cause loss of circulation in extremities such as fingers and toes, potentially leading to amputation.

Neurological problems such as hearing loss, weakness in the legs, numbness, bladder or bowel incontinence, and language problems have also been reported.

People who contract a milder case of RMSF and who receive quick treatment often recover completely within a few weeks or months.