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What Is Rocky Mountain Spotted Fever?

Medically Reviewed by Dan Brennan, MD on May 16, 2021

Rocky Mountain spotted fever (RMSF) is a bacterial infection that you can get after a tick bite. Most people get this infection in spring and summer, warm months when ticks are most active. More than 2,000 Americans are affected each year.

What Is RMSF?

Rocky Mountain spotted fever, sometimes called mountain fever, is an infectious disease that was first discovered in the Rocky Mountains. Today, RMSF is now most commonly found in the southwest United States. Parts of Canada, Mexico, and South and Central America have also reported cases.

Most cases happen in March through September since this is when ticks are most active. As these are warm months in the Western Hemisphere, this is when people are most likely to be out in nature where these ticks are. In warm southern states, cases are reported all year long.

Several different species of ticks can pass mountain fever on to humans. The risk of getting this infection depends on whether or not you are close to areas with ticks. The only way that you can get RMSF is through a tick bite as this infection is not passed from person to person.

Symptoms

The main symptom of RMSF is a rash that starts on your wrists and ankles and then makes its way up your arms and legs until it reaches your torso. The rash also covers the palms of your hands and the soles of your feet. This rash looks like small, red spots in the beginning and gradually appear like bruises or bloody dots. Sometimes, the rash can also look like red splotches on the skin.

The rash usually begins 5 to 10 days after you get a tick bite. Other symptoms of Rocky Mountain spotted fever that you may experience in addition to the rash include:

  • Moderate or high fever that may last up to 2 or 3 weeks
  • Serious headache
  • Loss of appetite
  • Nausea and vomiting 
  • Chills 
  • Fatigue 
  • Sore throat
  • Achy muscles and joints

You will start to notice symptoms about a week after getting a tick bite. The fever and headache are usually the first symptoms, and the rash typically starts 3 to 5 days after that.

Some people might not know that they’ve been bitten by a tick. If you know that you’ve recently been bitten by a tick and have any of these symptoms, you should contact your doctor as soon as possible.

Diagnosis and Treatment

Diagnosing RMSF can be a bit tricky since the early symptoms are so similar to other diseases. Your doctor will examine your physical symptoms, like the rash. They may also order blood tests. These tests can help rule out any other possible infections or diseases and confirm that you have Rocky Mountain spotted fever. It may take a few weeks to get the results of your bloodwork.

Treatment. RMSF needs to be treated as soon as possible. To help determine the best way to treat your infection, your doctor will ask you about your history. Some factors that can affect your treatment are:

  • Your age
  • Overall health
  • Severity of symptoms

Treatment for RMSF usually involves antibiotics, most typically doxycycline. You can stop the antibiotic treatment about three days after you’ve been fever-free for a full 24 hours.

Risks and complications. With proper treatment, most people recover from RMSF within a few days. Even so, the mortality rate among people who are treated is between 3% and 5%. The rate among people who don’t seek treatment for RMSF is 13% to 25%.

Rocky Mountain spotted fever causes damage to the lining of your small blood vessels. This can cause them to possibly leak or clot. This can cause further complications, such as:

  • Inflammation of the heart, lungs, or brain
  • Kidney failure
  • Infection of the fingers and toes that could result in amputation
  • Death

Prevention

There is currently no vaccine for mountain fever. The only way that you can prevent it is to lower your chances of getting a tick bite. Ticks live in wooded areas with grass and bushes, so prepare yourself if you'll be in a place like this.

Clothing. If you’re going camping or doing outdoor activities in areas where there may be ticks, wear sleeves and long pants. Tuck your pants into your socks to prevent ticks from getting in around your ankles. If possible, treat your clothing with permethrin, an insect repellent that will stay on clothes and camping gear for a few washings.

Insect repellent. Use insect repellent that contains DEET as it helps to keep ticks at bay. Be sure to follow all of the instructions on the product. You should apply insect repellent to all areas except for your face.

Pets. If you have pets that frequently go outside, be sure to check them for ticks when they come in. While you can’t catch RMSF from your pet, the ticks that they carry can transmit the disease to you.

WebMD Medical Reference

Sources

SOURCES:

CDC: “Rocky Mountain Spotted Fever.”

IDPH: “Rocky Mountain Spotted Fever.”

Johns Hopkins Medicine: “Rocky Mountain Spotted Fever.”

KidsHealth from Nemours: “Rocky Mountain Spotted Fever.”

Mayo Clinic: “Rocky Mountain spotted fever.”

MERCK MANUAL Professional Version: “Rocky Mountain Spotted Fever (RMSF).”

New York State: “Rocky Mountain Spotted Fever (tick-borne typhus fever).”

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