Rocky Mountain spotted fever (RMSF) is a serious illness you get from a tick bite. It’s caused by the bacterium Rickettsia rickettsii. Symptoms include a high fever and headache. Rash may start three or more days after other symptoms. RMSF can be life-threatening if not treated quickly with antibiotics. RMSF is found in most states in the U.S.
Rocky Mountain spotted fever (RMSF) is an illness you get from the bacteria Rickettsia rickettsii (R. rickettsii). It spreads through tick bites. Symptoms start out similar to many other illnesses, including headache, fever and rash. But if not treated right away, RMSF can be life-threatening.
RMSF falls under a category of illnesses known as Spotted Fever Rickettsiosis (SFR).
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Rocky Mountain spotted fever and Lyme disease are both infections you get from tick bites, but they’re different illnesses. Lyme disease happens because of different bacterium than RMSF and has different symptoms. You can’t get Lyme disease from RMSF.
Rocky Mountain spotted fever can affect anyone who’s around ticks, which usually live in tall grass, in wooded areas and on pets that are allowed outdoors. Cases of RMSF occur in the U.S., Canada, Mexico and South and Central America. Although reported cases happen in every month of the year, most cases occur in warmer months.
Adults and children of all demographics can get Rocky Mountain spotted fever. But there are more reported cases of RMSF in people assigned male at birth and people over 40. You’re at higher risk for getting severely ill with RMSF if you:
There are about 6,000 cases of Rocky Mountain spotted fever each year in the U.S. Despite its name, it’s most common in North Carolina, Tennessee, Missouri, Arkansas and Oklahoma. You’re more likely to get RMSF in the summer months, when ticks are common and people are outdoors a lot.
R. rickettsii, the bacterium that causes Rocky Mountain spotted fever, gets into your bloodstream from the bite of a tick. It attacks your blood vessels, muscle cells and tissues. This can lead to leaking blood vessels, excess fluid in your tissues, and damage to your muscles, nerves and organs.
Symptoms of Rocky Mountain spotted fever start two days to two weeks after an infected tick bites you. Symptoms usually develop over a few days, starting with fever, headache, nausea, vomiting and muscle pains.
Rash develops within three days in about 50% of people. Don’t wait for rash to appear to seek treatment.
Symptoms of Rocky Mountain fever include:
Later, more severe symptoms include:
Ticks carry and spread Rocky Mountain spotted fever. In the U.S., the American dog tick and the Rocky Mountain wood tick are the main carriers. Other types of ticks, such as the brown dog tick, also carry RMSF in some places.
No, Rocky Mountain spotted fever can’t spread from person to person (it’s not contagious).
If you don’t find a tick on you, it can be hard to know if a tick bit you. A tick bite sometimes leaves a mark similar to other bug bites, causes a rash or barely leaves a mark at all.
Your healthcare provider will diagnose RMSF based on a physical exam, your symptoms and whether or not it’s possible that a tick bit you. There are blood and skin tests that can help diagnose Rocky Mountain spotted fever, but they don’t give results fast enough for treatment.
Make sure you tell your provider if you traveled anywhere that you could’ve been bitten by a tick in the past two weeks, even if you don’t remember finding a tick bite or a roaming tick on you. It’s important for them to be able to decide if they should treat you for Rocky Mountain spotted fever.
Your provider can use blood and skin tests to diagnose Rocky Mountain spotted fever, but the results may not be available right away. Your provider will probably have to decide whether to treat you for RMSF before you test positive.
Treatment of Rocky Mountain spotted fever involves antibiotics. You usually have to take antibiotics for seven to 10 days.
Treatment is most effective when it starts within five days of your symptoms appearing. If antibiotics begin too late, RMFS can damage your body and cause life-threatening complications.
Doxycycline is the only antibiotic recommended to treat Rocky Mountain spotted fever. If you’re allergic to doxycycline, your healthcare provider may give you chloramphenicol as an alternative. Chloramphenicol can be hard to get in some countries and doesn’t work as well as doxycycline for RMSF.
If your symptoms are mild, you might be able to manage them at home with over-the-counter medications. Ask your provider which medications are safe to take.
If you start antibiotics soon after the symptoms of RMSF appear, you should feel better within 48 hours. You’ll still have to take antibiotics for several more days. Continue taking all medications as prescribed, even if you feel better. If your symptoms don’t improve, contact your healthcare provider right away.
You can reduce your risk of Rocky Mountain spotted fever by avoiding tick bites.
Most people recover from Rocky Mountain spotted fever with no lasting issues if they receive quick treatment after symptoms start. Some people have serious complications that need treatment in a hospital.
Even after you recover, it’s possible to have long-term health issues.
Even with antibiotic treatment, some people with Rocky Mountain spotted fever have serious or life-threatening complications, including:
The outlook for RMSF is good if treated promptly. In the U.S., the fatality (death) rate for Rocky Mountain spotted fever is 5% to 10% with treatment. In some countries, like Mexico and Brazil, the rate is much higher.
If you’ve been severely ill from Rocky Mountain spotted fever, you may have long-term effects even after you recover, including:
Rocky Mountain spotted fever goes away with treatment. Some people have lasting nerve and tissue damage that can cause ongoing symptoms, even when the infection is gone.
Without treatment, RMSF has a 20% to 30% fatality rate.
It’s unlikely that you can get Rocky Mountain spotted fever more than once. Experts think that once you get RMSF, you have immunity — that is, your body knows how to fight it off before you get sick, so you won’t get it again.
If your provider is treating you for Rocky Mountain spotted fever, make sure you take all of your medicine as prescribed. If you stop taking antibiotics before the end of the course, you may get sick again.
Your provider can tell you how to manage your symptoms at home best. RMSF can get worse quickly. Call your provider right away if you have new or worsening symptoms.
If you have a tick bite or have been in an area with ticks and have symptoms of RMSF, see your healthcare provider right away.
If you have a tick bite but don’t have any symptoms, you don’t need to see your provider yet — taking antibiotics when you’re not sick won’t help prevent RMSF.
Go to the nearest ER if you have any of these symptoms:
A note from Cleveland Clinic
Ticks aren’t just an annoyance — their tiny bite can make you very sick. The best way to prevent Rocky Mountain spotted fever is to avoid tick bites. But if a tick bites you and you have symptoms, contact your healthcare provider right away. Early treatment is the best way to get better fast.
Last reviewed by a Cleveland Clinic medical professional on 08/25/2022.
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