Rocky Mountain Spotted Fever and Other Spotted Fevers

Quick answer

Rocky Mountain spotted fever (RMSF) is a tickborne Rickettsia infection that can become life-threatening within days if not treated early. It starts with fever, headache and aches; the rash often appears 2 to 4 days after the fever, or not at all. CDC says doxycycline is the treatment for all ages, including children, started without waiting for test results.

What spotted fever rickettsioses are

RMSF is caused by the bacterium Rickettsia rickettsii. It belongs to the “spotted fever group,” a family of closely related Rickettsia bacteria. Others in the U.S. include Rickettsia parkeri and a rare type called Rickettsia species 364D. Blood tests often cross-react between these related bacteria, and CDC reports cases under the combined name spotted fever rickettsiosis.

These infections are not Lyme disease. CDC says the American dog tick, Rocky Mountain wood tick and brown dog tick cannot transmit Lyme bacteria; Lyme is spread by blacklegged ticks. Spotted fevers are covered here because they are among the tickborne infections people often ask about alongside Lyme (see our co-infections guide).

Which ticks spread spotted fevers

Ticks are most active from April through September, but exposure can happen year-round. To identify a tick, see our types of ticks guide.

Rickettsia symptoms and rash timing

RMSF symptoms usually start 3 to 12 days after an infected tick bite. People who go on to have severe disease often get sick sooner, within about 5 days. Early symptoms include:

• Sudden fever and chills
• Headache
• Muscle pain and feeling unwell
• Nausea, vomiting, stomach pain or loss of appetite

The rash comes late, if at all. According to CDC, the rash usually appears 2 to 4 days after fever begins. Fewer than half of patients have a rash in the first 3 days of illness, and some never get one. It can look like red splotches or pinpoint dots, and it can change over time. A spotted rash that includes the palms and soles usually appears around day 5 or 6 and signals advanced disease. Children under 15 are more likely to get a rash, and to get it earlier.

This is very different from the expanding erythema migrans rash of Lyme disease; see our Lyme rash guide to compare.

Why early treatment is so urgent

CDC’s 2016 clinical recommendations explain how much timing matters:

• Today, about 5 to 10% of people with RMSF die, compared with about 25% before antibiotics.
• Patients treated after day 5 of illness are more likely to die; among those treated on days 8 or 9, the death rate was 40 to 50%.
• Children under 10 face the highest risk. From 1999 to 2012 they were five times more likely to die from RMSF than older children and adults.
• Other risk factors for death include age 40 or older, alcohol misuse and G6PD deficiency (an inherited enzyme condition).
• On some American Indian reservations in Arizona, where brown dog ticks spread RMSF, the death rate has been 7 to 10%, mainly because of delays in recognition and treatment.

People who survive severe RMSF can have permanent damage, including amputation of fingers, toes or limbs, hearing loss or mental disability. CDC notes that RMSF does not cause a chronic or persistent infection.

Treatment: doxycycline, started early

• Doxycycline for every age. CDC recommends doxycycline as the treatment of choice for adults and children of all ages. Some parents worry about tooth staining; CDC cites a study finding that short courses did not stain permanent teeth.
• Start within the first 5 days. Doxycycline works best at preventing severe complications when started early, and treatment should never be delayed while waiting for lab confirmation.
• Other antibiotics are not substitutes. Most other broad-spectrum antibiotics do not work against RMSF, and sulfa drugs may make it worse.
• Pregnancy. CDC says doxycycline is unlikely to cause major harm in pregnancy, though a risk cannot be ruled out; clinicians weigh this with patients.

With treatment, fever usually goes away within 24 to 48 hours. Your clinician decides how long treatment lasts.

R. parkeri and other spotted fevers

Rickettsia parkeri rickettsiosis is spread by the Gulf Coast tick and is milder than RMSF. Symptoms start a median of 5 days after the bite. Nearly everyone first notices an eschar, a dark scab at the bite site, followed within a few days by fever; about 90% get a rash. Fewer than a third are hospitalized, and no deaths had been reported as of CDC’s 2016 report, which counted at least 40 cases in 10 states from 2004 to 2015.

Rickettsia species 364D is likely spread by the Pacific Coast tick. Fewer than 10 cases had been reported, all in California.

Prevention

There is no vaccine. CDC advises preventing tick bites on yourself, on your pets and in your yard, and learning which ticks are common where you live. See our guides to tick bite prevention, tick-proofing your yard and keeping kids safe from ticks. Knowing these warning signs is step 3 of our plan, recognize the signs.

Frequently asked questions