Rocky Mountain Spotted Fever: What You Need to Know

Rocky Mountain spotted fever (RMSF) is a bacterial illness caused by a bite from an infected tick. Symptoms include high fever and widespread rash. In the United States, there are 4,000–6,000 reports of tick-borne spotted fevers, including RMSF, each year. It's the deadliest tick-borne illness in the world.

Infected ticks can be anywhere; however, in the United States, they are most common in Southeastern and South Central states. You can lower your risk by avoiding ticks whenever possible. It's also important to promptly remove any you find on your body or clothing. 

This article discusses what you need to know about RMSF and signs that you should see a healthcare provider.

What Does Rocky Mountain Spotted Fever Look Like?

About five to 10 days after a tick bite, you might develop a non-itchy rash on your hands, arms, feet, and legs that spreads over the body. In atypical cases, the rash may start on the trunk or be widespread at the onset. In rare cases, there's no rash at all.

Signs of RMSF rash are:

• Spots are small, flat, pink, and turn white when you apply pressure
• Spots eventually become darker and raised, sometimes with small reddish spots (petechiae)
• Spots may merge into larger patches, and skin may break (ulcerate)
  

Rocky Mountain Spotted Fever Symptoms

Symptoms usually begin three to 12 days after the bite of an infected tick. In addition to the rash, these may include:

• Fever as high as 103 or 104 degrees F
• Chills
• Severe headache
• Sore throat
• Muscle pain (myalgia)
• Confusion
• Poor appetite
• Light sensitivity
• Abdominal tenderness, stomachache
• Nausea, vomiting, diarrhea
• Extreme exhaustion

The rash typically appears on the third to fifth day after the fever but can occur earlier, later, or not at all.

How Rocky Mountain Spotted Fever Spreads

RMSF is caused by the bacterium Rickettsia rickettsii (R Rickettsii). It's passed to humans through the bites of infected ticks, including several species of ticks in the United States, such as:

• American dog tick (Dermacentor variabilis)
• Rocky Mountain wood tick (Dermacentor andersoni)
• Brown dog tick (Rhipicephalus sanguineus)

Once RMSF is in your body, the bacterium enters the bloodstream or lymphatic vessels (channels that carry lymphatic fluid and white blood cells through the lymphatic system) and begins to multiply. As it does, it damages cells that line the inside of small blood vessels, along with smooth muscle cells.

Where Is RMSF Most Commonly Found (and When)?

RMSF has been reported in North America, Central America, and South America. It can be found just about anywhere in the United States but is reported most often in:

• North Carolina
• Tennessee
• Missouri
• Arkansas
• Oklahoma
  

You can get a tick bite any time of the year when temperatures are warm, but most people are bitten from April through September.

Who Is Most at Risk for Rocky Mountain Spotted Fever?

Outdoor activities, such as camping, hiking, or golfing, in certain areas may raise your risk of contracting a tick-borne illness. Living in tick-infested areas and frequent exposure to dogs may also increase risk.

Up to one-third of people who get RMSF don't remember being bitten by a tick or having been in contact with a tick.

Rocky Mountain Spotted Fever vs. Lyme Disease 

Tick bites cause RMSF and Lyme disease, but they're different. Lyme disease is caused by bacteria called Borrelia burgdorferi (B. burgdorferi), usually from an infected black-legged deer tick. While RMSF is most common in Southeastern and South Central states, Lyme disease is more common in the Northeast and Upper Midwest.

Though many symptoms are the same, the rashes look different. The spotted RMSF rash usually starts on wrists, ankles, palms, and soles and then spreads to arms, legs, and trunk. Lyme disease typically presents with a bull's-eye rash at the site of the tick bite. It can take days, weeks, or even months for symptoms to appear.

RMSF and Lyme disease are treated with antibiotics, which can lead to long-term complications. You can get Lyme disease multiple times. Once you get RMSF, you can't get it again.

What Tests Help Diagnose Rocky Mountain Spotted Fever?

Your provider will likely start with a thorough clinical exam and blood testing. It's important to report recent travel or suspected insect bites.

The RMSF blood test can help rule out or confirm the diagnosis. This test is also called Rocky Mountain spotted fever antibody test or indirect immunofluorescence antibody (IFA) assay for immunoglobulin G (IgG). However, antibodies may not be detectable until seven to 10 days after disease onset. 

Can Rocky Mountain Spotted Fever Go Away Without Treatment?

RMSF progresses quickly and is potentially fatal, even in healthy people. Without treatment, death can occur within eight days of the start of symptoms. The fatality rate is between 13% and 25%. For those who quickly start on the right therapy, the fatality rate is between 3% and 5%.

Rocky Mountain Spotted Fever Treatment

Treatment within the first five days of illness significantly reduces disease severity and the likelihood of death. Because lab tests take time, your provider may decide to start treatment based on clinical symptoms and a history of tick bites.

The first line of treatment for all age groups is an antibiotic (drug that kills bacteria) called doxycycline. Other antibiotics, such as chloramphenicol, can be used if you can't take doxycycline. Most people are cured after five to seven days on antibiotics.

Severe complications may require additional treatments and supportive therapies.

Long-Term Effects of Rocky Mountain Spotted Fever

Without treatment, serious complications can occur, such as:

• Gangrene of toes or fingers
• Hearing loss
• Incontinence
• Nerve damage
• Partial paralysis
  

Other health problems may include:

• Brain damage
• Clotting problems
• Heart failure
• Kidney failure
• Lung failure
• Meningitis (swelling of protective linings around the brain and spinal cord)
• Pneumonitis (lung inflammation)
• Shock
  

How to Prevent Rocky Mountain Spotted Fever

Right now, there's no vaccine to prevent RMSF. You can reduce the risk of illness by lowering the risk of tick bites. Small and difficult to spot, ticks range from light-colored to red to dark brown and live in brushy, grassy, or wooded areas and on animals. Here are some ways to avoid tick bites:

• Avoid woodsy, brushy areas and places with tall grasses and leaf litter. If you can, walk in the middle of the trail.
• Dress in light-colored clothes. Wear long sleeves and tuck your shirt into your pants. Wear socks and closed-toe shoes, and tuck long pants into socks.
• Treat clothing and outdoor gear with products containing 0.5% permethrin.
• Use insect repellents containing DEET, picaridin, IR3535, oil of lemon eucalyptus (OLE), para-menthane-diol (PMD), or 2-undecanone. (Do not use OLE or PMD products on children under age 3.)

Ticks can hitch a ride on your clothes, gear, or pets. Once inside, check for ticks. Putting clothes in the dryer on high heat for at least 10 minutes will kill ticks. Washing in cold or warm water will not.

You don't always feel a tick on your skin, even when it bites, and it can stay attached to your body for days. Removing the tick before it bites makes you less likely to get infected.

When checking your body for ticks, be sure to look under the arms, in and around the ears and hair, belly button, back of the knees, between the legs, and around the waist.

Showering can help remove any ticks that aren't attached to your skin. If you find a tick, use tweezers and grab the tick as close to your skin as you can. Be sure to pull straight up. Twisting can leave the mouth attached. Then clean the area and your hands thoroughly.

A Word From Verywell

It is important to seek antibiotic treatment if you think you may have RMSF because the symptoms can be severe. Wear long sleeves and pants, use insect repellent, and check for ticks after outdoor activities to prevent disease transmission.

— JOSEPHINE HESSERT, DO, MEDICAL EXPERT BOARD

When to Go to the ER

If you remove a tick, but the mouth or head remains attached, leave it and go to an urgent care facility or emergency room (ER) so it can be safely removed. You should also visit the ER if you have redness, swelling, or other signs of infection at the site of the bite.

Other symptoms that may appear within a week or two may also require urgent attention. these include:

• Rash at the site or elsewhere on your body, especially if it's getting larger
• Fever
• Flu-like symptoms
  

Summary

RMSF is a bacterial infection passed to humans and animals by the bite of an infected tick. You don't have to be in the Rocky Mountains to get it. In the United States, it's most common in the Southeast and South Central states during the warmer months.

Symptoms include widespread rash and high fever. Without treatment, RMSF can lead to serious complications and can quickly become fatal. In most cases, prompt treatment with antibiotics can cure the infection.