Rocky Mountain Spotted Fever (RMSF)

How RMSF spreads

Infected ticks transmit the bacteria while feeding, usually after several hours of attachment. Ticks involved in the US include:

• American dog tick (eastern, central and Pacific coast states)
• Rocky Mountain wood tick (Rocky Mountain states)
• Brown dog tick (southwestern US, especially in some Arizona communities, and Mexico)

Infection can also occur when crushing a tick with bare hands. RMSF does not spread from person to person. Despite its name, most US cases occur outside the Rocky Mountains, mainly in North Carolina, Tennessee, Missouri, Arkansas and Oklahoma, peaking from May to August.

Symptoms

Early (days 1 to 4)

• sudden high fever
• severe headache
• muscle aches
• nausea, vomiting and abdominal pain (especially in children)
• loss of appetite and tiredness
• swelling around the eyes and backs of the hands

Rash

• typically appears 2 to 4 days after fever begins
• starts as small, flat, pink, non-itchy spots on the wrists, forearms and ankles
• spreads to the trunk, and often the palms and soles
• by day 5 or 6, may become red to purple dots (petechiae) that do not fade with pressure
• about 1 in 10 people never develop a rash, and in many it appears late, so its absence does not rule out RMSF

Severe disease

The bacteria damage the lining of small blood vessels, causing leaks and clots:

• confusion, seizures, coma
• low blood pressure and shock
• breathing difficulty from fluid in the lungs
• kidney failure
• bleeding problems
• gangrene of fingers, toes or limbs, sometimes requiring amputation

Diagnosis

RMSF is a clinical diagnosis: doctors decide to treat based on symptoms and possible tick exposure, because early tests are often negative.

• Blood tests: low platelets, low sodium and raised liver enzymes are common clues.
• Antibody tests: usually negative in the first week; a rise between an early and a later sample 2 to 4 weeks apart confirms the diagnosis.
• PCR or skin biopsy of the rash can detect the bacteria in some cases.

Many people with RMSF do not remember a tick bite.

Treatment

• Doxycycline is the treatment of choice for adults and children of all ages. Short courses do not stain children's teeth. It should begin within the first 5 days of illness and is continued until at least 3 days after fever resolves, typically 5 to 7 days or more.
• Improvement is usually seen within 24 to 48 hours. Lack of improvement suggests another diagnosis.
• Severe illness needs hospital care, including IV doxycycline, fluids and support for organ failure.
• Chloramphenicol is an alternative in rare situations, such as some pregnancies, but is less effective.

Starting treatment early is the single most important factor in survival.

Outlook

With prompt doxycycline, most people recover fully. Delayed treatment greatly increases the risk of death and lasting effects. Before effective antibiotics, about 1 in 5 or more people died. Children under 10 and adults over 70 are at higher risk of fatal disease. Survivors of severe illness may have long-term nerve damage, hearing loss, weakness or limb loss.

Prevention

• Use EPA-registered repellents (DEET, picaridin, IR3535, oil of lemon eucalyptus) on skin and permethrin on clothing.
• Wear long sleeves and trousers in wooded and grassy areas.
• Check yourself, children and pets for ticks daily and remove them promptly with fine-tipped tweezers.
• Treat dogs with tick prevention products and keep them out of tick-heavy areas.
• Avoid crushing ticks with bare fingers.
• Keep grass short and clear brush around homes.

Other tick-borne illnesses

Ehrlichiosis and anaplasmosis cause similar fever and headache and are also treated with doxycycline. Lyme disease typically begins with an expanding rash rather than spots.

Frequently asked questions

What are the first symptoms of Rocky Mountain spotted fever?

The first symptoms are sudden fever, severe headache and muscle aches, often with nausea, vomiting and stomach pain, starting 3 to 12 days after a tick bite. A spotted rash on the wrists and ankles usually follows 2 to 4 days after the fever begins.

What does the Rocky Mountain spotted fever rash look like?

It starts as small, flat, pink spots on the wrists, forearms and ankles, then spreads to the body, often including the palms and soles. Later the spots may become red or purple pinpoint dots. Some people never get a rash.

Is Rocky Mountain spotted fever deadly?

It can be. RMSF is one of the most dangerous tick-borne diseases, especially if treatment is delayed beyond the fifth day of illness. With prompt doxycycline treatment, most people recover fully.

Can children take doxycycline for Rocky Mountain spotted fever?

Yes. The CDC and American Academy of Pediatrics recommend doxycycline for children of all ages with suspected RMSF. Short courses do not cause tooth staining, and the risk of delaying effective treatment is far greater.