Rocky Mountain spotted fever (RMSF)

RMSF is caused by the bacterium Rickettsia rickettsii, which certain ticks can pass to a person while feeding. Despite the name, it is not limited to the Rocky Mountains. Most US cases are actually reported in South-Central and Southeastern states. It belongs to a group of illnesses called spotted fever rickettsioses. A common antibiotic can treat it when it is caught early.

• Sudden fever and headache
• Rash: often small, flat, pink spots that start on the wrists and ankles. They may spread to the trunk, palms, and soles. Fewer than half of patients have a rash in the first 3 days
• Muscle aches
• Nausea, vomiting, or stomach pain
• Loss of appetite
• Swelling (edema) around the eyes or on the backs of the hands

Symptoms usually begin about 3–12 days after the bite of an infected tick (CDC). When a rash appears, it usually shows up 2–4 days after the fever starts. The more typical spotted (petechial) rash often does not appear until day 5 or 6 of illness.

A doctor diagnoses RMSF based on your symptoms, any possible tick exposure, and where you live or have traveled. They will often start treatment before lab results come back, because acting early is important. Blood tests can support the diagnosis, but they are often negative in the first days of illness. So a normal early test does not rule it out. Do not wait for a rash to get care, since fewer than half of patients have one in the first 3 days. Only a licensed doctor can diagnose RMSF.

Doxycycline is the recommended first-choice antibiotic for RMSF in patients of all ages, including young children, CDC says. It works best when started early. CDC notes it is most effective at preventing death when started within the first 5 days of symptoms. There is no benefit to waiting for test results. Fast treatment can prevent severe illness and complications. A licensed doctor prescribes and manages treatment, including the dose and how long to take it. Do not try to treat yourself.

There is no vaccine for RMSF, so prevention means avoiding tick bites. Use EPA-registered repellents (DEET, picaridin, IR3535, oil of lemon eucalyptus, PMD, or 2-undecanone). Treat clothing and gear with permethrin, but not your skin. Avoid tall grass and leaf litter, check for ticks every day, and shower soon after coming inside. If you find an attached tick, remove it right away with fine-tipped tweezers, pulling upward with steady, even pressure. The brown dog tick can live around homes, yards, and kennels, so keep pets on tick control your vet recommends.

Despite its name, RMSF is most often reported in South-Central and Southeastern states. CDC notes that more than 60% of US cases come from North Carolina, Oklahoma, Arkansas, Tennessee, and Missouri. Cases occur across the lower 48 states. Most illness happens in the warmer months, especially spring and summer. In parts of Arizona and northern Mexico, the brown dog tick spreads RMSF all year. CDC has linked this to unusually high rates of cases and deaths there, especially among children.