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Rocky Mountain Spotted Fever (RMSF)

Information for the Public

What is Rocky Mountain spotted fever (RMSF)?
Rocky Mountain spotted fever (RMSF) is a disease caused by the bacteria (germ) Rickettsia rickettsii.

Where do cases of RMSF occur?
RMSF was a rare disease in Arizona until 2005, but since then over 100 cases have been reported, mostly from eastern Arizona in areas with many free-roaming dogs and severe tick infestations. To learn more about how many cases of RMSF occur in Arizona, visit RMSF Statistics.

How is RMSF spread?
In Arizona, RMSF is usually spread through the bite of an infected brown dog tick (Rhipicephalus sanguineus), but in northern Arizona, the Rocky Mountain wood tick (Dermacentor andersoni) can occasionally transmit RMSF. The longer a tick remains attached and feeding, the higher the likelihood that it may spread the bacteria.

How soon do symptoms of RMSF appear after a tick bite?
Symptoms usually start to appear about 7 days after the bite of an infected tick, but can begin anywhere between 3 and 14 days.

What are the symptoms of RMSF?
Symptoms usually begin with a sudden onset of fever and severe headache, may also include deep muscle pain, nausea and vomiting, and less frequently include stomach pain and cough. Many people develop a rash on their arms and legs about 3 to 5 days after the fever starts. This rash often spreads to the palms, soles, and over the rest of the body.

Is there treatment for RMSF?
RMSF can be treated with a common antibiotic called doxycycline. Serious complications, including death, can occur if the disease is not recognized and treated early.

Can animals get RMSF?
Yes. Dogs can develop RMSF just like humans. Cats, horses and other species do not get RMSF. Dogs get the disease because the most common tick vector in Arizona is the brown dog tick and this tick prefers to live and feed on dogs. For more information about RMSF in dogs, see RMSF Information for Veterinarians.

Can animals transmit RMSF to me?
Yes, but not directly. People get this disease when they are bitten by a tick that is carrying the bacterium R. rickettsia. Because ticks on dogs can be infected with R. rickettsii, dogs and people can get RMSF from the same ticks. These ticks can also bite other animals and pass RMSF to them. Dogs that are allowed to roam free can become "tick buses" that spread infected ticks all over the community. This is one reason dogs should be kept confined to the owner's property (by fences or chains), be kept on a leash, and be treated with tick control products regularly when in areas where ticks may live. It is very important to use appropriate products to control ticks on your pets as this protects them and you from diseases like RMSF.

What can I do to lower my chances of getting RMSF, or any other disease, from ticks?
Prevention begins with you! Take steps to reduce your chances of being bitten by any tick. Ticks are most active during warm weather, generally early spring through late fall. However, ticks can be out any time that temperatures are above freezing. When you are outside in an area likely to have ticks (e.g. brushy, wooded or grassy places, areas with many free roaming dogs), follow the simple steps to protect yourself and your loved ones found here RMSF Prevention.

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