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Rocky Mountain Spotted Fever
Rocky Mountain spotted fever (RMSF) is a bacterial disease caused by the bacterium, Rickettsia rickettsii. Rocky Mountain spotted fever is transmitted by ticks, most commonly the American dog tick (Dermacentor variabilis). Although the American dog tick is the most common tick in Michigan, RMSF is rarely reported to cause human illness in the state. The disease is characterized by acute fever, headache, muscle pain, vomiting, and general discomfort. A rash may also develop in the majority of infected individuals. The most effective treatment for patients of any age is doxycycline. Rocky Mountain spotted fever can be fatal if treatment is not started soon after symptoms begin. Preventing tick bites is the best way to avoid getting RMSF.
Rocky Mountain spotted fever (RMSF) is rarely reported in Michigan. Anyone living or recreating where the ticks are present, may be at risk. Rocky Mountain spotted fever has been diagnosed throughout the U.S., however most cases are documented within the southeast and south central regions, particularly, North Carolina, Oklahoma, Arkansas, Tennessee, and Missouri.
Children under 10 years old, American Indians, people with a compromised immune system, and people with delayed treatment are at an increased risk of fatal outcome from RMSF. The majority of cases reported have an illness onset during the months of June and July. However, the seasonality varies for different regions of the country.
What are the signs and symptoms of RMSF?
The first symptoms of Rocky Mountain spotted fever (RMSF) typically begin 2-14 days after the bite of an infected tick. The disease is characterized by acute fever, headache, muscle pain, vomiting, and general discomfort. A rash may also develop 2-5 days after the onset of fever and often spreads with time. Approximately 90% of infected individuals will develop some type of rash, however, the rash may not develop until later in the disease process. Without treatment, this disease may be fatal yet, most cases are not fatal if appropriate treatment is administered.
Patients who had a particularly severe infection requiring prolonged hospitalization may have long-term health problems caused by this disease. The bacterium infects the endothelial cells that line the blood vessels. The damage that occurs in the blood vessels results in a disease process called a "vasculitis", and bleeding or clotting in the brain or other vital organs may occur. Loss of fluid from damaged vessels can result in loss of circulation to the extremities and damaged fingers, toes or even limbs may ultimately need to be amputated. Patients who suffer this kind of severe vasculitis in the first two weeks of illness may also be left with permanent long-term health problems such as profound neurological deficits, or damage to internal organs. Those who do not have this kind of vascular damage in the initial stages of the disease typically recover fully within several days to months.
How is RMSF diagnosed?
Rocky Mountain spotted fever (RMSF) is a difficult disease to diagnose. The disease symptoms may vary from person to person and may resemble other diseases. Diagnostic tests, especially those based on the detection of antibodies, will often appear negative for the first 7-10 days of illness. Treatment is most effective at preventing death if started in the first five days of symptoms. Thus, there is no test available at this time that can provide definitive results in time to make important decisions about treatment.
The diagnosis of RMSF is based on clinical suspicion alone. The diagnosis must be made based on clinical signs and symptoms, and can later be confirmed using specialized confirmatory laboratory tests.
What should I do if I have a tick that I want to identify or test?
Knowing what kind of tick bit you may be important in knowing what your risk of disease is. The Michigan Department of Health and Human Services (MDHHS) provides tick identification at no charge to Michigan citizens. Ticks that are submitted from people that are identified as blacklegged ticks (also known as deer tick) and are alive will be forwarded to the MDHHS Bureau of Laboratories for Lyme disease screening only at no cost. Ticks that are dead when they are received or are from animals (dog, cat, horse, etc.) will not be tested however, they will be identified to species and lifestage.
Information regarding the tick identification and testing program, in addition to instructions on how to ship the tick.
RMSF information for clinicians
Quick reference table for health care providers that includes vector species, incubation period, signs and symptoms, general laboratory findings, laboratory diagnosis, and treatment for the following tickborne diseases: Lyme disease, anaplasmosis, babesiosis, and Rocky Mountain spotted fever.
What is the treatment for RMSF?
Treatment should never be delayed pending the receipt of laboratory test results, or be withheld on the basis of an initial negative finding.
The antibiotic doxycycline is the first line treatment for adults and children of all ages and should be initiated immediately whenever RMSF is suspected.
Treatment is most effective at preventing death if doxycycline is started within the first 5 days of symptoms.
Ticks are the primary vector and must be attached for at least 4-6 hours in order for the bacterium to be transmitted. The American dog tick (Dermacentor variabilis), the Rocky Mountain wood tick (Dermacentor andersoni), and the brown dog tick (Rhipicephalus sanguineus) are all known vectors.
How can I prevent RMSF?
The most effective way to prevent RMSF is to prevent tick attachment.
- Avoid direct contact with ticks
- Ticks are typically found in wooded and brushy areas with high grass
- Stay in the center of hiking trails
- Repel ticks with DEET or permethrin
- Use repellents containing 20 to 30% DEET (N, N-diethyl-m-toluamide) on exposed skin and clothing
- Treat clothing and gear with products containing 0.5% permethrin
- Find and remove ticks from your body
- Perform frequent tick checks throughout your day
- Conduct a full-body tick check upon return from tick-infested areas
- Wear light-colored clothing to make it easier to see the ticks
- Tuck long pants into high socks
- Wear a long-sleeve shirt
- Avoid direct contact with ticks
- The Tick Management Handbook
An integrated guide for homeowners, pest control operators, and public health officials for the prevention of tick-associated disease (Connecticut Agricultural Experiment Station)
- CDC: Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis - A Practical Guide for Health Care and Public Health Professionals
- Michigan's Five Most Common Ticks
Ticks are significant vectors (carriers) of pathogens that cause human and animal disease. In Michigan, tick-borne diseases are rare, but they do occur and can be serious if not properly diagnosed and treated.
- Michigan Tick ID Card
Pocket-sized card for identifying common ticks in Michigan. Information regarding tick removal and tick-bite prevention.
- Tickborne Diseases of the U.S.
- Ticks and Your Health
Brochure describing Lyme disease and other tick-borne diseases in Michigan. Other topics covered include tick-bite prevention, preventing ticks on pets, and landscape techniques to minimize tick risk.
- Tick Removal