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Rocky Mountain Spotted Fever (RMSF)

Rocky Mountain Spotted Fever is a reportable disease in Oklahoma. Rocky Mountain Spotted Fever (RMSF) is a disease caused by the bacteria Rickettsia rickettsii (R. rickettsii). In Oklahoma, the tick most closely associated with RMSF is the American dog tick (Dermacentor variabilis). The other known tick vectors of R. rickettsii include the Rocky Mountain wood tick (Dermacentor andersoni), brown dog tick (Rhipicephalus sanguineus), and the cayenne tick (Amblyomma cajennense). Humans nearly always become infected with the bacteria following the bite of an infected tick. Tick bites due to the American dog tick are common in Oklahoma, but fortunately only 1–3% of the tick population is infected with R. rickettsii and capable of transmitting RMSF.

At least 4–6 hours of tick attachment and feeding are usually required to pass on the infection to humans. The symptoms of RMSF usually begin 3–14 days following the infected tick bite. There is usually a sudden onset of fever, fatigue, headache, and muscle soreness. A fine, bumpy red rash often appears on the extremities about 3–5 days after the fever, which may quickly spread to the palms, soles, and trunk.  However, not all persons with RMSF develop a rash. Other common symptoms of RMSF include nausea, vomiting, abdominal pain, and red eyes.  

Diagnosis is based upon clinical signs and symptoms, but laboratory testing can also be used to help diagnose RMSF. Blood samples taken in the early stage of illness (acute phase) and follow up samples taken 2–4 weeks later (convalescent phase) are used to confirm cases of RMSF through serologic testing. However, laboratory testing can take days to weeks for results to become available, so treatment should never be delayed while awaiting laboratory confirmation.

The first line treatment for all cases of RMSF is antibiotics (doxycyline). Treatment should be started immediately whenever RMSF is suspected because it can be a very serious disease; overall, 3–5% of all persons with RMSF die, but death is uncommon with prompt diagnosis and treatment. Factors associated with worse outcomes include delayed antibiotic therapy and age over 40 years. Although RMSF can be severe, preventive antibiotic therapy in non-ill persons following a tick bite is not recommended.

All persons are susceptible to RMSF, but persons who spend long amounts of time outdoors are more likely to be bitten by infected ticks. In addition, persons who remove ticks from their pets are at an increased risk for RMSF. There is a seasonal risk for becoming infected with RMSF because American dog ticks are most active and numerous from May through August. Personal tick bite prevention precautions should be taken before undergoing summer activities, especially during the spring and summer months. 

Rocky Mountain Spotted Fever is a reportable disease in Oklahoma. 

Avoiding tick bites is the best way to reduce your risk of developing RMSF or other tickborne illnesses. Personal tick bite prevention precautions include: 

  • Wear light colored clothing to make ticks easier to see. 
  • Wear long-sleeved shirts and long pants tucked into socks to deprive ticks of attachment sites. 
  • Wear closed-toe shoes, not sandals. 
  • Hikers and bikers should stay in the center of trails to avoid grass and brush. 
  • Check for ticks AT LEAST once per day; particularly along waistbands, in the armpits, and groin area. Don’t forget the back and the hair. 
  • Use a tick repellant with DEET on skin and clothing according to directions. 7
  • Use a tick repellant with permethrin ON CLOTHING ONLY and as directed by the label. 

If you have symptoms of RMSF (fever, headache, rash, nausea, vomiting, stomach pain, muscle pain, and lack of appetite) contact your healthcare provider. Make sure to explain if you have recently been bitten by a tick or been in an area where ticks are common. 

Treatment for RMSF with certain antibiotics, such as doxycycline, is very effective in treating the disease and can prevent sever illness.