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About Spotted Fever Group Rickettsiosis

In Wisconsin, spotted fever group rickettsioses (SFGR) are uncommon illnesses spread by the bite of an infected tick.

Rocky Mountain spotted fever (RMSF), caused by the bacterium Rickettsia rickettsii, is the most severe of all SFGR. RMSF can be spread by the wood tick, also known as the American dog tick (Dermacentor variabilis). Wood ticks are commonly found in grassy or wooded areas throughout the state, but they rarely spread disease in Wisconsin. Wood ticks are most active in our state during April through August, but it is important to use caution year-round.

Very little is known about which other spotted fever bacteria are spread in Wisconsin, if any, but all types of SFGR are rare throughout the Upper Midwest. 

SFGR cases occur throughout the U.S., but are most common in south-central and southeastern states. Anyone can get SFGR, but can be more severe in children under 10, in the elderly, and in those who have a weakened immune system. SFGR can range from relatively mild to life threatening. 

Tick crawling on tip of leaf


In Wisconsin, Rocky Mountain spotted fever can be spread to people through the bite of an infected wood tick.  

A pair of runner shoes walking through tall grasses

  • It is important to remove ticks as soon as they are found to prevent illness.
  • Adult wood ticks commonly bite people, but rarely spread RMSF in Wisconsin.  
    • Adult wood ticks are typically active during April through August.
    • Adult wood ticks are relatively large, but people may not feel their bite.
  • Immature ticks, called larvae and nymphs, rarely bite people. 
    • Immature wood ticks are typically active during April through September.
    • Immature wood ticks are very small, and are capable of spreading RMSF, but don't commonly bite people. 
  • Ticks can attach to any part of the body but are often found in hard-to-see areas, such as:
    • Behind the knees
    • Armpits
    • Scalp
    • In and around the ears
    • Inside the belly button
    • Groin

RMSF, and all SFGR, are preventable and treatable. Visit our Tick Bite Prevention page to learn how to prevent tick bites, and how to properly remove a tick if you are bitten.

Symptoms can show up three to 12 days after being bitten by an infected tick.

Early signs and symptoms are usually mild. However, if untreated, the disease can quickly progress to a serious and life-threatening illness. Those who recover from serious illness can suffer from long-term health problems. 

Common signs and symptoms: 

  • Fever
  • Headache
  • Rash (usually appears two to four days after fever begins)
  • Nausea and/or vomiting
  • Stomach pain
  • Muscle pain
  • Lack of appetite

Long-term health problems:

  • Amputation of arms, legs, fingers, or toes (from damage to blood vessels in these areas)
  • Hearing loss
  • Paralysis
  • Mental disability

RMSF can be treated with antibiotics. Doxycycline is the antibiotic of choice for people of all ages. Treatment should be started whenever RMSF is suspected and is most effective at preventing severe complications if started within the first five days of illness. Most people treated with oral antibiotics during the early stages of RMSF recover completely.

If not treated early, RMSF can cause very serious illness or death. It is important to get treatment as soon as possible after symptoms start. The following table shows the current treatment recommendations from the Centers for Disease Control and Prevention (CDC) for RMSF in adults and children.

Treatment for RMSF
Age Category Drug Dosage Maximum Duration, Days
Adults Doxycycline 100 mg, twice per day 100 mg/dose 7–14
Children under 45 kg (100 lbs) Doxycycline 2.2 mg/kg body weight, twice per day 100 mg/dose 7–14

Patients should be treated for at least three days after the fever subsides and until there is evidence of clinical improvement. Minimum total course of five to seven days for uncomplicated cases. Antibiotic treatment following a tick bite is not recommended to prevent RMSF. There is no evidence this practice is effective, and this may only delay onset of disease. Instead, if you get bitten by a tick, be alert for symptoms listed above and call your doctor if fever, rash, or other symptoms develop.

Department of Health Services Resources
CDC Resources
Partner Resources
SFGR is preventable and treatable. Visit our Tick Bite Prevention page to learn how to protect yourself from illnesses spread by ticks.

Questions about illnesses spread by ticks? Contact us!
Phone: 608-267-9003 | Fax: 608-261-4976

Last revised July 7, 2021