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Rocky Mountain Spotted FeverAmerican Dog Tick

Rocky Mountain spotted fever (RMSF) is a tick-borne infection caused by the bacterium Rickettsia rickettsii.  This organism is transmitted to humans in Ohio by the bite of infected American dog ticks (Dermacentor variabilis) (see current human case map).  Another tick found in Ohio, the brown dog tick (Rhipicephalus sanguineus), has recently been implicated with human RMSF cases in the southwestern United States.  RMSF is a serious illness that can be fatal in the first eight days of symptoms if not treated correctly, even in previously healthy people.  The progression of the disease varies greatly.  Patients who are treated early may recover quickly on outpatient medication, while those who experience a more severe illness may require intravenous antibiotics, prolonged hospitalization or intensive care.

Rash from Rocky Mountain Spotted FeverTypical symptoms of RMSF include fever, headache, abdominal pain, vomiting and muscle pain.  A rash may also develop, but is often absent in the first few days, and in some patients, never develops.  Rocky Mountain spotted fever can be a severe or even fatal illness if not treated in the first few days of symptoms.  Doxycycline is the first line treatment for adults and children of all ages, and is most effective if started before the fifth day of symptoms.  The initial diagnosis is based on clinical signs and symptoms and medical history, and can later be confirmed by using specialized laboratory tests.  RMSF and other tick-borne diseases can be prevented.

Animals associated with Rocky Mountain spotted fever in Ohio include:

  • Dogs:  Dogs are susceptible to tick bites and tick-borne diseases like RMSF.  They can also bring infected ticks into the home.
  • Rodents and other mammals:  Ticks can become infected with RMSF bacteria while feeding on blood from an infected rodent or other mammal.
  • Ticks:  Ticks, specifically the American dog tick, Dermacentor variabilis, are the primary vector and reservoir host of RMSF bacteria.  A female tick can transmit the bacteria to her eggs, known as vertical transmission, causing infection in her offspring.

Rocky Mountain spotted fever resources:

Ohio statistics and maps:


Disease reporting and surveillance:

Fact sheets:

Tick-borne disease prevention literature:


Page Updated:  01/30/2018

Zoonotic Disease Program