Web Content Viewer

Rocky Mountain Spotted Fever

American dog tick

Rocky Mountain spotted fever (RMSF) is caused by an infection with a bacterium called Rickettsia rickettsii.  In Ohio, R. rickettsii is transmitted to humans through the bite of the infected American dog tick, Dermacentor variabilis.  Rocky Mountain spotted fever is one of several diseases caused by the spotted fever group rickettsia.

American dog ticks are the most commonly encountered type of tick in Ohio, and they are found throughout the state.  They live in areas of tall grass and in clearings that have little tree cover.  This species feeds on small rodents and medium-sized wild animals, as well as domestic cats and dogs.  They will also readily attach to humans.  Most cases of RMSF occur from spring through autumn when this tick is active.

The best way to prevent RMSF is to prevent tick bites.

If you find a tick on your body, remove it quickly to reduce the risk of contracting RMSF disease.  See a healthcare provider if you do get sick.  RMSF is curable.  Early diagnosis and treatment are important in order to avoid further health problems related to RMSF.

Where does RMSF occur in Ohio?

American dog ticks that carry RMSF can be found throughout most or all of Ohio.  On the map below, each dot represents one case of RMSF and is placed randomly in the patient's county of residence.  The presence of a dot does not necessarily mean that RMSF was acquired in Ohio.  The place of residence can be different from the place where the patient became infected.

Map: Rocky Mountain spotted fever in Ohio (2021: 30 cases)

What are the signs and symptoms of RMSF?

Early signs and symptoms are not specific to RMSF (including fever and headache).  However, the disease can rapidly progress to a serious and life-threatening illness.  See your healthcare provider if you become ill after having been bitten by a tick or having been in the woods or in areas with high brush where ticks commonly live.

  • FeverEarly-stage rash in a patient with Rocky Mountain spotted fever
  • Headache
  • Rash
  • Nausea
  • Vomiting
  • Muscle pain
  • Stomach pain
  • Lack of appetite

Rash is a common sign in people who are sick with RMSF.  Rash usually develops two to four days after fever begins.  The look of the rash can vary widely over the course of the illness.  Some rashes can look like red splotches, and some look like pinpoint dots.  While almost all patients with RMSF will develop a rash, it often does not appear early in the illness, which can make RMSF difficult to diagnose.

RMSF does not result in chronic or persistent infections.  Some patients who recover from severe RMSF may be left with permanent damage, including:

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

Any permanent damage is caused by the acute illness and does not result from a chronic infection.

How is RMSF diagnosed?

RMSF can only be diagnosed by a healthcare provider.  A blood specimen may be collected for laboratory testing.  Please visit the Centers for Disease Control and Prevention (CDC)'s website for information on diagnosis and testing.

What is the treatment for RMSF?

Please visit the CDC's website for additional information on treatment for RMSF.

Who is at risk in Ohio?

Anyone who spends time outdoors can be at risk for RMSF.  The tick that transmits RMSF in Ohio, the American dog tick, is the most commonly encountered tick in Ohio and is often found in overgrown lots and along weedy roadsides, paths and hiking trails.  People who frequent these settings (hikers, campers, hunters, farmers, gardeners, landscapers, other outdoor workers) may be at increased risk for contracting RMSF.

Ohioans of all ages can get sick with RMSF, but data collected by the Zoonotic Disease Program suggest that males are more at risk for RMSF than females.  Men between the ages of 55 and 59 years appear to be at particularly high risk.  Many cases of RMSF are reported in females between the ages of 30 and 34 years.

Graph: Rocky Mountain spotted fever by age and sex in Ohio

What time of year are Ohioans at risk for contracting RMSF?

In Ohio, cases of RMSF are reported in every month of year.  However, the number of reported cases is lowest in the winter, gradually rises in the spring, peaks in the summer, then declines through late summer and autumn.

It can take anywhere from three to 14 days from when the tick bite occurs to when symptoms of RMSF appear.  Since most cases get sick in July and August, that means most cases are bitten by an infected American dog tick between the end of June and August.  Therefore, late spring through late summer is the time of year when Ohioans are most at risk for contracting RMSF.

Graph: Rocky mountain spotted fever by week of illness onset in Ohio

What are the trends over time?

Trends in RMSF incidence vary over time, but are generally increasing.

Table: Rocky Mountain spotted fever annual case statistics Ohio

How can I reduce my risk of RMSF?

Steps to prevent RMSF include using insect repellent, removing ticks promptly, applying pesticides and reducing risk habitat.

What are the roles of other animals in RMSF transmission?

Dogs Dogs are susceptible to tick bites and tickborne diseases like RMSF.  They can also bring infected ticks into the home.
Rodents Rodents and other mammals can infect ticks with RMSF bacteria when they feed on them.
Ticks Ticks, specifically the American dog tick, Dermacentor variabilis, are the primary vector and reservoir host for RMSF bacteria.  A female tick can transmit the bacteria to her eggs, known as vertical transmission, causing infection in her offspring.