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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 Rocky Mountain spotted fever 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

Rocky Mountain Spotted Fever in Ohio
2022* Cases Compared to Incidence 2012-2021

County Rate 2012-2012
(per 100,000 per year)
2022 Cases*
 Adams 1.08 0
 Allen 0.19 0
 Ashland 0.38 0
 Ashtabula 0.00 0
 Athens 0.31 1
 Auglaize 0.00 0
 Belmont 0.00 0
 Brown 0.00 0
 Butler 0.18 1
 Carroll 0.00 0
 Champaign 0.26 0
 Clark 0.00 0
 Clermont 0.79 1
 Clinton 0.24 0
 Columbiana 0.10 0
 Coshocton 0.55 0
 Crawford 0.00 0
 Cuyahoga 0.05 0
 Darke 0.00 0
 Defiance 0.00 0
 Delaware 0.20 0
 Erie 0.13 0
 Fairfield 0.26 0
 Fayette 0.35 0
 Franklin 0.18 0
 Fulton 0.00 0
 Gallia 3.66 3
 Geauga 0.11 0
 Greene 0.06 0
 Guernsey 0.77 0
 Hamilton 0.26 1
 Hancock 0.00 0
 Hardin 0.00 0
 Harrison 0.66 0
 Henry 0.00 0
 Highland 0.93 0
 Hocking 0.00 0
 Holmes 0.00 0
 Huron 0.00 0
 Jackson 6.75 8
 Jefferson 0.00 0
 Knox 0.33 0
 Lake 0.09 0
 Lawrence 1.16 0
 Licking 0.00 0
 Logan 0.00 0
 Lorain 0.10 0
 Lucas 0.21 1
 Madison 0.46 0
 Mahoning 0.09 0
 Marion 0.15 0
 Medina 0.11 0
 Meigs 1.74 0
 Mercer 0.24 0
 Miami 0.09 0
 Monroe 1.43 0
 Montgomery 0.08 1
 Morgan 0.69 0
 Morrow 0.29 0
 Muskingum 0.23 0
 Noble 0.00 0
 Ottawa 0.00 0
 Paulding 0.00 0
 Perry 0.00 0
 Pickaway 0.35 0
 Pike 8.21 2
 Portage 0.12 0
 Preble 0.24 0
 Putnam 0.29 0
 Richland 0.08 0
 Ross 1.17 1
 Sandusky 0.17 0
 Scioto 2.62 0
 Seneca 0.00 0
 Shelby 0.00 0
 Stark 0.11 1
 Summit 0.07 0
 Trumbull 0.00 0
 Tuscarawas 0.00 0
 Union 0.00 0
 Van Wert 0.00 0
 Vinton 3.83 0
 Warren 0.18 1
 Washington 0.00 0
 Wayne 0.09 0
 Williams 0.00 0
 Wood 0.23 0
 Wyandot 0.00 0
TOTAL 0.23 22

Source: Ohio Department of Health.
* 2022 data as of September 16, 2022.
County-level data are based on the county of residence of the case.

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.

  • Fever.Early-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 Rocky Mountain spotted fever.

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

Rocky Mountain Spotted Fever by Age and Sex, Ohio, 2012-2021

Age Male Female
 0-4 years 6 3
 5-9 years 5 3
 10-14 years 2 2
 15-19 years 7 4
 20-24 years 6 3
 25-29 years 6 3
 30-34 years 16 5
 35-39 years 9 8
 40-44 years 17 13
 45-49 years 11 7
 50-54 years 15 6
 55-59 years 21 12
 60-64 years 14 16
 65-69 years 16 5
 70-74 years 9 5
 75-79 years 7 1
 80-84 years 1 0
 85+ years 2 1

Source: Ohio Department of Health.

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

Rocky Mountain Spotted Fever by Week of Illness Onset, Ohio, 2012-2021

Month Week of Illness Onset Cases 2012-2021
 January 1 1
  2 2
  3 1
  4 0
 February 5 2
  6 4
  7 2
  8 1
 March 9 1
  10 1
  11 0
  12 2
  13 4
 April 14 3
  15 1
  16 8
  17 7
 May 18 5
  19 9
  20 7
  21 5
 June 22 16
  23 9
  24 13
  25 11
  26 11
 July 27 15
  28 19
  29 10
  30 11
 August 31 8
  32 9
  33 13
  34 6
 September 35 8
  36 3
  37 4
  38 3
  39 9
 October 40 2
  41 3
  42 3
  43 2
 November 44 1
  45 4
  46 0
  47 2
 December 48 1
  49 1
  50 2
  51 1
  52 1

Source: Ohio Department of Health.

What are the trends over time?

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

Ohio RMSF Annual Case Statistics
Year Human Cases Deaths Median Age (Years) Age Range of Cases (Years) Counties with Reported RMSF Cases
2012 23 0 46 3 – 73 16
2013 23 1 55 16 – 89 13
2014 12 0 53.5 4 – 69 7
2015 12 0 32.5 6 – 65 9
2016 24 0 43 3 – 76 13
2017 34 0 41.5 6 – 77 22
2018 38 0 58.5 6 – 79 22
2019 49 0 52 4 – 77 25
2020 22 0 50.5 4 – 94 11
2021 30 0 50 2 – 79 15
 AVERAGE  27 0 46 n/a 15
TOTAL 267 1 n/a n/a n/a

How can I reduce my risk of RMSF?

Steps to prevent Rocky Mountain spotted fever 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.