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Spotted Fever Group Rickettsioses

Information for Healthcare Professionals


Spotted fever group (SFG) Rickettsia are a group of intracellular bacterial pathogens transmitted to humans primarily through ticks.

SFG rickettsioses of concern in California include Rocky Mountain spotted fever (RMSF) and Pacific Coast tick fever (PCTF). In California, 1–3 confirmed cases of RMSF and 0–3 confirmed cases of PCTF are reported each year. The fatality potential of RMSF makes it critical to recognize and report suspected cases of these diseases.

Healthcare providers are required to report cases of SFG rickettsiosis to the local health department within one week (seven calendar days) of identification.

Collect Patient History

Information about recent tick bites, exposure to tick habitats, contact with dogs, similar illnesses in family members or pets, or history of recent travel to areas of high incidence can be helpful in making a diagnosis. Tick bites are often painless, and many patients with rickettsioses do not remember being bitten by a tick.

Rocky Mountain Spotted Fever (RMSF)

RMSF is considered one of the most severe tick-borne illnesses in California and the United States. For more information on RMSF, please see CDC RMSF Information for Healthcare Providers.

Key Points:

  • Disease agent: Rickettsia rickettsii

  • Tick vector(s):

    • American dog tick (Dermacentor variabilis/similis)

    • Brown dog tick (Rhipicephalus sanguineus)

    • Pacific Coast tick (Dermacentor occidentalis)

    • Rocky Mountain wood tick (Dermacentor andersoni)

  • Areas of higher RMSF incidence include the southeastern U.S., southwestern U.S., and Mexico. 

  • Signs and symptoms:

    • RMSF typically manifests with fever, rash, headache, and myalgia; early-stage, non-specific signs and symptoms can resemble other common illnesses like flu or appendicitis.

    • Rash appearance can vary, but spreads quickly across much of the body (including palms of hands and soles of feet).

Note: RMSF is rapidly progressing and requires empiric treatment with doxycycline within the first 5 days of illness to prevent severe illness and death.

Eschar after tick bite?
It could be PCTF. Differentiate from scab or other bite wound and collect eschar scab (PDF) or swab wound for PCR test.

Pacific Coast Tick Fever (PCTF)

PCTF was first recognized in 2010, with all subsequent cases having exposure in California.  For more information on PCTF, please see The Eco-epidemiology of Pacific Coast Tick Fever in California.

Key Points:

  • Disease agent: Rickettsia sp. 364D (Rickettsia philipii)

  • Tick vector:

    • Pacific Coast tick (Dermacentor occidentalis)

      • Common in California from May-September

      • Infected D. occidentalis ticks have been found in Colusa, Contra Costa, Kern, Lake, Los Angeles, Marin, Mendocino, Orange, Riverside, San Bernardino, San Diego, San Luis Obispo, Santa Barbara, Santa Clara, and Ventura counties in California.

  • Most human PCTF cases have been reported from northern California. Infected ticks have been recovered from both northern and southern California, and thus PCTF should be a differential in patients presenting with eschar-associated tick bites throughout the state.

  • Sample images of eschars on the skinSigns and symptoms:

    • Typical to PCTF are ulcerated, necrotic skin lesions called eschars that usually develop a few days to a week following the bite of an infected tick.

      • An eschar is often at the site of a tick bite, but multiple eschars may appear later, with or without fever and myalgia. 

    • Rash is less common

Diagnostic Testing for SFG Rickettsioses

Many diagnostic tests for spotted fevers, especially tests based on the detection of antibodies, will frequently appear negative in the first 7-10 days of illness and cannot be relied upon for initiation of antibiotic therapy (doxycycline).

The CDPH Viral and Rickettsial Disease Laboratory (VRDL) offers the following diagnostic testing for SFG rickettsioses:

  • PCR testing of eschars or swabs for PCTF

  • PCR assays for several Rickettsia species
    (a pan-rickettsial assay and species-specific assays for R. rickettsii, R. 364D, R. typhi, and R. felis)

    • An acceptable sample is an acute (within 10 days of onset) EDTA whole blood (purple top) and/or plasma or serum collected preferably before antibiotic administration or as soon as possible after first antibiotic administration.

Samples must be accompanied with the General Purpose Specimen Submittal Form (PDF) found on the VRDL Specimen Submittal Forms webpage. Please indicate rickettsial species suspected.

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