• Disease agent: Rickettsia rickettsii
  

• Tick vector(s):
  

• American dog tick (Dermacentor similis/variabilis*)
• 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). ​​​
  

​* The American dog tick has been divided into two different species: Dermacentor variabilis primarily occurring east of the Rocky Mountains in North America and Dermacentor similis occurring west of the Rocky Mountains (Lado et al​., 2021). While the predominant species in California has been found to be D. similis, there may be areas in California where D. variabilis occurs.​​​

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
  

• 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, Santa Cruz, Tulare, 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.
  

• Signs 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
  

• Diagnoses can be made from PCR of an eschar scab or from a dry swab of the wound under the scab. See CDC Eschar-associated Rickettsioses (PDF) and CDC Collecting an Eschar Swab (PDF) for diagnostic sampling information. 
  

• 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 found on the VRDL Specimen Shipping Guidelines and Current Submittal Forms webpage. Please indicate rickettsial species suspected.