August 19, 2013
Rickettsia philipii in Monterey County
To date, two human cases have been reported among Monterey County residents.
Rickettsia philipii (formerly known as Rickettsia 364D) is an emerging human tickborne disease in California. In 2008, the first human case was identified in a resident of Lake County, California. By the end of 2012, 10 cases had been confirmed among residents of Lake, Contra Costa, Monterey, Orange, and Santa Clara counties. There have been 2 cases reported among Monterey County residents, one confirmed and one suspected.
Rickettsia philipii is a member of the Spotted Fever group Rickettsia (SFGR). Symptoms of Rickettsia philipii rickettsiosis include fever, rash, eschar, headache, myalgia, anemia, thrombocytopenia, and/or hepatic transaminase elevation. The eschar is usually an isolated ulcer with raised erythematous margins and a black core (see photo at the end of this Update). It is often surrounded by generalized edema and erythema. Symptoms develop 3 to 14 days after exposure at the site of a known or presumed tick bite.
Rickettsia philipii is transmitted by Pacific Coast ticks (Dermacentor occidentalis, see photo at the end of this Update). Rickettsia philipii has been detected in ticks collected from Alameda, Contra Costa, Lake, Los Angeles, Mendocino, Monterey, Orange, Riverside, San Bernardino, San Mateo, Santa Clara, Shasta, and Ventura counties. Adult Pacific Coast ticks are active January through June and can be found in dry, grassy areas. Nymphal ticks are active May through August and likely live in leaf litter and wood products. Both adults and nymphs are thought to transmit Rickettsia philipii to humans. Tick attachment time prior to transmitting Rickettsia philipii is likely between 2 and 20 hours, which is shorter than seen with Western black legged ticks and Lyme disease (greater than 24 hours).
Recommendations for Healthcare Providers
At this time, the Health Department recommends that medical providers:
- Take a detailed history from patients presenting with isolated ulcers and/or eschars. Although patients may not recall a tick bite, presence in a grassy or wooded area 3 to 14 days prior to onset of symptoms may indicate possible exposure.
- If Rickettsia philipii rickettsiosis is suspected, consider laboratory testing. Because Rickettsia philipii shares antigens with many other SFGR, profound cross-reactivity occurs with conventional serological assays. In general, paired sera showing a four-fold rise in IgG antibody titer reactive for R. rickettsii or other rickettsial antigen will confirm acute infection with Rickettsia but cannot differentiate between species. The California Department of Public Health (CDPH) Viral and Rickettsial Disease Laboratory (VRDL) has developed a polymerase chain reaction (PCR) test to confirm the identity of specific SFGR including Rickettsia philipii. To submit a specimen for testing, providers must:
- Contact the Monterey County Communicable Disease Unit at (831) 755-4521 and provide clinical and exposure information on the suspected case. CDPH Viral and Rickettsial Disease Laboratory (VRDL) will not test specimens that do not meet CDC clinical case definitions and have not been approved for testing by the local health department.
- Collect appropriate specimens:
- To confirm SFGR, at minimum 2 paired serum specimens in 5-10 cc red/tiger top tubes must be collected (one specimen within 10 days of symptom onset; second specimen 3-4 weeks following the acute specimen).
- To specifically identify Rickettsia philipii, the following specimens should also be submitted (in addition to paired sera as outlined above):
- Eschar/scab (if present) (place in dry sterile container)
- Swab(s) of open lesions, pustules, or vesicles (Dacron swab in dry sterile container)
- Ticks removed from suspected case (dry sterile container)
- Transport specimens with cold packs to the Monterey County Public Health Laboratory for testing. If transporting the specimen to the Public Health Laboratory is a barrier to testing, please contact the Communicable Disease Unit at 831-755-4521 for assistance.
- Treat suspected cases of Rickettsia philipii rickettsiosis appropriately. Doxycycline is the first line treatment for adults and children of all ages:
- Adults: 100 mg po q 12 hours
- Children under 45 kg: 2.2 mg/kg body weight po bid
Patients should be treated for at least 3 days after the fever subsides and until there is evidence of clinical improvement. Standard duration of treatment is 7-14 days. Do not delay treatment while awaiting laboratory confirmation. Treatment decisions should be based on epidemiologic and clinical evidence.
- Educate your patients about tick bite prevention (apply DEET, wear light colored clothes, check for ticks frequently, shower after being in tick habitat).
- Report all suspected cases of Rickettsia philipii rickettsiosis (whether or not you require assistance with laboratory testing) to the Monterey County Health Department’s Communicable Disease Unit (phone: 831‑755‑4521; fax: 831‑754-6682).
For additional information about tickborne diseases in Monterey County, please contact the Communicable Disease Unit at 831‑755‑4521. For information about laboratory testing at the Monterey County Public Health Laboratory, call 831‑755‑4516.
R. philipii cutaneous eschar
(Shapiro et. al, CID, 2009)
Pacific Coast Tick
(photo courtesy of the California Department of Public Health)
Health Alert: Warrants immediate action or attention. Health Advisory: Provides information for a specific incident or situation; may not require immediate action. Health Update: Provides updated information regarding an incident or situation; unlikely to require immediate action.