Rickettsia 364D: a newly recognized cause of eschar-associated illness in California.
BACKGROUND
Four spotted fever group rickettsiae (SFGR) are known to infect humans in the United States. A member of the SFGR designated 364D and detected in Dermacentor occidentalis ticks has not previously been identified as a human pathogen.


METHODS
An 80-year-old man from a rural northern California community presented with an eschar on his forearm. A skin punch biopsy of the lesion was evaluated by immunohistochemistry and molecular analysis. Serum specimens obtained from the patient and 3 other area residents with similar illnesses were tested by immunofluorescence and Western immunoblot for antibodies to SFGR. Ticks were collected near the patient's residence and tested for SFGR.


RESULTS
Abundant intracellular rickettsiae and fragmented rickettsial antigens were observed in the mononuclear inflammatory infiltrates of the biopsy. Nucleotide sequences of DNA fragments amplified from the biopsy were identical to those of 364D. Convalescent sera from all four patients exhibited high immunoglobulin G titers to Rickettsia rickettsii, Rickettsia rhipicephali, and 364D antigens. Three adult D. occidentalis were positive for 364D, R. rhipicephali, and an unidentified Rickettsia species.


CONCLUSIONS
This is the first confirmation of human disease associated with the SFGR 364D, which was likely transmitted by D. occidentalis. Although the patients described here presented with a single cutaneous eschar as the principal manifestation, the full spectrum of illness associated with 364D has yet to be determined. Possible infection with 364D or other SFGR should be confirmed through molecular techniques in patients who present with "spotless" Rocky Mountain spotted fever or have serum antibodies to R. rickettsii with group-specific assays.
Shapiro
Marc R
MR
St Helena Hospital Clearlake, Clearlake, California, USA. shapirmr@ah.org
Fritz
Curtis L
CL
Tait
Karen
K
Paddock
Christopher D
CD
Nicholson
William L
WL
Abramowicz
Kyle F
KF
Karpathy
Sandor E
SE
Dasch
Gregory A
GA
Sumner
John W
JW
Adem
Patricia V
PV
Scott
Jamesina J
JJ
Padgett
Kerry A
KA
Zaki
Sherif R
SR
Eremeeva
Marina E
ME
D000369:Aged, 80 and over; D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood / Q000276:immunology; D015153:Blotting, Western; D002140:California; D003870:Dermacentor / Q000382:microbiology; D005260:Female; D005542:Forearm / Q000382:microbiology; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D012281:Rickettsia / Q000235:genetics*; D012282:Rickettsia Infections / Q000382:microbiology*; D012883:Skin Ulcer / Q000382:microbiology
D000907:Antibodies, Bacterial