Spotted Fever Group Rickettsiae in Ticks Feeding on Humans in Northwestern Spain Is Rickettsia conorii Vanishing? PEDRO FERN ´ ANDEZ-SOTO, a RICARDO P ´ EREZ-S ´ ANCHEZ, b RUFINO ´ ALAMO-SANZ, c AND ANTONIO ENCINAS-GRANDES a a Laboratorio de Parasitolog´ ıa, Facultad de Farmacia, Universidad de Salamanca, 37007 Salamanca, Spain b Departamento de Patolog´ ıa Animal, IRNA (CSIC), 37007 Salamanca, Spain c Direcci´ on General de Salud P´ ublica, Consejer´ ıa de Sanidad, Junta de Castilla y Le´ on, 47011 Valladolid, Spain ABSTRACT: During a 7-year study, we identified and analyzed by PCR 4,049 ticks removed from 3,685 asymptomatic patients in Castilla y Le´ on (northwestern Spain). A total of 320 ticks (belonging to 10 species) were PCR-positive for rickettsiae. Comparison of amplicon sequences in databases enabled us to identify eigth different spotted fever group (SFG) rickettsiae: Rickettsia slovaca, Rickettsia sp. IRS3/IRS4, R. mas- siliae/Bar29, R. aeschlimannii, Rickettsia sp. RpA4/DnS14, R. helvetica, Rickettsia sp. DmS1, and R. conorii. Although Mediterranean spotted fever (MSF) is an endemic disease in Castilla y Le´ on, R. conorii was found in only one Rhipicephalus sanguineus tick, whereas other pathogenic SFG rickettsiae were much more prevalent in the same area. Our data suggest that in Castilla y Le´ on, many MSF or MSF-like cases attributed to R. conorii could have been actually caused by other SFG rickettsiae present in ticks biting people in this region of Spain. KEYWORDS: Mediterranean spotted fever; Rickettsia conorii; R. slovaca; R. aeschlimannii; Castilla y Le ´ on; Spain Castilla y Le´ on is the largest regional community in the northwestern part of Spain and the largest regional area of Europe. Traditionally, the Mediterranean spotted fever (MSF) caused by R. conorii was thought to be the only prevailing rickettsial disease in this community and the main sources of knowledge are Address for correspondence: Dr. Pedro Fern´ andez-Soto, Laboratorio de Parasitolog´ ıa, Facultad de Farmacia, Universidad de Salamanca, Avenida Campo Charro s/n. 37007, Salamanca, Spain. Voice: +34-923-294535; fax: +34-923-294515. e-mail: pfsoto@usal.es Ann. N.Y. Acad. Sci. 1078: 331–333 (2006). C  2006 New York Academy of Sciences. doi: 10.1196/annals.1374.063 331