Ann. N.Y. Acad. Sci. 990:149–151 (2003). ©2003 New York Academy of Sciences. A Follow-up Study on Newly Recognized Spotted Fever Group Rickettsiae in Ticks Collected in Southern Croatia DARJA DUH , a MIROSLAV PETROVEC, a TOMI TRILAR, b VOLGA PUNDA-POLI å, c NIKOLA BRADARI å, c ZORANA KLISMANI å, d AND TATJANA AV · I â-Î UPANC a a Institute of Microbiology and Immunology, Medical Faculty of Ljubljana, 1000 Ljubljana, Slovenia b Slovenian Museum of Natural History, Ljubljana, Slovenia c Departments of Clinical Microbiology and of Infectious Diseases, University Hospital and School of Medicine, Split, Croatia d Institute for Public Health, Split, Croatia KEYWORDS : ticks; Rickettsiae ; molecular biology; climate; Croatia INTRODUCTION Two rickettsial diseases are commonly recognized in southern Croatia: Mediter- ranean spotted fever, caused by Rickettsia conorii , and rickettsial pox, caused by R. akari . In a recent study by Punda-Polic and colleagues, two additional spotted fever group (SFG) rickettsiae have been described in ticks in southern Croatia. R. slovaca and R. aeschlimannii were detected in Dermacentor marginatus and Hyalomma marginatum ticks, respectively. 1 Although, rickettsiae are transmitted by numerous arthropods (ticks, fleas, lice, and mites), ixodid ticks are the most important vectors of SFG rickettsiae. Efficient transovarial and transstadial transmission of rickettsiae allows ticks to serve as reservoir hosts for SFG rickettsiae. 2 Vector-pathogen-host systems are limited by climate. As tick development rates and host-questing activity are dependent on temperature and moisture, variation in seasonal population dynam- ics of tick species exists, which in turn affects pathogens vectored by ticks. 3 Our aim was to study the impact of environmental conditions on seasonal popu- lation dynamics of tick species found in southern Croatia with the consequences for rickettsiae vectored by them. Therefore, a follow-up study was conducted in which ticks were collected from domestic animals in the same regions, but in a different time period. Address for correspondence: Institute of Microbiology and Immunology, Medical Faculty of Ljubljana, Zalo ‰ ka 4, 1000 Ljubljana, Slovenia. Fax: +386-1-543-7450. duh@mf.uni-lj.si