Rickettsia felis, West Indies

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To the Editor: A spay–neuter (sterilization) program for feral cats from Basseterre, the capital of the Caribbean Island St. Kitts, found that most (45/58; 66%) cats had antibodies to spotted fever group rickettsiae (SFGR). The antibodies were detected with Rickettsia rickettsii antigen in a standard microimmunofluorescence assay (1). Titers for 13 (20%) cats were >320. Most SFGR are transmitted by ticks, but because of their grooming habits, cats seldom have many ticks (2), and we did not find any ticks on the cats we saw through the program. We did, however, commonly find cat fleas, Ctenocephalides felis, which are the main vector of R. felis, a recently described member of the SFGR. R. felis seems to be apathogenic in cats (3) but is the agent of flea-borne spotted fever in humans (4). Although R. felis has been reported from North and South America, Europe, Africa, the Middle-East, and Oceania (4), its presence in the Caribbean islands has not been established. To provide this information we tested DNA extracted with the QIAamp DNA Mini-Kit (QIAGEN, Valencia, CA, USA) from C. felis fleas preserved in 70% ethanol. Of 57 (19%) C. felis fleas from St. Kitts, 11 were positive for R. felis DNA when tested by PCR using primers targeting SFGR ompA (5) or TaqMan assay using primers targeting gltA and a probe specific for the organism (6,7). For a negative control we used distilled water; for a positive control we used DNA from R. montanensis cultures or recombinant control plasmids constructed by amplifying target fragments from R. typhi strain Wilmington and R. felis strain LSU (7). The sequences of the ompA and gltA amplicons obtained had 100% nucleotide sequence similarity with homologous fragments of the type reference isolate R. felis URRxCal2. We used the National Center for Biotechnology Information basic local alignment sequence tool, BLAST (www.ncbi.nlm.nih.gov/blast/Blast.cgi). To determine whether R. felis occurs on another Caribbean island, we tested 32 C. felis fleas from Dominica and found 1 (3%) to be positive by PCR when primers targeting ompA were used. The sequence obtained was also identical to that of R. felis URRxCal2. Our study provides further evidence that cats can be sentinels for the presence of rickettsiae (1). However, although rickettsemia can develop in cats experimentally infected with R. felis (3), no compelling evidence shows that cats help maintain the organism or transmit it to humans (8,9). Rather, it appears that C. felis fleas, which are also commonly found on dogs and to a lesser extent other mammals, are the major reservoir hosts and vectors of infection, although the exact mechanisms are unknown (10). Our study also expands the known distribution of R. felis and should alert healthcare workers who see residents of or vacationers from the Caribbean islands of the possibility of flea-borne spotted fever in their patients.