Rickettsiae Within the Fleas of Feral Cats in Galveston, Texas

Murine typhus is a flea-borne typhus group rickettsiosis caused by Rickettsia typhi. Once a prevalent disease in the United States, the use of dichlorodiphenyltrichloroethane in the 1940s broke the classic rat-rat flea cycle of transmission, and the remaining endemic foci are now believed to be associated with opossums and the cat flea (Ctenocephalides felis). In Galveston, Texas murine typhus has re-emerged as a cause of febrile illness, and 7% of fleas collected from opossums are infected with R. typhi. In this study, we sought to explore the prevalence of rickettsiae associated with fleas on cats, as these animals have been speculated to play a role in the epidemiology of murine typhus. Fleas were collected from feral cats entering a local veterinary clinic as part of a trap, spay, neuter, and release program. Fleas were identified and subjected to analysis by PCR and sequencing. An estimation of the minimum infection rate (MIR) of pooled samples was performed. Three hundred fourteen fleas (all C. felis) were collected from 24 cats. Sequences for the outer membrane protein B gene revealed R. typhi in one pool (MIR 0.3%), Rickettsia felis in four pools (MIR 1.3%), Rickettsia asembonensis in one pool (MIR 0.3%), and "Candidatus R. senegalensis" in six pools (MIR 2.0%). Results were confirmed by sequencing portions of the rickettsial citrate synthase and 17-kD protein gene. In this study, the presence of R. typhi in fleas from cats suggests that in Galveston, there exists a small but measurable risk to humans who come into contact with flea-infested cats. Despite this, we believe that the low prevalence from cat-collected fleas, compared with that previously detected from opossums, makes cats less likely to play a role in the maintenance of R. typhi in this region. The significance of other identified flea-borne rickettsiae is yet to be elucidated.