Rickettsia typhi and Rickettsia felis are flea-borne rickettsiae that are distributed throughout the world. This mini-review outlines the ecology and epidemiology of flea-borne rickettsioses; highlights important clinical, diagnostic, and therapeutic considerations; and discusses areas of uncertainty regarding Rickettsia felis and other rickettsiae harbored by fleas.

Murine typhus is an acute undifferentiated febrile illness caused by Rickettsia typhi. The classic reservoir (Rattus spp.) and flea vector (Xenopsylla cheopis) were once culprits of murine typhus in the United States. Vector and rodent control efforts have drastically decreased the prevalence of disease, except in a few endemic foci where opossums and cat fleas play a role in transmission. Since 2012, there has been a reemergence of murine typhus in Galveston, TX. We hypothesize that opossums and cat fleas are involved in the transmission of R. typhi in Galveston. To explore this, we sought to find the seroprevalence of typhus group antibodies from opossums. We also sought to find the prevalence of R. typhi in fleas parasitizing these animals. We collected blood from 12 opossums and found that eight (66.7%) had the presence of anti-R. typhi antibodies. All opossums were infested with fleas; a total of 250 Ctenocephalides felis fleas were collected from these animals. Seven opossums (53.8%) were infested with fleas that had molecular evidence of R. typhi infection, while six (46.2%) were infested with fleas that contained Candidatus Rickettsia senegalensis, an organism closely related to R. felis. The minimum flea infection rate for R. typhi was 7.0%. The minimum infection rate for Candidatus R. senegalensis was 6.1%. Our study demonstrates that fleas infected with R. typhi parasitize opossums in Galveston. It is therefore likely that opossums and their fleas play a role in the city's recent reemergence of murine typhus.

Twelve patients with murine typhus were identified in Galveston, Texas, USA, in 2013. An isolate from 1 patient was confirmed to be Rickettsia typhi. Reemergence of murine typhus in Galveston emphasizes the importance of vector control and awareness of this disease by physicians and public health officials.

The purpose of this review is to describe recent advances in our understanding of the pathogenesis, epidemiology, and clinical features of rickettsial diseases with emphasis placed on those relating to travel and tropical medicine. Rickettsioses are becoming increasingly recognized as causes of febrile illness in travelers and in those residing in the tropics. In South and Central America, infection with Rickettsia rickettsii continues to have severe consequences. Resurgence of Mediterranean spotted fever in Bulgaria highlights the threat of rickettsial infections when there is a lapse in vector and reservoir control. Similar to African tick-bite fever, Rickettsia parkeri is an emerging cause of eschar-associated infection in Brazil, Argentina, and Uruguay. Several reports of murine typhus requiring hospitalization demonstrate the risk of this infection to the traveler. The use of fluoroquinolones for milder spotted fevers may fall out of favor with evidence of deleterious effects in those treated with ciprofloxacin. With globalization and increased access to travel, clinical awareness of rickettsial diseases is of increasing importance. Although the growing number of rickettsial species may be daunting to the clinician, recognition of the patterns of rickettsial disease will ensure prompt and effective therapy.

Murine typhus is an acute febrile illness caused by Rickettsia typhi, an obligately intracellular Gram-negative coccobacillus. Rats (Rattus species) and their fleas (Xenopsylla cheopis) serve as the reservoir and vector of R. typhi, respectively. Humans become infected when R. typhi-infected flea feces are rubbed into flea bite wounds or onto mucous membranes. The disease is endemic throughout much of the world, especially in tropical and subtropical seaboard regions where rats are common. Murine typhus is reemerging as an important cause of febrile illness in Texas and Southern California, where an alternate transmission cycle likely involves opossums (Didelphis virginiana) and cat fleas (Ctenocephalides felis). Although primarily an undifferentiated febrile illness, a range of neurologic manifestations may occur, especially when treatment is delayed. Serology is the mainstay of diagnostic testing, but confirmation usually requires demonstrating seroconversion or a fourfold increase in antibody titer from acute- and convalescent-phase sera (antibodies are seldom detectable in the first week of illness). Thus, early empiric treatment with doxycycline, the drug of choice, is imperative. The purpose of this review is to highlight murine typhus as an important emerging and reemerging infectious disease, review its neurologic manifestations, and discuss areas in need of further study.