Abstract
BackgroundCat fleas, Ctenocephalides felis, are known biological vectors for Rickettsia felis. Rickettsial transmission can be vertical via transovarial transmission within a flea population, as well as horizontal between fleas through a bloodmeal. The previously undescribed infection kinetics of bloodmeal-acquired R. felis in cat fleas provides insight into the R. felis-flea interaction.FindingsIn the present study, dissemination of R. felis in previously uninfected cat fleas fed an R. felis-infected bloodmeal was investigated. At weekly intervals for 28 days, rickettsial propagation, accumulation, and dissemination in gut epithelial cells, specifically in the hindgut and the specialized cells in the neck region of midgut, were observed on paraffin sections of infected cat fleas by immunofluorescence assay (IFA) and confirmed by PCR detection of R. felis 17-kDa antigen gene. IFA results demonstrate ingested rickettsiae in vacuoles during early infection of the gut; lysosomal activity, indicated by lysosome marker staining of freshly-dissected gut, suggests the presence of phagolysosome-associated vacuoles. Subsequent to infection in the gut, rickettsiae spread to the hemocoel and other tissues including reproductive organs. Densely-packed rickettsiae forming mycetome-like structures were observed in the abdomen of infected male cat fleas during late infection. Ultrastructural analysis by transmission electron microscopy (TEM) confirmed the presence and infection characteristics of Rickettsia including rickettsial destruction in the phagolysosome, rickettsial division, and accumulation in the flea gut.ConclusionsThis study intimately profiles R. felis dissemination in cat fleas and further illuminates the mechanisms of rickettsial transmission in nature.
Highlights
Cat fleas, Ctenocephalides felis, are known biological vectors for Rickettsia felis
In order to examine the incidence of rickettsial infection of cat fleas fed on R. felis-infected bloodmeal, eight fleas collected at 5 dpe were analyzed for the presence of rickettsial 17-kDa antigen gene by PCR
Results indicated all cat fleas exposed to an R. felis-infected bloodmeal were rickettsial infected (Figure 1)
Summary
Rickettsia felis has emerged as a cosmopolitan arthropodborne pathogen infecting various arthropod hosts. Rickettsial transmission by arthropod vectors can be vertical, horizontal, or for dynamic organisms such as R. felis, both. Rickettsia spp. conferring a negative fitness effect require horizontal transmission for maintenance in arthropod populations. Identification of both transmission paradigms is unique to R. felis. In the cat flea, Ctenocephalides felis, vertical transmission of R. felis varies, not influencing flea fitness, and horizontal. While molecular methods confirm detection of R. felis in a variety of hematophagous arthropods, only cat fleas are known biological vectors. The ability to infect cat fleas with R. felis via an infectious bloodmeal [12] and show transmission of R. felis between fleas [13] was recently demonstrated using an artificial host system. Through mapping the infection process in the natural host, an appreciation of the ecology of this emerging pathogen and potential points of intervention may be identified
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