The diversity and geographical distribution of fleas parasitizing small mammals have been poorly investigated on Indian
Ocean islands with the exception of Madagascar where endemic plague has stimulated extensive research on these
arthropod vectors. In the context of an emerging flea-borne murine typhus outbreak that occurred recently in Reunion
Island, we explored fleas’ diversity, distribution and host specificity on Reunion Island. Small mammal hosts belonging to
five introduced species were trapped from November 2012 to November 2013 along two altitudinal transects, one on the
windward eastern and one on the leeward western sides of the island. A total of 960 animals were trapped, and 286 fleas
were morphologically and molecularly identified. Four species were reported: (i) two cosmopolitan Xenopsylla species which
appeared by far as the prominent species, X. cheopis and X. brasiliensis; (ii) fewer fleas belonging to Echidnophaga gallinacea
and Leptopsylla segnis. Rattus rattus was found to be the most abundant host species in our sample, and also the most
parasitized host, predominantly by X. cheopis. A marked decrease in flea abundance was observed during the cool-dry
season, which indicates seasonal fluctuation in infestation. Importantly, our data reveal that flea abundance was strongly
biased on the island, with 81% of all collected fleas coming from the western dry side and no Xenopsylla flea collected on
almost four hundred rodents trapped along the windward humid eastern side. The possible consequences of this sharp
spatio-temporal pattern are discussed in terms of flea-borne disease risks in Reunion Island, particularly with regard to
plague and the currently emerging murine typhus outbreak.