Louse- and flea-borne rickettsioses: biological and genomic analysesJoseph J. Gillespie1, 2, Nicole C. Ammerman2, Magda Beier-Sexton2, Bruno S. Sobral1 and Abdu F. Azad2
1 Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, Virginia, USA
2 Department of Microbiology and Immunology, University of Maryland School of Medicine, 660 West Redwood St. HH Room 324, Baltimore, MD 21201, USA
Received 15 May 2008; accepted 24 November 2008; published online 28 November 2008
Abstract - In contrast to 15 or more validated and/or proposed tick-borne spotted fever group species, only three named medically important rickettsial species are associated with insects. These insect-borne rickettsiae are comprised of two highly pathogenic species, Rickettsia prowazekii (the agent of epidemic typhus) and R. typhi (the agent of murine typhus), as well as R. felis, a species with unconfirmed pathogenicity. Rickettsial association with obligate hematophagous insects such as the human body louse (R. prowazekii transmitted by Pediculus h. humanus) and several flea species (R. typhi and R. felis, as well as R. prowazekii in sylvatic form) provides rickettsiae the potential for further multiplications, longer transmission cycles and rapid spread among susceptible human populations. Both human body lice and fleas are intermittent feeders capable of multiple blood meals per generation, facilitating the efficient transmission of rickettsiae to several disparate hosts within urban/rural ecosystems. While taking into consideration the existing knowledge of rickettsial biology and genomic attributes, we have analyzed and summarized the interacting features that are unique to both the rickettsiae and their vector fleas and lice. Furthermore, factors that underlie rickettsial changing ecology, where native mammalian populations are involved in the maintenance of rickettsial cycle and transmission, are discussed.
Key words: epidemic and murine typhus / ecology / rickettsial biology / recrudescent typhus
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© INRA, EDP Sciences 2009