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      Flea-Borne Rickettsioses and Rickettsiae

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          Abstract

          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.

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          Rickettsia Phylogenomics: Unwinding the Intricacies of Obligate Intracellular Life

          Background Completed genome sequences are rapidly increasing for Rickettsia, obligate intracellular α-proteobacteria responsible for various human diseases, including epidemic typhus and Rocky Mountain spotted fever. In light of phylogeny, the establishment of orthologous groups (OGs) of open reading frames (ORFs) will distinguish the core rickettsial genes and other group specific genes (class 1 OGs or C1OGs) from those distributed indiscriminately throughout the rickettsial tree (class 2 OG or C2OGs). Methodology/Principal Findings We present 1823 representative (no gene duplications) and 259 non-representative (at least one gene duplication) rickettsial OGs. While the highly reductive (∼1.2 MB) Rickettsia genomes range in predicted ORFs from 872 to 1512, a core of 752 OGs was identified, depicting the essential Rickettsia genes. Unsurprisingly, this core lacks many metabolic genes, reflecting the dependence on host resources for growth and survival. Additionally, we bolster our recent reclassification of Rickettsia by identifying OGs that define the AG (ancestral group), TG (typhus group), TRG (transitional group), and SFG (spotted fever group) rickettsiae. OGs for insect-associated species, tick-associated species and species that harbor plasmids were also predicted. Through superimposition of all OGs over robust phylogeny estimation, we discern between C1OGs and C2OGs, the latter depicting genes either decaying from the conserved C1OGs or acquired laterally. Finally, scrutiny of non-representative OGs revealed high levels of split genes versus gene duplications, with both phenomena confounding gene orthology assignment. Interestingly, non-representative OGs, as well as OGs comprised of several gene families typically involved in microbial pathogenicity and/or the acquisition of virulence factors, fall predominantly within C2OG distributions. Conclusion/Significance Collectively, we determined the relative conservation and distribution of 14354 predicted ORFs from 10 rickettsial genomes across robust phylogeny estimation. The data, available at PATRIC (PathoSystems Resource Integration Center), provide novel information for unwinding the intricacies associated with Rickettsia pathogenesis, expanding the range of potential diagnostic, vaccine and therapeutic targets.
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            Flea-borne rickettsioses: ecologic considerations.

            Ecologic and economic factors, as well as changes in human behavior, have resulted in the emergence of new and the reemergence of existing but forgotten infectious diseases during the past 20 years. Flea-borne disease organisms (e.g., Yersinia pestis, Rickettsia typhi, R. felis, and Bartonella henselae) are widely distributed throughout the world in endemic-disease foci, where components of the enzootic cycle are present. However, flea-borne diseases could reemerge in epidemic form because of changes in vector-host ecology due to environmental and human behavior modification. The changing ecology of murine typhus in southern California and Texas over the past 30 years is a good example of urban and suburban expansion affecting infectious disease outbreaks. In these areas, the classic rat-flea-rat cycle of R. typhi has been replaced by a peridomestic animal cycle involving, e.g., free-ranging cats, dogs, and opossums and their fleas. In addition to the vector-host components of the murine typhus cycle, we have uncovered a second typhuslike rickettsia, R. felis. This agent was identified from the blood of a hospitalized febrile patient and from opossums and their fleas. We reviewed the ecology of R. typhi and R. felis and present recent data relevant to the vector biology, immunology, and molecular characterization and phylogeny of flea-borne rickettsioses.
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              Rickettsia felis: from a rare disease in the USA to a common cause of fever in sub-Saharan Africa.

              P. Parola (2011)
              Rickettsia felis is a spotted fever group rickettsia that has been definitely described in 2002. Within the last 20 years, there have been a growing number of reports implicating R. felis as a human pathogen, parallel to the fast-growing reports of the worldwide detection of R. felis in arthropod hosts, mainly the cat flea Ctenocephalides felis felis. R. felis is now known as the agent of the so-called flea-borne spotted fever, with more than 70 cases documented in the literature. Recently, two studies respectively conducted in Senegal and Kenya, have challenged the importance of R. felis infection in patients with unexplained fever in sub-Saharan Africa. We focus here on the epidemiological and clinical aspects of R. felis infection. More studies are needed, including the study of other arthropod vectors, but it can be speculated that R. felis infection might be an important neglected agent of fever in sub-Saharan Africa. © 2011 The Author. Clinical Microbiology and Infection © 2011 European Society of Clinical Microbiology and Infectious Diseases.
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                Author and article information

                Journal
                Am J Trop Med Hyg
                Am. J. Trop. Med. Hyg
                tpmd
                The American Journal of Tropical Medicine and Hygiene
                The American Society of Tropical Medicine and Hygiene
                0002-9637
                1476-1645
                11 January 2017
                11 January 2017
                : 96
                : 1
                : 53-56
                Affiliations
                [1 ]Division of Infectious Diseases, Department of Internal Medicine, University of Texas Medical Branch, Galveston, Texas.
                [2 ]Department of Pathology, University of Texas Medical Branch, Galveston, Texas.
                Author notes
                * Address correspondence to David H. Walker, Department of Pathology, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-0609. E-mail: dwalker@ 123456utmb.edu
                Article
                10.4269/ajtmh.16-0537
                5239709
                27799640
                5dbe4c77-e010-483a-a27e-4e7a22940c05
                © The American Society of Tropical Medicine and Hygiene

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 30 June 2016
                : 20 September 2016
                Categories
                Review Articles

                Infectious disease & Microbiology
                Infectious disease & Microbiology

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