Rickettsia

About: Rickettsia is a research topic. Over the lifetime, 2262 publications have been published within this topic receiving 57470 citations.

Rickettsia Species Infecting Amblyomma cooperi Ticks from an Area in the State of São Paulo, Brazil, Where Brazilian Spotted Fever Is Endemic

Abstract: Owing to the potential role of the tick Amblyomma cooperi in the enzootic cycle of Rickettsia rickettsii, the etiologic agent of Brazilian spotted fever (BSF), this study evaluated infection by Rickettsia species in A. cooperi ticks collected from an area in Brazil where BSF is endemic. Among a total of 40 A. cooperi adult ticks collected in an area of BSF endemicity in the state of Sao Paulo, PCR analysis detected DNA of Rickettsia bellii in 16 ticks (40%), and 3 other ticks (7.5%) were positive for a previously unidentified spotted-fever-group (SFG) rickettsia. Cultivation in Vero cell cultures by the shell vial technique with individual A. cooperi ticks resulted in two isolates of R. bellii and one isolate genotypically characterized as an SFG rickettsia. The two R. bellii isolates were established in Vero cell cultures in the laboratory and were confirmed to be R. bellii by molecular analysis of the gltA and 17-kDa protein-encoding genes and by electron microscopic analysis. The SFG rickettsial isolate could not be stably passaged in cell culture in the laboratory, but molecular analysis of early passages suggested that it was closely related to Rickettsia parkeri, Rickettsia africae, and Rickettsia sibirica. These results do not support the role of A. cooperi in the ecology of R. rickettsii in the area studied, but they add two more species of rickettsiae to the poorly developed list of species occurring in ticks in South America.

Phylogenetic analysis of members of the genus Rickettsia using the gene encoding the outer-membrane protein rOmpB (ompB).

Abstract: To confirm the phylogenetic analysis previously inferred by comparison of the citrate synthase and rOmpA gene sequences (gitA and ompA, respectively), the rOmpB gene (ompB) of 24 strains of the genus Rickettsia was amplified and sequenced. rOmpB is an outer-membrane protein of high molecular mass, the presence of which can be demonstrated in most rickettsiae by immunological cross-reactivity in Western blots. No PCR amplification was obtained with Rickettsia bellii or Rickettsia canadensis. For the other rickettsiae, phylogenetic analysis was inferred from the comparison of both the gene and derived protein sequences by using parsimony, maximum-likelihood and neighbour-joining methods which gave the same organization. All nodes were well supported (>86% bootstrap values), except in the cluster including Rickettsia africae strain S and Rickettsia parkeri, and this analysis confirmed the previously established phylogeny obtained from combining results from gltA and ompA. Based on phylogenetic data, the current classification of the genus Rickettsia is inappropriate, specifically its division into two groups, typhus and spotted fever. Integration of phenotypic, genotypic and phylogenetic data will contribute to the definition of a polyphasic taxonomy as has been done for other bacterial genera.

Rickettsia parkeri: A newly recognized cause of spotted fever rickettsiosis in the United States

Abstract: Ticks, including many that bite humans, are hosts to several obligate intracellular bacteria in the spotted fever group (SFG) of the genus Rickettsia. Only Rickettsia rickettsii, the agent of Rocky Mountain spotted fever, has been definitively associated with disease in humans in the United States. Herein we describe disease in a human caused by Rickettsia parkeri, an SFG rickettsia first identified >60 years ago in Gulf Coast ticks (Amblyomma maculatum) collected from the southern United States. Confirmation of the infection was accomplished using serological testing, immunohistochemical staining, cell culture isolation, and molecular methods. Application of specific laboratory assays to clinical specimens obtained from patients with febrile, eschar-associated illnesses following a tick bite may identify additional cases of R. parkeri rickettsiosis and possibly other novel SFG rickettsioses in the United States.

Human infection with Ehrlichia canis, a leukocytic rickettsia

Abstract: RICKETTSIA that are pathogenic for humans include five main antigenic groups that cause, respectively, typhus, spotted fever, scrub typhus, Q fever, and trench fever.1 There is also a group of intr...

The emerging diversity of Rickettsia.

Abstract: The best-known members of the bacterial genus Rickettsia are associates of blood-feeding arthropods that are pathogenic when transmitted to vertebrates. These species include the agents of acute human disease such as typhus and Rocky Mountain spotted fever. However, many other Rickettsia have been uncovered in recent surveys of bacteria associated with arthropods and other invertebrates; the hosts of these bacteria have no relationship with vertebrates. It is therefore perhaps more appropriate to consider Rickettsia as symbionts that are transmitted vertically in invertebrates, and secondarily as pathogens of vertebrates. In this review, we highlight the emerging diversity of Rickettsia species that are not associated with vertebrate pathogenicity. Phylogenetic analysis suggests multiple transitions between symbionts that are transmitted strictly vertically and those that exhibit mixed (horizontal and vertical) transmission. Rickettsia may thus be an excellent model system in which to study the evolution of transmission pathways. We also focus on the emergence of Rickettsia as a diverse reproductive manipulator of arthropods, similar to the closely related Wolbachia, including strains associated with male-killing, parthenogenesis, and effects on fertility. We emphasize some outstanding questions and potential research directions, and suggest ways in which the study of non-pathogenic Rickettsia can advance our understanding of their disease-causing relatives.