Children from South Texas were evaluated for immunoglobulin G to Rickettsia typhi, the causative agent of murine typhus. Of 513 children, 8.6% of those 1-5 years of age, 13.3% of those 6-11 years of age, and 13.8% of those 12-17 years of age had positive results. (+info)
Molecular typing of isolates of Rickettsia rickettsii by use of DNA sequencing of variable intergenic regions.
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Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever, is found throughout the Americas, where it is associated with different animal reservoirs and tick vectors. No molecular typing system currently exists to allow for the robust differentiation of isolates of R. rickettsii. Analysis of eight completed genome sequences of rickettsial species revealed a high degree of sequence conservation within the coding regions of chromosomes in the genus. Intergenic regions between coding sequences should be under less selective pressure to maintain this conservation and thus should exhibit greater nucleotide polymorphisms. Utilizing these polymorphisms, we developed a molecular typing system that allows for the genetic differentiation of isolates of R. rickettsii. This typing system was applied to a collection of 38 different isolates collected from humans, animals, and tick vectors from different geographic locations. Serotypes 364D, from Dermacentor occidentalis ticks, and Hlp, from Haemaphysalis leporispalustris ticks, appear to be distinct genotypes that may not belong to the species R. rickettsii. We were also able to differentiate 36 historical isolates of R. rickettsii into three different phylogenetic clades containing seven different genotypes. This differentiation correlated well, but not perfectly, with the geographic origin and likely tick vectors associated with the isolates. The few apparent typing discrepancies found suggest that the molecular ecology of R. rickettsii needs more investigation. (+info)
Prevalence of antibodies against spotted fever group rickettsiae in a rural area of Colombia.
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We recently rediscovered Rocky Mountain spotted fever in Villeta, Colombia, near the same locality (Tobia) where it was first recognized in 1937. To have a better idea of the magnitude of this problem, sera from 392 randomly recruited healthy adults from Villeta were analyzed by indirect immunofluorescent antibody assay to detect IgG against Rickettsia rickettsii as antigen. The seropositivity rate for spotted fever group rickettsiae was 40.3%. We did not find any association between the presence of antibodies to spotted fever group rickettsiae and several demographic and epidemiologic variables, which could be a reflection of unique features of this area. (+info)
Tick-borne zoonotic bacteria in wild and domestic small mammals in northern Spain.
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The prevalence and diversity of tick-borne zoonotic bacteria (Borrelia spp., Anaplasma phagocytophilum, Coxiella burnetii, and spotted fever group rickettsiae) infecting 253 small mammals captured in the Basque Country (Spain) were assessed using PCR and reverse line blot hybridization. Trapping sites were selected around sheep farms (study 1, 2000 to 2002) and recreational parks (study 2, 2003 to 2005). The majority of the studied mammals (162) were wood mice (Apodemus sylvaticus), but six other different species were also analyzed: yellow-necked mice (Apodemus flavicollis), shrews (Crocidura russula and Sorex coronatus), bank voles (Clethrionomys glareolus), domestic mice (Mus domesticus), and moles (Talpa europaea). The results showed an infection rate ranging from 10.7% to 68.8%, depending on the small mammal species. One C. russula shrew and one A. sylvaticus mouse gave positive reactions for A. phagocytophilum, and C. burnetii was detected in two domestic mice and one A. sylvaticus mouse in a farm. The DNA of Borrelia spp. was detected in 67 animals (26.5%), most of them presenting positive hybridization with the probe for Borrelia sp. strain R57, the new Borrelia species previously detected in small mammals in our region. Furthermore, a second PCR and reverse line blot hybridization specific for B. burgdorferi sensu lato revealed the presence of Borrelia afzelii in 6.3% of C. glareolus voles and 14.3% of S. coronatus shrews. All small mammals were negative for spotted fever group rickettsiae. These results highlight the relevance of small mammals as reservoirs of some zoonotic bacteria. (+info)
Host defenses to Rickettsia rickettsii infection contribute to increased microvascular permeability in human cerebral endothelial cells.
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Rickettsiae are arthropod-borne intracellular bacterial pathogens that primarily infect the microvascular endothelium leading to systemic spread of the organisms and the major pathophysiological effect, increased microvascular permeability, and edema in vital organs such as the lung and brain. Much work has been done on mechanisms of immunity to rickettsiae, as well as the responses of endothelial cells to rickettsial invasion. However, to date, no one has described the mechanisms of increased microvascular permeability during acute rickettsiosis. We sought to establish an in vitro model of human endothelial-target rickettsial infection using the etiological agent of Rocky Mountain spotted fever, Rickettsia rickettsii, and human cerebral microvascular endothelial cells. Endothelial cells infected with R. rickettsii exhibited a dose-dependent decrease in trans-endothelial electrical resistance, which translates into increased monolayer permeability. Additionally, we showed that the addition of pro-inflammatory stimuli essential to rickettsial immunity dramatically enhanced this effect. This increase in permeability correlates with dissociation of adherens junctions between endothelial cells and is not dependent on the presence of nitric oxide. Taken together, these results demonstrate for the first time that increased microvascular permeability associated with rickettsial infection is partly attributable to intracellular rickettsiae and partly attributable to the immune defenses that have evolved to protect the host from rickettsial spread. (+info)
Genomic comparison of virulent Rickettsia rickettsii Sheila Smith and avirulent Rickettsia rickettsii Iowa.
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Rickettsia rickettsii is an obligate intracellular pathogen that is the causative agent of Rocky Mountain spotted fever. To identify genes involved in the virulence of R. rickettsii, the genome of an avirulent strain, R. rickettsii Iowa, was sequenced and compared to the genome of the virulent strain R. rickettsii Sheila Smith. R. rickettsii Iowa is avirulent in a guinea pig model of infection and displays altered plaque morphology with decreased lysis of infected host cells. Comparison of the two genomes revealed that R. rickettsii Iowa and R. rickettsii Sheila Smith share a high degree of sequence identity. A whole-genome alignment comparing R. rickettsii Iowa to R. rickettsii Sheila Smith revealed a total of 143 deletions for the two strains. A subsequent single-nucleotide polymorphism (SNP) analysis comparing Iowa to Sheila Smith revealed 492 SNPs for the two genomes. One of the deletions in R. rickettsii Iowa truncates rompA, encoding a major surface antigen (rickettsial outer membrane protein A [rOmpA]) and member of the autotransporter family, 660 bp from the start of translation. Immunoblotting and immunofluorescence confirmed the absence of rOmpA from R. rickettsii Iowa. In addition, R. rickettsii Iowa is defective in the processing of rOmpB, an autotransporter and also a major surface antigen of spotted fever group rickettsiae. Disruption of rompA and the defect in rOmpB processing are most likely factors that contribute to the avirulence of R. rickettsii Iowa. Genomic differences between the two strains do not significantly alter gene expression as analysis of microarrays revealed only four differences in gene expression between R. rickettsii Iowa and R. rickettsii strain R. Although R. rickettsii Iowa does not cause apparent disease, infection of guinea pigs with this strain confers protection against subsequent challenge with the virulent strain R. rickettsii Sheila Smith. (+info)
Prevalence of seropositivity to spotted fever group rickettsiae and Anaplasma phagocytophilum in a large, demographically diverse US sample.
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