The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Marcelo B Labruna - One of the best experts on this subject based on the ideXlab platform.
-
comparative analysis of infection by Rickettsia rickettsii sheila smith and taiacu strains in a murine model
Pathogenetics, 2020Co-Authors: Eliane Esteves, Marcelo B Labruna, Kevin R. Macaluso, Sirlei Daffre, Andréa Cristina Fogaça, Sean P Riley, Chanida Fongsaran, Ingeborg M LangohrAbstract:Rocky Mountain spotted fever (RMSF) is a life-threatening tick-borne disease caused by Rickettsia rickettsii, which is widely distributed throughout the Americas. Over 4000 cases of RMSF are recorded annually in the United States, while only around 100 cases are reported in Brazil. Conversely, while case fatality rates in the United States oscillate around 5%, in Brazil they can surpass 70%, suggesting that differences in tick vectoring capacity, population sensitivity, and/or variability in virulence of the Rickettsial strains may exist. In this study, we compared the susceptibility of C3H/HeN mice to two highly virulent strains of R. rickettsii, one from the United States (Sheila Smith) and the other from Brazil (Taiacu). Animals inoculated with the Taiacu strain succumbed to infection earlier and exhibited severe histological lesions in both liver and spleen sooner than mice infected with the Sheila Smith strain. These differences in survival and signs of the disease are not related to a greater proliferation of the Taiacu strain, as there were no significant differences in the Rickettsial load in mice tissues inoculated with either strain. The present study is the first step to experimentally assess differences in fatality rates of RMSF in two different regions of the American continent.
-
clinical and serological evaluation of capybaras hydrochoerus hydrochaeris successively exposed to an amblyomma sculptum derived strain of Rickettsia rickettsii
Scientific Reports, 2020Co-Authors: Alejandro Ramirezhernandez, Andréa Cristina Fogaça, Lina C Binder, Francisco Uchoa, Maria Carolina De Azevedo Serpa, Alessandra Castro Rodrigues, Matias Pablo Juan Szabo, Celso Eduardo De Souza, Marcelo B LabrunaAbstract:Brazilian spotted fever (BSF), caused by Rickettsia rickettsii, is the most lethal tick-borne disease in the western hemisphere. In Brazil, Amblyomma sculptum ticks are the main vector. Capybaras (Hydrochoerus hydrochaeris), the largest living rodents of the world (adults weighing up to 100 Kg), have been recognized as amplifying hosts of R. rickettsii for A. sculptum in BSF-endemic areas; i.e., once primarily infected, capybaras develop bacteremia for a few days, when feeding ticks acquire Rickettsial infection. We conducted experimental infections of five capybaras with an A. sculptum-derived strain of R. rickettsii and performed clinical and bacteremia evaluation during primary and subsequent infections. Bacteremia was detected in all capybaras during primary infection, but not in subsequent infections. All animals seroconverted to R. rickettsii (titres range: 64-32,768), and remained seropositive throughout the study. Primary infection resulted in clinical spotted fever illness in four capybaras, of which two had a fatal outcome. Subsequent infections in seropositive capybaras resulted in no clinical signs. Capybaras developed a sustained immune response that prevented a second bacteremia. This condition may imply a high reproduction rate of capybaras in BSF-endemic areas, in order to continuously generate capybaras susceptible to bacteremia during primary infection.
-
Rickettsia rickettsii Rickettsiales Rickettsiaceae infecting amblyomma sculptum acari ixodidae ticks and capybaras in a brazilian spotted fever endemic area of brazil
Journal of Medical Entomology, 2020Co-Authors: Francisco B Costa, Monize Gerardi, Lina C Binder, Maria Carolina De Azevedo Serpa, Hector R Benatti, Beatriz Lopes, Hermes Ribeiro Luz, Katia Maria Paschoaletto Micchi De Barros Ferraz, Marcelo B LabrunaAbstract:The bacterium Rickettsia rickettsii is the agent of Brazilian spotted fever (BSF), a highly fatal disease that is transmitted in Brazil mainly by the tick Amblyomma sculptum Berlese, which uses capybaras (Hydrochoerus hydrochaeris Linnaeus) as major hosts. In 2015, we captured nine capybaras in a BSF-endemic area of southeastern Brazil. From each capybara, we collected blood sera that were tested through the immunofluorescence assay using Rickettsia spp. antigens, and A. sculptum ticks, processed for isolation of R. rickettsii through guinea pig inoculation. All capybaras (100%) were seroreactive to Rickettsia spp., with highest titers to R. rickettsii. A total of 166 A. sculptum ticks were macerated and inoculated into nine guinea pigs, from which only one presented high fever and seroconverted to R. rickettsii. Blood from this febrile animal was inoculated into additional guinea pigs (guinea pig passages), which also became febrile and seroconverted, or when euthanized during the fever period, their internal organs (spleen, lung) were shown to contain R. rickettsii DNA. The present Rickettsial isolate has been maintained cryopreserved as infected guinea pig organs. There was at least one R. rickettsii-infected tick among the 166 macerated ticks, giving a minimal infection rate of 0.6% (1/166). This infection rate is within the range of previous studies, which reported that only 0.05% to at most 1.28% A. sculptum ticks were infected by R. rickettsii in other BSF-endemic areas. These low infection rates support the low incidence of BSF, despite of A. sculptum being the most frequent human-biting tick in southeastern Brazil.
-
comparative analysis of the midgut microbiota of two natural tick vectors of Rickettsia rickettsii
Developmental and Comparative Immunology, 2020Co-Authors: Daniel Brisotto Pavanelo, Marcelo B Labruna, Maria Fernanda Bandeira De Melo Galletti, Camila D. Malossi, Sirlei Daffre, Nicolas C H Schroder, Natalia Daniela Pin Viso, Larissa Almeida Martins, Marisa Diana Farber, Andréa Cristina FogaçaAbstract:Abstract Although the ticks Amblyomma sculptum and Amblyomma aureolatum are important vectors of Rickettsia rickettsii, causative agent of the life-threatening Rocky Mountain spotted fever, A. aureolatum is considerably more susceptible to infection than A. sculptum. As the microbiota can interfere with the colonization of arthropod midgut (MG) by pathogens, in the current study we analyzed the MG microbiota of both tick species. Our results revealed that the MG of A. aureolatum harbors a prominent microbiota, while A. sculptum does not. Remarkably, a significant reduction of the bacterial load was recorded in R. rickettsii-infected A. aureolatum. In addition, the taxonomy analysis of the MG bacterial community of A. aureolatum revealed a dominance of the genus Francisella, suggesting an endosymbiosis. This study is the first step in getting insights into the mechanisms underlying the interactions among Amblyomma species, their microbiota and R. rickettsii. Additional studies to better understand these mechanisms are required and may help the development of novel alternatives to block Rickettsial transmission.
-
comparative susceptibility of different populations of amblyomma sculptum to Rickettsia rickettsii
Frontiers in Physiology, 2019Co-Authors: Monize Gerardi, Alejandro Ramirezhernandez, Lina C Binder, Felipe Da Silva Krawczak, Fabio Gregori, Marcelo B LabrunaAbstract:The bacterium Rickettsia rickettsii is the etiological agent of Brazilian spotted fever (BSF), which is transmitted in Brazil mainly by the tick Amblyomma sculptum. Herein, larvae and nymphs of six populations of A. sculptum were exposed to R. rickettsii by feeding on needle-inoculated guinea pigs, and thereafter reared on uninfected guinea pigs or rabbits. Two tick populations were exposed to autochthone R. rickettsii strains, whereas four tick populations were exposed to non- autochthone strains. The six geographically different populations of A. sculptum showed different susceptibilities to R. rickettsii, higher among the two tick populations that were exposed to their autochthone R. rickettsii strain. In addition, higher rates of transovarial transmission of R. rickettsii and vector competence success also included the two tick populations that were exposed to autochthone R. rickettsii strains. These results indicate that the susceptibility of A. sculptum to R. rickettsii varies among different tick populations, with a clear bias for higher susceptibility to an autochthone R. rickettsii strain that has already coevolved with a the tick population for some time. Our results demonstrated that the R. rickettsii infection induces higher mortality of engorged larvae and nymphs, and tend to reduce the reproductive fitness of engorged females. All together, these results might explain the low R. rickettsii-infection rates of A. sculptum under natural conditions (usually <1%), and indicate that an A. sculptum population should not be able to sustain a R. rickettsii infection for successive tick generations without the creation of new cohorts of infected ticks via horizontal transmission on vertebrate rickettsemic hosts (amplifying hosts). Finally, despite of the ubiquitous distribution of A. sculptum in southeastern and central-western Brazil, most of the populations of this tick species are devoid of R. rickettsii infection. This scenario might be related to two major factors: (i) insufficient numbers of susceptible amplifying hosts; and (ii) lower susceptibilities of many tick populations. While the first factor has been demonstrated by mathematical models in previous studies, the second is highlighted by the results observed in the present study.
Ted Hackstadt - One of the best experts on this subject based on the ideXlab platform.
-
proteolytic cleavage of the immunodominant outer membrane protein rompa in Rickettsia rickettsii
Journal of Bacteriology, 2017Co-Authors: Nicholas F Noriea, Tina R Clark, David J Mead, Ted HackstadtAbstract:Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever, contains two immunodominant proteins, rOmpA and rOmpB, in the outer membrane. Both rOmpA and rOmpB are conserved throughout spotted fever group Rickettsiae as members of a family of autotransporter proteins. Previously, it was demonstrated that rOmpB is proteolytically processed, with the cleavage site residing near the autotransporter domain at the carboxy-terminal end of the protein, cleaving the 168-kDa precursor into apparent 120-kDa and 32-kDa fragments. The 120- and 32-kDa fragments remain noncovalently associated on the surface of the bacterium, with implications that the 32-kDa fragment functions as the membrane anchor domain. Here we present evidence for a similar posttranslational processing of rOmpA. rOmpA is expressed as a predicted 224-kDa precursor yet is observed on SDS-PAGE as a 190-kDa protein. A small rOmpA fragment of ∼32 kDa was discovered during surface proteome analysis and identified as the carboxy-terminal end of the protein. A rabbit polyclonal antibody was generated to the autotransporter region of rOmpA and confirmed a 32-kDa fragment corresponding to the calculated mass of a proteolytically cleaved rOmpA autotransporter region. N-terminal amino acid sequencing revealed a cleavage site on the carboxy-terminal side of Ser-1958 in rOmpA. An avirulent strain of R. rickettsii Iowa deficient in rOmpB processing was also defective in the processing of rOmpA. The similarities of the cleavage sites and the failure of R. rickettsii Iowa to process either rOmpA or rOmpB suggest that a single enzyme may be responsible for both processing events.IMPORTANCE Members of the spotted fever group of Rickettsiae, including R. rickettsii, the etiologic agent of Rocky Mountain spotted fever, express at least four autotransporter proteins that are protective antigens or putative virulence determinants. One member of this class of proteins, rOmpB, is proteolytically processed to a passenger domain and an autotransporter domain that remain associated on the Rickettsial outer membrane. The protease responsible for this posttranslation processing remains unknown. Here we show that another autotransporter, rOmpA, is similarly processed by R. rickettsii Similarities in sequence at the cleavage site and predicted secondary protein structure suggest that all four R. rickettsii autotransporters may be processed by the same outer membrane protease.
-
comparative genome sequencing of Rickettsia rickettsii strains that differ in virulence
Infection and Immunity, 2015Co-Authors: Tina R Clark, Erika I Lutter, Craig Martens, Damon W Ellison, Nicholas F Noriea, Deanna C Bublitz, Ted HackstadtAbstract:Rickettsia rickettsii is an obligate intracellular pathogen that is the causative agent of Rocky Mountain spotted fever. Strains of R. rickettsii differ dramatically in virulence. In a guinea pig model of infection, the severity of disease as assessed by fever response varies from the most virulent, Sheila Smith, to Iowa, which causes no fever. To identify potential determinants of virulence in R. rickettsii, the genomes of two additional strains were sequenced for comparison to known sequences (comparative genome sequencing [CGS]). R. rickettsii Morgan and R strains were compared to the avirulent R. rickettsii Iowa and virulent R. rickettsii Sheila Smith strains. The Montana strains Sheila Smith and R were found to be highly similar while the eastern strains Iowa and Morgan were most similar to each other. A major surface antigen, Rickettsial outer membrane protein A (rOmpA), is severely truncated in the Iowa strain. The region of ompA containing 13 tandem repeats was sequenced, revealing only seven shared SNPs (four nonsynonymous) for R and Morgan strains compared to Sheila Smith, with an additional 17 SNPs identified in Morgan. Another major surface antigen and autotransporter, rOmpB, exhibits a defect in processing in the Iowa strain such that the beta fragment is not cleaved. Sequence analysis of ompB reveals identical sequences between Iowa and Morgan strains and between the R and Sheila Smith strains. The number of SNPs and insertions/deletions between sequences of the two Montana strains and the two eastern strains is low, thus narrowing the field of possible virulence factors.
-
transformation frequency of a mariner based transposon in Rickettsia rickettsii
Journal of Bacteriology, 2011Co-Authors: Tina R Clark, Amanda M Lackey, Betsy Kleba, Lonnie O Driskell, Erika I Lutter, Craig Martens, David O Wood, Ted HackstadtAbstract:Transformation frequencies of a mariner-based transposon system in Rickettsia rickettsii were determined using a plaque assay system for enumeration and isolation of mutants. Sequence analysis of insertion sites in both R. rickettsii and R. prowazekii indicated that insertions were random. Transposon mutagenesis provides a useful tool for Rickettsial research.
-
complementation of Rickettsia rickettsii rela spot restores a nonlytic plaque phenotype
Infection and Immunity, 2011Co-Authors: Tina R Clark, Betsy Kleba, Damon W Ellison, Ted HackstadtAbstract:Spotted fever group Rickettsiae are known to produce distinct plaque phenotypes. Strains that cause lytic infections in cell culture form clear plaques, while nonlytic strains form opaque plaques in which the cells remain intact. Clear plaques have historically been associated with more-virulent species or strains of spotted fever group Rickettsiae. We have selected spontaneous mutant pairs from two independent strains of Rickettsia rickettsii, the virulent R strain and the avirulent Iowa strain. A nonlytic variant of R. rickettsii R, which typically produces clear plaques, was isolated and stably maintained. A lytic variant of the Iowa strain, which characteristically produces opaque plaques, was also selected and maintained. Genomic resequencing of the variants identified only a single gene disrupted in each strain. In both cases, the mutation was in a gene annotated as relA/spoT-like. In the Iowa strain, a single mutation introduced a premature stop codon upstream from region encoding the predicted active site of RelA/SpoT and caused the transition to a lytic plaque phenotype. In R. rickettsii R, the nonlytic plaque phenotype resulted from a single-nucleotide substitution that shifted a tyrosine residue to histidine near the active site of the enzyme. The intact relA/spoT gene thus occurred in variants with the nonlytic plaque phenotype. Complementation of the truncated relA/spoT gene in the Iowa lytic plaque variant restored the nonlytic phenotype. The relA/spoT mutations did not affect the virulence of either strain in a Guinea pig model of infection; R strain lytic and nonlytic variants both induced fever equally, and the mutation in Iowa to a lytic phenotype did not cause them to become virulent.
-
limited transcriptional responses of Rickettsia rickettsii exposed to environmental stimuli
PLOS ONE, 2009Co-Authors: Damon W Ellison, Tina R Clark, Daniel E Sturdevant, Kimmo Virtaneva, Ted HackstadtAbstract:Rickettsiae are strict obligate intracellular pathogens that alternate between arthropod and mammalian hosts in a zoonotic cycle. Typically, pathogenic bacteria that cycle between environmental sources and mammalian hosts adapt to the respective environments by coordinately regulating gene expression such that genes essential for survival and virulence are expressed only upon infection of mammals. Temperature is a common environmental signal for upregulation of virulence gene expression although other factors may also play a role. We examined the transcriptional responses of Rickettsia rickettsii, the agent of Rocky Mountain spotted fever, to a variety of environmental signals expected to be encountered during its life cycle. R. rickettsii exposed to differences in growth temperature (25°C vs. 37°C), iron limitation, and host cell species displayed nominal changes in gene expression under any of these conditions with only 0, 5, or 7 genes, respectively, changing more than 3-fold in expression levels. R. rickettsii is not totally devoid of ability to respond to temperature shifts as cold shock (37°C vs. 4°C) induced a change greater than 3-fold in up to 56 genes. Rickettsiae continuously occupy a relatively stable environment which is the cytosol of eukaryotic cells. Because of their obligate intracellular character, Rickettsiae are believed to be undergoing reductive evolution to a minimal genome. We propose that their relatively constant environmental niche has led to a minimal requirement for R. rickettsii to respond to environmental changes with a consequent deletion of non-essential transcriptional response regulators. A minimal number of predicted transcriptional regulators in the R. rickettsii genome is consistent with this hypothesis.
Marina E. Eremeeva - One of the best experts on this subject based on the ideXlab platform.
-
Rickettsia rickettsii in rhipicephalus ticks mexicali mexico
Journal of Medical Entomology, 2011Co-Authors: Marina E. Eremeeva, Maria L Zambrano, Luis Anaya, Lorenza Beati, Sandor E Karpathy, Maria Margarida Santossilva, Beatriz Salceda, Donald Macbeth, Hector OlguinAbstract:Circulation of a unique genetic type of Rickettsia rickettsii in ticks of the Rhipicephalus sanguineus complex was detected in Mexicali, Baja California, Mexico. The Mexican R. rickettsii differed from all isolates previously characterized from the endemic regions of Rocky Mountain spotted fever in northern, central, and southern Americas. Rhipicephalus ticks in Mexicali are genetically different from Rh. sanguineus found in the United States.
-
closing the gaps between genotype and phenotype in Rickettsia rickettsii
Annals of the New York Academy of Sciences, 2009Co-Authors: Marina E. Eremeeva, Gregory A. DaschAbstract:Rocky Mountain spotted fever (RMSF) caused by Rickettsia rickettsii is a severe rickettsiosis that occurs in nearly every state of the continental USA. RMSF is endemic in Central and Southern America, with recent well-documented cases in Mexico, Costa Rica, Panama, Colombia, Brazil, and Argentina. RMSF is the most malignant among known rickettsioses causing severe multiorgan dysfunction and high case fatality rates, which can reach 73% in untreated cases. Variations in pathogenic biotypes of R. rickettsii isolates have been described, and potential correlations of these differences to various clinical manifestations of RMSF have been suggested. We have recently reported on a method of genetic comparison employing sequence differences in intergenic regions (IGR typing) in isolates of R. rickettsii of human, tick, and animal origin. The grouping obtained correlated well with 2 other genotyping systems we have developed, which target the presence and distribution of variable numbers of tandem repeats (TR) and insertion/deletion (INDEL) events. Twenty-five total genotypes of R. rickettsii in 4 primary groups could be distinguished: isolates from Montana, isolates associated with Rhipicephalus sanguineus ticks and human infections in Arizona, other isolates from the USA where Dermacentor variabilis is thought to be the primary vector, and the isolates primarily associated with Amblyomma ticks from Central and South America. In addition, isolate Hlp#2, which is often considered to be a nonpathogenic isolate of R. rickettsii and closely related serotype 364D, exhibited the most diversity from the other isolates compared, and they differ significantly from each other. Because complex interactions underlie the pathogenesis of R. rickettsii in vivo, it is difficult to define the causality of individual events that occur in infected vertebrate hosts and humans. Many microbial factors are likely to contribute to the varied ability of R. rickettsii to cause cellular injury; some of them may also contribute importantly to its virulence for vertebrate hosts and may be linked to the variable genetic markers we have identified. Since circulation of R. rickettsii in nature includes vertical transstadial and transovarial transmission within tick vectors and horizontal passages through vertebrate hosts, it is plausible that isolates of different virulence arose when they became isolated during adaptation to novel vertebrate and tick hosts. Characterization of the physiologically important changes in Rickettsial gene expression that occur immediately after tick-to-human or tick-to-animal transitions may require development of new experimental systems.
-
molecular typing of isolates of Rickettsia rickettsii by use of dna sequencing of variable intergenic regions
Journal of Clinical Microbiology, 2007Co-Authors: Sandor E Karpathy, Gregory A. Dasch, Marina E. EremeevaAbstract: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.
-
detection of Rickettsia rickettsii and bartonella henselae in rhipicephalus sanguineus ticks from california
Journal of Medical Entomology, 2007Co-Authors: Marco E Metzger, Mary E Wikswo, Marina E. EremeevaAbstract:Sixty-two questing adult Rhipicephalus sanguineus (Latreille) ticks were collected by direct removal from blades of turfgrass and adjacent concrete walkways at a suburban home in Riverside County, CA, and tested for the presence of Rickettsia, Bartonella, and Ehrlichia DNA. Polymerase chain reaction (PCR) was used to amplify fragments of the 17-kDa antigen gene and the rOmpA gene of the spotted fever group Rickettsiae. One male tick contained R. rickettsii DNA; its genotype differed from R. rickettsii isolates found in Montana and Arizona that cause Rocky Mountain spotted fever and from Hlp#2 and 364D serotypes. One male tick and one female tick contained B. henselae DNA. No Ehrlichia platys or Ehrlichia canis DNAs were detected using nested PCR for their 16S rRNA genes. These findings extend the area where Rickettsia rickettsii may be vectored by Rh. sanguineus. Rh. sanguineus also may be infected with Bartonella henselae, a human pathogen that is typically associated with fleas and causes cat scratch disease.
-
molecular typing of novel Rickettsia rickettsii isolates from arizona
Annals of the New York Academy of Sciences, 2006Co-Authors: Marina E. Eremeeva, Maria L Zambrano, Elizabeth A Bosserman, Linda J Demma, Gregory A. DaschAbstract:Seven isolates of Rickettsia rickettsii were obtained from a skin biopsy, two whole-blood specimens, and from Rhipicephalus sanguineus ticks from eastern Arizona. Molecular typing of seven isolates of R. rickettsii and DNA samples from two other Rh. sanguineus ticks infected with R. rickettsii was conducted by PCR and DNA sequencing of rompA and 12 variable-number tandem repeat regions (VNTRs). All DNA specimens from Arizona were identical to each other and to reference human and Dermacentor andersoni isolates of R. rickettsii from Montana in their rOmpA gene sequences and 10 VNTRs. Two of the twelve VNTRs had differences in the number of repeat sequences in isolates from Arizona compared to those from Montana, thus conferring the novelty of the Rh. sanguineus-associated R. rickettsii.
Francisco B Costa - One of the best experts on this subject based on the ideXlab platform.
-
Rickettsia rickettsii Rickettsiales Rickettsiaceae infecting amblyomma sculptum acari ixodidae ticks and capybaras in a brazilian spotted fever endemic area of brazil
Journal of Medical Entomology, 2020Co-Authors: Francisco B Costa, Monize Gerardi, Lina C Binder, Maria Carolina De Azevedo Serpa, Hector R Benatti, Beatriz Lopes, Hermes Ribeiro Luz, Katia Maria Paschoaletto Micchi De Barros Ferraz, Marcelo B LabrunaAbstract:The bacterium Rickettsia rickettsii is the agent of Brazilian spotted fever (BSF), a highly fatal disease that is transmitted in Brazil mainly by the tick Amblyomma sculptum Berlese, which uses capybaras (Hydrochoerus hydrochaeris Linnaeus) as major hosts. In 2015, we captured nine capybaras in a BSF-endemic area of southeastern Brazil. From each capybara, we collected blood sera that were tested through the immunofluorescence assay using Rickettsia spp. antigens, and A. sculptum ticks, processed for isolation of R. rickettsii through guinea pig inoculation. All capybaras (100%) were seroreactive to Rickettsia spp., with highest titers to R. rickettsii. A total of 166 A. sculptum ticks were macerated and inoculated into nine guinea pigs, from which only one presented high fever and seroconverted to R. rickettsii. Blood from this febrile animal was inoculated into additional guinea pigs (guinea pig passages), which also became febrile and seroconverted, or when euthanized during the fever period, their internal organs (spleen, lung) were shown to contain R. rickettsii DNA. The present Rickettsial isolate has been maintained cryopreserved as infected guinea pig organs. There was at least one R. rickettsii-infected tick among the 166 macerated ticks, giving a minimal infection rate of 0.6% (1/166). This infection rate is within the range of previous studies, which reported that only 0.05% to at most 1.28% A. sculptum ticks were infected by R. rickettsii in other BSF-endemic areas. These low infection rates support the low incidence of BSF, despite of A. sculptum being the most frequent human-biting tick in southeastern Brazil.
-
amblyomma sculptum salivary pge2 modulates the dendritic cell Rickettsia rickettsii interactions in vitro and in vivo
Frontiers in Immunology, 2019Co-Authors: Eliane Esteves, Marcelo B Labruna, Francisco B Costa, Alejandro Ramirezhernandez, Bruna Bizzarro, Ana Paula Ferranti Peti, Allan Henrique Depieri Cataneo, Pryscilla Fanini Wowk, Rodolfo Pessato Timóteo, Pedro Ismael SilvaAbstract:Amblyomma sculptum is an important vector of Rickettsia rickettsii, causative agent of Rocky Mountain spotted fever and the most lethal tick-borne pathogen affecting humans. To feed on the vertebrate host's blood, A. sculptum secretes a salivary mixture, which may interact with skin resident dendritic cells (DCs) and modulate their function. The present work was aimed at depicting the A. sculptum saliva-host DC network and the biochemical nature of the immunomodulatory component(s) involved in this interface. A. sculptum saliva inhibits the production of inflammatory cytokines by murine DCs stimulated with LPS. The fractionation of the low molecular weight salivary content by reversed-phase chromatography revealed active fractions eluting from 49 to 55% of the acetonitrile gradient. Previous studies suggested that this pattern of elution matches with that observed for prostaglandin E2 (PGE2) and the molecular identity of this lipid mediator was unambiguously confirmed by a new high-resolution mass spectrometry methodology. A productive infection of murine DCs by R. rickettsii was demonstrated for the first time leading to proinflammatory cytokine production that was inhibited by both A. sculptum saliva and PGE2, a result also achieved with human DCs. The adoptive transfer of murine DCs incubated with R. rickettsii followed by treatment with A. sculptum saliva or PGE2 did not change the cytokine profile associated to cellular recall responses while IgG2a-specific antibodies were decreased in the serum of these mice. Together, these findings emphasize the role of PGE2 as a universal immunomodulator of tick saliva. In addition, it contributes to new approaches to explore R. rickettsii-DC interactions both in vitro and in vivo.
-
Rickettsia rickettsii co feeding transmission among amblyomma aureolatum ticks
Emerging Infectious Diseases, 2018Co-Authors: Jonas Moraesfilho, Francisco B Costa, Herbert Sousa Soares, Monize Gerardi, Marcelo B LabrunaAbstract:Amblyomma aureolatum ticks are vectors of Rickettsia rickettsii, the etiologic agent of Rocky Mountain spotted fever in Brazil. Maintenance of R. rickettsii in nature depends on horizontal transmission along tick generations. Although such transmission is known to occur when uninfected and infected ticks feed simultaneously on susceptible animals (co-feeding systemic transmission), we investigated co-feeding nonsystemic transmission, which was based on R. rickettsii-infected and -uninfected A. aureolatum ticks feeding simultaneously on guinea pigs immune to R. rickettsii. Our acquisition and transmission infestations demonstrated that horizontal transmission of R. rickettsii by co-feeding ticks on immune hosts with no systemic infection did not occur when uninfected larvae fed distantly from infected nymphs but did occur in a few cases when uninfected larvae fed side-by-side with infected nymphs, suggesting that they shared the same feeding site. The co-feeding nonsystemic transmission type might have no epidemiologic importance for Rocky Mountain spotted fever.
-
vectorial competence of amblyomma tonelliae to transmit Rickettsia rickettsii
Medical and Veterinary Entomology, 2016Co-Authors: Evelina Luisa Tarragona, Marcelo B Labruna, Francisco B Costa, Joao Favio Soares, Santiago NavaAbstract:The aim of this work was to test the vectorial competence of Amblyomma tonelliae (Ixodida: Ixodidae) to transmit Rickettsia rickettsii (Rickettsiales: Rickettsiaceae), the agent of Rocky Mountain spotted fever (RMSF). All parasitic stages of A. tonelliae were exposed to R. rickettsii by allowing each stage to feed on hosts inoculated with this pathogen. Thereafter, ticks were fed on uninfected hosts. All stages of A. tonelliae were able to acquire the R. rickettsii infection and maintain it by transstadial and transovarial transmission. When infected ticks fed on uninfected hosts, the hosts developed rickettsiosis disease. This study demonstrates the vectorial competence of A. tonelliae to transmit R. rickettsii. These results have epidemiological relevance because A. tonelliae is one of the tick species most likely to infest humans in Argentina, including in areas in which RMSF has been reported.
-
experimental infection of horses with Rickettsia rickettsii
Parasites & Vectors, 2016Co-Authors: Tatiana E H Ueno, Jonas Moraesfilho, Francisco B Costa, Washington C Agostinho, Wilson Roberto Fernandes, Marcelo B LabrunaAbstract:Rickettsia rickettsii is vectored by ticks, and some vertebrate hosts can be sources of infection to ticks during bacteremic periods. In Brazil, the main vector for R. rickettsii is the tick Amblyomma sculptum, a member of the A. cajennense complex. Horses, in turn, are one of the major hosts for A. sculptum. In this study, horses experimentally infected with R. rickettsii were assessed for clinical changes and their capability to transmit the infection to A. sculptum ticks. Four horses were infected with R. rickettsii through either intraperitoneal injection or infestation with R. rickettsii-infected A. sculptum ticks. Simultaneously, the animals were infested with non-infected A. sculptum ticks. The horses were monitored for 30 days by clinical examination, hematological and biochemical tests, real-time PCR of blood for the detection of Rickettsia, and inoculation of blood in guinea pigs. IgG antibody titers were followed until the horses have shown seronegativity or until the end of the experiment. Uninfected ticks that fed on horses were subjected to real-time PCR and/or were fed on susceptible rabbits. The horses showed no clinical, hematological or blood biochemical alterations, and bacteremia was not detected by real-time PCR or by inoculation of horse blood into guinea pigs. Anti-R. rickettsii antibodies were detected in horses from 10 days to 2 years after infection. Uninfected ticks, after feeding on infected horses, showed 2.1 % positivity in real-time PCR, but failed to transmit the infection to rabbits at a next feeding stage. Rickettsia rickettsii-infected horses did not manifest illness and are not competent amplifier hosts of R. rickettsii for A. sculptum ticks.
Gregory A. Dasch - One of the best experts on this subject based on the ideXlab platform.
-
assessment of real time pcr assay for detection of Rickettsia spp and Rickettsia rickettsii in banked clinical samples
Journal of Clinical Microbiology, 2013Co-Authors: Cecilia Y Kato, Gregory A. Dasch, Ida H Chung, Lauren K Robinson, Amy L Austin, Robert F MassungAbstract:ABSTRACT Two novel real-time PCR assays were developed for the detection of Rickettsia spp. One assay detects all tested Rickettsia spp.; the other is specific for Rickettsia rickettsii. Evaluation using DNA from human blood and tissue samples showed both assays to be more sensitive than nested PCR assays currently in use at the CDC.
-
closing the gaps between genotype and phenotype in Rickettsia rickettsii
Annals of the New York Academy of Sciences, 2009Co-Authors: Marina E. Eremeeva, Gregory A. DaschAbstract:Rocky Mountain spotted fever (RMSF) caused by Rickettsia rickettsii is a severe rickettsiosis that occurs in nearly every state of the continental USA. RMSF is endemic in Central and Southern America, with recent well-documented cases in Mexico, Costa Rica, Panama, Colombia, Brazil, and Argentina. RMSF is the most malignant among known rickettsioses causing severe multiorgan dysfunction and high case fatality rates, which can reach 73% in untreated cases. Variations in pathogenic biotypes of R. rickettsii isolates have been described, and potential correlations of these differences to various clinical manifestations of RMSF have been suggested. We have recently reported on a method of genetic comparison employing sequence differences in intergenic regions (IGR typing) in isolates of R. rickettsii of human, tick, and animal origin. The grouping obtained correlated well with 2 other genotyping systems we have developed, which target the presence and distribution of variable numbers of tandem repeats (TR) and insertion/deletion (INDEL) events. Twenty-five total genotypes of R. rickettsii in 4 primary groups could be distinguished: isolates from Montana, isolates associated with Rhipicephalus sanguineus ticks and human infections in Arizona, other isolates from the USA where Dermacentor variabilis is thought to be the primary vector, and the isolates primarily associated with Amblyomma ticks from Central and South America. In addition, isolate Hlp#2, which is often considered to be a nonpathogenic isolate of R. rickettsii and closely related serotype 364D, exhibited the most diversity from the other isolates compared, and they differ significantly from each other. Because complex interactions underlie the pathogenesis of R. rickettsii in vivo, it is difficult to define the causality of individual events that occur in infected vertebrate hosts and humans. Many microbial factors are likely to contribute to the varied ability of R. rickettsii to cause cellular injury; some of them may also contribute importantly to its virulence for vertebrate hosts and may be linked to the variable genetic markers we have identified. Since circulation of R. rickettsii in nature includes vertical transstadial and transovarial transmission within tick vectors and horizontal passages through vertebrate hosts, it is plausible that isolates of different virulence arose when they became isolated during adaptation to novel vertebrate and tick hosts. Characterization of the physiologically important changes in Rickettsial gene expression that occur immediately after tick-to-human or tick-to-animal transitions may require development of new experimental systems.
-
molecular typing of isolates of Rickettsia rickettsii by use of dna sequencing of variable intergenic regions
Journal of Clinical Microbiology, 2007Co-Authors: Sandor E Karpathy, Gregory A. Dasch, Marina E. EremeevaAbstract: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.
-
molecular typing of novel Rickettsia rickettsii isolates from arizona
Annals of the New York Academy of Sciences, 2006Co-Authors: Marina E. Eremeeva, Maria L Zambrano, Elizabeth A Bosserman, Linda J Demma, Gregory A. DaschAbstract:Seven isolates of Rickettsia rickettsii were obtained from a skin biopsy, two whole-blood specimens, and from Rhipicephalus sanguineus ticks from eastern Arizona. Molecular typing of seven isolates of R. rickettsii and DNA samples from two other Rh. sanguineus ticks infected with R. rickettsii was conducted by PCR and DNA sequencing of rompA and 12 variable-number tandem repeat regions (VNTRs). All DNA specimens from Arizona were identical to each other and to reference human and Dermacentor andersoni isolates of R. rickettsii from Montana in their rOmpA gene sequences and 10 VNTRs. Two of the twelve VNTRs had differences in the number of repeat sequences in isolates from Arizona compared to those from Montana, thus conferring the novelty of the Rh. sanguineus-associated R. rickettsii.
-
evaluation of a pcr assay for quantitation of Rickettsia rickettsii and closely related spotted fever group Rickettsiae
Journal of Clinical Microbiology, 2003Co-Authors: Marina E. Eremeeva, Gregory A. Dasch, David J SilvermanAbstract:A spotted fever Rickettsia quantitative PCR assay (SQ-PCR) was developed for the detection and enumeration of Rickettsia rickettsii and other closely related spotted fever group Rickettsiae. The assay is based on fluorescence detection of SYBR Green dye intercalation in a 154-bp fragment of the rOmpA gene during amplification by PCR. As few as 5 copies of the rOmpA gene of R. rickettsii can be detected. SQ-PCR is suitable for quantitation of R. rickettsii and 10 other genotypes of spotted fever group Rickettsiae but not for R. akari, R. australis, R. bellii, or typhus group Rickettsiae. The sensitivity of SQ-PCR was comparable to that of a plaque assay using centrifugation for inoculation. The SQ-PCR assay was applied successfully to the characterization of Rickettsial stock cultures, the replication of Rickettsiae in cell culture, the recovery of Rickettsial DNA following different methods of extraction, and the quantitation of Rickettsial loads in infected animal tissues, clinical samples, and ticks.
