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At least 19 recordsLinked to original sources
PubMed1985

Mechanisms of immunity to infection with typhus rickettsiae: infected fibroblasts bear rickettsial antigens on their surfaces.

As with any immune response to infectious organisms, both antibody and T cell-mediated immune responses to infection with Rickettsia typhi require the appropriate presentation of rickettsial antigens to immunocompetent cells. Considering the obligate intracellular nature of rickettsiae, the exact mechanisms by which lymphocytes and macrophages encounter and respond to rickettsial antigens may depend on certain aspects of pathogenesis and on the availability of organisms or their antigens to cells of the immune system. One potential mode of rickettsial antigen presentation, not previously identified, is the appearance in vitro of rickettsial antigens on the cell membrane of R. typhi-infected L-929 fibroblasts. Polyvalent fluoresceinated rabbit antisera directed against whole R. typhi cells used in flow cytometric analysis of infected fibroblasts showed an increasing presence of R. typhi antigen on the host cell membrane 1 to 3 days postinfection. The significance of this finding in the pathophysiology of rickettsia-host interactions and the generation of cytotoxic T cell-mediated immunity and antibody immunity is discussed.

Animals↗
PubMed2005

Rickettsia infection in natural leech populations.

Field-collected specimens of glossiphoniid leeches, Torix tagoi, Torix tukubana, Hemiclepsis marginata, and Hemiclepsis japonica, were surveyed for Rickettsia infection by using a diagnostic PCR assay. Rickettsia was detected in 96% (69/72) of T. tagoi, 83% (24/29) of T. tukubana, 29% (33/113) of H. marginata, and 0% (0/30) of H. japonica. The frequencies of Rickettsia infection were stably maintained in different seasons. In H. marginata and T. tukubana, distant local populations exhibited remarkably different frequencies of Rickettsia infection. Eggs carried by infected females of T. tagoi and H. marginata were all Rickettsia-positive, indicating nearly 100% vertical transmission. Analysis of 16S rDNA sequences revealed that phylogenetic relationship of the leech-associated Rickettsia reflected the specific and populational divisions of the host leeches. However, circumstantial lines of evidence strongly suggested that horizontal transmission of Rickettsia must have occurred in the ancestors of these leeches. In T. tagoi and T. tukubana, infected individuals were remarkably larger in size than uninfected individuals, wheras in H. marginata, infected and uninfected individuals were almost comparable in size. This study first provides information on ecological aspects of leech-bone endocellular bacteria of the genus Rickettsia. On the basis of these data, we discuss possible mechanisms whereby Rickettsia infection is maintained in natural populations of these leeches in the freshwater ecosystem.

Animals↗
PubMed1988

Recognition of typhus group rickettsia-infected targets by human lymphokine-activated killer cells.

Lymphokine-activated killer cells caused significant lysis of target cells infected with typhus group rickettsiae (TGR) but not cells infected with Rickettsia tsutsugamushi. Monoclonal and polyclonal antibodies against TGR or TGR-infected cells failed to bind specifically to infected targets, as determined by flow cytometry or by immunoprecipitation of radiolabeled cell surface proteins. Major unaltered antigenic determinants of TGR therefore cannot be detected on the surface of infected targets.

Cytotoxicity, Immunologic↗
PubMed2005

Motor and sensory polyneuritis with distal conduction failure as uncommon complication of an acute Rickettsia conorii infection.

Rickettsia conorii is endemic in the Mediterranean region. Infections are mostly benign and neurological involvement is unusual. We describe a case of a man who presented with acute facial nerve palsy followed by flaccid tetraparesis due to an electrophysiologically established polyneuritis with distal conduction failure. Elevated IgM antibody titres for R. conorii were documented by indirect immunofluorescent antibody test. After doxycycline therapy, the patient presented a rapid clinical improvement. Repeated electrophysiological examinations revealed significantly restored compound muscles, and sensory action potentials, corresponding to the clinical course after treatment and ex juvantibus, indicate the causative relation between R. conorii infection and the described clinical syndrome.

Aged↗
PubMed1993

Directional actin polymerization associated with spotted fever group Rickettsia infection of Vero cells.

Members of the spotted fever group (SFG) of rickettsiae spread rapidly from cell to cell by an unknown mechanism(s). Staining of Rickettsia rickettsii-infected Vero cells with rhodamine phalloidin demonstrated unique actin filaments associated with one pole of intracellular rickettsiae. F-actin tails greater than 70 microns in length were seen extending from rickettsiae. Treatment of infected cells with chloramphenicol eliminated rickettsia-associated F-actin tails, suggesting that de novo protein synthesis of one or more rickettsial proteins is required for tail formation. Rickettsiae were coated with F-actin as early as 15 min postinfection, and tail formation was detected by 30 min. A survey of virulent and avirulent species within the SFG rickettsiae demonstrated that all formed actin tails. Typhus group rickettsiae, which do not spread directly from cell to cell, lacked F-actin tails entirely or exhibited only very short tails. Transmission electron microscopy demonstrated fibrillar material in close association with R. rickettsii but not Rickettsia prowazekii. Biochemical evidence that actin polymerization plays a role in movement was provided by showing that transit of R. rickettsii from infected cells into the cell culture medium was inhibited by treatment of host cells with cytochalasin D. These data suggest that the cell-to-cell transmission of SFG rickettsiae may be aided by induction of actin polymerization in a fashion similar to that described for Shigella flexneri and Listeria monocytogenes.

Actin Cytoskeleton↗
PubMed1999

[African Rickettsia infections].

EPIDEMIOLOGY: African rickettsiasis is transmitted by Rickettsia africae, a cattle tick. Amblyomma spp. is an emerging rickettsiasis in sub-sehalian Afric described in 1992. Seroepidemiology studies conducted in Africa show that it is probably the most widespread rickettsiasis in the sorld. In addition, the development of tourist activities in southern African countries has led to an increase in the number of reported cases in subjects returning from endemic areas. A high serprevalence of anti R. africae anticodies has been recently reported in the guadeloupe (French East Indies) population as well as one documented infection. CLINIC: The clinical expression of African tick rickettsiasis includes fevder, headache, inoculation scar, locoredgional node enlargement, and an inconsistent sometimes vesicular rash. The diagnosis is made on the basis of serological findings and cross absorption of anti R. africae and R. conorii antibodies and/or isolation or gene amplification of R. africae from inoculation scar biopsies.

Africa↗
PubMed2002

[The onset of chronic Lyme-borreliosis after the cure of tick-borne rickettsia infection in simultaneous infection].

A case of a male patient with chronic Lyme borreliosis running with marked neurological symptoms (Garin-Bujardoux-Bannwarth syndrome) is reported. Two years before the disease manifestation the patient was infected by the tick with both borrelia and Rickettsia sibirica. The latter infection provoked an acute fever in tick-borne rickettsiosis immediately after the tick's bite. This masked development of Lyme borreliosis which manifested only 5 months later as a neurological disease. It is thought necessary to propose a rational scheme of antibiotic treatment of patients with tick-transmissible diseases.

Adult↗
PubMed2006

Serological evidence of Rickettsia infections in forestry rangers in north-eastern Italy.

The prevalence of antibodies to Rickettsiae and other tick-borne microrganisms in the sera of 181 forestry rangers from Friuli-Venezia-Giulia, Italy, was examined. Seven (3.9%) sera were positive for Rickettsia conorii and Rickettsia helvetica, as single or dual infections; four of these sera had been found previously to be positive for Borrelia burgdorferi. Antibodies to Coxiella burnetii were detected in five (2.8%) sera, four of which were also positive for B. burgdorferi. These findings indicate that patients in this north-eastern Italian region with fever subsequent to tick-bite should be investigated for Rickettsia and Coxiella infections.

Animals↗
PubMed1996

Comparison of serological reactions of Rickettsiae-infected patients and rabbit anti-Proteus OX antibodies with Proteus OX2, OX19 and OXK lipopolysaccharides.

The reactivity of anti-Rickettsiae human antibodies with Proteus OX cells is used as a presumptive rickettsial diseases diagnostic test Weil-Felix reaction. In presented studies we compare the reactivity of human anti-Rickettsiae and rabbit anti-Proteus antibodies with series of Proteus OX2, OX19 and OXK lipopolysaccharides (LPS). Polyclonal rabbit anti-OX2, anti-OX19 and anti-OXK sera reacted only with the homologous LPS--OX2, OX19 and OXK, respectively. The antibodies of Japanese spotted fever patients were less specific and reacted with OX2 as well as OX19 LPS. The antibodies of scrub typhus patients recognized Proteus OXK LPS, only. The serological reactions of O-antigen of P. mirabilis S1959 indicated that this, previously serologically not classified, strain may belong to the OXK group. Bacteria, used in the studies, came from the American, Japanese and European strain collections. The series of OX2, OX19 and OXK LPS, isolated from these Proteus strains, presented pattern of electrophoretic mobility and serological reactivities specific for each of OX-group types.

Animals↗
PubMed1997

[Serological study of rickettsia infections in Niamey, Niger].

Rickettsioses is a possible alternative to presumptive diagnosis of malaria. A serologic study was carried out in 1994 to determine the prevalence of rickettsioses in children under 5 years of age from three different areas of Niamey, Niger. Indirect immunofluorescent assays using the micromethod were performed with antigens for Rickettsia conori, Rickettsia mooseri, and Coxiella burneti. Results were read from a positive threshold of 1/160 up to 1/640. Out of a randomized population of 177 children 35 were positive for at least one antigen: 17.5% for Rickettsia conori, 15.8% for Rickettsia mooseri, and 9.6% for Coxiella burneti. The incidence of positivity for Rickettsia mooseri and Coxiella burneti. was significantly higher in an area where contact between people and animals was particularly close. This high rate of positivity is in agreement with previous reports in other countries in West Africa and suggests that close contact between man and rickettsiae is common. Although dogs carry ticks in Niger, direct contact with Rickettsia conori is probably the most mode of transmission. Rodents like Cricetomys gambianus and Rattus norvegicus carry Rickettsia mooseri and goats and sheep which are often kept in the courtyards of buildings carry Coxiella burneti. The recently identified species Rickettsia africae could be transmitted by other vectors such as cattle ticks.

Animals↗
PubMed1986

Behavioral fever and therapy in a rickettsia-infected Orthoptera.

Gryllus bimaculatus were infected with an intracellular prokaryote, Rickettsiella grylli, then reared either at fixed temperatures or in a temperature gradient (22-36 degrees C) where they could select the temperature they preferred. Only 50% of the infected insects reared at 28 degrees C or less survived after 20 days, against 75% of those reared at 30 degrees C or more and 90% of those in the temperature gradient. Examination of smears of insect tissue showed that all (100%) of the infected insects reared between 23 and 29 degrees C had developed a strong rickettsial infection. Only 20% of the insects reared in a gradient of temperature showed signs of strong infection. Body temperature of crickets in the temperature gradient, recorded using thin thermocouples, was 33 degrees C in infected crickets and 26.6 degrees C in controls. It is concluded that thermoregulatory behavior was used by the insects to produce a fever when infected with Rickettsiella grylli. This protected them and increased survival capacity.

Animal Husbandry↗
PubMed1976

In vitro studies on Rickettsia-host cell interactions: lag phase in intracellular growth cycle as a function of stage of growth of infecting Rickettsia prowazeki, with preliminary observations on inhibition of rickettsial uptake by host cell fragments.

Two Rickettsia prowazeki seeds, an "early" seed in the logarithmic or exponential growth phase and a "late" seed in the stationary or possibly early decline phase, were prepared in chicken embryo (CE) cell cultures and compared with respect to morphology and infection cycle in CE cells in culture. Differences in size and ultrastructure of the organisms in the two seeds were similar to those seen in other gram-negative bacteria at comparable stages to growth. Vacuolar structures, rare in log-phase organisms, were common in stationary-phase organisms. Minute spherical forms reminiscent of minicells were seen in the stationary-phase preparations. In quantitative uptake experiments, organisms, typical in size and morphology of each preparation, had comparable capacity per plaque-forming unit to penetrate into CE cells in suspension when the seeds had been depleted of host cell membrane fragments and other debris. This suggests that host cell fragments, presumably of membrane origin, competitively inhibit rickettsial uptake by intact CE cells. Organisms of the log-phase organisms displayed a lag phase of about 7.5 h, during which they enlarged and increased in intensity of staining, before entering the log phase of growth.

Cells, Cultured↗
PubMed2001

Evidence of rodent-associated Bartonella and Rickettsia infections among intravenous drug users from Central and East Harlem, New York City.

We tested serum samples collected in 1997 and 1998 from a cohort of 204 injection drug users (IDUs) recruited from Central and East Harlem, New York City, New York, for antibodies reactive with seven rickettsial or Bartonella spp. antigens. Rodent-associated Bartonella elizabethae and Rickettsia akari were the primary etiologic agents of interest. The testing panel also included Bartonella henselae, Bartonella quintana, Rickettsia prowazekii, Rickettsia rickettsii, and Rickettsia typhi. The highest prevalence of seroreactive serum samples (46%) was found with B. elizabethae antigens; 10% of the samples reacted with B. henselae antigens, while 2% reacted with B. quintana antigens. Reactivity to the latter two antigens was likely due to cross-reactivity with B. elizabethae antigens in most instances. Among the spotted fever group rickettsiae, 18 (9%) samples reacted with R. akari, including 10 samples (5%) that also reacted with R. rickettsii. Cross-adsorption studies demonstrated that most of the spotted fever group rickettsiae antibodies were due to R. akari infections. Among the typhus group rickettsiae, 5 samples reacted weakly to R. prowazekii antigens, and no samples reacted with R. typhi antigens. These findings suggest that Harlem IDUs are commonly exposed to two rodent-associated zoonotic agents. Further study of IDU populations may help elucidate transmission cycles of these agents in inner cities where higher levels of transmission occur.

Adolescent↗
PubMedDate not supplied

[Rickettsia infections in Sicily and mass media: attention not entirely groundless].

The aim of the study was to assess the prevalence of rickettsiosis cases in Sicily with special attention to possible occupational exposure. This research was prompted by the high number of cases reported in the press in the summer of 1999. Epidemiological data for previous years showed that Sicily was always the region where most cases of rickettsiosis occurred; we therefore examined the clinical data of patients admitted to the major infectious diseases hospital department in Palermo in the period 1996-1999. Analysis of the cases showed that an occupational risk existed (among small farmers), but that there was also an environmental risk for subjects living in rural areas due to contact with infected dogs or rural areas activities. It is therefore of fundamental importance to carry out a primary prevention programme against rickettsiosis for everyone exposed to the risk either occupationally or in leisure activities in rural areas.

Adult↗