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At least 1,117 records · Page 62Linked to original sources
PubMed2000

Establishment of a novel endothelial target mouse model of a typhus group rickettsiosis: evidence for critical roles for gamma interferon and CD8 T lymphocytes.

A mouse model of typhus rickettsiosis that reproduces the hematogenous dissemination to the critical target organs, including brain, lungs, heart, and kidneys, primary endothelial and, to a lesser degree, macrophage intracellular rickettsial infection, and typical vascular-based lesions of louse-borne typhus and murine typhus was established. Intravenous inoculation of C3H/HeN mice with Rickettsia typhi caused disease with a duration of the incubation period and mortality rate that were dependent on the infective dose of rickettsiae. Lethal infection was associated with high concentrations of R. typhi in the lungs and brain, despite a brisker humoral immune response to the rickettsiae than in the sublethal infection. Gamma interferon and CD8 T lymphocytes were demonstrated to be crucial to clearance of the rickettsiae and recovery from infection in experiments in which specific monoclonal antibodies were administered to deplete these components. Death of animals depleted of gamma interferon or CD8 T lymphocytes was associated with overwhelming rickettsial infection demonstrated by titers of infectious rickettsiae and by immunohistochemistry. An effective antirickettsial immune response was associated with elevated serum concentrations of IL-12 on Day 5 and increased secretion of IL-12 by concanavalin-A-stimulated spleen cells on Day 5. Evidence for transient suppression of the immune response consisted of marked reduction in the secretion of IL-2 and IL-12 by concanavalin-A-stimulated spleen cells on Days 10 and 15. This model offers excellent opportunities for study of attenuation and pathogenetic mechanisms of typhus rickettsiae, which are established biologic weapons of potential use in bioterrorism.

Animals↗
PubMed1998

A DNA vaccine protects mice against the rickettsial agent Cowdria ruminantium.

A DNA vaccine (VCL1010/MAP1) containing the major antigenic protein 1 (MAP1) gene of Cowdria ruminantium, driven by the human cytomegalovirus (HCMV) enhancer-promoter, was injected intramuscularly into 8-10 week-old female DBA/2 mice after treating them with 50 microliters/muscle of 0.5% bupivacaine three days previously. Up to 75% of the immunized mice seroconverted and reacted with C. ruminantium antigen blots. Splenocytes from immunized mice, but not from control mice, proliferated in response to the recombinant MAP1 and to C. ruminantium antigens in in vitro lymphocyte proliferation tests. These proliferating cells secreted IFN-gamma and IL-2 at concentrations ranging from 610 pg/ml to 1290 pg/ml and from 152 pg/ml to 310 pg/ml, respectively. Only up to 45 pg/ml and 42 pg/ml of IFN-gamma and IL-2, respectively, were detected in supernatants of splenocytes from control mice. In experiments testing different VCL1010/MAP1 DNA vaccine dose regimens (25-100 micrograms/dose, two or four immunizations), survival rates of 23% to 88% (35/92 survivors/total in all VCL1010/MAP1 immunized groups) were observed on challenge with a lethal dose of cell culture-derived C. ruminantium organisms. In contrast, survival rates of 0% to 3% (1/144 survivors/total in all control groups) were recorded for control mice. This study demonstrates that MAP1 is a protective antigen and validates the concept of DNA vaccines against heartwater.

Animals↗
PubMed1966

Natural history of tick-borne spotted fever in the USA. Susceptibility of small mammals to virulent Rickettsia rickettsii.

In the ecology of spotted fever rickettsiae, one of the as yet unsolved problems concerns the significance of small animals in the distribution of Rickettsia rickettsii in nature. In the Bitter Root Valley of western Montana, a great variety of rodents, rabbits and hares are known to serve as the preferred hosts for the immature stages of the vector tick, Dermacentor andersoni.The authors analyse the susceptibility of various species of small mammals to virulent R. rickettsii and evaluate their efficiency as sources of infection for larval ticks. The results demonstrate that meadow-mice, Columbian ground-squirrels, golden-mantled ground-squirrels, chipmunks and snowshoe hares (the latter to a lesser extent), when bitten by infected ticks, respond with rickettsiaemias of sufficient length and degree to infect normal larval D. andersoni. High infection rates were obtained in ticks that fed during periods of high rickettsial concentrations in the blood.

Animals↗
PubMed1976

Chronic Q fever.

Sixteen cases of chronic Q fever are described. In eight there was a history of exposure to infection from farms or farm products. All had valvular heart disease, involving the mitral valve in nine and the aortic valve in seven. Infection occurred on a prosthetic valve in two patients. Arterial embolism was common. Venous thrombosis occured in three patients, and pulmonary embolism occurred in three other patients. Complement fixing antibodies to phase 1 antigen were found in a titre of 1:200 or greater in all except two patients. In one of these post-mortem examination revealed rickettsial bodies in mitral valve vegetations, and in the other Coxiella burneti was isolated from heart valve tissue. The majority presented with infective endocarditis but two presented primarily with liver disease. All patients had evidence of liver involvement and in one this led to death from cirrhosis. Abnormal tests of liver function, particularly hyperglobulinaemia, raised alkaline phsophatase and abnormal bromsulphthalein retention were found in all patients. Hepatic histology was abnormal in all eight patients in whom it was studied. The commonest features were mononuclear cell infiltration of the portal tracts and prominence of the sinusoidal Kupffer cells. Patchy focal necrosis of parenchymal cells, granulomata, fatty change, and eosinophilia of the sinusoidal walls were also noted in several patients and cirrhosis developed in one. Six patients had a purpuric rash, and in 12 there was thrombocytopenia. It is suggested that the presence of hepatomegaly and liver involvement and thrombocytopenia may help to differentiate Q fever endocarditis from bacterial endocarditis. Raised serum IgM and IgA levels occured frequently, but with only a moderate dominance of IgM. Sheep cell agglutination and latex fixation tests for rheumatoid factor were occasionally positive. Several features of the disease suggest the possibility that immune-complex mechanisms may play a role in chronic Q fever. Treatment was with prolonged courses of tetracycline usually combined with lincomycin. Seven patients underwent valve replacement surgery for haemodynamic reasons. Five patients died; two from heart failure, one from cirrhosis, one seven days after valve replacement and one from intraperitoneal haemorrhage following percutaneous liver biopsy. Three patients have survived for more than five years, and another six for more than three and a half years after diagnosis. Of these nine patients, three received medical therapy alone and six required valve replacement as well. Antibiotics have been discontinued in four patients who have had valve surgery and three others. Six patients had received antibiotics for continuous periods varying from 29-62 months. In the period after stopping therapy varying from 15-21 months, no relapse has occured. A seventh patient, who had received antibiotics for four months prior to valve replacement, has survived 43 months after the withdrawal of antibiotics...

Adult↗
PubMed1999

Serologic testing for human granulocytic ehrlichiosis at a national referral center.

An indirect immunofluorescence assay (IFA) was used to identify patients with antibodies reactive to the human granulocytic ehrlichiosis (HGE) agent. Serum samples collected from clinically ill individuals were submitted to the Centers for Disease Control and Prevention by physicians via state health departments from throughout the United States and tested against a panel of ehrlichial and rickettsial pathogens. Antibodies reactive to the HGE agent were detected in 142 (8.9%) of 1,602 individuals tested. There were 19 confirmed and 59 probable (n = 78) cases of HGE as defined by seroconversion or a fourfold or higher titer to the HGE agent than to the Ehrlichia chaffeensis antigens. The average age of patients with HGE was 57 years, and males accounted for 53 (68%) of the patients. Cases of HGE occurred in 21 states; 47 (60%) of the cases occurred in Connecticut (n = 14), New York (n = 18), and Wisconsin (n = 15). Onset of HGE was identified from April through December, with cases peaking in June and July. The earliest confirmed cases of HGE occurred in 1987 in Wisconsin and 1988 in Florida. No fatalities were reported among the 78 patients with confirmed or probable HGE. Reactivity to the HGE agent and to either Coxiella burnetii, Rickettsia rickettsii, or Rickettsia typhi was infrequent; however, 74 (52%) of the 142 individuals who were positive for HGE had at least one serum sample that also reacted to the E. chaffeensis antigen. Thirty-four persons with confirmed or probable human monocytic ehrlichiosis due to E. chaffeensis also had antibodies to the HGE agent in at least one serum sample. The specific etiologic agent for 30 patients was not ascribed because of similarity of titers to both ehrlichial antigens. The use of both antigens may be required to correctly diagnose most cases of human ehrlichiosis, especially in geographic regions where both the HGE agent and E. chaffeensis occur.

Adolescent↗
PubMed1992

Spotted fever rickettsiae in ticks from the northern Sinai Governate, Egypt.

A field study was initiated in 1988 to investigate whether spotted fever group rickettsiae occur in geographic areas in Egypt that are adjacent to an area in the southern Israeli Negev that has a defined focus of spotted fever disease. Ticks were collected from dogs, sheep, and camels at four study sites in the northern Sinai. Tick hemolymph was processed for rickettsial detection by staining with fluorescein isothiocyanate-conjugated antibody to Rickettsia rickettsii. Of the 442 hemolymphs examined, 15 contained immunofluorescent rickettsiae. Eight hemolymph test-positive (HT+) ticks were Rhipicephalus sanguineus removed from dogs; the other HT+ ticks comprised three Hyalomma species, H. anatolicum, H. impeltatum, and H. dromedarii. Both HT+ and HT- ticks were tested for rickettsial DNA using the polymerase chain reaction (PCR). Eight of 10 HT+ field-collected ticks were PCR positive (PCR+). All laboratory colony R. rickettsii-infected ticks were PCR+. No HT- ticks from field or laboratory isolates were PCR+.

Animals↗
PubMed2002

Cytokins in the pathogenesis of astrakhan spotted Fever and North Asian scrub typhus: problems of immunocorrection.

Comparative study of interleukin-1 and tumor necrosis factor production under conditions of experimental rickettsial infection caused by agents of Astrakhan spotted fever and North Asian scrub typhus showed that therapy with galavit reduced manifestations of the disease, decreased mortality of experimental animals, and decreased the concentrations of interleukin-1 and tumor necrosis factor to normal values.

Animals↗
PubMed2005

Evaluation of PCR-based assay for diagnosis of spotted fever group rickettsiosis in human serum samples.

A nested PCR assay was developed for the detection of spotted fever group (SFG) rickettsiae in serum samples. The assay was based on specific primers derived from the rickettsial outer membrane protein B gene (rompB) of Rickettsia conorii. An SFG rickettsia-specific signal is obtained from R. akari, R. japonica, R. sibirica, and R. conorii. Other bacterial species tested did not generate any signal, attesting to the specificity of the assay. As few as seven copies of the rompB gene of R. conorii could be detected in 200 microl of serum sample. The assay was evaluated with a panel of sera obtained from patients with acute-phase febrile disease tested by immunofluorescent antibody assay (IFA). The SFG rickettsia-specific DNA fragment was detected in 71 out of 100 sera, which were proven to have immunoglobulin M antibodies against SFG rickettsial antigen by IFA. The results were further confirmed by restriction fragment length polymorphism and sequencing analysis of the DNA fragments. The results indicated that this PCR assay is suitable for the diagnosis of spotted fever group rickettsiosis in Korea.

Antibodies, Bacterial↗
PubMed1990

Cyclic rickettsemia during persistent Anaplasma marginale infection of cattle.

Submicroscopic levels of Anaplasma marginale rickettsemia in persistently infected cattle were determined by using nucleic acid hybridization. Within individuals, the rickettsemia levels steadily increased from less than 10(4) infected erythrocytes per ml to a peak of more than 10(6) infected erythrocytes per ml and then rapidly declined. This logarithmic variation parallels the variation of the rickettsemia level seen in acute infection and suggests that cyclic emergence of antigenic variants is a mechanism of rickettsial persistence.

Anaplasma↗