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PubMed2003

Scrub typhus: vector competence of Leptotrombidium chiangraiensis chiggers and transmission efficacy and isolation of Orientia tsutsugamushi.

A total of 4,281 rodents, belonging to 20 species, was collected from three villages in Chiangrai Province, northern Thailand, from January 1994 to December 2001. The predominant species were Rattus rattus, R. losea and Bandicota indica, accounting for 96% of the total. More than 135,000 chigger mites were removed from wild rodents of which 1% were identified as Leptotrombidium chiangraiensis, a new species vector of scrub typhus. Five Orientia tsutsugamushi-infected L. chiangraiensis colonies established from chiggers removed from R. rattus and R. losea rodents. The prevalence of O. tsutsugamushi infection in colonies ranged from 7-89%. Vertical and horizontal transmission efficacies of O. tsutsugamushi were stable between generations among colonies of L. chiangraiensis. The two isolates of O. tsutsugamushi obtained from individual adult L. chiangraiensis mites represent the first successful isolation of this bacterium from individual adult mites. Characterization of the O. tsutsugamushi isolates is under way.

Animals↗
PubMed1985

Transovarial transmission of murine typhus rickettsiae in Xenopsylla cheopis fleas.

It has been generally accepted that infected fleas do not pass on Rickettsia mooseri, or indeed any other known pathogen, to their progeny. It is reported here that such transovarial transmission does occur in laboratory-infected Xenopsylla cheopis fleas. By means of the direct fluorescent antibody test, Rickettsia mooseri was observed in cells of the hemolymph of infected fleas. As many as 11 percent of the adults and 2.9 percent of the larvae of the generation reared therefrom, had demonstrable rickettsiae. Moreover, batches of the F1 fleas were capable of transmitting the infection to more than 18 percent of the rats they infested. The data support the contention that Xenopsylla cheopis fleas play an important role in the maintenance of murine typhus in rats in nature.

Animals↗
PubMed1988

Chloramphenicol, gentamicin, and ciprofloxacin against murine scrub typhus.

Ciprofloxacin (120 mg/kg of body weight per day), chloramphenicol (300 mg/kg per day), and gentamicin (30 mg/kg per day) were compared with placebo in a BALB/cj mouse model of scrub typhus. All animals treated with ciprofloxacin and chloramphenicol survived. All animals treated with gentamicin or placebo died. All surviving animals showed evidence of seroconversion. Ciprofloxacin and chloramphenicol were statistically more effective in preventing death than gentamicin or placebo.

Animals↗
PubMed1999

Azithromycin activities against Orientia tsutsugamushi strains isolated in cases of scrub typhus in Northern Thailand.

Azithromycin was given to mice and humans infected with strains of Orientia tsutsugamushi from northern Thailand, where drug-resistant scrub typhus occurs. Azithromycin and doxycycline yielded comparable mouse survival rates (73 and 79%, respectively; P > 0.5). Symptoms, signs, and fever in two pregnant women abated rapidly with azithromycin. Prospective human trials are needed.

Adult↗
PubMed1976

Host defenses in experimental scrub typhus: histopathological correlates.

Intraperitoneal (i.p.) infection of BALB/c mice with 1,000 50% mouse lethal doses of the Karp strain of Rickettsia tsutsugamushi was inevitably lethal, and associated pathological alterations were confined to the peritoneal cavity. These included: (i) continuous proliferation of rickettsial organisms in peritoneal macrophages until death; (ii) hepatic granulomas appearing 6 days after infection and increasing in size and number until death; (iii) splenomegaly, resulting principally from proliferation of lymphoid tissue, and (iv) terminal peritonitis. Under two circumstances, i.p. infections with R. tsutsugamushi were not lethal: (i) infection with 100 50% mouse infectious doses of the Gilliam strain, which, in fact, resulted in immune protection against otherwise lethal Karp challenge; and (ii) Karp infection of animals immunized with the Gilliam strain. In both cases, the associated pathological abnormalities were, as with primary Karp infection, restricted to the peritoneal cavity. Also similar was the striking splenomegaly due to lymphoid proliferation, which was particularly prominent in immunized animals. In contrast to primary and lethal Karp infection, however, these infections were characterized by: (i) minimal and transient proliferation of rickettsial organisms in peritoneal macrophages; (ii) disappearance of hepatic granulomas; and (iii) absence of peritonitis. It was concluded that the survival of an animal bearing an i.p. infection of scrub typhus depended on its ability to concentrate a sufficiently vigorous immune response in the peritoneal cavity, resulting in the evolution of rickettsiacidal macrophages capable of suppressing the infection.

Animals↗
PubMed1976

Host defenses in experimental scrub typhus: role of cellular immunity in heterologous protection.

The relative contributions of cellular and humoral immunity in scrub typhus infections were studied in inbred mice employing paired strains of Rickettsia tsutsugamushi differing in virulence. An infectious dose (100 MID50) of the less virulent Gilliam strain resulted in heterologous immune protection against an otherwise lethal challenge (1,000 MLD50) of the virulent Karp strain. Partial heterologous protection against lethal Karp challenge was observed in animals preimmunized with the Gilliam strain as early as 3 days prior to challenge, whereas complete protection against illness and death existed in animals immunized at least 7 days prior to challenge. In the heterologous protection provided by prior Gilliam infection, the role of humoral immunity was not of primary importance for the following reasons: (i) significant levels of complement-fixing antibody against R. tsutsugamushi were not detectable until long after animals were solidly immune; (ii) antibody eventually appearing after Gilliam immunization exhibited a consistently low complement-fixing titer against the immunizing homologous (Gilliam) strain and contained no detectable activity against the heterologous challenge (Karp) strain; and (iii) passive transfer of large quantities of serum from Gilliam immune mice, themselves immune to Karp challenge, failed to protect recipients against a similar challenge. However, protection was afforded by the passive transfer of serum containing antibody against Karp, suggesting a major role for antibody in protection against homologous infection. This heterologous challenge system was particularly useful because it minimized the role of humoral immunity, at least early in the course of infection, and allowed a definitive examination of the cellular response. Cell-mediated immunity played a major role in the heterologous protection observed after Gilliam immunization. This was evidenced by the significant protection against Karp challenge afforded by the passive transfer of spleen cells from animals immunized with Gilliam 7 to 63 days previously. Of the immune spleen cells, only those which were nonadherent, presumably lymphocytes, were capable of transferring passive heterologous protection. This protective effect of nonadherent cells could be ablated by depleting the cell population of thymus-derived or T cells with anti-theta serum and complement prior to transfer but not by use of anti-immunoglobulin serum and complement, which selectively removes bone marrow-derived or B cells. These results suggested that the cell in immune spleens capable of conferring heterologous protection was a T lymphocyte.

Animals↗
PubMed1976

Mechanisms of immunity in typhus infections. V. Demonstration of Rickettsia mooseri-specific antibodies in convalescent mouse and human serum cytophilic for mouse peritoneal macrophages.

Antibodies in both mouse and human Rickettsia mooseri (Rickettsia typhi) convalescent serum that were cytophilic for mouse macrophages were demonstrated by the rosette technique. Mouse peritoneal macrophages, passively sensitized with early and late serum from mice with a sublethal infection of R. mooseri, were washed and exposed to rickettsiae. Rosettes of rickettsiae were found around macrophages, maintained at 4 degrees C, which had been sensitized with immune serum (direct sensitization of macrophages), but no rosettes were found around macrophages sensitized with serum from normal mice. When the macrophages were maintained at 34 degrees C after addition of the rickettsiae, phagocytosis of rickettsiae occurred, indicating one probable role for cytophilic antibodies in typhus infections. If the rickettsiae were mixed with serum from infected mice, washed, and then added to macrophages (indirect sensitization of macrophages), more rosettes were found around the macrophages than around directly sensitized macrophages. The presence of mouse immunoglobulin G on the macrophage surface was also shown by staining living sensitized macrophages with rabbit fluroescein-conjugated anti-mouse immunoglobulin G.

Animals↗
PubMed1977

Host defenses in experimental scrub typhus: effect of chloramphenicol.

The effect of chloramphenicol treatment on the development of immunity to scrub typhus in mice was studied. Chemotherapy was administered either shortly before infection and for 14 days thereafter (group I), or from 7 to 21 days postinfection (group II). Although the full course of either regimen resulted in complete protection of the mice against subsequent challenge with the homologous strain of Rickettsia tsutsugamushi, initiation of chemotherapy at 7 days postinfection resulted in more rapid development of immunity against both the original infection and subsequent challenge. In both treatment groups, a 1- to 2- day hiatus was observed between immunity to challenge in the treated animal and the ability to transfer this immunity to syngeneic recipients with lymphocyte-enriched spleen cells. Similarly, complement-fixing antibodies were not detectable until shortly after the animals were able to resist challenge. These data supported the conclusion that the rickettsiostatic effect of chloramphenicol allows the infected animal time to mount an effective immune response and, further, that initiation of chemotherapy early in the infection may delay development of this response.

Animals↗
PubMed1978

Gamma-irradiated scrub typhus immunogens: development and duration of immunity.

The development and duration of immunity to lethal scrub typhus infection was studied in BALB/c mice vaccinated with gamma-irradiated Rickettsia tsutsugamushi, strain Karp. One intraperitoneal injection containing approximately 10(8) 50% mouse lethal doses (MLD(50)) of irradiated organisms elicited an immune response protective against challenge with 10(5) MLD(50) of viable Karp. The same mass of immunogen given in three injections at 5-day intervals increased homologous (Karp strain) protection 25-fold and heterologous (Kato strain) protection 60-fold. Further temporal expansion of the immunization regimen did not increase protection. Subcutaneous vaccination provided significant, but lower, levels of protection than were achieved by intraperitoneal immunization, but the levels of cell-transferable immunity elicited by the two routes were approximately the same. Immunologically specific protection after intraperitoneal vaccination developed rapidly enough to provide resistance against simultaneous challenge with 200 MLD(50) of Karp. Homologous immunity was protective against a 10(6)-MLD(50) challenge 7 days after completion of the three-injection regimen, remained at that level for 3 months, dropped to 10(4) MLD(50) by 9 months, and was effective against a 50-MLD(50) Karp challenge at 12 months. Protection against heterologous challenge was first observed on day 17 and peaked on day 38, when the mice resisted a 10(5)-MLD(50) Kato challenge. Thereafter, heterologous protection waned rapidly and was not significant at 6 months.

Animals↗
PubMed1979

Gamma-irradiated scrub typhus immunogens: broad-spectrum immunity with combinations of rickettsial strains.

Scrub typhus immunogens were prepared from Rickettsia tsutsugamushi strains Karp, Kato, Gilliam, Kostival, and Buie by exposing frozen infected yolk sac suspensions to 300 krad of gamma radiation. Mouse protection tests showed that each of the irradiated immunogens protected C3H/HeDub mice against high challenge levels of Karp and Gilliam, but that none of these single-strain immunogens were capable of protecting against all five of the challenge strains. Broad-spectrum protection was achieved by using combinations of three strains of irradiated rickettsiae in a vaccination regimen of three injections at 5-day intervals. A comparison of vaccination efficacy employing three such combinations (Karp-Gilliam-Kato, Karp-Kostival-Kato, and Buie-Kostival-Kato) indicated that both sequential administration of strains on successive vaccination days and multiple injections of trivalent mixtures produced protective responses superior to those obtained with single-strain immunogens. Trivalent mixtures of rickettsiae exhibited a striking synergistic effect on the immune response of C3H/HeDub mice and elicited a protective response against Kato challenge that could not be obtained with any single-strain immunogen. Mice vaccinated with the trivalent Karp-Gilliam-Kato immunogen resisted challenge with more than 10(3) 50% mouse lethal doses of Karp and Gilliam for 12 months, and were resistant to similar levels of challenge with Kato and Buie for 6 months.

Animals↗
PubMed1979

Host defenses in experimental scrub typhus: role of normal and activated macrophages.

Resident peritoneal macrophage from BALB/c mice were infected in vitro with Rickettsia tsutsugamushi strain Gilliam, and rickettsial growth was estimated by microscopic examination of Giemsa-stained cells. Both number of infected macrophage per culture and number of intracellular rickettsiae per cell increased with time during culture. Treatment of rickettsiae with immune serum before infection macrophage cultures reduced the number of infected macrophage by 50%. Macrophage treated in vitro with lymphokines were able to suppress rickettsial growth in the absence of detectable antibody and exhibited a 75% reduction in infection compared with normal macrophage. We also obtained activated macrophage from immune mice and found that they were refractory to in vitro rickettsial infection. Macrophage populations activated in vitro or in vivo contained a small percentage of cells which supported unrestrained growth of rickettsiae. These data suggest that an early immunological event in experimental scrub typhus infection may be the development of activated macrophage capable of suppressing rickettsial proliferation before the appearance of circulating antibody.

Animals↗
PubMed1982

Host defenses in experimental scrub typhus: delayed-type hypersensitivity responses of inbred mice.

Delayed-type hypersensitivity responses of inbred mice during the course of lethal and chronic infections with strains of Rickettsia tsutsugamushi were evaluated by using the influx of radiolabeled cells into antigen-injected ears. Congenic strains of C3H mice, which previously have been shown to be resistant (C3H/RV) or sensitive (C3H/HeDub) to lethal intraperitoneal infection with the Gilliam strain of rickettsiae, both expressed delayed-type hypersensitivity early in the course of infection (5 to 7 days). The sensitive C3H/HeDub mice, however, exhibited a marked decline in reactivity just before death. In contrast, reactivity of C3H/RV mice remained high through day 9 and declined slowly through day 15 after infection. Similar results were obtained when BALB/c mice were infected with either the Karp or the Gilliam strain of rickettsiae, which produce a lethal or nonlethal infection, respectively, in this strain of mice. Rechallenge of C3H/RV mice elicited a rapid increase in reactivity, suggesting a secondary memory response. To analyze delayed-type hypersensitivity during chronic infection, C3H/HeDub mice were immunized by subcutaneous infection with the Gilliam strain of R. tsutsugamushi, and both delayed-type hypersensitivity reactivity and resistance to intraperitoneal challenge were examined. Delayed-type hypersensitivity reactivity developed slowly and peaked at 21 days postimmunization, which correlated with resistance to intraperitoneal challenge. Delayed-type hypersensitivity reactivity declined thereafter, but resistance to intraperitoneal challenge remained through 28 days postimmunization. Delayed-type hypersensitivity reactivity increased after secondary challenge at 28 days, again suggesting antigen memory generated by primary immunization. Transfer of delayed-type hypersensitivity reactivity was accomplished by using immune thymus-derived splenic lymphocytes isolated with nylon-wool columns. Abrogation of the ability of immune spleen cells to transfer delayed-type hypersensitivity reactivity after treatment with anti-Thy 1.2 alloantiserum and complement further supported the view that delayed-type hypersensitivity responses to scrub typhus rickettsiae were mediated by thymus-derived lymphocytes.

Animals↗
PubMed1986

Effect of sublethal gamma radiation on host defenses in experimental scrub typhus.

The effect of sublethal gamma radiation on inbred mice chronically infected with scrub typhus rickettsiae was examined. Inbred mice which were inoculated with the Gilliam or Karp strain of Rickettsia tsutsugamushi by the subcutaneous route harbored the infection for at least 1 year. Irradiation of these animals at 12 or 52 weeks postinoculation with normally sublethal levels induced a significantly higher percentage of rickettsemic mice (recrudescence) than was seen in the unirradiated, similarly infected control animals. In addition, sublethal irradiation at 12 weeks induced a quantitative increase in total rickettsiae. Homologous antibody titers to the rickettsiae were examined for 5 weeks after irradiation to determine the role of the humoral response in radiation-induced recrudescence. Unirradiated, infected mice showed consistent titers of about 320 throughout the 5-week observation period, and the titer was not affected by exposure of up to 500 rads of gamma radiation. Drug dose-dependent radioprotection and modification of recrudescence was noted in infected, irradiated mice treated with the antiradiation compound S-2-(3-aminopropylamino)ethyl phosphorothioic acid. The results of this investigation supported the conclusion that the recrudescence of a chronic rickettsial infection in the appropriate host after immunological impairment due to gamma radiation can result in an acute, possibly lethal rickettsemia.

Amifostine↗
PubMed1982

Serodiagnosis of tsutsugamushi fever (scrub typhus) by the indirect immunoperoxidase technique.

The indirect immunoperoxidase technique was assessed for the serodiagnosis of tsutsugamushi fever (scrub typhus). The antigens were peritoneal smears prepared from mice infected intraperitoneally with the Karp, Kato, and Gilliam strains of Rickettsia tsutsugamushi. Treatment of the mice with cyclophosphamide apparently increased the number of the rickettsiae, and it minimized the exudate that interfered with the specific staining. The rickettsiae were seen as clusters in the juxtanuclear region of the mesothelial cells and also as free particles outside of the cells. By the indirect immunoperoxidase technique, the sera from all of the patients (49 samples from 30 patients) were positive for the R. tsutsugamushi antibody. The antibody titers (immunoglobulin G [IgG] and IgM) determined by the indirect immunoperoxidase technique correlated with those determined by the indirect immunofluorescence technique. Thus, the indirect immunoperoxidase technique was useful for quantifying both IgG and IgM antibodies to the rickettsia.

Antibodies, Bacterial↗
PubMed1997

Use of enzyme-linked immunosorbent assay techniques with cross-reacting human sera in diagnosis of murine typhus and spotted fever.

Enzyme-linked immunosorbent assay (ELISA) techniques for the determination of immunoglobulin G to rickettsial lipopolysaccharides were developed. These techniques provide a simple and convenient way to serodiagnose Mediterranean spotted fever and murine typhus with a single serum dilution. The results of the ELISAs correlated with the indirect immunofluorescence assay titers of cross-reacting sera.

Animals↗
PubMed1961

The rapid slide agglutination test in the diagnosis of typhoid fevers and typhus.

Of 10,000 sera examined for infectious diseases by both the rapid slide agglutination and the tube agglutination tests, 128 were found positive for typhus fever and 257 for typhoid and paratyphoid infections. Of 84 of the last mentioned cases of typhoid and paratyphoid, which were confirmed by cultural examination, 45 (53.5%) were negative to the tube test, whereas only one (1.2%) was negative to the slide test. Taking the total of 385 cases in which the clinical picture was typical and either one of the two serological tests positive, the tube test was negative in 183 cases (47.2%) whereas the slide test was negative once only (0.3%). Of 201 cases in which both the slide and tube tests were positive, the slide test gave the result, on an average, six days earlier in 19 cases (10%).A control test of 139 sera from patients suffering from various other diseases gave a negative result on the slide test.

Agglutination↗
PubMed1991

A typhus-like illness caused by acute HIV seroconversion.

A patient is described in whom an acute human immunodeficiency virus seroconversion illness occurred following a trip to southern Africa. The presentation was strikingly similar to that of African tick typhus and could only be distinguished by serological testing.

Adult↗