Isolation of Rickettsia tsutsugamushi antigenically different from Kato, Karp, and Gilliam strains from patients

Rickettsia tsutsugamushi strains from three recent patients of Tsutsugamushi disease in Niigata Prefecture were isolated primarily in mice and then in L cell cultures. By this procedure, low virulent strains to mice, as well as high virulent ones, could be isolated and cultivated serially in L cell cultures, suggesting the usefulness of L cells for isolation of this species of rickettsia. Each newly isolated strain was identified as a member of R. tsutsugamushi from the results of cross immunological tests and morphological observation. On the other hand, it was recognized that one of these rickettsiae showed immunological properties distinguishable from the prototype strains of Kato, Karp, and Gilliam by the cross complement fixation test, and also had low virulence in mice.

Association of an inflammatory I region-associated antigen-positive macrophage influx and genetic resistance of inbred mice to Rickettsia tsutsugamushi

Strains of C3H mice differing in susceptibility to intraperitoneal infection with the Gilliam strain of Rickettsia tsutsugamushi were used to investigate the role of the I region-associated (Ia) antigen-bearing macrophage in the genetic resistance of mice to this organism. Resistant mice (C3H/RV) were found to produce a quantitatively greater Ia antigen-positive macrophage response after infection compared to mice (C3H/HeDub) which underwent a lethal infection. The macrophage influx produced in response to infection of the C3H/HeDub mice was deficient in Ia antigen-bearing cells, as evaluated by antigen presentation function and by the use of macrophages as stimulator cells in a mixed lymphocyte response. The resistance to infection, as well as the Ia-positive macrophage response in C3H/RV mice, was sensitive to 450 to 600 rads of irradiation. C3H/HeDub mice produced exudates rich in Ia-positive macrophages if stimulated with concanavalin A or after challenge with R. tsutsugamushi (if previously immunized), ruling out an innate inability of this strain of mice to produce Ia-positive macrophages exudates. Challenge of either strain of mice immunized by a prior subcutaneous infection resulted in a rapid (3 to 5 days) peak of Ia-positive macrophages responding to the peritoneal cavity. It also was noted that subcutaneous infection alone resulted in an increase in the proportion and number of "resident" macrophages which were Ia positive. These data suggest that the macrophage influx in terms of Ia-bearing cells is at least associated with the genetic resistance of C3H/RV mice to infection with this rickettsiae and may play a role in resistance. Furthermore, it would appear that the Ia-positive macrophage is a factor in acquired immunological resistance to reinfection.

Role of macrophages in innate and acquired host resistance to experimental scrub typhus infection of inbred mice

Mechanisms of innate resistance to infection with the Gilliam strain of Rickettsia tsutsugamushi were examined using congenic strains of mice resistant (C3H/RV) or susceptible (C3H/He) to intraperitoneal infection. Both strains of mice were resistant to infection with 1,000 50% mouse lethal doses of rickettsiae if given intravenously. In both systems rickettsial replication occurred after intravenous infection, as evidenced by an increase in rickettsial numbers in the spleens of infected animals, followed by a decrease in rickettsiae to low levels by day 14 postinfection. Administration of the antimacrophage agents silica and carrageenan to C3H/He mice intravenously rendered these animals susceptible to lethal infection. Neither irradiation nor silica given individually rendered C3H/RV mice susceptible to intravenous infection. However, if silica and irradiation were given together, a lethal infection occurred after intravenous infection. C3H/RV mice became susceptible to lethal infection after sublethal doses of irradiation only if they were infected intraperitoneally. Administration of silica or carrageenan had no effect on the outcome of intraperitoneal infection of these mice with Gilliam rickettsiae. These data suggest that both strains of mice share innate resistance mechanisms to intravenous infection that consist of fixed macrophages. Resistance of C3H/RV mice to intraperitoneal infection, in contrast, apparently was dependent only on an irradiation-sensitive process.

Serological analysis of Rickettsia tsutsugamushi isolates from North Queensland

Fifty-two Rickettsia tsutsugamushi isolates from humans, rodents and chiggers in North Queensland were serologically characterized by the direct immunofluorescence test. A majority (71%) of the isolates was a mixture of two or more strains. The most frequently detected strains in the 52 isolates were TA716 (84%), TA763 (42%), TA686 (33%), and Karp (31%). The Gilliam strain was detected in only 4% of the isolates.

Scrub typhus 1980

Scrub typhus is a widespread and at times serious infection in Asia. If results from central Malaysia can be applied, it appears to be economically important. Diagnosis is often difficult and treatment prone to fail if short courses of antibiotics are used. Prophylaxis is the key area of research with the development of a vaccine being the ultimate goal.

Intracellular localization of Rickettsia tsutsugamushi in polymorphonuclear leukocytes

Rickettsia tsutsugamushi (Gilliam strain) was serially propagated in BHK-21 cell cultures and incubated with guinea pig peritoneal polymorphonuclear leukocytes to study the ultrastructural features of rickettsial uptake and entry into the leukocytes. Significant numbers of rickettsiae were phagocytized selectively by these leukocytes within 30 min. About one-half of these rickettsiae remained sequestered in phagosomes but the other one-half were free from the phagosome and localized directly in the polymorphonuclear leukocyte cytoplasm. Various stages of rickettsial release from the phagosomes were observed. Once free within the polymorphonuclear leukocyte cytoplasm, the rickettsiae were preferentially localized in the glycogen-packed areas which are devoid of lysosomes and other cytoplasmic organelles. This study indicates that rickettsiae phagocytized by polymorphonuclear leukocytes can escape from the phagosome into the cytoplasm.

Early detection of Rickettsia tsutsugamushi in peripheral monocyte cultures derived from experimentally infected monkeys and dogs

Rickettsia tsutsugamushi organisms were identified in Giemsa and fluorescent antibody stained monocyte cell cultures derived from experimentally infected monkeys and dogs. The identification of organisms in monocyte cell cultures compared favorably with the standard technique of mouse inoculation.

Scrub typhus infection in rats in four habitats in Peninsular Malaysia

Rickettsia tsutsugamushi isolations were attempted from blood samples obtained from rats captured in four adjacent habitats near Kuala Lumpur, Malaysia. Antibody surveys were also made. Rickettsial infections were most frequent in rats captured in the forest and in lalang grass (Imperata cylindrica) and least frequent in the most extensively disturbed habitat, an Orang Asli (aborigine) village. Forest rats such as Rattus sabanus (31%), as well as rats in the subgenus R. (Rattus), i.e. R. tiomanicus (26%) and R. argentiventer (35%) had frequent active infections. The house rat R. exulans had less frequent infections (15%). Frequency of antibody occurrence followed a similar pattern. No marked seasonal differences in the frequency of infections could be detected during the 18-month study.

Clinical response of silvered leaf monkeys (Presbytis cristatus) to infection with strains of Rickettsia tsutsugamushi virulent and avirulent for mice

Silvered leaf monkeys (Presbytis cristatus) inoculated with avirulent strains of Rickettsia tsutsugamushi showed little or no signs of disease, whereas those inoculated with moderately or fully virulent strains developed severe disease. Infection with the virulent strains produced early leukocytosis followed by leukopenia and significant decreases in packed-cell volumes. In animals infected with avirulent strains, these parameters were normal throughout the experimental period.

[Peritoneal reaction to infection with tsutsugamushi rickettsia in mice with different sensitivity to the agent]

Infection of white random-bred mice and C57B1(6) mice with a culture of R. tsutsugamushi demonstrated that white mice were highly susceptible to the infection which ended in death of the animals and accumulation of rickettsia in the body and necrotization of cell elements of the exudate. Mice of C57B1(6) strain developed acymptomatic infection, rickettsia did not multiply in the peritoneal cavity and exudate cells did not undergo necribiosis. The mechanism of resistance of cells of these mice to the agent requires a further study.

Different allotypic susceptibility of mice to Rickett-sia tsutsugamushi

Some lines of mice and random-bred mice show different susceptibility to infection with Rickettsia tsutsugamushi, displayed mainly in the development of overt infection. The latter is most markedly manifested in random-bred and Swiss mice, causing high death rates and massive accumulation of rickettsiae in the peritoneum. Black mice respond to inoculation with asymptomatic infection with no microscopically detectable rickettsiae. The infection is accompanied in either case by immunological response and persistence of the agent in mice. One of the mechanisms of resistance to R. tsutsugamushi in some mouse lines is due to phagocytosis at the inoculation site of the main mass of rickettsiae by macrophages which digest the agent and retain their viability.