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Erythrocyte-aggregating relapsing fever spirochete Borrelia crocidurae induces formation of microemboli
A Shamaei-Tousi1, P Martin, A Bergh
1Department of Microbiology, Umeâ University, Umeâ, Sweden.
Abstract:
The African relapsing fever spirochete Borrelia crocidurae forms aggregates with erythrocytes, resulting in a delayed immune response. Mice were infected with B. crocidurae and monitored during 50 days after infection. Spirochetes were observed extravascularly at day 2 after infection. Two days later, inflammatory responses, cell death, and tissue damage were evident. The pathologic responses in lungs and kidneys were similar, whereas the symptoms in the brains were delayed, with a less pronounced inflammatory response. Microemboli were found in the blood vessels, possibly a result of the erythrocyte aggregation. The B. crocidurae invasion emerged more rapidly than has been described for Lyme disease-causing Borrelia species. In addition to erythrocyte rosetting, the presence of extravascular B. crocidurae indicates a novel route for these bacteria to propagate and cause damage in the mammalian host. The histopathologic findings in this study may explain the clinical manifestations of human relapsing fever.
Insights
African relapsing fever spirochete Borrelia crocidurae rapidly invades hosts, forming erythrocyte aggregates and causing tissue damage. Extravascular spread offers a novel bacterial propagation route, potentially explaining human relapsing fever symptoms.
Area of Science:
- Microbiology
- Immunology
- Pathology
Background:
- Borrelia crocidurae, the African relapsing fever spirochete, is known to aggregate with erythrocytes.
- This aggregation is associated with a delayed immune response in the host.
Purpose of the Study:
- To investigate the pathogenic mechanisms and host-pathogen interactions of Borrelia crocidurae infection in a murine model.
- To elucidate the timeline of spirochetal invasion, dissemination, and resulting pathology.
Main Methods:
- Infection of mice with Borrelia crocidurae.
- Monitoring of infected mice over 50 days post-infection.
- Histopathological examination of tissues (lungs, kidneys, brain) and blood vessels.
Main Results:
- Spirochetes were observed extravascularly as early as day 2 post-infection.
- Inflammatory responses, cell death, and tissue damage were evident by day 4.
- Pathology in lungs and kidneys was similar; brain involvement showed delayed and less pronounced inflammation.
- Microemboli were observed in blood vessels, linked to erythrocyte aggregation.
- Borrelia crocidurae invasion was more rapid than observed for Lyme disease Borrelia species.
Conclusions:
- Borrelia crocidurae exhibits rapid invasion and extravascular dissemination, representing a novel pathogenic route.
- Erythrocyte aggregation and extravascular spread contribute to spirochetal propagation and host damage.
- The observed histopathological findings provide insights into the clinical manifestations of human relapsing fever.