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Chapter: Microbiology and Immunology: Bacteriology: Bordetella and Francisella

Pathogenesis and Immunity - Francisella tularensis

F. tularensis is one of the most infectious bacteria known. It isclassified as a category A agent because of (i) its high infectivity, (ii) ease of dissemination, and (iii) ability to cause substantial illness and death.

Pathogenesis and Immunity

F. tularensis is one of the most infectious bacteria known. It isclassified as a category A agent because of (i) its high infectivity, (ii) ease of dissemination, and (iii) ability to cause substantial illness and death. Humans become infected after introduction of the bacteria by intradermal injection, inhalation, or oral ingestion. Clinical manifestations of disease depend on the mode of infection.

Intradermal injection or inhalations of 10–50 bacilli are required to cause disease. Nearly, 100 million bacteria are required to cause disease on oral ingestion. F. tularensis is an intracellular parasite. In infected animals, the bacteria are found in large numbers in the reticuloendothelial cells of spleen, liver, etc. These bacteria remain viable for a lon-ger period in macrophages of the reticuloendothelial system, because the organisms inhibit phagosome–lysosome fusion. Like other Gram-negative bacilli, F. tularensis has endotoxin, but is relatively less biologically active than that found in Escherichiacoli and other Gram-negative bacilli.

Capsulated strains of F. tularensis are pathogenic, while non-capsulated strains are nonpathogenic.


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Microbiology and Immunology: Bacteriology: Bordetella and Francisella : Pathogenesis and Immunity - Francisella tularensis |


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