Tularemia pathophysiology: Difference between revisions

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Revision as of 14:39, 16 March 2016

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Tularemia is caused by the bacterium Francisella tularensis found in animals (especially rodents, rabbits, and hares). Francisella tularensis (F. tularensis) is a tiny, pleomorphic, nonmotile, gram-negative, facultative intracellular coccobacillus (0.2 to 0.5 μm by 0.7 to 1.0 μm). It is a fastidious organism and may require cysteine supplementation for good growth on general laboratory media.

Pathogenesis

Transmission

Mechanism of infection

Francisella tularensis is one of the most infective bacteria known; fewer than ten organisms can cause disease leading to severe illness.
The bacteria penetrate into the body through damaged skin and mucous membranes, or through inhalation.
Humans are most often infected by tick bite or through handling an infected animal. Ingesting infected water, soil, or food can also cause infection.
Tularemia can also be acquired by inhalation; hunters are at a higher risk for this disease because of the potential of inhaling the bacteria during the skinning process.
Tularemia is not spread directly from person to person.
Francisella tularensis is an intracellular bacterium, meaning that it is able to live as a parasite within host cells.
It primarily infects macrophages, a type of white blood cell. It is thus able to evade the immune system.
The course of disease involves spread of the organism to multiple organ systems, including the lungs, liver, spleen, and lymphatic system.
The course of disease is similar regardless of the route of exposure. Mortality in untreated (pre-antibiotic-era) patients has been as high as 50% in the pneumoniac and typhoidal forms of the disease, which however account for less than 10% of cases.^[1]
Overall mortality was 7% for untreated cases, and the disease responds well to antibiotics with a fatality rate of about 2%.
The exact cause of death is unclear, but it is thought be a combination of multiple organ system failures.

References

↑ http://www.cidrap.umn.edu/cidrap/content/bt/tularemia/biofacts/tularemiafactsheet.html#_Overview_1

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[1] ttp://www.cidrap.umn.edu/cidrap/content/bt/tularemia/biofacts/tularemiafactsheet.html#_Overview_1

[1]

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 ==Pathogenesis==
 ===Transmission===
-*[[Bacteremia]] may be common in the early phase of infection.
-*The initial tissue reaction to infection is a focal, intensely suppurative [[necrosis]] consisting largely of accumulations of polymorphonuclear [[leukocyte]]s, followed by invasion of [[macrophage]]s, [[epithelioid]] cells, and [[lymphocytes]].
-*Suppurative lesions become [[granulomatous]], and [[histopathological]] examination of the [[granulomas]] shows a central necrotic, sometimes caseating, zone surrounded by a layer of epithelioid cells, [[multinucleated giant cell]]s, and [[fibroblast]]s in a radial arrangement, typical of other granulomatous conditions such as [[tuberculosis]] and [[sarcoidosis]].
-*Humans with inhalational exposures also develop hemorrhagic [[inflammation]] of the airways early in the course of illness, which may progress to [[bronchopneumonia]].
-*Histopathological examination of the lungs shows alveolar spaces filled with an exudate of mononuclear cells.
-*[[Pleuritis]] with adhesions and effusion and [[hilar]] [[lymphadenopathy]] are common in radiological and pathological findings.
-*Primary clinical forms vary in severity and presentation according to virulence of the infecting organism, dose, and site of inoculum.
-*The onset of tularemia is usually abrupt, with [[fever]] (38oC–40oC), [[headache]], [[chills]] and rigors, generalized body aches (often prominent in the low back), [[coryza]], and sore throat. A pulse-temperature dissociation has been noted in as many as 42% of patients. A dry or slightly productive cough and substernal pain or tightness frequently occur with or without objective signs of [[pneumonia]], such as purulent sputum, [[dyspnea]], [[tachypnea]], pleuritic pain, or [[hemoptysis]]. [[Nausea]], [[vomiting]], and [[diarrhea]] may occur.
-*Sweats, [[fever]], [[chills]], progressive weakness, [[malaise]], [[anorexia]], and [[weight loss]] characterize the continuing illness.
-*In general, tularemia would be expected to have a slower progression of illness and a lower case-fatality rate than either inhalational [[plague]] or [[anthrax]]. Milder forms of inhalational tularemia would be indistinguishable from [[Q fever]]; another potential bioterrorism agent; establishing a diagnosis of either would be problematic without reference laboratory testing.<ref>http://www.bt.cdc.gov/agent/tularemia/facts.asp</ref><ref>http://www.asm.org/ASM/files/LEFTMARGINHEADERLIST/DOWNLOADFILENAME/0000000525/tularemiaprotocol%5B1%5D.pdf</ref><ref>http://www.bt.cdc.gov/agent/tularemia/tularemia-biological-weapon-abstract.asp#2
-</ref>
 ===Mechanism of infection===
 * ''[[Francisella|Francisella tularensis]]'' is one of the most infective bacteria known; fewer than ten organisms can cause disease leading to severe illness.