Francisella: Difference between revisions
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* Overall mortality was 7% for untreated cases, and the disease responds well to antibiotics with a fatality rate of about 2%. | * 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. | * The exact cause of death is unclear, but it is thought be a combination of multiple organ system failures. | ||
== References == | == References == |
Revision as of 16:09, 16 March 2016
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Francisella is a genus of pathogenic, Gram-negative bacteria.They are small coccobacillary or rod-shaped, non motile organisms, which are also facultative intracellular parasites of macrophages.[1] Strict aerobes, Francisella colonies bear a morphological resemblance to those of the genus Brucella.[2]
Causes
Causative Agent
- The type species, F. tularensis, causes the disease tularemia or rabbit fever.[3] F. novicida and F. philomiragia (previously Yersinia philomiragia) are associated with septicemia and invasive systemic infections.
- It should be noted that the taxonomy of the genus is somewhat uncertain, especially in the case of F. novicida (may be a subspecies of F. tularensis). *In general, identification of species is accomplished by biochemical profiling or 16S rRNA sequencing.
- F. tularensis is found in widely diverse animal hosts and habitats and can be recovered from contaminated water, soil, and vegetation.
- A variety of small mammals, including voles, mice, water rats, squirrels, rabbits, and hares are natural reservoirs of infection.
- They acquire infection through tick, fly, and mosquito bites and by contact with contaminated environments.
- Epizootics with sometimes extensive die-offs of animal hosts may herald outbreaks of tularemia in humans.
- Humans can become incidentally infected through diverse environmental exposures: bites by infected arthropods; handling infectious animal tissues or fluids; direct contact with or ingestion of contaminated food, water, or soil; and inhalation of infective aerosols.
- Humans can develop severe and sometimes fatal illness, but do not transmit the disease to others.
Genomics
- Studies conducted on a strain of the Schu S4 genome report a genome size of less than 2 Mbp.
- F. tularensis is composed of a large majority of genes, unique to the species.
- Lesser amount of genes responsible for the encoding of transport and binding.
- There are few matches for genes responsible for gene regulation and energy metabolism between F. tularensis and other documented
Pathogenesis
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.[4]
- 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
- ↑ Allen LA (2003). "Mechanisms of pathogenesis: evasion of killing by polymorphonuclear leukocytes". Microbes Infect. 5 (14): 1329–35. PMID 14613776.
- ↑ Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed. ed.). McGraw Hill. pp. 488&ndash, 90. ISBN 0-8385-8529-9.
- ↑ Collins FM (1996). Pasteurella, Yersinia, and Francisella. In: Baron's Medical Microbiology (Baron S et al, eds.) (4th ed. ed.). Univ of Texas Medical Branch. ISBN 0-9631172-1-1.
- ↑ http://www.cidrap.umn.edu/cidrap/content/bt/tularemia/biofacts/tularemiafactsheet.html#_Overview_1