Legionellosis pathophysiology: Difference between revisions

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Revision as of 16:26, 15 January 2016

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

Overview

Legionella is transmitted by aerosol droplets when individuals breathe in contaminated mist or vapor (e.g. whirlpool spa, river, cruise ships, cooling towers, air conditioners, water supply systems). L. pneumophila is an intracellular parasite that can invade and replicate inside amoebae and, in humans, in macrophages. Legionella is internalized using pseudopods and protects itself in a membrane-bound vacuole that does not fuse with lysosomes.

Transmission

Legionella is transmitted by aerosol droplets when individuals breathe in contaminated mist or vapor (e.g. whirlpool spa, river, cruise ships, cooling towers, air conditioners, water supply systems)
Legionella is not transmitted from one person to another person.
Healthcare-associated transmission of Legionella is common.

Pathogenesis

Legionella is an intracellular parasite that can invade and replicate inside amoebae and, in humans, in macrophages.
The internalisation of the bacteria can be enhanced by the presence of antibody and complement but is not absolutely required.
A pseudopod coils around the bacterium in this unique form of phagocytosis.
Once internalised, the bacteria surround themselves in a membrane-bound vacuole that does not fuse with lysosomes that would otherwise degrade the bacteria. In this protected compartment the bacteria multiply.
The bacteria use a Type IVB Secretion System known as Icm/Dot to inject effector proteins into the host.
These effectors are involved in increasing the bacteria's ability to survive inside the host cell. They also secrete a 39kDa metalloprotease into culture fluids, which is cytotoxic for some cultured tissue culture cells.

References

Template:WikiDoc Sources

@@ Line 5: / Line 5: @@
 ==Overview==
-==Pathophysiology==
+''Legionella'' is transmitted by aerosol droplets when individuals breathe in contaminated mist or vapor (e.g. whirlpool spa, river, cruise ships, cooling towers, air conditioners, water supply systems). ''L. pneumophila'' is an intracellular parasite that can invade and replicate inside [[amoebae]] and, in humans, in [[macrophage]]s. ''Legionella'' is internalized using pseudopods and protects itself in a membrane-bound vacuole that does not fuse with lysosomes.
-''Legionella pneumophila'' and other Legionella species. At least 46 species and 70 serogroups have been identified. ''L.pneumophila'', an ubiquitous aquatic organism that thrives in warm environments (32°- 45°C) causes over 90% of LD in the United States. The disease has two distinct forms:
-*Legionnaires' disease, the more severe form of infection which includes pneumonia, and
-*Pontiac fever, a milder illness.
-*Pontiac fever and Legionnaires’ disease may also be called “Legionellosis” (LEE-juh-nuh-low-sis) separately or together.
 ===Transmission===
+*''Legionella'' is transmitted by aerosol droplets when individuals breathe in contaminated mist or vapor (e.g. whirlpool spa, river, cruise ships, cooling towers, air conditioners, water supply systems)
+*''Legionella is not transmitted from one person to another person.
+* Healthcare-associated transmission of ''Legionella'' is common.
-People get Legionnaires' disease when they breathe in a mist or vapor (small droplets of water in the air) that has been contaminated with the bacteria. One example might be from breathing in the steam from a whirlpool spa that has not been properly cleaned and disinfected.
+==Pathogenesis==
+*''Legionella'' is an intracellular parasite that can invade and replicate inside [[amoebae]] and, in humans, in [[macrophage]]s.
-The bacteria are NOT spread from one person to another person.
+*The internalisation of the bacteria can be enhanced by the presence of [[antibody]] and [[Complement system|complement]] but is not absolutely required.
+*A [[pseudopod]] coils around the bacterium in this unique form of [[phagocytosis]].
-Outbreaks are when two or more people become ill in the same place at about the same time, such as patients in hospitals. Hospital buildings have complex water systems, and many people in hospitals already have illnesses that increase their risk for Legionella infection.
+*Once internalised, the bacteria surround themselves in a membrane-bound vacuole that does not fuse with lysosomes that would otherwise degrade the bacteria. In this protected compartment the bacteria multiply.
+*The bacteria use a Type IVB Secretion System known as Icm/Dot to inject effector proteins into the host.
-Other outbreaks have been linked to aerosol sources in the community, or with cruise ships and hotels, with the most likely sources being whirlpool spas, cooling towers (air-conditioning units from large buildings), and water used for drinking and bathing.
+*These effectors are involved in increasing the bacteria's ability to survive inside the host cell. They also secrete a 39kDa [[metalloprotease]] into culture fluids, which is [[cytotoxic]] for some cultured tissue culture cells.
-===Infections===
-'''Intestinal Infections''': These may only occur as part of [[respiratory infection]]s, and where gastrointestinal symptoms have on occasion been described.
-'''Extraintestinal Infections''': ''L. pneumophila'' is specifically considered as a [[pathogen]] of the [[respiratory tract]], where it is a cause of atypical pneumonia, also known as Legionnaires' disease. Other infections have also been reported, including [[haemodialysis fistulae]], [[pericarditis]] and wound and skin infections. [[Bacteraemia]] is often associated with Legionnaires' disease.
-'''Infections of [[Protozoa]]''': Protozoa such as ''Harmanella vermiformis'' and related protozoa have been shown to be able to support the growth of ''L. pneumophila'' in tap water. Also ''[[Acanthamoeba]]'', ''Naegleria'' and ''[[Tetrahymena]]'' can be infected by ''L. pneumophila''. This pathway may be how these organisms survive in the environment.
-==Pathology==
-Legionella pneumophila are [[Gram-negative]] bacteria. Using H&E stain, these organisms, if present in the specimen, would stain a pink or red color.  The [[alveola]]r spaces are congested with a [[leukocytic]] [[infiltrate]] in response to the infection.
-==Sources==
-* CDC Legionellosis [http://wwwnc.cdc.gov/travel/yellowbook/2012/chapter-3-infectious-diseases-related-to-travel/legionellosis-legionnaires-disease-and-pontiac-fever.htm][http://www.cdc.gov/legionella/patient_facts.htm]
 ==References==
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 [[Category:Bacterial diseases]]
 [[Category:Medical disasters]]
-[[Category:Needs overview]]