Legionellosis pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Legionella is usually 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 usually invades the host cells and replicates intracellularly. Legionella is internalized using pseudopods and protects itself in a membrane-bound vacuole that does not fuse with lysosomes.
Pathophysiology
Transmission
- Legionella is usually 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. longbeachae is thought to be transmitted by compost during gardening activity.[1]
- Legionella is not transmitted from one person to another person.
- Healthcare-associated transmission of Legionella is common.
Pathogenesis
- Legionella invades the host cells and replicates intracellularly.
- 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
- ↑ Graham FF, White PS, Harte DJ, Kingham SP (2012). "Changing epidemiological trends of legionellosis in New Zealand, 1979-2009". Epidemiol Infect. 140 (8): 1481–96. doi:10.1017/S0950268811000975. PMID 21943591.