Legionellosis pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Ogechukwu Hannah Nnabude, MD
Overview
Legionella is often transmitted by aerosolized droplets produced from contaminated 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 acquired by inhaling droplets from contaminated water sources such as faucets, showers, humidifiers, whirlpool spa, river, cruise ships, cooling towers, air conditioners, water supply systems [1]. L. longbeachae is thought to be transmitted by compost during gardening activity[2]. However, it has also been seen in industrial coolers [3].
- Although is is believed that Legionella is not transmitted from one person to another person [4], there have been reports of person to person transmission [5].
- Healthcare-associated transmission of Legionella is common and has a higher mortality rate.
Pathogenesis
- Legionella are able to live within amoebic cells. Free-living amoebae may be responsible for enabling Legionella to better survive environmental hazards, adapt to living within macrophages, and may be a significant reservoir of Legionella. These amoebae may assist Legionella to remain undetected within the human environments [6].
- 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
- ↑ Prussin AJ, Schwake DO, Marr LC (2017). "Ten Questions Concerning the Aerosolization and Transmission of Legionella in the Built Environment". Build Environ. 123: 684–695. doi:10.1016/j.buildenv.2017.06.024. PMC 5665586. PMID 29104349.
- ↑ 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.
- ↑ Thornley CN, Harte DJ, Weir RP, Allen LJ, Knightbridge KJ, Wood PRT (2017). "Legionella longbeachae detected in an industrial cooling tower linked to a legionellosis outbreak, New Zealand, 2015; possible waterborne transmission?". Epidemiol Infect. 145 (11): 2382–2389. doi:10.1017/S0950268817001170. PMID 28625225.
- ↑ Boamah DK, Zhou G, Ensminger AW, O'Connor TJ (2017). "From Many Hosts, One Accidental Pathogen: The Diverse Protozoan Hosts of Legionella". Front Cell Infect Microbiol. 7: 477. doi:10.3389/fcimb.2017.00477. PMC 5714891. PMID 29250488.
- ↑ Correia AM, Ferreira JS, Borges V, Nunes A, Gomes B, Capucho R; et al. (2016). "Probable Person-to-Person Transmission of Legionnaires' Disease". N Engl J Med. 374 (5): 497–8. doi:10.1056/NEJMc1505356. PMID 26840151.
- ↑ Segovia Hernández M (2005). "[The journey of Legionella pneumophila from amoebae to macrophage. Reflections on the largest outbreak of legionnaire's disease]". An R Acad Nac Med (Madr). 122 (3): 489–98, discussion 498-504. PMID 16524240.