June 6, 2012

expert reaction to outbreak of Legionnaires’ disease in Scotland

An outbreak of Legionnaires’ disease in Edinburgh, suspected to have originated from industrial cooling towers, had led to one death and a steadily increasing number of suspected cases.

Gad Frankel, Professor of Molecular Pathogenesis at Imperial College London, said:

“The bacterial pathogen Legionella pneumophila is the causative agent of Legionnaires’ disease, which is an acute form of pneumonia elicited upon inhalation of Legionella contaminated aerosols (droplets in the air). Legionnaire’s is not transmitted from person to person, but rather sporadic cases and outbreaks are often linked to human-made aquatic environments (e.g. air-conditioning water systems and swimming pools) where L. pneumophila resides in amoeba and biological films. The elderly and immunocompromised are most susceptible to infection, making Legionella a major health risk in hospitals and communal facilities (e.g. nursing homes). The global demographic change towards an older population most probably accounts for the increased incidence of Legionella infections during the last 30 years, a trend that is likely to intensify in the future.

“The ability of Legionella to survive and replicate in amoebae has equipped it with the capacity to replicate within human cells. If the bacteria are inhaled into the lungs, immune cells called macrophages engulf them as though to destroy them. However Legionella are able to survive inside macrophages where they replicate within a vacuole that evades the cellular degradation pathway. Evasion of degradation pathways and Legionella replication is dependent on the use of a molecular syringe to inject bacterial proteins, known as effectors, into the cytosol of the human cells. Legionella injects nearly 300 such effectors, which scientists such as ourselves are working on in order to understand how Legionella causes disease and to find ways to fight the infection.”