Legionnaires disease: historical perspective

Abstract

In the summer of 1976, a mysterious epidemic of fatal respiratory disease in Philadelphia launched an intensive investigation that resulted in the definition of a new family of pathogenic bacteria, the Legionellaceae. In retrospect, members of the family had been isolated from clinical specimens as early as 1943. Unsolved epidemics of acute respiratory disease dating to the 1950s were subsequently attributed to the newly described pathogens. In the intervening years, the Legionellaceae have been firmly established as important causes of sporadic and epidemic respiratory disease. The sources of the infecting bacteria are environmental, and geographic variation in the frequency of infection has been documented. Airborne dissemination of bacteria from cooling towers and evaporative condensers has been responsible for some epidemics, but potable water systems are perhaps more important sources. The mode of transmission from drinking water is unclear. The Legionellaceae are gram-negative, facultative, intracellular pathogens. The resident alveolar macrophage, usually an effective antibacterial defense, is the primary site of growth. Cell-mediated immunity appears to be the most important immunological defense; the role of humoral immunity is less clear. Erythromycin remains the antibiotic of choice for therapy of infected patients, but identification and eradication of environmental sources are also essential for the control of infection.

Intrazelluläres Überleben und Expression der Virulenzdeterminanten von Legionella pneumophila

“…It is also a facultative intracellular pathogen that invades and grows ~n human alveolar macrophages leading to acute bronchopneumonia referred to as legionellosis [1,2]. In addition, L. pneumophila isolates are able to live and multiply within protozoan organisms such as environmental amoebae [3).…”

“…The cytopathology of lungs infected by L. pneumophila suggests involvement of extracellular proteolytic enzymes or taxins in the pathogenesis of Legionella [2,18]. In order to select cloned toxin determinants of Legionella the recombinant E. coli K-12 clones were screened on blood agar plates containing human and canine erythrocytes.…”

Legionella pneumophila mip gene potentiates intracellular infection of protozoa and human macrophages

“…Strains of this bacterium are ubiquitous within aquatic environments and can infect humans following the inhalation of contaminated aerosols generated by air-conditioners, fountains, and other man-made devices (1,3). Within the lower respiratory tract, L. pneumophila invades and proliferates to large numbers within alveolar macrophages (1).…”

“…Strains of this bacterium are ubiquitous within aquatic environments and can infect humans following the inhalation of contaminated aerosols generated by air-conditioners, fountains, and other man-made devices (1,3). Within the lower respiratory tract, L. pneumophila invades and proliferates to large numbers within alveolar macrophages (1). In the absence of an adequate cell-mediated immune response, the rapid intracellular replication of legionellae and the release of tissue-destructive substances from either the bacteria, the host, or both result in acute bronchopneumonia (2,4).…”

“…Legionella pneumophila, the etiologic agent of Legionnaires' disease, represents a major environmental pathogen (1,2). Strains of this bacterium are ubiquitous within aquatic environments and can infect humans following the inhalation of contaminated aerosols generated by air-conditioners, fountains, and other man-made devices (1,3).…”