Pathogenesis Legionella

1 pathogenesis

1.1 sources of legionella
1.2 airborne transmission cooling towers
1.3 vaccine research

pathogenesis

a legionella pneumophila bacterium (green) caught vermamoeba vermiformis amoeba (orange)

in natural environment, legionella lives within amoebae such acanthamoeba spp., naegleria spp., , vermamoeba vermiformis, or other protozoa such tetrahymena pyriformis.

upon inhalation, bacteria can infect alveolar macrophages, bacteria can replicate. results in legionnaires disease , less severe illness pontiac fever. legionella transmission via inhalation of water droplets contaminated source has allowed organism grow , spread (e.g., cooling towers). transmission occurs less commonly via aspiration of drinking water infected source. person-to-person transmission has not been demonstrated; though, possible in rare cases.

once inside host, incubation period may 2 weeks. prodromal symptoms flu-like, including fever, chills, , dry cough. advanced stages of disease cause problems gastrointestinal tract , nervous system , lead diarrhea , nausea. other advanced symptoms of pneumonia may present. however, disease not threat healthy individuals, , tends lead severe symptoms more in immunocompromised hosts , elderly. consequently, water systems of hospitals , nursing homes should periodically monitored. texas department of state health services provides recommendations hospitals detect , prevent spread of hospital acquired disease due legionella infection. according infection control , hospital epidemiology, hospital-acquired legionella pneumonia has fatality rate of 28%, , source water distribution system.

legionella species typically exist in nature @ low concentrations, in groundwater, lakes, , streams. reproduce after entering man-made equipment, given right environmental conditions. in united states, disease affects between 8,000 , 18,000 individuals year.

sources of legionella

documented sources include cooling towers, swimming pools (especially in scandinavian countries), domestic water systems , showers, ice-making machines, refrigerated cabinets, whirlpool spas, hot springs, fountains, dental equipment, soil, automobile windshield washer fluid, , industrial coolant.

airborne transmission cooling towers

the largest , common source of legionnaires disease outbreaks cooling towers (heat rejection equipment used in air conditioning , industrial cooling water systems) because of risk widespread circulation. many governmental agencies, cooling tower manufacturers, , industrial trade organisations have developed design , maintenance guidelines controlling growth , proliferation of legionella within cooling towers.

research in journal of infectious diseases (2006) provided evidence l. pneumophila, causative agent of legionnaires disease, can travel @ least 6 km source airborne spread. believed transmission of bacterium restricted shorter distances. team of french scientists reviewed details of epidemic of legionnaires disease took place in pas-de-calais, northern france, in 2003–2004. of 86 confirmed cases during outbreak, 18 resulted in death. source of infection identified cooling tower in petrochemical plant, , analysis of affected in outbreak revealed infected people lived far 6–7 km plant.

vaccine research

no vaccine available legionellosis, , antibiotic prophylaxis not effective. vaccination studies using heat-killed or acetone-killed cells have been carried out in guinea pigs, given legionella intraperitoneally or aerosol. both vaccines shown give moderately high levels of protection. protection dose-dependent , correlated antibody levels measured enzyme-linked immunosorbent assay outer membrane antigen , indirect immunofluorescence heat-killed cells. however, licensed vaccine people in still many years away.