Introduction
Legionella pneumophila
The
bacterium L. pneumophila was first identified in 1977, as the cause of an
outbreak of severe pneumonia in a convention Centre in the USA in 1976. The
most common form of transmission of Legionella is inhalation of contaminated
aerosols produced in conjunction with water sprays. Infection can also occur by
aspiration of contaminated water or ice, particularly in susceptible hospital
patients. Legionnaires’ disease has an
incubation period of 2 to 10 days. Death occurs through progressive pneumonia
with respiratory failure and/or shock and multi-organ failure. Legionellosis’ varies in severity
from a mild febrile illness to a serious and sometimes fatal form of pneumonia.
The infective dose is unknown but can be assumed to be low for susceptible
people. The likelihood of illness depends on the concentrations of Legionella
in the water source, the production and dissemination of aerosols, host factors
such as age and pre-existing health conditions, and the virulence of the
particular strain of Legionella. Most infections do not cause illness.
What is legionella pneumophila?
Legionella
pneumophila is a Gram-negative bacterium that causes a serious type
of pneumonia known as Legionnaires’ disease,
and a milder illness called Pontiac fever. It was
first discovered in 1976, after an outbreak
at an American Legion convention in Philadelphia (hence the name Legionella). Legionella pneumophila is a water-associated bacterium that infects humans
through inhaled contaminated aerosols, causing pneumonia (Legionnaires’
disease) or a mild flu-like illness (Pontiac fever). The pathogenesis of
Legionella infections begins with a supply of water containing virulent
bacteria and with a means for dissemination to humans. Legionella is not a
member of the bacterial flora of humans.
Structure of Legionella pneumophila
1. Cell Wall:
The cell
wall of Legionella pneumophila is Gram-negative, with a thin peptidoglycan layer, an
outer LPS-rich membrane, and a periplasmic space. Its special structure allows
it to resist immune attack, adapt to water environments, and survive inside
host cells. Gram-negative bacterium with a thin peptidoglycan layer.
2. Motility Structures:
The
motility structures of legionella pneumophila is Polar flagella provide motility. Pili
(fimbriae) help in attachment to surfaces and host cells.
3. Intracellular Adaptation:
Can survive and multiply inside macrophages and amoebae. Forms a Legionella-containing vacuole (LCV) to avoid
destruction by lysosomes.
4. Type IV Secretion System (Dot/Icm system):
Specialized
secretion system that injects effector proteins into host cells. Critical for
survival and replication inside macrophages and amoebae.
Haw to transmission Legionella pneumophila
The most
common form of transmission of Legionella is inhalation of contaminated
aerosols from contaminated water. Sources of aerosols that have been linked
with transmission of Legionella include air conditioning cooling towers, hot
and cold water systems. To date, there has been no reported direct
human-to-human transmission.
Types of Legionella infection
Legionella
infection, or legionellosis, refers to two different, but related, conditions: Legionnaires’
disease and Pontiac fever. Both of these conditions are caused by the
Legionella bacteria. However, Legionnaires’ disease is the more serious of the
two. Legionnaires’ disease is characterized by the presence of pneumonia,
whereas Pontiac fever is non-pneumonic.
1. Legionnaires’ disease:
Legionella
infections are caused bacteria and most often affect the lubgs, causing
pneumonia and flu-like symptoms. People have fever, chills, and muscle aches,
and breathing may be difficult and painful. The infection is often acquired by
inhaling contaminated water droplets, as may be sprayed from shower heads or
air-conditioning system. Legionnaire’s disease is not spread from person to
person.
2. Pontiac fever:
Pontiac fever is a mild, flu-like illness caused by the Legionella
bacteria. It is one of two diseases collectively known as legionellosis, the
other being the more severe Legionnaires' disease.
Symptoms of Legionnaires’ disease
Legionnaires’
disease is a more severe illness, and symptoms tend to appear between 2 to 10 days
after becoming infected. Respiratory symptoms are usually a key feature
of Legionnaires’ disease. Respiratory symptoms may include: A cough which is
dry at first, but begins to produce mucus and phlegm as the condition
progresses. This is the most common respiratory symptom of Legionnaires’
disease. Shortness of breath, Chest pain and Bloody phlegm. Flu-like symptoms
are also a common sign of Legionnaires’ disease and can include: Fever, Chills,
Muscle aches, Headache, Fatigue, and Weakness.
Haw to diagnoses legionella pneumophila
The most
commonly used laboratory test for diagnosis of Legionnaires' disease is the
urinary antigen test (UAT), which detects a molecule of the Legionella
bacterium in urine. A definitive diagnosis of Legionnaires’ disease can
typically be made following a positive laboratory test result, usually on a
sample of phlegm, urine or blood. The main tests used to detect Legionella
infection include: Polymerase chain reaction (PCR), Urinary antigen testing and
Culture testing.
How to treatment
Legionnaires' disease is treated with antibiotics. The sooner therapy is started, the less likely the chance of developing serious complications. In many cases, treatment requires hospitalization. Pontiac fever goes away on its own without treatment
Haw to prevention legionella pneumophila
Control Legionella
by cleaning water systems, controlling temperature, disinfecting water, and
regular monitoring. Personal prevention
(for individuals) is limited, but institutions (hospitals, hotels, industries)
must ensure safe water systems. Since the bacteria live in water
systems, prevention mainly focuses on controlling and
disinfecting water sources. Since this bacterium naturally lives in freshwater environments but causes outbreaks when
it grows in man-made water systems,
prevention focuses on environmental control measures
rather than person-to-person protection.
Conclusion
Legionella
pneumophila
is a waterborne bacterium that causes Legionnaires’ disease, a severe form of
pneumonia. Early detection, proper water system maintenance, and effective
antibiotic treatment are key to prevention and control.
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