L. pneumophila is still unknown. The disease was discovered
in 1976 during the annual meeting of veterans of the American Legion in Philadelphia (USA). Thirty people died of the
disease, and since the reporting is mandatory, there are more
and more reported cases (2,000 to 3,000 cases in France in
1995 and from 8,000 to 18,000 cases in the United States each
year). The main reservoir is freshwater, including water
relatively warm (35–45
C) and stagnant encountered in the
natural environment, sanitation, and air conditioning. Pathogen transmission is by aerosolization from these reservoirs.
The incubation period is 2–10 days depending on the dose
ingested. The pathogen can survive long enough in the water,
but its life cycle is still poorly understood. Interactions with
some aquatic protozoa are particularly important. This organism is able to grow and protect in the interior of some
amoebae* and stay well protected inside the cysts*.
Legionella are highly resistant to conventional disinfection
treatments such as chlorination (Box 15.1).
15.2.3 Particular Case of Toxic
Cyanobacteria (Box 15.2)
Cyanobacteria (formerly blue-green algae) contain pigments
such as chlorophylls, carotenoids, and phycobilins, giving
them a blue-green color characteristic of the group (cf. Sect.
6.2.2; Figs. 6.12 and 6.13). Their size is highly variable
(1–100 μm), some cells being filamentous or colonial.
During blooms cyanobacteria can give a very characteristic
color to surface waters where they grow ranging from green
to red. Only some species produce toxins harmful to humans
and animals. Cyanobacteria can withstand very specific living conditions like those encountered in highly saline lakes
or hot springs (Box 15.2).
Box 15.1: Classification of Infectious Agents
in Risk Groups According to the World
Health Organization (WHO)
Philippe Lebaron
In many countries, infectious agents are categorized
in risk groups based on their relative individual,
collectivity, and environmental risks. The “American
Biological Safety Association” (ASBA) presents a
well-documented website on risk groups (http://
www.absa.org/riskgroups/index.html). Depending on
the country and/or organization, this classification
system might take different factors into consideration,
such as type of infectious agent (virus, bacteria, fungi,
protozoa), pathogenicity of the organism, mode of
transmission and host range, and availability of effective preventive measures (e.g., vaccines) or effective
treatment (e.g., antibiotics). Despite these regional
differences, there is a worldwide agreement on the
four risk group classification:
– Risk Group 1 (no or low individual and community
risk): A microorganism that is unlikely to cause
human disease or animal disease.
– Risk Group 2 (moderate individual risk, low community risk): A pathogen that can cause human or
animal disease but is unlikely to be a serious hazard
to laboratory workers, the community, livestock, or
the environment. Laboratory exposures may cause
serious infection, but effective treatment and
preventive measures are available and the risk of
spread of infection is limited.
(continued)
Box 15.1 (continued)
– Risk Group 3 (high individual risk, low community risk): A pathogen that usually causes serious
human or animal disease but does not ordinarily
spread from one infected individual to another.
Effective treatment and preventive measures are
available.
– Risk Group 4 (high individual and community risk):
A pathogen that usually causes serious human or
animal disease and that can be readily transmitted
from one individual to another, directly or indirectly. Effective treatment and preventive measures
are not usually available.
Box 15.2: Cyanobacteria, Environmental Pathogenic
Agents?
Jean-Franc ¸ois Humbert
Cyanobacteria have played a major role in the
evolution of the earth’s ecosystem by allowing,
through photosynthesis, the enrichment of our planet’s
atmosphere with oxygen. Currently, these microorganisms contribute to a large fraction of the primary
production in the ocean and are fundamental actors
in the marine cycles of carbon and nitrogen.
In continental aquatic ecosystems, particularly in
lentic ecosystems, cyanobacteria are involved as well
J.-F. Humbert
INRA, UMR BIOEMCO, ENS, Paris, France
(continued)
624
P. Lebaron et al.
in 1976 during the annual meeting of veterans of the American Legion in Philadelphia (USA). Thirty people died of the
disease, and since the reporting is mandatory, there are more
and more reported cases (2,000 to 3,000 cases in France in
1995 and from 8,000 to 18,000 cases in the United States each
year). The main reservoir is freshwater, including water
relatively warm (35–45
C) and stagnant encountered in the
natural environment, sanitation, and air conditioning. Pathogen transmission is by aerosolization from these reservoirs.
The incubation period is 2–10 days depending on the dose
ingested. The pathogen can survive long enough in the water,
but its life cycle is still poorly understood. Interactions with
some aquatic protozoa are particularly important. This organism is able to grow and protect in the interior of some
amoebae* and stay well protected inside the cysts*.
Legionella are highly resistant to conventional disinfection
treatments such as chlorination (Box 15.1).
15.2.3 Particular Case of Toxic
Cyanobacteria (Box 15.2)
Cyanobacteria (formerly blue-green algae) contain pigments
such as chlorophylls, carotenoids, and phycobilins, giving
them a blue-green color characteristic of the group (cf. Sect.
6.2.2; Figs. 6.12 and 6.13). Their size is highly variable
(1–100 μm), some cells being filamentous or colonial.
During blooms cyanobacteria can give a very characteristic
color to surface waters where they grow ranging from green
to red. Only some species produce toxins harmful to humans
and animals. Cyanobacteria can withstand very specific living conditions like those encountered in highly saline lakes
or hot springs (Box 15.2).
Box 15.1: Classification of Infectious Agents
in Risk Groups According to the World
Health Organization (WHO)
Philippe Lebaron
In many countries, infectious agents are categorized
in risk groups based on their relative individual,
collectivity, and environmental risks. The “American
Biological Safety Association” (ASBA) presents a
well-documented website on risk groups (http://
www.absa.org/riskgroups/index.html). Depending on
the country and/or organization, this classification
system might take different factors into consideration,
such as type of infectious agent (virus, bacteria, fungi,
protozoa), pathogenicity of the organism, mode of
transmission and host range, and availability of effective preventive measures (e.g., vaccines) or effective
treatment (e.g., antibiotics). Despite these regional
differences, there is a worldwide agreement on the
four risk group classification:
– Risk Group 1 (no or low individual and community
risk): A microorganism that is unlikely to cause
human disease or animal disease.
– Risk Group 2 (moderate individual risk, low community risk): A pathogen that can cause human or
animal disease but is unlikely to be a serious hazard
to laboratory workers, the community, livestock, or
the environment. Laboratory exposures may cause
serious infection, but effective treatment and
preventive measures are available and the risk of
spread of infection is limited.
(continued)
Box 15.1 (continued)
– Risk Group 3 (high individual risk, low community risk): A pathogen that usually causes serious
human or animal disease but does not ordinarily
spread from one infected individual to another.
Effective treatment and preventive measures are
available.
– Risk Group 4 (high individual and community risk):
A pathogen that usually causes serious human or
animal disease and that can be readily transmitted
from one individual to another, directly or indirectly. Effective treatment and preventive measures
are not usually available.
Box 15.2: Cyanobacteria, Environmental Pathogenic
Agents?
Jean-Franc ¸ois Humbert
Cyanobacteria have played a major role in the
evolution of the earth’s ecosystem by allowing,
through photosynthesis, the enrichment of our planet’s
atmosphere with oxygen. Currently, these microorganisms contribute to a large fraction of the primary
production in the ocean and are fundamental actors
in the marine cycles of carbon and nitrogen.
In continental aquatic ecosystems, particularly in
lentic ecosystems, cyanobacteria are involved as well
J.-F. Humbert
INRA, UMR BIOEMCO, ENS, Paris, France
(continued)
624
P. Lebaron et al.