Transcript Environmental Health for Microbial Agents

Environmental Health for Microbial Agents
• Environmentally transmitted infectious diseases
• -Water, food, fomites, vectors and air:
– routes or pathways for for microbial exposure and transmission
routes for infectious diseases.
• -A traditional and historical concern in environmental hlth. Sci.
• Sir John Snow, cholera in London and the Broad Street pump
– A key historical event in environmental health, epidemiology, infectious
disease, water hygiene, environmental engineering and GIS: he did it
all!
• Infectious disease risks from water, poor sanitation and hygiene, food
and air are still with us.
– A large number of households in RURAL Orange County, NC lack
indoor plumbing
– they have an outdoor well and a latrine (outhouse); year: 1999.
Classes or Categories of Pathogenic Microorganisms:
The Microbial World
Viruses: smallest (0.02-0.3 µm diameter); simplest:
nucleic acid + protein coat (+ lipoprotein envelope)
Bacteria: 0.5-2.0 µm diameter; prokaryotes; cellular; simple
internal organization; binary fission.
Protozoa: most >2 µm- 2 mm; eucaryotic; uni-cellular; nonphotosynthetic; flexible cell membrane; no cell wall; wide
range of sizes and shapes; hardy cysts
Groups: flagellates, amoebae, ciliates, sporozoans
(complex life cycle) and microsporidia.
Helminths (Worms): multicellular animals; some are parasites;
eggs are small enough (25-150 µm) to pose health risks
from human and animal wastes in water.
THE MICROBIAL WORLD:
SIZES OF MICROBES
Viruses
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smallest (0.02-0.3 micrometers diameter
simplest (nucleic acid + protein coat (+ lipoprotein envelope)
spherical (icosahedral) or rod-shaped (helical)
no biological activity outside of host cells/or host organisms
– obligate intracellular parasites; recruit host cell to make new
viruses, often destroying the cell
• non-enveloped viruses are most persistent in the environment
– protein coat confers stability
• enteric viruses are most important for environmental health
– transmitted by direct and indirect contact, fecally contaminated water,
food, fomites and air.
• respiratory viruses also important
– transmitted by direct and indirect contact, air and fomites (some by
water and food, too).
ENTERIC VIRUSES: ~25-100 nm diameter
Nucleic acid + protein coat (+envelope)
Nucleic acid:
•DNA or RNA
•single or double-stranded
•1 or several segments
•Capsid (protein coat):
• multiple copies of 1 or
more proteins in an array
Envelope:
•lipid bilayer membrane +
glycoproteins)
•typically acquired from
host cell membranes
Enteroviruses:
~27-30 nm diameter; singlestranded RNA; icosahedral protein coat (capsid)
Human Rotavirus: ~75 nm diameter;
double-layered capsid; double-stranded, segmented RNA
ADENOVIRUSES: ~80 nm diameter; double-stranded
DNA; protein coat with attachment fibers
Procaryotes: Bacteria and Others
Cellular organisms
Simple internal organization
Multiply by binary fission
Diameter ~0.5-1.0 micrometer
Envelope: cytoplasmic membrane, cell wall & capsule
(polysaccharide)
Some have appendages:
flagella: for locomotion
pili:
• attachment to other cells for genetic transfer;
• virus receptor site
Pathogenic Bacteria
Pathogenic bacteria possess virulence properties in the form of
structures or chemical constituents that contribute to
pathophysiology
– Outer cell membrane of Gram negative bacteria:
endotoxin (fever producer)
– Exotoxins
Pili: for attachment and effacement to cells and tissues
Invasins: to invade cells
Some bacteria make spores:
– highly to physical and chemical agents and
– very persistent in the environment
Enteric and respiratory bacteria are important in environmental
health
Escherichia coli cells: ~0.5 x 1.0 micrometers
Typical rod-shaped bacteria:
fecal indicator and pathogenic strains
Procaryotic Cell (left) and Eucaryotic Cell (right)
Unicellular Eucaryotes: The Protists
• Complex internal organization:
– organelles: nucleus, mitochondria, etc.
•
Wide range of sizes; 2 micrometers and larger
Protozoa
• Important group of protists for environmental health
• Uni-cellular; non-photosynthetic; flexible cell membrane; no
cell wall
• Wide range of sizes and shapes; 2 micrometers to 2 mm
– flagellates
– amoeba
– ciliates
– sporozoans (complex life cycle)
– microsporidia
Cryptosporidium parvum oocysts: ~5 m diameter
Acid fast stain of fecal preparation
Giardia lamblia: flagellate protozoan parasite
Giardia lamblia cyst: ~10 x 8 micrometers
More Protists: Fungi
Fungi (yeasts and molds):
•non-photosynthetic
• immotile;
•rigid cell wall
Molds:
•grow as branched, interlacing
chains or filaments (hyphae)
called mycelia
•Yeasts:
• do not form mycelia
•grow as single cells that bud
•sexual reproduction possible
Mitospores (conidia) of
Penicillium, one of the
asexual Ascomycota
Yeasts
More Protists: Algae
• Photosynthetic
• Rigid cell wall
• Wide range of sizes
and shapes
Nostoc
– 2 micrometers and
larger
Anabaena and Aphanocapsa
Helminths (Worms)
• Multicellular animals
• Some are human and/or animal parasites
• Eggs are small enough to pose environmental health
problems from human and animal excreta in water, food, soil,
etc.
• Several major groups:
– Nematodes (roundworms): ex. Ascaris
– Trematodes (flukes): ex. Schistosomes
– Cestodes (tapeworms): pork and beef tapeworms
Transmission
• Infective stage: larvae
– Necator americanus (hookworm)
– Trichinella spiralis (trichinosis)
Trematodes
• Schistosomes (blood flukes)
Microbial Ecology:
Colonization and the Normal Flora of the Body
• Microbes colonize and inhabit the
environment as well as humans and
other living things.
• -So-called "normal flora" colonize the
skin, the oral cavity, the gastrointestinal
tract, the upper respiratory tract (throat,
nasal passages and nasopharynx), and
parts of the genitourinary tract (urethra
and vagina)
• Colonization by normal flora is often
beneficial or neutral
– harmful outcomes possible; can lead to
disease and invasion of other parts of the
body.
Transmission/Exposure Routes of Infectious Agents:
Entry to and/or Exit From the Body
Sites or Portals of
Exit or Entry:
• Respiratory
• Enteric or
Gastrointestinal
• Skin: especially if
skin barrier is
penetrated
• Genitourinary
• Eye
Routes or Methods of Entry
• Direct Personal Contact: Person (animal)-to-Person
• Indirect Personal Contact: Droplet, Fomites, Other
Vehicles
• Water and Food (Gastrointestinal Tract)
• Vector-borne: often insects
• Intrauterine or Transplacental
• Organ Transplants, Blood and Blood Products