Download Microbes and Health Risks

Environmental Health Microbiology
ENVR 133
Lecture 1
Mark D. Sobsey
Microbes and the Environment
• Microbes are fundamental and essential to life on earth
• Most microbes in the environment are harmless or beneficial
• A small proportion of microbes are capable of causing
disease in humans and/or other hosts
– Some are “frank” pathogens and amost always have the potential to
cause illness
– Others are “opportunistic” pathogens and only cause illness in
compromised hosts or unusual conditions of exposure
– Yet others are capable of causing illness when they get into parts of
the body by unusual circumstances that are normally unavailable to
microbes (deep tissues)
• Microbes are almost everywhere on the planet and the more
we look the more places we find them
Routes or Pathways of Exposure for
Environmentally Transmitted Infectious Diseases
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Water
Wastes
Food
Fomites
Vectors
– many human pathogens have animal reservoirs; zoonoses
• Air
• Soil
• Many pathogens are potentially transmitted
by multiple routes
History of Microbiology and Infectious Diseases:
Role of Water in Cholera Transmission - London
• Water, wastes and microbes are traditional/historical concerns
• 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!
– Developed a population-based approach to track the spread of
cholera in individual London boroughs; source was unknown
– Plotted the distribution of reported cases on a map
– In one London borough the source was water polluted by
sewage, which entered the Thames above the water intake.
– In another it was one water pump.
• Snow ordered the handle to be removed from the "Broad Street
Pump“; locally the epidemic subsided.
• Explained the etiology of cholera and the mechanism of its
transmission via contaminated water.
Sir John Snow and his Maps of the
Water Plants of London
Sir John Snow’s 1854 Map of the
Broad Street Pump Outbreak
Cholera cases,
each marked by
a hash, were
clustered around
the Broad Street
Pump and were
associated with
drinking water
from this pump
Microbiology and Infectious Diseases
• Infectious disease risks from water, poor sanitation and
hygiene, food and air are still with us in the developed and
developing world
• Global Water Supply and Sanitation Assessment 2000
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2.4 billion people have inadequate sanitation
1.1 billion people have inadequate/unsafe water
4 billion cases of diarrhea every year
2.2 million deaths from diarrheal disease every year
Most illness and death in children <5 years old
Less services in rural than in urban areas
Urban settlement/slums remain a problem
In the developing world wastewater treatment is rare
Water losses in large urban systems is typically 40%
• Millennium Development Goals call for halving by 2015 the
number of people lacking sustained access to safe water
– a key goal for reducing World poverty
Global Burden of Infectious Diarrheal
Disease and the Role of Water
• Burden of infectious diarrhea is higher in developing than in
developed countries
– Developed: 1 illness per person per year
– Undeveloped: about 5 illnesses per person per year
• The attributable fraction of diarrheal illness for different
exposure routes or sources may not be very different in
developed versus developing countries:
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1/4th contact
¼ water
¼ food
1/4 other
• Most waterborne disease is caused by microbes – not chemicals
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;
non-photosynthetic; 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 doublestranded
•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.
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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; flatworms): ex.
Schistosomes
– Cestodes (tapeworms): pork and beef
tapeworms
• Most helminthic disease is not waterborne, but it is
associated with water contact, food, and exposure
to fecal wastes and fecally contaminated soil.
Roundworm:
Ascaris lumbricoides
Roundworms: Hookworms