Environmental Health MicrobiologyENVR 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

• 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– 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:– 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• 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 arrayEnvelope:•lipid bilayer membrane + glycoproteins) •typically acquired from host cell membranes

Enteroviruses: ~27-30 nm diameter; single-stranded 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 micrometersTypical 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 diameterAcid fast stain of fecal preparation

Giardia lamblia: flagellate protozoan parasiteGiardia 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 – 2 micrometers and

larger

Anabaena and Aphanocapsa

Nostoc

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