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; 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 organismsSimple internal organizationMultiply by binary fissionDiameter ~0.5-1.0 micrometerEnvelope: 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)– ExotoxinsPili: 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): 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