Global Water, Sanitation and HygieneENVR 890-2

Lecture 3Infectious Diseases and WSH Pathogens

Mark D. Sobsey

Microbes, the Environment & Human Infectious Disease

• Microbes: fundamental, essential to earthly life & everywhere!• The earth is covered with microbes and so are we!• Most are harmless or beneficial; 109/gm. soil; 1012/gram feces

– http://commtechlab.msu.edu/sites/dlc-me/zoo/zdmain.html• A small proportion cause disease in humans and/or other hosts

– Some are “frank” pathogens; usually able to cause illness– Others are “opportunistic” pathogens; cause illness in compromised

hosts or with unusual conditions of exposure– Others cause illness only when they get into parts of the body by

circumstances not normally available (wounds; deep tissues)• Some have intermediate hosts besides humans, such as other

vertebrates, insects, plants and other microbes• Some inhabit the environment and have an existence independent

of humans or other hosts

Routes or Pathways of Exposure for Environmentally Transmitted Infectious Diseases

Transmission routes, pathways, vehicles:• Water• Wastes• Food • Fomites (inanimate surfaces)• Vectors

– Biological– Mechanical– 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

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; eukaryotic; uni-cellular; non-photosynthetic; flexible cell membrane; no cell wall; wide range of sizes and shapes; hardy cystsGroups: 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

Helminth ova (eggs) are about 10 times bigger than protozoan parasites

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; 103s to 106s/infected cell

• non-enveloped viruses are most persistent in the environment– protein coat confers stability

• enteric viruses are very 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: Infect the Gastrointestinal Tract; Fecal-oral Route of Spread – Many Kinds

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

• Shed at levels of millions, billions even trillions per gram of feces• Highly infectious: ID50 as low as 1 virus particle per human dose• Many persist long periods in the environment• Relatively resistant to water and waste treatment processes

Enteroviruses• Diameter: ~27-30 nm• No envelope• Single-stranded RNA• Icosahedral protein coat

(capsid)• More than 71 different ones• Poliovirus: best known

– Poliomyelitis– Paralytic, neurological disease– Successful vaccines

developed in 1950s and 1960s– Eradication goal set in 1980s is

still not achieved– Billions spent on eradication

• Other enteroviruses cause encephalitis, myocarditis, diabetes, rashes, URI, GI, etc.

Human Rotavirus: ~75 nm diameter; double-layered capsid; double-stranded, segmented RNA

• Diameter ~75 nmdouble-layered capsid

• double-stranded, segmented RNA– 11 segments

• Non-enveloped• Many groups, sub-types & serotypes

• Group A is most common• Cause infantile diarrhea & gastroenteritis• Most children infected by age 3• Many deaths and hospitalizations• Vaccines have been developed

• High cost and effectiveness uncertain

Noroviruses, Hepatitis A & E Viruses and Adenoviruses• Noroviruses

Isosahedral, 30-35 nm diameterssRNA, capsid, no envelope2 major human genogroupsMajor global cause of gastroenteritisLow infectious dose

• Hepatitis A and E VirusesIsosahedral capsid, 25-35 nm diameterssRNA; no envelopeTaxonomically different virusesCause infectious hepatitisFood- & water-borne transmission

• ADENOVIRUSES: ~80 nm diameter; DS-DNA; no envelopeprotein coat/attachment fibers>40 types; some cause diarrhea; many cause respiratory disease

Prokaryotes: Bacteria and Other Cellular Microbes

Cellular organismsSimple internal organizationMultiply by binary fissionDiameter ~0.5-1.0 micrometerEnvelope: cytoplasmic membrane, cell wall & capsule

(polysaccharide)Some have appendages:

flagella: for locomotion; function as virulence factorspili:

• attachment to other cells for genetic transfer; • virus receptor sites• Function as virulence factors

Pathogenic BacteriaPossess virulence properties: structures or

chemical constituents that contribute to pathophysiology– Outer cell membrane of Gram negative

bacteria: endotoxin (fever producer)– Flagella for locomotion– Exotoxins: substance released from the

cells– Pili: attachment/effacement to cells and

tissues– Invasins: to invade cells

Some bacteria make spores:– Resistant to physical and chemical agents – Persistent in the environment

• Enteric and respiratory bacteria are important in environmental health and WSH disease burden

Escherichia coli cells: ~0.5 x 1.0 micrometersTypical rod-shaped bacteriaPrevalent in feces; fecal indicator Many different pathogenic strains

Some Important Enteric Bacterial Pathogens and Their Sources

Bacterium/Group DiseasesPathogenic E. coli Gastroenteritis and dysenterySalmonella spp. Typhoid (enteric) fever; gastroenteritisCampylobacter spp. Gastroenteritis; dysenteryEscherichia coli Gastroenteritis; dysenteryHelicobacter pylori Stomach ulcers; stomach cancerAeromonas hydrophila GastroenteritisYersinia enterocolitica GastroenteritisListeria monocytogenes Listeriosis: GI illness; meningitis & septicemia

Vibrio cholerae Cholera some other Vibrio sp. Gastroenteritis

Shigella spp. Dysentery

Unicellular Eukaryotes: The Protists• Complex internal

organization:– organelles:

• nucleus • mitochondria • etc.

• Wide size range – 2 micrometers and larger

• Wide range of microbe types: Protozoa: euglenozoa, alveolates, ciliates, diatoms, sporozoans (Apicomplexa), dinoflagellates

• Algae : golden, brown, red

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

Some Enteric Protozoa and their Diseases

Protozoa Disease• Amoebas: Entamoeba histolytica Amebic dysentery• Flagellates: Giardia lamblia giardiasis; GI illness• Coccidians: Cryptosporidium parvum Cryptosporidiosis, GI• Ciliophora: Ciliates: Balantidium coli GI illness• Microsporidia: Enterocytozoon beinusi GI illness

Giardia lamblia cyst ~10 x 8 micrometer diam.

C. parvum oocystsSpherical/oval, 3-7 um diam.(acid fast stain)

Entamoeba histolyticaL: Active, motile, feeding trophozoite (12-50 um) R: Resistant, infective cyst (10-20 um)

More Protists: Algae

• Photosynthetic• Rigid cell wall • Wide range of sizes and

shapes – 2 micrometers and larger

• Some Algae are pathogens due to toxins

• Harmful algal blooms– Toxic Dinoflagellates

• “Red Tides”– Cyanobacteria

• (blue-green algae)• possess cyanotoxins

Microcystin flos aquaeA toxic cyanobacterium

“Red Tide” Dinoflagellate: Karenia brevis(formerly known as Gymnodinium breve).

More Eukaryotic Microbes: 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

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.

Roundworms: Hookworms

Human Hookworm Infection----------------------------------------------------------------------

• Soil-transmitted• Caused by nematodes

– Necator americanus– Ancylostoma duodenale

• A leading cause of anaemia and protein malnutrition, – afflicts an estimated 740

million people in tropical developing nations

Trichinella and Trichinosis:• Human infection caused by the domestic pig varies from country to country • Eastern Europe and Asia report hundreds or thousands of cases annually

Roundworm: Ascaris lumbricoides

Ascariasis: • Major cause of enteric illness and infection, anemia, child malnutrition, stunting and other developmental deficiencies• Most of the World’s population is infected; disease burden greatest in children in developing countries

Ascaris ovum (egg):

Schistosomiasis

• Also known as bilharziasis• A snail-transmitted, water-

borne parasitic helminth• Second only to malaria in

public health importance. • Estimated 200 million people

worldwide are infected• Estimated 20 000 deaths are

associated with the severe consequences of infection– bladder cancer or renal

failure (Schistosoma haematobium)

– liver fibrosis and portal hypertension (S. mansoni)

Scolex: Head

Proglottids: Segments

= Tapeworms

Suggested Readings and Resources• Microbes and Man, John Postgate, 4th edition, 2008,

388 pages, Cambridge University Press. • Man and Microbes: Disease and Plagues in History and

Modern Times, Arno Karlen, 272 pages, Simon & Schuster, 1996.

• Power Unseen: How microbes rule the world, Bernard Dixon, 272 pages, Oxford University Press, 1998.

• Infectious Disease: A Scientific American Reader (Scientific American Readers), 368 pages, University Of Chicago Press, 2008

• Clinical Microbiology Made Ridiculously Simple (Medmaster), Mark Gladwin and Bill Trattler, 392 pages. MedMaster Inc. 4th edition