Global Water, Sanitation and Hygiene ENVR 890-2

Transcription

1 Global Water, Sanitation and Hygiene ENVR Lecture 3 Infectious Diseases and WSH Pathogens Mark D. Sobsey

2 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; 10 9 /gm. soil; /gram feces 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

3 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

4 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.

5 Sir John Snow and his Maps of the Water Plants of London

6 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

7 Classes or Categories of Pathogenic Microorganisms: The Microbial World Viruses: smallest ( µm diameter); simplest: nucleic acid + protein coat (+ lipoprotein envelope) Bacteria: 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 cysts Groups: flagellates, amoebae, ciliates, sporozoans (complex life cycle) and microsporidia. Helminths (Worms): multicellular animals; some are parasites; eggs are small enough ( µm) to pose health risks from human and animal wastes in water.

8 THE MICROBIAL WORLD: SIZES OF MICROBES Helminth ova (eggs) are about 10 times bigger than protozoan parasites

9 Viruses Smallest: 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; 10 3s to 10 6 s/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).

10 ENTERIC VIRUSES: Infect the Gastrointestinal Tract; Fecal-oral Route of Spread Many Kinds 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 Shed at levels of millions, billions even trillions per gram of feces Highly infectious: ID 50 as low as 1 virus particle per human dose Many persist long periods in the environment Relatively resistant to water and waste treatment processes

11 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.

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

13 Noroviruses, Hepatitis A & E Viruses and Adenoviruses Noroviruses Isosahedral, nm diameter ssrna, capsid, no envelope 2 major human genogroups Major global cause of gastroenteritis Low infectious dose Hepatitis A and E Viruses Isosahedral capsid, nm diameter ssrna; no envelope Taxonomically different viruses Cause infectious hepatitis Food- & water-borne transmission ADENOVIRUSES: ~80 nm diameter; DS-DNA; no envelope protein coat/attachment fibers >40 types; some cause diarrhea; many cause respiratory disease

14 Prokaryotes: Bacteria and Other Cellular Microbes Cellular organisms Simple internal organization Multiply by binary fission Diameter ~ micrometer Envelope: cytoplasmic membrane, cell wall & capsule (polysaccharide) Some have appendages: flagella: for locomotion; function as virulence factors pili: attachment to other cells for genetic transfer; virus receptor sites Function as virulence factors

15 Pathogenic Bacteria Possess 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 micrometers Typical rod-shaped bacteria Prevalent in feces; fecal indicator Many different pathogenic strains

16 Some Important Enteric Bacterial Pathogens and Their Sources Bacterium/Group Pathogenic E. coli Salmonella spp. Campylobacter spp. Escherichia coli Helicobacter pylori Aeromonas hydrophila Yersinia enterocolitica Listeria monocytogenes Vibrio cholerae some other Vibrio sp. Shigella spp. Diseases Gastroenteritis and dysentery Typhoid (enteric) fever; gastroenteritis Gastroenteritis; dysentery Gastroenteritis; dysentery Stomach ulcers; stomach cancer Gastroenteritis Gastroenteritis Listeriosis: GI illness; meningitis & septicemia Cholera Gastroenteritis Dysentery

17 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

18 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

19 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 Entamoeba histolytica L: Active, motile, feeding trophozoite (12-50 um) R: Resistant, infective cyst (10-20 um) Giardia lamblia cyst ~10 x 8 micrometer diam. C. parvum oocysts Spherical/oval, 3-7 um diam. (acid fast stain)

20 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 Red Tide Dinoflagellate: Karenia brevis (formerly known as Gymnodinium breve). Microcystin flos aquae A toxic cyanobacterium

21 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

22 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.

23 Roundworms: Hookworms 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 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

24 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):

25 Schistosomiasis Also known as bilharziasis A snail-transmitted, waterborne parasitic helminth Second only to malaria in public health importance. Estimated 200 million people worldwide are infected Estimated deaths are associated with the severe consequences of infection bladder cancer or renal failure (Schistosoma haematobium) liver fibrosis and portal hypertension (S. mansoni)

26 = Tapeworms Scolex: Head Proglottids: Segments

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