Giardia and Giardiasis - Springer978-1-4899-0594-9/1.pdf · Giardia and Giardiasis Biology, ......
Transcript of Giardia and Giardiasis - Springer978-1-4899-0594-9/1.pdf · Giardia and Giardiasis Biology, ......
Giardia and Giardiasis Biology, Pathogenesis, and Epidemiology
Giardia and Giardiasis Biology, Pathogenesis, and Epidemiology
Edited by
Stanley L. Erlandsen University of Minnesota Minneapolis, Minnesota
and
Ernest A. Meyer Oregon Health Sciences University Portland, Oregon
Springer Science+Business Media, LLC
Library of Congress Cataloging in Publication Data
Main entry under title:
Giardia and giardiasis.
Includes bibliographies and index. 1. Giardia. 2. Giardiasis —Transmission. 3. Epidemiology. I. Erlandsen, Stanley L. II.
Meyer, Ernest A. (Ernest Alan) [DNLM: 1. Giardia. 2. Giardiasis. WC 700 G435] QR201.G45G53 1984 616.3'427 84-2122 ISBN 978-1-4899-0596-3
ISBN 978-1-4899-0596-3 ISBN 978-1-4899-0594-9 (eBook) DOI 10.1007/978-1-4899-0594-9
© Springer Science+Business Media New York 1984 Originally published by Plenum Press, New York in 1984 Softcover reprint of the hardcover 1st edition 1984
All rights reserved
No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher
Contributors
R. F. Anders Laboratory of Immunoparasitology and Clinical Research Unit
The Walter and Eliza Hall Institutf' of Medical Research and Royal Melbourne Hospital
Victoria 3050, Australia
Robert J. Barnard Division of Microbiology
Food and Drug Administration Washington, D.C. 20204
William J. Bemrick Department of Pathobiology
College of Veterinary Medicine University of Minnesota
St. Paul, Minnesota 55108
Miriam A. Bertram Clinical Microbiology Laboratory
UCLA Hospital and Clinics Los Angeles, California 90024
David G. Chase Cell Biology Laboratory
Veterans Administration Hospital Sepulveda, California 91343
v
VI CONTRIB UTORS
Gunther F. Craun United States Environmental Protection Agency
Cincinnati, Ohio 45268
Foppe B. DeWalle Department of Environmental Health
University of Washington Seattle, Washington 98195
Stanley L. Erlandsen Department of Anatomy
School of Medicine University of Minnesota
Minneapolis, Minnesota 55455
Dennis E. Feely Department of Oral Biology
College of Dentistry University of Nebraska Medical Center
Lincoln, Nebraska 68583
Anne Ferguson Castro-Intestinal Unit
University of Edinburgh and
Western General Hospital Edinburgh EH4 2XU, Scotland, United Kingdom
Frances D. Gillin Laboratory of Parasitic Diseases
National Institute of Allergy and Infectious Diseases National Institutes of Health Bethesda, Maryland 20205
Present address: Department of Pathology, H 811-F
University of California at San Diego Medical Center San Diego, California 92103
J. Gillon Castro-Intestinal Unit
University of Edinburgh and
Western Ceneral Hospital Edinburgh EH4 2XU, Scotland, United Kingdom
CONTRIBUTORS
George R. Healy Centers for Disease Control
Public Health Service United States Department of Health and Human Services
Atlanta, Georgia 30333
David W. Hendricks Department of Civil Engineering
Colorado State University Fort Collins, Colorado 80523
John C. Hoff Drinking Water Research Division
United States Environmental Protection Agency Cincinnati, Ohio 45268
George J. Jackson Division of Microbiology
Food and Drug Administration Washington, D.C. 20204
Walter Jakubowski Health Effects Research Laboratory
United States Environmental Protection Agency Cincinnati, Ohio 45268
Edward L. J arroll Department of Preventive Medicine
New York State College of Veterinary Medicine Cornell University
Ithaca, New York 14850
Donald G. Lindmark Department of Preventive Medicine
New York State College of Veterinary Medicine Cornell University
Ithaca, New York 14850
Gary S. Logsdon Drinking Water Research Division
United States Environmental Protection Agency Cincinnati, Ohio 45268
VII
viii CONTRIBUTORS
Ernest A. Meyer Department of Microbiology and 1/11/111/1/(//11,1;.")'
Oregon Health Sciences University Portland, Oregon 97201
Patrick Muller Department of Microbiology and Immunology
Oregon Health Sciences University Portland, Oregon 97201
Robert L. Owen Department of Medicine
University of California, San Francisco, California 94132 and
Cell Biology Section Veterans Administration Medical Center
San Francisco, California 94121
Simona Radulescu Cantacuzino Institute Bucharest, Romania
I. C. Roberts-Thomson Laboratory of Immunoparasitology
and Clinical Research Unit The Walter and Eliza Hall Institute of Medical Research
and Royal Melbourne Hospital Victoria 3050, Australia
Frank W. Schaefer, III Microbiology Branch
Toxicology and Microbiology Division Health Effects Research Laboratory
United States Environmental Protection Agency Cincinnati, Ohio 45268
Phillip D. Smith Laboratory of Microbial Immunity
National Institute of Allergy and Infectious Diseases National Institutes of Health Bethesda, Maryland 20205
CONTRIBUTORS
Govinda S. Visvesvara Centers for Disease Control
Public Health Service United States Department of Health and Human Services
Atlanta, Georgia 30333
Martin S. Wolfe Department of Medicine
George Washington Medical School and
Georgetown Medical School Washington, D.C.
and Office of Medical Services
Department of State Washington, D.C. 20520
Patrick K. Woo Department of Zoology
College of Biological Science University of Guelph
Guelph, Ontario NIG 2WI, Canada
ix
Preface
The intestinal protozoan Giardia was first described over 300 years ago in 1681 by Leeuwenhoek, from his own stools. In his description of Giardia, he noted the size, movement, and morphology of the organism, and associated its presence with the diarrheic nature of his stools and his dietary habits. This truly remarkable account contains the first description of Giardia in morphologic, pathogenic, and epidemiologic terms.
Our knowledge of the organisms in the genus Giardia has advanced tremendously in the past two decades. With the advent of new technologies, including techniques in electron microscopy, biochemistry, immunochemistry, tissue culture, and physiology, a tidal wave of information has appeared on the organization and function of this parasitic protozoan and its interaction with its host.
The purpose of this book is to celebrate the tricentennial discovery of Giardia by Leeuwenhoek by presenting the above-mentioned advances in our knowledge of Giardia and giardiasis. In the first section of this book, the dominant theme is the biology of the organism and the correlation of structure-function relationships. How does the trophozoite attach to surfaces? What are the similarities and differences between members of this genus? What is known about its metabolism and requirements for growth and attachment? Are there morphological or biochemical parameters that may help to facilitate speciation? What factors are involved in excystation?
The second section of this volume deals with the diagnosis and treatment of giardiasis and the immunological reactions that occur within the host. What are the best treatments for giardiasis? Does the
xi
XII PREFACE
immune system play a role in regulating the growth and attachment of Giardia in the small intestine? Can cellular or humoral immune responses be used to assist diagnosis of giardiasis? What animal models exist for the study of giardiasis?
The third section contains recent studies related to the epidemiology of giardiasis. How important is drinking water as a source of giardiasis? What is the status of techniques for detecting, removing, and disinfecting Giardia cysts in drinking water? What types of factors are involved in the spread of giardiasis? Are there distinct species of Giardia and can certain animals serve as potential reservoirs for Giardia spp. that infect man?
These questions and more are addressed by the authors of this volume. It is hoped that the variety of information from these multidisciplinary sources will give the reader a greater understanding of Giardia as an individual cell, the interaction of this parasite with the small intestinal mucosa of its host to produce the disease giardiasis, and the factors involved in the epidemiology of the disease.
S. L. Erlandsen E. A. Meyer
Contents
I. STRUCTURE AND PHYSIOLOGY
CHAPTER 1
Structure of the Trophozoite and Cyst
DENNIS E. FEELY, STANLEY L. ERLANDSEN, and DAVID G. CHASE
1. Introduction ..................................... 3 2. Morphology of the Trophozoite ...................... 4
2.1. General Morphology ........................... 4 2.2. The Ventral Disc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.3. Flagella and Flagella-Associated Structures .......... 13 2.4. The Median Body . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 17 2.5. Other Organelles. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 19 2.6. Bacterial and Viral Symbionts .................... 20
3. Morphology of the Cyst ............................ 23 3.1. General Description ........................... 23 3.2. Excystation .................................. 27
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 29
Xlll
XIV CONTENTS
CHAPTER 2
Trophozoite Motility and the Mechanism of Attachment
STANLEY L. ERLANDSEN and DENNIS E. FEELY
1. Description of Motility ............................. 33 1.1. Discovery of Trophozoite Motility and Organelles of
Locomotion ...... . . . . . . . . . . . . . . . . . . . . . . . . . . .. 33 1.2. Motility of Giardia Trophozoites .................. 34 1.3. Types of Motile Systems in Giardia ................ 37
2. Attachment of Giardia Trophozoites to Substratum. . . . . . .. 41 2.1. Early Descriptions of Giardia Attachment ........... 41 2.2. Mechanism for Attachment of Giardia Trophozoites to
Substratum .................................. 42 3. Detachment of Trophozoites from Substratum ........... 51 4. Relationship of Trophozoites Attachment to Giardiasis . . . .. 55
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 60
CHAPTER 3
Metabolism of Trophozoites
DONALD G. LINDMARK and EDWARD L. JARROLL
1. Introduction ..................................... 65 2. Carbohydrate and Energy Metabolism ................. 66
2.1. Respiration ........................... '....... 66 2.2. End Products of Metabolism ..................... 66 2.3. Enzymes .................................... 68
3. Lipid Metabolism ................................. 73 3.1. Cellular Lipids ............................... 73 3.2. Uptake of Lipids and Lipid Precursors ............. 74
4. Nucleic Acid Metabolism. . . . . . . . . . . . . . . . . . . . . . . . . . .. 77 4.1. Purines ..................................... 77 4.2. Pyrimidines' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 77
5. Hydrolases ...................................... 78 6. Summary ....................................... 79
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 79
CONTENTS xv
CHAPTER 4
Giardia Isozymes
MIRIAM A. BERTRAM, PATRICK MULLER, and ERNEST A. MEYER
1. Introduction ..................................... 81 2. Materials and Methods ............................. 83 3. Results ......................................... 84 4. Discussion ....................................... 84
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 86
CHAPTER 5
Methods of Isolating Trophozoites and Cysts
DENNIS E. FEELY
1. Introduction ..................................... 89 2. Methods for Isolation of Trophozoites ................. 90
2.1. Isolation and Purification by Nylon Fiber Columns . . .. 90 2.2. Isolation by Vibration and Sedimentation ........... 91 2.3. Isolation by Attachment of Trophozoites . . . . . . . . . . .. 91
3. Methods for Isolation of Cysts ....................... 95 3.1. Method of Rendtorff .......................... 95 3.2. Sucrose Density Gradient Centrifugation. . . . . . . . . . .. 95
References .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 96
CHAPTER 6
In Vitro Cultivation of Giardia Trophozoites
ERNEST A. MEYER and SIMONA RADULESCU
1. Introduction ..................................... 99 2. Trophozoites of the C. duodenalis Type . . . . . . . . . . . . . . . .. 99 3. Trophozoites of the C. muris Type .................... 106 4. Trophozoites of the C. agilis Type .................... 106 5. Future Prospects .................................. 106
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
XVI CONTENTS
CHAPTER 7
The Role of Reducing Agents and the Physiology of Trophozoite Attachment
FRANCES D. GILLIN
1. Introduction ..................................... III 2. Trophozoite Attachment during Axenic Growth .......... 112 3. The Role of Reducing Agents in the Biology of G. LambLia . .. 113
3.1. Reducing Agents in the Growth of G. LambLia ........ 114 3.2. The Role of Cysteine and Ascorbic Acid in Protecting
G. LambLia Trophozoites from Oxygen .............. 115 3.3. Cysteine Is Required for Attachment in Complex
Growth Medium .............................. 117 3.4. The Role of Reducing Agents in Trophozoite
Attachment in Maintenance Media in the Absence of Growth ..................................... 121
4. The Role of Serum Factors in Trophozoite Attachment .... 122 4.1. Stimulation of Trophozoite Attachment and Survival by
Serum ...................................... 122 4.2. Activity of Various Serum Fractions ............... 123 4.3. Effect of Serum Cohn Fraction III on the Kinetics of
Attachment and Survival ........................ 125 5. Physiological Factors in Attachment ................... 125
5.1. Effect of pH ................................. 126 5.2. Effect of Ionic Composition ..................... 126 5.3. Effect of Temperature ......................... 128
6. Summary ....................................... 129 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
CHAPTERS
Models for Excystation
ERNEST A. MEYER and FRANK W. SCHAEFER, III
1. Introduction ..................................... 131 2. The Studies of Bingham and Meyer ................... 132 3. The Studies of Rice and Schaefer ..................... 137 4. Summary ....................................... 143
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
CONTENTS
II. GIARDIASIS
CHAPTER 9
Symptomatology, Diagnosis, and Treatment
MARTIN S. WOLFE
XVII
1. Clinical Features .................................. 147 1.1. Incubation and Prepatent Periods .:... . . . . . . . . . . . . 147 1.2. Acute Stage .................................. 148 1.3. Subacute and Chronic Stage ..................... 149 1.4. Asymptomatic Cyst-Passing Stage ................. 151 1.5. Post-Giardia Lactose Intolerance .................. 151
2. Diagnosis ....................................... 152 2.1. Stool Examinations ............................ 152 2.2. Examination of Intestinal Fluid ................... 153 2.3. Small Bowel Biopsy ............................ 154 2.4. Serologic Tests ............................... 154 2.5. Gastrointestinal Radiology ....................... 154 2.6. Empiric Treatment ............................ 155
3. Treatment ...................................... 155 3.1. Quinacrine (Atabrine) .......................... 155 3.2. Metronidazole (Flagyl) .......................... 156 3.3. Furazolidone (Furoxone) ........................ 157 3.4. Paromomycin (Humatin) ........................ 158 3.5. Drugs Unavailable in the United States ............. 158 3.6. Pregnancy ................................... 158 3.7. Asymptomatic Cyst Passers ...................... 159 3.8. Posttreatment Considerations .................... 159
References .......................................... 159
CHAPTER 10
Changes in the Small Intestinal Mucosa in Giardiasis
J. GILLON and ANNE FERGUSON
1. General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 1.1. Distribution of Parasites in the Intestine ............ 164 1.2. Attachment of Trophozoites to the Mucosa and
Penetration of the Epithelium .................... 165
xviii CONTENTS
2. Pathological Changes in the Mucosa of the Small Intestine in Human Giardiasis ................................ . 2.1. Histological Changes in Patients without
Immunodeficiency ........................... . 2.2. Intraepithelial Lymphocyte Counts in Patients with
Giardiasis .................................. . 2.3. Changes in Lamina Propria Plasma Cells and Secretory
Antibodies in Patients with Giardiasis ............. . 2.4. Histological Changes in Hypogammaglobulinemic
Patients with Giardiasis ........................ . 2.5. Ultrastructural Abnormalities of Mucosal Morphology
2.6. Abnormalities of Jejunal Disaccharidases in Giardiasis Patients .................................... .
3. Small Intestinal Abnormalities in Experimental Murine Giardiasis ...................................... . 3.1. General Aspects ............................. . 3.2. Small Intestinal Mucosa in Primary Giardia Infection in
Mice ...................................... . 3.3. Effects of Chronic G. muris Infection on the Intestinal
166
166
167
168
169
169
170
171 171
172
Mucosa ..................................... 177 4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
CHAPTER 11
Cellular and Humoral Immunity in Giardiasis
I. C. ROBERTS·THOMSON and R. F. ANDERS
1. Introduction ..................................... 185 2. Immunologic Mechanisms ........................... 186 3. Giardia Antigens .................................. 187
3.1. G. Lamblia .................................... 187 3.2. G. muris ..................................... 187
4. Immunoglobulin Levels ............................ 188 4.1. Human Studies ............................... 188 4.2. Experimental Studies .......................... 190
5. Anti-Giardia Antibodies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 5.1. G. Lamblia .................................... 190 5.2. G. muris ..................................... 191
CONTENTS XIX
6. Cell-Mediated Immunity ............................ 192 6.1. Human Studies ............................... 192 6.2. Experimental Studies .......................... 193
7. Passive Transfer of Immunity ........................ 195 8. Stimulation of Immunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 9. Nonlymphoid Effector Cells ......................... 196
9.l. Mast Cells ................................... 196 9.2. Macrophages ................................. 196 9.3. Eosinophils .................................. 197
10. Conclusion ...................................... 197 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
CHAPTER 12
Human Immune Responses to Giardia lamblia
PHILLIP D. SMITH
l. Introduction ..................................... 201 2. G. Lamblia Strain .................................. 202 3. Humoral Response ................................ 202 4. Cell-Mediated Response ............................ 203
4.l. Lymphocyte Proliferation ....................... 203 4.2. Spontaneous Cell-Mediated Cytotoxicity ............ 203 4.3. Antibody-Dependent Cellular Cytotoxicity (ADCC) .... 210
5. Conclusions ...................................... 213 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
CHAPTER 13
Antigenicity of Giardia lamblia and the Current Status of Serologic Diagnosis of Giardiasis
GOVINDA S. VISVESV ARA and GEORGE R. HEALY
1. Introduction ..................................... 219 2. Immunologic Response in Giardiasis ................... 220 3. Current Status of Serologic Tests ..................... 221
3.l. Indirect Immunofluorescence (IIF) Test ............ 221 3.2. Immunodiffusion (ID) Test ...................... 225 3.3. Enzyme-Linked Immunosorbent Assay (ELISA) ...... 225
xx CONTENTS
3.4. Counterimmunoelectrophoresis (CIE) Test .......... 226 3.5. Role of Antibody in Protection ................... 226
4. Antigenic Makeup of C. lamblia ....................... 227 References .......................................... 230
CHAPTER 14
Animal Models for Giardiasis
ERNEST A. MEYER, STANLEY L. ERLANDSEN, and SIMONA RADULESCU
l. Introduction ..................................... 233 2. Animal Models Employing C. muris-Type Organisms in Mice
234 3. Animal Models Employing C. duodenalis-Type Organisms
236 4. Summary ....................................... 238
References .......................................... 238
III. EPIDEMIOLOGY
CHAPTER 15
Waterborne Outbreaks of Giardiasis: Current Status
GUNTHER F. CRAUN
l. Waterborne Giardiasis in Travelers .................... 243 2. Endemic Waterborne Giardiasis ...................... 246 3. Outbreaks of Waterborne Giardiasis in the United States,
1965-1979 ...................................... 247 4. Water Supply Considerations ........................ 258
References .......................................... 259
CHAPTER 16
Detection of Giardia Cysts in Drinking Water: State of the Art
WALTER JAKUBOWSKI
l. Introduction ..................................... 263 2. Estimated Levels of Cysts in Sewage and Water .......... 264
CONTENTS XXI
3. Detection Methods ................................ 266 3.1. Membrane Filter Methods ....................... 266 3.2. Particulate Filter Methods ....................... 267 3.3. Microporous Depth Filters ...................... 268 3.4. Primary Concentration versus Processing ........... 270
4. Multilaboratory Evaluation of Giardia-Seeded Water Samples ............................................... 271
4.1. Background ................................. 271 4.2. Protocol ..................................... 272 4.3. Results and Discussion ......................... 273
5. Recommendations of a Giardia Methods Workshop ........ 275 5.1. Background ................................. 275 5.2. Issues and Recommendations .................... 275 5.3. Reference Method ............................. 278 5.4. Discussion ................................... 282
6. State of the Art ................................... 282 References .......................................... 285
CHAPTER 17
Filtration as a Barrier to Passage of Cysts in Drinking Water GARY S. LOGSDON, FOPPE B. DEWALLE, and DAVID W. HENDRICKS
1. Introduction ..................................... 287 2. Experimental Methods ............................. 288
2.1. Microspheres ................................. 288 2.2. Giardia Cysts ................................. 289 2.3. Raw Water Sources ............................ 290 2.4. Pilot Filter Facilities ............................ 290
3. Results ......................................... 292 3.1. DE Filtration Results ........................... 293 3.2. Granular Media Filtration Results ................. 293 3.3. Slow Sand Filtration Results ..................... 301
4. Discussion ....................................... 303 4.1. DE Filtration ................................. 303 4.2. Granular Media Filtration ....................... 304 4.3. Slow Sand Filtration ........................... 306
5. Summary and Conclusions .......................... 307 5.1. DE ........................................ 307 5.2. Granular Media Filtration ....................... 307
XXII CONTENTS
5.3. Slow Sand Filtration ........................... 308 5.4. Multiple Barrier Concept ....................... 308
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
CHAPTER 18
Resistance of Cysts to Disinfection Agents
EDWARD L. JARROLL, JOHN C. HOFF, and ERNEST A. MEYER
1. Early Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311 1.1. Determination of Cyst Viability by Vital Stain Exclusion
........................................... 311 1.2. Disinfection Experiments ....................... 312
2. Modern Concept .................................. 314 2.1. Determination of Cyst Viability ................... 314 2.2. Disinfection Experiments ....................... 317
References .......................................... 326
CHAPTER 19
Direct Fecal-Oral Transmission of Giardiasis
ROBERT L. OWEN
1. Parasite Factors in Direct Transmission ................. 329 2. Host Factors in Direct Transmission ................... 330 3. Institutional Transmission by Infants and the Retarded .... 331 4. Venereal Transmission ............................. 334 5. Pets as a Possible Focus of Direct Transmission ........... 337
References .......................................... 338
CHAPTER 20
Evidence for Animal Reservoirs and Transmission of Giardia Infection between Animal Species
PATRICK K. WOO
1. Introduction ..................................... 341 2. Toward Species Definition in Giardia .................. 342
XXllI
3. Review of Host Specificity of Giardia ................... 344 3.1. Giardia in Humans ............................ 344 3.2. Giardia in Nonprimates ......................... 348 3.3. Discussions on the Cross-Transmission Studies ....... 349
4. Characterization of Giardia spp. . ..................... 350 4.1. Host Specificity ............................... 351 4.2. Morphological ................................. 352 4.3. Morphometrical .............................. 354 4.4. Biochemical .................................. 355 4.5. Immunological ............................... 358
5. Conclusion ...................................... 358 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
CHAPTER 21
Giardia lamblia: The Transfer of Human Infections by Foods
ROBERT J. BARNARD and GEORGE J. JACKSON
1. Historical Aspects and Transmission of Related Protozoa through Foods ................................... 365
2. Methods for Detecting Giardia Cysts in Foods ............ 367 2.1. Formalin-Ether Sedimentation ................... 367 2.2. Sucrose Gradient .............................. 368 2.3. Discontinuous Density Sucrose Gradient ............ 369 2.4. Sedimentation/Zinc Sulfate Flotation .............. 369
3. Outbreaks of Foodborne Giardiasis .................... 369 4. Current and Future Status of Foodborne Giardiasis ....... 373
References .......................................... 376
CHAPTER 22
Some Perspectives on the Transmission of Giardiasis
WILLIAM J. BEMRICK
1. Introduction ..................................... 379 2. Animal Feeding Experiments ........................ 380 3. Chemical Tagging Methods ......................... 386 4. Immunological Methods for Detecting Giardia Populations
............................................... 386
XXIV CONTENTS
5. Other Methods with Potential for Specifically Identifying Giardia Populations ................................ 387
6. Waterborne Transmission of Human Giardiasis and the Role of the Beaver .................................... 388 6.1. Waterborne Transmission in General .............. 388 6.2. The Beaver .................................. 389
7. Transmission by Contaminated Food .... : ............. 393 8. Sexual Transmission ............................... 395 9. Final Analysis of Present Data ........................ 395
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
Index ............................................. 401