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