Diseases of Poultry

By Wiley

Diseases of Poultry is the most comprehensive reference for all aspects of poultry health and diseases, including pathogenesis, diagnostics, epidemiology, and control methods. Published in partnership with the American Association of Avian Pathologists, the Thirteenth Edition remains the international definitive reference, adding newer diagnostic methods and a new chapter on the emerging importance of zoonotic infections for poultry pathogens. Other updates include new high-quality photographs, additional discussion of conceptual operational biosecurity and disease control in organic production systems, and a greater emphasis throughout on the differences in disease incidence and treatments for the United States and other areas around the globe.

Organized logically by disease type, the book offers detailed coverage of the history, etiology, pathobiology, diagnosis, and intervention strategies, as well as the economic and public health significance, for an exhaustive list of common and uncommon diseases. Diseases of Poultry, 13th Edition is an essential purchase for poultry veterinarians, veterinary diagnosticians, poultry scientists, students specializing in poultry health, and government officials who deal with poultry health in regulatory climate.

• Language: English
• Publisher: Wiley
• Release date: Jul 16, 2013
• ISBN: 9781118719732

Book preview

Contents

Contributors

Preface: Historical Review of Diseases of Poultry

Introduction

I General Concepts of Poultry Diseases

Chapter 1: Principles of Disease Prevention, Diagnosis, and Control

Introduction

Principles of Disease Prevention, Diagnosis, and Control Introduction

Antimicrobial Therapy (Including Resistance)

Public Health Significance of Poultry Diseases

Chapter 2: Host Factors for Disease Resistance

Introduction

The Avian Immune System

Genetics of Disease Resistance

II Viral Diseases

Chapter 3: Newcastle Disease, Other Avian Paramyxoviruses, and Avian Metapneumovirus Infections

Introduction

Newcastle Disease

Avian Paramyxoviruses 2–11

Avian Metapneumovirus

Chapter 4: Infectious Bronchitis

Chapter 5: Infectious Laryngotracheitis

Chapter 6: Influenza

Chapter 7: Infectious Bursal Disease

Chapter 8: Chicken Infectious Anemia Virus and Other Circovirus Infections

Introduction

Chicken Infectious Anemia

Circovirus Infections of Avian Species

Chapter 9: Adenovirus Infections

Introduction

Aviadenovirus Infections

Atadenovirus (Egg Drop Syndrome and Related Infections)

Hemorrhagic Enteritis and Related Infections

Quail Bronchitis

Chapter 10: Pox

Chapter 11: Reovirus Infections

Introduction

Viral Arthritis

Other Reovirus Infections

Chapter 12: Viral Enteric Infections

Introduction

Turkey Coronavirus Enteritis

Rotavirus Infections

Astrovirus Infections

Avian Enterovirus-Like Virus Infections

Enteric Parvovirus Infections of Chickens and Turkeys

Chapter 13: Viral Infections of Waterfowl

Introduction

Duck Hepatitis

Duck Virus Enteritis (Duck Plague)

Hemorrhagic Nephritis Enteritis of Geese

Parvovirus Infections of Waterfowl

Chapter 14: Other Viral Infections

Introduction

Miscellaneous Herpesvirus Infections

Avian Nephritis

Arbovirus Infections

Turkey Viral Hepatitis

Avian Encephalomyelitis

Avian Hepatitis E Virus Infections

Chapter 15: Neoplastic Diseases

Introduction

Marek’s Disease

Leukosis/Sarcoma Group

Reticuloendotheliosis

Other Tumors

III Bacterial Diseases

Chapter 16: Salmonella Infections

Introduction

Pullorum Disease and Fowl Typhoid

Paratyphoid Infections

Arizonosis

Chapter 17: Campylobacteriosis

Chapter 18: Colibacillosis

Chapter 19: Pasteurellosis and Other Respiratory Bacterial Infections

Introduction

Fowl Cholera

Riemerella anatipestifer Infection

Ornithobacterium rhinotracheale Infection

Bordetellosis (Turkey Coryza)

Chapter 20: Infectious Coryza and Related Bacterial Infections

Chapter 21: Mycoplasmosis

Introduction

Mycoplasma gallisepticum Infection

Mycoplasma meleagridis Infection

Mycoplasma synoviae Infection

Mycoplasma iowae Infection

Other Mycoplasmal Infections

Chapter 22: Clostridial Diseases

Introduction

Ulcerative Enteritis

Necrotic Enteritis

Botulism

Gangrenous Dermatitis

Chapter 23: Other Bacterial Diseases

Introduction

Staphylococcosis

Streptococcus and Enterococcus

Erysipelas

Avian Intestinal Spirochetosis

Tuberculosis

Miscellaneous and Sporadic Bacterial Infections

Chapter 24: Avian Chlamydiosis

IV Fungal Diseases

Chapter 25: Fungal Infections

Aspergillosis

Candidiasis (Crop Mycosis)

Sporadic Fungal Infections

V Parasitic Diseases

Chapter 26: External Parasites and Poultry Pests

Chapter 27: Internal Parasites

Introduction

Nematodes and Acanthocephalans

Chapter 28: Protozoal Infections

Introduction

Coccidiosis

Cryptosporidiosis

Histomoniasis (Blackhead) and Other Protozoan Diseases of the Intestinal Tract

Miscellaneous and Sporadic Protozoal Infections

VI Noninfectious Diseases

Chapter 29: Nutritional Diseases

Chapter 30: Developmental, Metabolic, and Other Noninfectious Disorders

Chapter 31: Mycotoxicoses

Chapter 32: Toxins and Poisons

VII Other Diseases

Chapter 33: Emerging Diseases and Diseases of Complex or Unknown Etiology

Introduction

Multicausal Respiratory Diseases

Multicausal Enteric Diseases

Hypoglycemia-Spiking Mortality Syndrome of Broiler Chickens

Proventriculitis and Proventricular Dilatation of Broiler Chickens

Index

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Library of Congress Cataloging-in-Publication Data

Diseases of poultry. – 13th ed. / editor-in-chief, David E. Swayne ; associate editors, John R. Glisson … [et al.].

p. ; cm.

Includes bibliographical references and index.

ISBN 978-0-470-95899-5 (hardback : alk. paper)

I. Swayne, David E.

[DNLM: 1. Poultry Diseases. SF 995]

SF995

636.5′0896–dc23

2013007104

A catalogue record for this book is available from the British Library.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.

Cover design by Modern Alchemy LLC

Dedicated to

Dr. Y.M. Saif, Associate Editor,

Diseases of Poultry, 10th edition

Editor-in-Chief, 11th and 12th editions

Dr. A.M. Fadly, Associate Editor,

Diseases of Poultry, 11th and 12th editions

Contributors

Tahseen Abdul-Aziz

Veterinary Pathologist

Rollins Animal Disease Diagnostic Laboratory

North Carolina Department of Agriculture and Consumer Services

Raleigh, North Carolina, USA

Claire B. Andreasen

Associate Dean for Academic and Student Affairs

Professor

College of Veterinary Medicine

Iowa State University

Ames, Iowa, USA

H. John Barnes

Professor

Department of Population Health and Pathobiology

College of Veterinary Medicine

North Carolina State University

Raleigh, North Carolina, USA

Paul A. Barrow

Professor

Veterinary Infectious Diseases

School of Veterinary Medicine and Science

Nottingham University

Sutton Bonington, Leicestershire, United Kingdom

Viveca Båverud

Associate Professor, HeadDepartment of Bacteriology

National Veterinary Institute

Uppsala, Sweden

Roy D. Berghaus

Associate Professor

Department of Population Health

College of Veterinary Medicine

University of Georgia

Athens, Georgia, USA

Alex J. Bermudez*

Director

Veterinary Medical Diagnostic Laboratory

College of Veterinary Medicine

University of Missouri

Columbia, Missouri, USA

Pat J. Blackall

Senior Principal Research Fellow

Queensland Alliance for Agriculture and Food Innovation

The University of Queensland

Queensland, Australia

Gunilla Blomqvist

Department of Virology, Immunology and Parasitology

National Veterinary Institute

Uppsala, Sweden

Janet M. Bradbury

Emeritus Professor

School of Veterinary Science—Leahurst Campus

University of Liverpool

Neston, Wirral, United Kingdom

Joseph M. Bricker

Global Bios Research

Zoetis

Kalamazoo, Michigan, USA

Bruce R. Charlton

Professor

California Animal Health and Food Safety Laboratory System

University of California—Davis

Turlock, California, USA

Hans H. Cheng

Supervisory Research Geneticist

Avian Disease and Oncology Laboratory

Agricultural Research Service

U.S. Department of Agriculture

East Lansing, Michigan, USA

Richard P. Chin

Professor

California Animal Health and Food Safety Laboratory System

University of California—Davis

Tulare, California, USA

Jens P. Christensen

Associate Professor

Department of Veterinary Disease Biology

Faculty of Life Sciences

University of Copenhagen

Frederiksberg, Copenhagen, Denmark

Stephen R. Collett

Clinical Associate Professor

Poultry Diagnostic and Research Center

Department of Population Health

College of Veterinary Medicine

University of Georgia

Athens, Georgia, USA

Robert M. Corrigan

Private Consultant

Urban Rodentologist

RMC Pest Management Consulting

Richmond, Indiana, USA

Rocio Crespo

Associate Professor

Avian Health and Food Safety Laboratory (WADDL) Department of Veterinary Microbiology and PathologyWashington State University

Pullman, Washington, USA

James F. Davis

Veterinary Director of Diagnostics—North Georgia

Georgia Poultry Laboratory Network

Oakwood, Georgia, USA

J. Michael Day

Microbiologist

Endemic Poultry Viral Diseases Research Unit

Southeast Poultry Research Laboratory

Agricultural Research Service

U.S. Department of Agriculture

Athens, Georgia, USA

Sjaak de Wit

Poultry Veterinarian

Animal Health Service

Deventer, The Netherlands

Jean Pierre Duchatel

Department of Infectious and Parasitic Diseases

Faculty of Veterinary Medicine

University of Liege

Liege, Belgium

Michael J. Dykstra

Director and Research Professor

Laboratory for Advanced Electron and Light Microscopy Methods

Department of Population Health and Pathobiology

College of Veterinary Medicine

North Carolina State University

Raleigh, North Carolina, USA

Nicolas Eterradossi

Agence Nationale de Securite Sanitaire de l’Alimentation, de l’Environnement et du Travail (Anses)

Laboratoire de Ploufragan/Plouzane

Unite de Virologie Immunologie et Parasitologie Aviaires et Cunicoles

Laboratoire de reference de l’Organisation Mondiale de la Sante Animale pour la bursite infectieuse aviaire

Ploufragan, France

Aly M. Fadly

Research Leader and Laboratory Director

Avian Disease and Oncology Laboratory

Agricultural Research Service

U.S. Department of Agriculture

East Lansing, Michigan, USA

Naola Ferguson-Noel

Assistant Professor

Poultry Diagnostic and Research Center

Department of Population Health

College of Veterinary Medicine

University of Georgia

Athens, Georgia, USA

Scott D. Fitzgerald

Professor

Department of Pathobiology and Diagnostic Investigation

College of Veterinary Medicine

Michigan State University

East Lansing, Michigan, USA

Steve H. Fitz-Coy

Poultry Parasitologist

Merck Animal Health

Salisbury, Maryland, USA

Richard M. Fulton

Associate Professor

Diagnostic Center for Population and Animal Health

College of Veterinary Medicine

Michigan State University

East Lansing, Michigan, USA

Maricarmen García

Professor

Poultry Diagnostic and Research Center

Department of Population Health

College of Veterinary Medicine

University of Georgia

Athens, Georgia, USA

Richard K. Gast

Supervisory Microbiologist

Egg Safety and Quality Research Unit

Agricultural Research Service

U.S. Department of Agriculture

Athens, Georgia, USA

John R. Glisson

Professor Emeritus

Poultry Diagnostic and Research Center

Department of Population Health

College of Veterinary Medicine

University of Georgia

Athens, Georgia, USA

Jean-Luc Guérin

Associate Professor

Poultry Health and Virology

National Veterinary College of Toulouse

Toulouse, France

James S. Guy

Professor

Department of Population Health and Pathobiology

College of Veterinary Medicine

North Carolina State University

Raleigh, North Carolina, USA

Hafez M. Hafez

Head

Institute of Poultry Diseases

Faculty of Veterinary Medicine

Free University of Berlin

Berlin, Germany

Scott Hafner

Veterinary Medical Officer

Eastern Laboratory

Food Safety Inspection Service

U.S. Department of Agriculture

Athens, Georgia, USA

David J. Hampson

Professor and Dean

School of Veterinary and Life Sciences

Murdoch University

Murdoch, Western Australia, Australia

Christopher S. Hayhow

Director of Regulatory Affairs

Biologics, North AmericaMerial, Inc.

Athens, Georgia, USA

Michael Hess

Head

Clinic for Avian, Reptile and Fish MedicineDepartment for Farm Animals and Veterinary Public Health

University of Veterinary Medicine

Vienna, Austria

Nancy C. Hinkle

Professor

Department of Entomology

College of Agricultural and Environmental Sciences

University of Georgia

Athens, Georgia, USA

Fredric J. Hoerr

Pathologist

Veterinary Diagnostic Pathology, LLC

Auburn, Alabama, USA

Charles L. Hofacre

Professor

Poultry Diagnostic and Research Center

Department of Population Health

College of Veterinary Medicine

University of Georgia

Athens, Georgia, USA

Tadao Imada

One-time Research Manager (Emeritus)

National Institute of Animal Health

Kammondai, Tsukuba, Japan

Sherman W. Jack

Professor

Department of Pathobiology and Population Medicine

College of Veterinary Medicine

Mississippi State University

Mississippi State, Mississippi, USA

Mark W. Jackwood

Head and J. R. Glisson Professor of Veterinary Medicine

Poultry Diagnostic and Research Center

Department of Population Health College of Veterinary Medicine

University of Georgia

Athens, Georgia, USA

Timothy J. Johnson

Associate Professor

Department of Veterinary and Biomedical Sciences

College of Veterinary Medicine

University of Minnesota

St. Paul, Minnesota, USA

Richard C. Jones

Emeritus Professor

School of Veterinary Science—Leahurst Campus

University of Liverpool

Neston, Wirral, United Kingdom

Kirk C. Klasing

Professor

Department of Animal Science

College of Agricultural and Environmental Sciences

University of California—Davis

Davis, California, USA

Guus Koch

Senior Scientist

Department of Virology

Central Veterinary Institute Wageningen UR

Lelystad, The Netherlands

Susan J. Lamont

C.F. Curtiss Distinguished Professor of Agriculture and Life Sciences

Department of Animal Science

Iowa State University

Ames, Iowa, USA

Kenneth S. Latimer

Research Clinical Pathologist

Covance Laboratories, Inc.

Madison, Wisconsin, USA

David H. Ley

Professor

Department of Population Health and Pathobiology

College of Veterinary Medicine

North Carolina State University

Raleigh, North Carolina, USA

Catherine M. Logue

ProfessorDepartment of Veterinary Microbiology and Preventive Medicine

College of Veterinary Medicine

Iowa State University

Ames, Iowa, USA

Larry R. McDougald

Professor

Department of Poultry Science

College of Agricultural and Environmental Sciences

University of Georgia

Athens, Georgia, USA

X.J. Meng

Professor

Department of Biomedical Sciences and Pathobiology

College of Veterinary Medicine

Virginia Polytechnic Institute and State University (Virginia Tech)Blacksburg, Virginia, USA

Samia A. Metwally

Animal Health Officer (Virologist)

Food and Agriculture Organization of the United Nations

Animal Health and Production Division

Rome, Italy

Patti J. Miller

Veterinary Medical Officer

Exotic and Emerging Avian Viral Diseases Research Unit

Southeast Poultry Research Laboratory

Agricultural Research Service

U.S. Department of Agriculture

Athens, Georgia, USA

Egbert Mundt

Animal Health

IDT Biologika GmbH

Am Pharmapark

Dessau-Rossiau, Germany

Venugopal Nair

Head

Avian Viral Diseases Programme

The Pirbright Institute

Compton Laboratory

Compton, Berkshire, United Kingdom

Lisa K. Nolan

Professor and Dr. Stephen G. Juelsgaard Dean

College of Veterinary Medicine

Iowa State University

Ames, Iowa, USA

Amir H. Noormohammadi

Associate Professor

School of Veterinary Science

University of Melbourne

Werribee, Victoria, Australia

Kenneth Opengart

Vice President

Live Operations and Processing

Keystone Foods

Huntsville, Alabama, USA

Vilmos J. Palya

Director

Scientific Support and Investigation Laboratory Ceva Phylaxia Veterinary Biological Co.

Budapest, Hungary

Mary J. Pantin-Jackwood

Veterinary Medical Officer

Exotic and Emerging Avian Viral Diseases Research Unit

Southeast Poultry Research Laboratory

Agricultural Research Service

U.S. Department of Agriculture

Athens, Georgia, USA

F. William Pierson

Professor and Director

Veterinary Teaching Hospital

Virginia and Maryland Regional College of Veterinary Medicine

Virginia Polytechnic Institute and State University (Virginia Tech)

Blacksburg, Virginia, USA

Silke Rautenschlein

Professor and Director

Clinic for Poultry

University of Veterinary Medicine

Hannover, Germany

Ziv Raviv

Assistant Professor and Head of Poultry Medicine Studies

Koret School of Veterinary Medicine

The Hebrew University of Jerusalem

Rehovot, Israel

Rodney L. Reece

Senior Veterinary Research Officer

NSW Department of Primary Industries

State Veterinary Diagnostic Laboratory

Elizabeth MacArthur Agricultural Institute

New South Wales, Australia

Willie M. Reed

Dean and Professor

College of Veterinary Medicine

Purdue University

West Lafayette, Indiana, USA

Jaime A. Ruiz

Director

Cornell University Duck Research Laboratory

New York State Animal Health Diagnostic Center

College of Veterinary Medicine

Cornell University

Eastport, New York, USA

Orhan Sahin

Research Assistant Professor

Department of Veterinary Microbiology and Preventive Medicine

College of Veterinary Medicine

Iowa State University

Ames, Iowa, USA

Y.M. Saif

Professor and Head Emeritus

Food Animal Health Research Program

Ohio Agricultural Research and Development Center

The Ohio State University

Wooster, Ohio, USA

Susan Sanchez

Professor

Athens Veterinary Diagnostic Laboratory

College of Veterinary Medicine

University of Georgia

Athens, Georgia, USA

Tirath S. Sandhu

Director (retired)

Cornell University Duck Research Laboratory

College of Veterinary Medicine

Cornell University

Eastport, New York, USA

Karel A. Schat

Professor Emeritus

Department of Microbiology and Immunology

College of Veterinary Medicine

Cornell University

Ithaca, New York, USA

Stacey L. Schultz-Cherry

Associate Member

Department of Infectious Diseases

St. Jude Children’s Research Hospital

Memphis, Tennessee, USA

Jagdev M. Sharma

Research Professor, Biodesign Institute

Visiting Professor of Life Sciences, School of Life Sciences

Arizona State University

Tempe, Arizona, USA

H.L. Shivaprasad

Professor

California Animal Health and Food Safety Laboratory System—Tulare Branch

University of California—Davis

Tulare, California, USA

Leslie D. Sims

Director

Asia Pacific Veterinary Information Services Pty. Ltd.

Montmorency, Victoria

Australia

Randall S. Singer

Associate Professor

Department of Veterinary and Biomedical Sciences

College of Veterinary Medicine

University of Minnesota

St. Paul, Minnesota, USA

Hanna Skarin

Department of Bacteriology

National Veterinary Institute

Uppsala, Sweden

Joan A. Smyth

Professor

Department of Pathobiology and Veterinary Science

University of Connecticut

Storrs, Connecticut, USA

J. Glenn Songer

Professor

Department of Veterinary Microbiology and Preventive Medicine

College of Veterinary Medicine

Iowa State University

Ames, Iowa, USA

Edgardo Soriano-Vargas

Professor

Centro de Investigacion y Estudios Avanzados en Salud Animal

Facultad de Medicina Veterinaria y Zootecnia

Universidad Autonoma del Estado de Mexico

Toluca, Mexico

Stephan Spatz

Microbiologist

Endemic Poultry Viral Diseases Research Unit

Southeast Poultry Research Laboratory

Agricultural Research Service

U.S. Department of Agriculture

Athens, Georgia, USA

Bruce Stewart-Brown

Senior Vice President

Food Safety and Quality

Perdue Farms

Salisbury, Maryland, USA

David L. Suarez

Research Leader

Exotic and Emerging Avian Viral Diseases Research Unit

Southeast Poultry Research Laboratory

Agricultural Research Service

U.S. Department of Agriculture

Athens, Georgia, USA

David E. Swayne

Laboratory Director

Southeast Poultry Research Laboratory

Agricultural Research Service

U.S. Department of Agriculture

Athens, Georgia, USA

Stephan G. Thayer

Retired

Poultry Diagnostic and Research Center

Department of Population Health

College of Veterinary Medicine

University of Georgia

Athens, Georgia, USA

Daniel Todd

Virology Branch

Agri-Food and Biosciences Institute

Stormont, Belfast, United Kingdom

Deoki N. Tripathy

Professor Emeritus

Department of Pathobiology

College of Veterinary Medicine

University of Illinois

Urbana, Illinois, USA

Hsiang-Jung Tsai

Professor

School of Veterinary Medicine

National Taiwan University

Taipei, Taiwan

Francisco A. Uzal

Professor

California Animal Health and Food Safety Laboratory System

San Bernadino Branch

School of Veterinary Medicine

University of California—Davis

San Bernadino, California, USA

Jean-Pierre Vaillancourt

Professor

Department of Clinical Sciences

Faculty of Veterinary Medicine

University of Montreal

St-Hyacinthe, Quebec, Canada

Paul C.M. van Empel

Global Technical Manager Bacteriology

MSD-Animal Health

Boxmeer, The Netherlands

Daisy Vanrompay

Professor

Faculty of Bioscience Engineering Department of Molecular Biotechnology

Ghent University

Ghent, Belgium

Vicky L. van Santen

Professor

Department of Pathobiology

College of Veterinary Medicine

Auburn University

Auburn, Alabama, USA

H. Vindevogel

ProfessorClinic of Avian Diseases

Faculty of Veterinary Medicine

University of Liege

Liege, Belgium

W. Douglas Waltman

Technical Director for Bacteriology

Georgia Poultry Laboratory Network

Oakwood, Georgia, USA

Susan M. Williams

Associate Professor

Poultry Diagnostic and Research Center

Department of Population Health

College of Veterinary Medicine

University of Georgia

Athens, Georgia, USA

Leslie W. Woods

Professor

California Animal Health and Food Safety Laboratory System

School of Veterinary Medicine

University of California—Davis

Davis, California, USA

Peter R. Woolcock

Professor

California Animal Health and Food Safety Laboratory System

School of Veterinary Medicine

University of California—Davis

Davis, California, USA

Guillermo Zavala

Associate Professor

Poultry Diagnostic and Research Center

Department of Population Health College of Veterinary Medicine

University of Georgia

Athens, Georgia, USA

Qijing Zhang

Professor

Department of Veterinary Microbiology and Preventive Medicine

College of Veterinary Medicine

Iowa State University

Ames, Iowa, USA

Laszlo Zsak

Research Leader

Endemic Poultry Viral Diseases Research Unit

USDA ARS SAA Southeast Poultry Research Laboratory

Agricultural Research Service

U.S. Department of Agriculture

Athens, Georgia

* Deceased

Preface: Historical Review of Diseases of Poultry

Forewords for Diseases of Poultry, beginning with the first one written by John R. Mohler in 1943, have briefly described the nature and contents of the edition, along with substantive reasons for its publication and distribution to potential users. Mohler pointed out that for a profitable poultry industry, Knowledge of the characteristics of each disease is necessary....as the first step in building up an effective barrier against it. He further noted that This unusually comprehensive book is intended for students, veterinarians, pathologists, and workers in specialized fields. These words are as applicable today as they were 70 years ago and the importance of the text is supported by publication of 13 editions.

For the 6th edition in 1972, Dr. P.P. Levine offered an accounting of some of the changes in the poultry industry that moved it from a small-scale farm activity to a highly sophisticated industry marketing products worth over $6 ­billion per year in the United States alone. He correctly attributed some of the many advances in disease control through eradica­tion, genetic selection, immunization prac­tices, management improvements, etc. to major advances founded in research. Such new knowledge strongly dictates a need for revised texts. Levine further predicted that infectious diseases will decline in importance; toxicologic, nutritional, genetic, and husbandry problems will demand increasing attention. Change is the order of life, and avian diseases are no exception. In the 7th edition (1978), he pointed out many of the important new advances in identifying the etiology of several conditions, and the need for Diseases of Poultry to keep up with the rapid developments in avian diseases.

Ben Pomeroy, in the 8th (1984) and 9th (1991) editions, reiterated the need for new editions to keep up with the explosion of knowledge on the prevention and control of avian diseases. The inclusion of contributions from experts from many countries of the world, and the importance of such in the face of global issues of disease control, was emphasized by Charles Beard in the Foreword of the 10th (1997) edition. He pointed out that understanding the molecular genetics of causative agents is also important and the use of molecular methods is necessary for poultry disease researchers to understand and control infectious diseases; yet another reason for timely updates.

The message is clear: a changing and global poultry industry and its many allied industries need the most recent information available to keep pace with the challenges of providing ­adequate health care and disease prevention. It is important not only to poultry flocks, but also to the consumers who expect safe, as well as nutritious, poultry products. This, the 13th edition, upholds the long-standing reputation of this book for keeping scientists, breeders, poultry producers, and poultry health professionals supplied with the latest and most comprehensive information available.

Seventy years have passed since the first edition was printed. Before all details are lost forever, it is fitting to look back at how this Bible in the field of poultry diseases came to be and how it has evolved into what it is today. It all began in the 1930s. In a memorandum addressed to the American Association of Avian Pathologists (AAAP) dated December 22, 1965, H.E. Biester related the events that preceded the decision by the Iowa State College (now University) Press (ISU Press) to undertake the publication of Diseases of Poultry. During the 1930s, Louis DeVries, a member of the Department of Modern Languages at the college, translated a 1929 German book entitled Handbuch der Geflüge­lkrankheiten und der Geflügerzucht, published by Ferdinand Enke, Stuttgart. The translation laid dormant for several years until Dr. D.M. Campbell, the Chicago publisher of Veterinary Medicine, saw the translation and expressed some interest in it. Dr. Biester, who described himself as an innocent bystander, having no special interest in the project, told Dr. Campbell that the manuscript was unacceptable for a variety of reasons and he suggested that if he were serious about publication, then selected specialists should edit or rewrite the material. Dr. Biester later was pulled into the project and he ultimately concluded that the German book was obsolete. Apparently, a number of men had accepted invitations to cooperate in developing an American book, and according to Biester, they agreed that it would be better to prepare a totally new book based on American conditions.

Thus, the die was cast. Dr. Campbell gave up his plans, and the ISU Press decided to publish an original text. Drs. Biester and DeVries served as editors, and 34 American investigators were engaged in the project. There were chapters on general subjects such as anatomy, digestion, genetics, hematology, hygiene and sanitation, nutrition, and surgery, as well as those dealing with specific infectious and noninfectious diseases and conditions. A separate chapter dealt with diseases of turkeys. In 1943, the 1st edition was ready. The publication costs were considerable for a book that was thought to have limited distribution, so it was decided to omit royalties and accept a subsidy for illustrations from the Dean of the College. Fifteen hundred copies were printed and placed on sale for $7.50; to everyone’s surprise, a second printing of 2,500 copies was needed after less than 9 months and there was yet another printing of 2,500 copies 2 years later. Royalties were then instituted! The ISU Press was concerned that without some remuneration, the authors might be reluctant to remain dedicated.

The inclusion of Dr. DeVries as an editor is a bit puzzling since he had no medical background; perhaps it was in recognition of his effort with the translation of the German text. In any case, he was replaced in subsequent editions by Dr. L.H. Schwarte, a member of the Veterinary Research Institute in Ames who had written 4 chapters in the 1st ­edition. The book was thereafter referred to by many as Biester and Schwarte, even for a period after they were no longer associated with it. They continued at the helm through the 5th edition, published in 1965. Although Dr. Schwarte contributed several chapters in each of the first 5 editions, Dr. Biester apparently confined his efforts to editorial tasks. Their memo to the AAAP stated that they both were responsible for making the index, and they personally checked practically all of the references because they felt that they owed to the reader accuracy. A total of 61 persons served as authors under their editorial supervision; 12 of them contributed to all five editions.

Ultimately, the passage of time dictated that Drs. Biester and Schwarte should relinquish their roles as editors and they decided that the 5th edition (1965) would be their last. As noted in the Preface to the 6th edition, it was their wish that future editions of the book become the responsibility of the AAAP… which had become a strong and representative organization to which many of the users of Diseases of Poultry belonged. Also the AAAP was already in the business of publishing the journal Avian Diseases and so it was considered a logical move. The AAAP appointed a committee, chaired by Dr. M. S. Hofstad who had been one of the book’s authors and who was on the faculty in Ames. Drs. Biester, J.E. Williams, B.S. Pomeroy, and C.F. Helmboldt filled out the committee and, in June 1966, they recommended that the AAAP sponsor future editions of Diseases of Poultry which would continue to be published by ISU Press in Ames. They asked the Board of Directors to appoint an editorial committee consisting of an editorial chairman and 4 associate editors by January 1, 1967. A letter from Dr. G.H. Snoeyenbos (AAAP secretary-treasurer) to Dr. C.A. Bottorff (AAAP president) dated November 23, 1966, suggested that Dr. P.P. Levine had declined a proposal that he assume the editorship for the book. Dr. Hofstad was subsequently named editor, and he personally requested that Drs. Helmboldt, B.W. Calnek, W.M Reid, and H.W. Yoder, Jr., be invited to be the associate editors. Each was given responsibility for a group of chapters that largely ­represented their individual interests and strengths. An agreement between the AAAP and the ISU Press was executed on May 8, 1967, and it was agreed that manuscripts would be delivered to the publisher by September 1, 1969. So the transfer was complete and official.

The 6th edition, under totally new editorial support, underwent some significant changes. The length of the book was beginning to be of concern and there was some discussion about perhaps needing to split it into 2 volumes. To avoid this, several chapters (anatomy, nutrition, genetics, and hematology) were eliminated based on good coverage in other publications. Also, there was a consolidation of other material; for instance, all neoplastic diseases were placed in a single chapter and turkey diseases were incorporated in other chapters based on etiology. There were sweeping changes in authorship. Only 14 of the 40 contributors to the 6th edition had participated in the 5th. Clearly, a new era had arrived!

Also, following concern for the book’s length, Dr. Hofstad asked that the number of listed references be reduced by selective citation. He agreed that the reader should find, or be directed to, all pertinent literature on each of the covered topics, the latter through citation of review papers, etc. Space allocated to references became an issue in subsequent editions as well. In the 7th and 8th editions, titles of all references were removed. This was controversial and not all editors agreed, including B.W. Calnek—senior author of this review—and reference titles appeared again beginning with his tenure as editor of the 9th edition. Interestingly, based on the number of pages, the 3rd edition (1,245 pages) was actually longer than the 11th (1,231 pages), but by increasing page size, decreasing type size, and splitting into 2 columns/page, it was possible to include more than twice the amount of written material in the latter.

Unlike the situation with Drs. Biester and Schwarte, citations and their accuracy became the responsibility of the ­individual authors. When it was observed that many errors existed, authors of the 9th edition were asked by Dr. Calnek to check every single reference against the original work to assure accuracy. This met with an enormous number of groans and considerable resistance until each author (with perhaps an exception or 2) followed this strict instruction. The subsequent turn-around in their attitude was truly amazing when nearly all of them found errors, including the citation of references that did not even exist. It was not uncommon to detect mistakes in as many as 10% of citations in some ­chapters, probably due in large part to a common practice of copying reference citations from other lists.

Beginning with the 9th edition, the book entered the ­electronic age. All material was submitted or copied into a word processing program that allowed spell-checking and reformatting. Initially, it was a tedious job, particularly because personal computers at that time were slow and the skill of the individual authors in mastering a new approach varied considerably. However, improvements in software and ­computers and the possibility of rapid transfer of texts between authors, editors, and the publisher made the preparation of a new edition pleasurable compared to the old hard-copy approach.

There has been a continuum of changes that have improved Diseases of Poultry and kept it relevant over the years. For the 10th edition, the editors carefully reviewed and upgraded illustrations and for the first time included a number of color plates. Another major improvement that was gradually incorporated was the inclusion of molecular biology in many of the chapters. This was particularly important with regard to new applications of molecular techniques in diagnostic procedures, descriptions of etiological agents and significant elements of their molecular makeup, understanding the ­significance of selected genes in the pathogenesis of the ­diseases, and the development of genetically engineered vaccines. Our understanding of the fundamental nature of many diseases is now founded on the use of molecular approaches in the research laboratory.

Another of the more significant evolutionary changes was the addition of foreign authors to make the book truly international in flavor. One of the original AAAP-appointed editors argued strongly that Diseases of Poultry should be an American book, and the authorship was so aligned. The 6th edition had the first foreign contributor, although she (Bela Tumova, from Prague, Czechoslovakia) was actually a visiting professor at the University of Wisconsin working with B.C. Easterday on avian influenza at the time. It wasn’t until the 8th edition that invitations to contribute to the book were extended to workers outside of the United States. Drs. P.M. Biggs and L.N. Payne from England and Drs. J.B. McFerran and M.S. McNulty from Northern Ireland thus paved the way by providing parts of the chapters on neoplastic diseases, adenoviruses and miscellaneous viral infections. The next edition (9th) was truly international with 17 contributors from 8 countries outside of the U.S., and by the 11th edition, there had been a total of 25 different contributors from 11 countries. The worldwide reputation the book was certainly enhanced by the selection of authors based on their knowledge and contributions to our understanding of individual diseases and conditions without regard to their geographic location.

The importance of Diseases of Poultry as a text for the world is also reflected in its translation into foreign languages or publication in a copied form in other countries. There have been several authorized translations into Spanish, Chinese, and Russian, and an agreement between the publisher and India has allowed what is essentially a photocopied version of the original to be made.

An ongoing review of the relative importance of individual diseases or conditions has led to a good deal of reshuffling over the years. Chapters have been added, combined, split, or eliminated to meet the changing picture of what is important to the field of avian diseases and disorders. Periodically, and especially with a change in authorship, major rewriting of some sections takes place. New chapters such as one dealing with new and emerging diseases appear when needed.

Beginning with the 12th edition emphasis was placed on the significance of each disease to public health considering the ever increasing interest in food safety. Emphasis was also placed on standardizing the format for all the subchapters by using the same headings thus making the book more reader friendly. In addition several non-USA residents became contributing authors.

Despite our increased understanding of disease processes there remains much to learn. Only in very few cases do we know the molecular markers of virulence, pathogenicity, or immunogenicity of pathogens and, needless to say, the molecular basis for disease resistance is a wide open field. In many cases, our understanding of disease-triggering mechanisms is poor and diseases of multiple etiologies remain problematic.

As indicated, the introduction of molecular techniques has greatly enhanced our understanding of disease but it has also created some confusion as we strive to understand the underlying genetics of important biologic characteristics of pathogens. The early euphoria from thinking that 1 gene is responsible for a given biologic characteristic is being replaced by the realization that more than 1 gene is usually involved. This makes it difficult to decipher our observations. Another point of confusion resulted from the definition of the term genotype and early attempts to relate it to serotype or protective type. Again, it became clear that such a relationship is lacking in most cases and genotyping is useful mainly for epidemiologic studies. Considering all these gaps in our knowledge, and the unprecedented speed of knowledge generation, it is understandable that we need a new edition every 5–6 years to keep our text continually updated.

Finally, the euphoria of the last century, suggesting that we will conquer infectious diseases as stated to the U.S. Congress in 1969, by then Surgeon General of the United States William H. Stewart (We can close the books on infectious diseases…), and our own P.P. Levine’s prediction in 1973 stated earlier in this section (Infectious diseases will decline in importance…) proved terribly wrong. Microbes are a tough and nimble foe capable of changing and adjusting to new environments mostly created by man. Thus, we think that infectious diseases will continue to be a top health priority for poultry, another reason why we continue to need new editions of this book.

Changes in editors occurred over the years so that by the 11th edition, none of the 1968 group appointed by the AAAP remained. After riding herd on 3 editions (6th–8th), Dr. Hofstad retired and was replaced by Dr. Calnek (9th and 10th) and he, in turn, passed the baton to Dr. Y.M. Saif ­(11th–12th), and most recently to Dr. D.E. Swayne (13th). Likewise, associate editors that have replaced or been added to the original group appointed by the AAAP in 1968 include Drs. H.J. Barnes (8th–11th), C.W. Beard (9th and 10th), L.R. McDougald (10th–13th), Y.M. Saif (10th), J.R. Glisson (11th–13th), A.M. Fadly (11th and 12th), D.E. Swayne (11th and 12th), L.K. Nolan (12th and 13th), and D.L. Suarez and V. Nair (13th). Dr Nair is the first non-USA resident to serve on the editorial board of the book, another indication of the universal reach of the book.

In summary, it is obvious that the Bible in the field of avian diseases is an evolving, vibrant, and ever-current source of information relevant to all practitioners in the field of poultry medicine. It continues to be a reference source of ­significance to a vast number of persons with many different relationships to the poultry industry.

Bruce W. Calnek

Y.M. Saif

David E. Swayne

Introduction

This edition is appropriately dedicated to 2 colleagues who have devoted their careers to creating new knowledge and passing on existing wisdom on poultry health through successive editions of Diseases of Poultry: Dr. Y.M. Saif, who served as Associate Editor for the 10th edition and Editor-in-Chief for the 11th and 12th editions, and Dr. Aly Fadly, who served as an Associate Editor for the 11th and 12th editions. Both have been instrumental in maintaining the high quality of this book, and, indeed, we are highly grateful for their efforts. In addition, I am personally grateful to Dr. Saif, who has mentored me over the past quarter century as a scientist, writer, and editor, especially in the past 5 years in transitioning to Editor-in-Chief for the 13th edition of Diseases of Poultry. With this edition, Drs. Venugopal Nair and David L. Suarez joined the existing Associate Editors, Drs. John R. Glisson, Larry R. McDougald, and Lisa K. Nolan. We are very appreciative of their services.

This edition has a major emphasis on electronic versions with expansion of color figures and availability of 3 specific electronic formats to accommodate a variety of media from traditional computers to stand-alone electronic books to smartphones. The new generation of poultry veterinarians and scientist are living and working in the electronic age and rely upon instantaneous access to crucial information to do their jobs, and Diseases of Poultry will be at their fingertips or in their pockets for daily and mobile use. In addition, the widely used high quality, hard copy is also preserved as a reference text, but with fewer color plates than in the electronic formats.

This 13th edition represents a continuation of the tradition established earlier of providing the latest information on poultry diseases. Earlier trends of expansion of authorship to include authors from around the globe were continued in this edition, as was the appointment of our first non-USA Associate Editor. The Preface was updated and expanded to a more comprehensive review of the history of Diseases of Poultry, including valuable new metric data.

All of the book chapters were updated with the most current and accurate knowledge and many with new figures, especially color figures of gross lesions. Much of the historical information was removed and readers are referred to prior editions. A new subchapter on public health significance of poultry diseases was added to Principles of Disease Prevention, Diagnosis, and Control, (Chapter 1) and public health information was reduced in the individual chapters. A new subchapter on enteric parvoviruses was added to Chapter 12, Viral Enteric Infections. Major revisions were accomplished for Principles of Poultry Production, Health and Disease Control in Commercial Systems; Newcastle Disease; Avian Paramyxoviruses 2-11, and Internal Parasites. With no new cases in 2 decades, the torovirus chapter was removed and readers are referred to prior editions of Diseases of Poultry for such information.

Subchapters on Dermal Squamous Cell Carcinoma and Multicentric Histiocytosis were merged into the subchapter on Other Tumors. Cochlo­soma anatis Infections was merged in with the subchapter on Miscellaneous and Sporadic Protozoal Infections. These changes were dictated by the increasing or decreasing significance of some diseases or the increasing knowledge on a given disease. Some subchapters have been moved to different chapters because of recent findings indicating that they fit within different areas.

A sincere thank you goes to the authors who contributed to the current and earlier editions of the book. It has been a wonderful experience working with all of you.

The personnel at Wiley-Blackwell that worked on this ­edition have been most helpful and accommodating, and we sincerely appreciate their support.

This is the first time that I served as Editor-in-Chief of Diseases of Poultry, and I (DES) am indebted to my colleagues, the associate editors, for their tireless efforts in the review process and their support and advice.

Finally, I would like to acknowledge special assistance provided by two students, Jessica Self and Jamie Conner, in reviewing and formatting reference lists and retyping figure legends.

Editor-in-Chief

David E. Swayne

Associate Editors

John R. Glisson

Larry R. McDougald

Venugopal Nair

Lisa K. Nolan

David L. Suarez

I  General Concepts of Poultry Diseases

Chapter 1  Principles of Disease Prevention, Diagnosis, and Control

Chapter 2  Host Factors for Disease Resistance

Chapter 1

Principles of Disease Prevention, Diagnosis, and Control

Introduction

Stephen R. Collett

Poultry product prices have not kept pace with rapidly escalating input costs, causing profit margins to diminish throughout the poultry industries. Producers are faced with the challenge of consistently achieving expected performance while satisfying stringent food safety and animal welfare requirements; they can no longer tolerate even the slightest deviation from expected performance.

In an effort to cost-effectively meet demand, producers have had to increase the size and throughput of their production systems. These large close confinement rearing systems, designed to improve economies of scale and maximize productivity by optimizing bird comfort, unfortunately also increase the risk of disease challenge. The physiological stress of keeping pace with genetic potential for production makes birds more vulnerable to disease challenge, and the close proximity of susceptible hosts increases the chance and rate of infectious disease spread. Diseases previously recognized as unimportant, because they have been adequately controlled, have now reemerged as significant concerns. Most of today’s disease challenges are not new problems; rather, they have merely expanded their geographic distribution or reemerged primarily because of management techniques and production system design constraints.

Methods of disease control have evolved with intensification of the industry. While initially focused on diseases of catastrophic nature, attention has rapidly shifted from defined, clinical disease at the individual house or farm level to less well-defined subclinical disease and bird welfare. Similarly, cost justification in decisions on whether or not to implement prevention or control measures has become more complex, requiring the aid of formal economic appraisal.

To maximize flock efficiency, disease challenge management requires a carefully designed, multi-tiered approach, which includes consideration of elements ranging from flock health and productivity to chick or poult viability. In addition, the term efficiency implies the all-important economic component. Because the production system is profit driven, decisions regarding disease challenge can rarely be made based solely on biological grounds. Disease management intervention also requires sound economic justification, which begins with clearly defining the financial risk associated with disease.

Unless a disease poses a specific risk to human health or animal welfare, its mere presence in a flock may not be significant from a business perspective. It is often difficult for the veterinarian, trained in disease prevention, diagnosis, and control, to appreciate that the presence of a disease in a flock could be considered superfluous. Unless it is economically advantageous to take action against a disease challenge, its presence in a flock is tolerated. Intervention strategies are consequently chosen based on both their economic and biological efficiency. This process requires a dynamic, integrated combination of an epidemiologic and economic analysis to determine and quantify the production effect of the disease challenge as well as a proposed intervention strategy. Such integrated analysis has become far more significant in today’s intensive production systems because the outcome of disease challenge is so markedly influenced by the environmental conditions.

The economic impact of disease is difficult to assess. This is particularly so in a production system in which the economic return is governed not only by flock productivity but also by product quality and viability. In addition, the consequential loss from disease challenge will be, at best, only partially recoverable. Using the cost of disease to justify intervention over-emphasizes the consequence of inaction and it is only useful in justifying intervention strategies directed at disease prevention. As the process of economic analysis has evolved, the focus has shifted from the cost of disease to the benefit derived from disease control strategies.

Bird performance continues to increase linearly because of efficient breeding and selection programs, but each increment in improvement is 1 step closer to the point of physiological limit and diminishing returns. Production systems need to be modified to better satisfy bird requirements, and disease prevention, diagnosis, and control strategies changed to preclude physiological, nutritional, and agent-induced pathologies from affecting performance.

Acknowledgement

The author is greatly indebted to Alex J. Bermudez for his contribution to earlier editions of this subchapter.

Principles of Disease Prevention, Diagnosis, and Control Introduction

Stephen R. Collett

Flock Health

Disease is the antithesis of health but neither state is easy to define in production animals. Health is defined in the human individual as a state of physical, mental, and spiritual well-being. It is impossible to apply this definition to an animal, and production animals have in the past been classified as healthy if they were free from clinical disease and performing to standard. Although individual animals are frequently described as healthy or diseased, these terms are not mutually exclusive. The impact of disease challenge on productivity is apparent long before clinical signs of disease appear. Production animals are expected to perform at their genetic potential, and to achieve this they need to be physically and mentally well or stress free.

Stress has been defined as a nonspecific response of the body to any demand made upon it. From a physiological point of view this can be restated as the metabolic response of the body to external factors that impact well-being (34). Stress is cumulative and only measurably impacts performance once the aggregate of each individual stress exceeds the host’s ­coping mechanisms. An interesting study by Klasing et al. (52) has shown that the degree to which an adverse stimulus or stress will negatively impact bird performance is directly proportional to the existing stress load. Any stress will impact productivity once the stress threshold is surpassed. In a production system in which animals are expected to produce at genetic potential, the definition of health needs to be expanded to freedom from disease or stress. In this context, health is proportional to the difference between stress level and stress threshold.

Disease prevention and control strategies tend to be too focused on addressing the precipitating cause, and too little attention is given to the predisposing causes of disease. The traditional paradigm of disease has been shaped by the study of specific diseases in individual animals and tends to overemphasize the importance of the infectious agent. In intensive animal agriculture it is the influence of environmental disease determinants that decides the economic outcome of infectious agent challenge. The focus of flock health management has consequently shifted. Initially aimed at avoiding mortality because of an inadequate immune response, health management is now directed at avoiding an exaggerated or inappropriate immune response because it may depress productivity. The task of the veterinarian has shifted from the prevention, diagnosis, and control of specific disease conditions in the individual bird to preventing and limiting the consequence of more complex multifactorial disease outcomes to maximize the productivity of the flock.

Resistance and Resilience

An animal’s resistance to disease can be defined as its capacity to prevent an overwhelming infection by a disease-causing organism. Disease resistance is determined by immune competence and health status at the time of challenge. Because stress negatively impacts health it also negatively impacts resistance. Ironically, the process of mounting an effective immune response is itself a source of stress because of the demands made on the immune system and the consequence of the resulting fever response. An immune response that is adequate to contain disease can be considered as the cost of health. There is a delicate balance between too little and too much because an inappropriate immune response, whether inadequate or excessive, will depress performance.

The resilience of an animal is a measure of its capacity to continue to perform while preventing a disease challenge from causing an overwhelming infection. As with resistance, resilience is negatively impacted by poor health but in this case the negative impact of the resulting stress is more significant. The chemical messengers (cytokines) released in response to a disease challenge depress production directly by influencing metabolism and indirectly by suppressing appetite and feed intake (52). While immune response is crucial to maintaining health, its consequence is depressed productivity.

The skin and respiratory, urogenital, and gastrointestinal tracts form the interface between foreign (antigenic) material and animal cells (self). To protect the bird from disease the immune system has to develop exquisite sensitivity as to whether foreign antigens are friend (nutrients or normal flora) or foe (pathogenic). An inappropriate immune response to gastrointestinal antigens will, for example, have a negative impact on feed efficiency. The fever response induced by foreign antigens will depress feed intake, while the inflammatory response damages the gut lining, thus reducing the nutrients available for production. The capacity of an animal to fight off a disease challenge while avoiding the negative impact of the induced immune response on productivity (resilience) depends on how close the prevailing level of stress is to the bird’s stress threshold. The success of any health program thus hinges on balancing immunity and health to maximize resilience. There is a dynamic interface between nutrition, immunity, and productivity. The aim of any production veterinarian should be to optimize feed utilization by modulating the immune response: enhancing the protective response to prevent clinical disease while simultaneously suppressing the acute phase or fever response.

Population Dynamics

Like human medicine, traditional veterinary medicine is focused on the study of the disease process in individuals. In modern flock medicine, where the emphasis is on prevention, diagnosis, and control of disease in finite and confined populations, the focus shifts to the epidemiology of the disease. Flock health is a rather nebulous term. Because health and disease are not mutually exclusive, individual birds within the flock will at any point in time be in various stages of health/disease (Poisson distribution). At what point is a flock diseased or healthy? Productivity gives a good estimate of an individual’s state of well-being and welfare. Similarly, a flock that is performing to standard is assumed to be healthy, based on the fact that the birds act and produce as an equivalent nonstressed sibling would in a laboratory situation. This approach unfortunately takes little cognizance of the flock variance, because flock performance indicators are based on flock averages. Population variance or range is a much better indicator of flock health.

Modern population-based health management requires the complex integration of animal husbandry (housing environment), medical management (host and agent factors), and epidemiological practice (analysis of causal relationships). Modern risk management approaches facilitate the transformation of epidemiologically derived statistical data into a population health management tool. The probability of exposure to health risk factors and their expected outcomes are used first, to guide the response to a disease challenge, and second to improve the health program design/management to better respond to future potential population health challenges.

Each component of the production process can be evaluated on the basis of cost and contribution. In the past, intensive agriculture has been production driven, and contribution measured in terms of performance. In today’s market-driven enterprise, value is regarded as a function of quality, yield, and cost of production with the emphasis shifting from performance to profit through the chain of realization. In this scenario the simplest strategy for improving productivity is to reduce within- and between-flock variance. By reducing variability and thus eliminating the extremes, it is possible to improve the quality, speed, and cost of production. Improved uniformity translates to improved productivity and hence profitability. Health (the difference between stress level and stress threshold) is probably the single most important determinant of flock uniformity. Within a group of animals the threshold and level of stress experienced by each individual will vary. The relative efficiency of a production manager to minimize in-house environmental variation, and therefore host-, agent-, and environment-dependent stress, is reflected in flock uniformity.

Challenges of Disease Prevention, Diagnosis, and Control in Modern Poultry Production

Because the goal of a poultry operation is to convert feed into food as economically as possible, it is critical to manage both the risk and consequence of disease challenge. While the biological efficiency of feed conversion is governed primarily by intrinsic or genetic determinants, in an intensive production system it is the extrinsic disease determinants that ultimately decide the efficiency of the operation in both biological and financial terms. Capital investment in the housing’s environmental control capability, and the effective operation of these controls, is fundamental to economic success. Even subtle disease challenge such as vaccination with live respiratory disease vaccines can compromise efficiency if exacerbated by environmental disease determinants.

Viral diseases are challenging to control because there are no effective treatment options, while bacterial, protozoal, and parasitic diseases present a challenge because the treatment options are either no longer available or no longer effective. The approach to controlling diseases within these 2 categories is very different.

The molecular structure of a virus particle is relatively simple, making immunological recognition very acute and the control of known viral diseases possible through immunization. Provided the immune system has been primed by vaccination, immunological protection against viral disease challenge is usually highly successful. Emerging and reemerging viral diseases arise when novel or immunologically distinct viruses are introduced into naïve populations (48). In the absence of prior exposure, immune recognition and activation is delayed and the extent of the primary immune response is frequently inadequate to prevent clinical disease (45). Under such conditions virus replication and spread occurs rapidly with potentially devastating consequences (22). While the majority of emerging viral diseases in humans are the result of exposure to novel viruses, it is the emergence of variant strains that pose the biggest threat to the poultry industry (88). Although controlled environment housing and good biosecurity practices have been highly effective in preventing the introduction of novel viruses, increased population density and vaccination have likely enhanced the emergence of variant strain viruses. The high population densities provide the opportunity for antigenic shift through gene recombination, while vaccination creates positive selection pressure for the variant strain viruses (79).

In contrast to viruses, bacteria and protozoa are structurally and immunologically complex, making protection through vaccination much less successful. Although a great deal of research effort is and has been focused on developing effective immunization strategies for these diseases, antibiotics have remained the primary means of control (24)—a point well illustrated by the escalating difficulties experienced in the European Union with the current systematic withdrawal of in-feed antibiotics (33). It is no coincidence that the downward trend in prophylactic (in-feed) antibiotic usage has been matched by an increase in therapeutic use (58). Many expert committees blame the use of in-feed antibiotics in food animal agriculture for the proliferation of antibiotic-resistant strains of bacteria and for the increase in prevalence of antibiotic-resistant infections in humans (47). This is undoubtedly providing the impetus to ban in-feed antibiotic use, even though a link to increased antibiotic-resistant bacterial disease in humans has not been conclusively established (29). Consumer pressure to remove antibiotics from the food animal nutritionist’s arsenal is, however, winning the battle and the trend toward reemergence of previously controlled bacterial and protozoal diseases will likely continue. The industry must adapt to remain competitive.

The Principles

Disease prevention and control involves the 3 interrelated processes of bioexclusion, surveillance, and biocontainment. Disease prevention is difficult, expensive, and requires total commitment because it invariably involves eradication. Eradication programs are appropriate when the economic consequence of the disease is so devastating that it is economically advantageous to implement such drastic control measures. It is only feasible if there is an effective means of detecting infection, containing the infection through clean-out and disinfection, and preventing dissemination of the disease causing agent (75). There are 3 categories of disease for which eradication is an appropriate means of control: those that significantly threaten public health, those that have a devastating effect on bird performance, and those that severely compromise product quality. With diseases of this nature, the control effort is focused on the complete elimination of the agent from the environment (75). This places the emphasis on preventing contact between the agent and the host (bioexclusion). Early diagnosis and containment is in this case the contingency plan for failure in bioexclusion.

In contrast to eradication, control programs are aimed at limiting disease challenge to a tolerable level. There is a subtle shift in emphasis from prevention, through bioexclusion, early detection, and elimination, to reducing the consequence or ­economic impact of the disease, i.e. damage control. Although monitoring and surveillance are still used to gather prevalence data, the primary focus is to measure the level of protection and challenge, not the mere presence of the disease. The principles of prevention through biosecurity still apply, but in a disease control program the focus shifts to limiting the extent and consequence of exposure. In reality, many of the biosecurity measures taken to eradicate the more devastating diseases provide a solid foundation for the control of the erosive diseases, and immunization is usually used to bolster host resistance.

Methods of disease management have evolved with intensification of the industry. While initially focused on diseases of catastrophic nature, focus has rapidly shifted from defined, clinical disease at the individual house or farm level to less well-defined sub-clinical disease and bird well-being or welfare. Similarly, cost justification in decisions on whether or not to implement control measures has become more complex, requiring the aid of formal economic appraisal.

The presence of disease in a flock only becomes significant when the functional derangement of normal metabolic and homeostatic processes causes a decline in productivity that is sufficiently large to affect economic efficiency. This occurs either as a result of disease-induced anorexia or through specific effects on the physiological processes of nutrient metabolism, respiration, and excretion. Only in severe cases does disease cause mortality, and yet mortality rate is used universally as a measure of flock health status. Health and disease are not mutually exclusive, yet a flock is assumed to be healthy when it is performing to standard and is free of clinical disease. Productivity provides a much more sensitive measure of flock health, but because it is the composite output of a population it gives no indication of the variance in health status between individuals within the flock. Within-flock variance provides the most sensitive measure of flock health status but flock uniformity is still a fairly coarse measure of health status.

Disease challenge management must be considered to be an integral part of any poultry business risk management program. It involves the development and implementation of a stringent biosecurity plan which comprises a hierarchy of components directed at preventing or limiting the risk and consequence of disease. Economic analysis is a critical step in biosecurity plan design because resource allocation must match risk (10). Although it is difficult to accurately determine the precise risk and consequence of a disease challenge, it is possible to rank disease challenge according to relative risk (39). From a risk analysis point