Guide for Aquatic Animal Health Surveillance

126 Pages·2009·1.97 MB·English

Guide for
Aquatic Animal
Health Surveillance
Primary authors:
Flavio Corsin
Aquaculture and Aquatic Animal Health Specialist
Hanoi
Vietnam
Marios Georgiadis
Lecturer of Epidemiology
Faculty of Veterinary Medicine
Aristotle University of Thessaloniki
Greece
K. Larry Hammell
Professor, Dept of Health Management
Director, AVC Centre for Aquatic Health Sciences Atlantic Veterinary College
University of Prince Edward Island
Canada

Barry Hill
Chief Advisor for Aquatic Animal Health
Centre for Environment, Fisheries and Aquaculture Science
United Kingdom
Published by
The World Organisation for Animal Health
(OIE)
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by international copyright law. Extracts may be copied, reproduced,
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and any other medium destined for the public, for information, educational or
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the material in this publication do not imply the expression of any opinion
whatsoever on the part of the OIE concerning the legal status of any country, territory, city or
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The views expressed in signed articles are solely the responsibility of the authors. The
mention of specifi c companies or products of manufacturers, whether or not these have
been patented, does not imply that these have been endorsed or recommended by the OIE
in preference to others of a similar nature that are not mentioned.
© Copyright
OIE (World Organisation for Animal Health)
12, rue de Prony, 75017 Paris, France
Tel.: [phone]
Fax: [phone]
http://www.oie.int
ISBN: 978-92-9044-767-2
Contents
Acknowledgements vii
Foreword ix
Chapter 1 General introduction 1
Purposes of aquatic animal health surveillance 1
Surveillance versus surveys 2
Surveillance versus monitoring 2
Surveillance methodologies 3
Demonstrating the absence of disease or infection 3
Determining the occurrence or distribution of endemic disease
or infection, including changes to their incidence or prevalence 4
Deciding which diseases to subject to surveillance 4
Chapter 2 Pathogen transmission in the aquatic environment 5
Transmission mechanisms 5
Routes of pathogen transmission among aquatic animals 5
Pathogen transmission in aquaculture 6
Transmission between farmed and wild aquatic animals 6
Chapter 3 Populations 8
The concept of populations 8
Host factors affecting population defi nitions 10
Epidemiological units 11
Zones and compartments 11
Clustering 13
Target population 14
Susceptibility of host species 14
Chapter 4 General design considerations 16
Types of surveillance system 16
Background information requirements 18
Prioritisation of resources 19
Sources of data 20
Case defi nition 20
Surveillance and denominator-based information 21
Chapter 5 Diagnostic tests 22
Diagnostic testing in aquatic animal health surveillance 22
Test sensitivity and specifi city 22
Predictive value of a test 23
Factors that affect test sensitivity and specifi city 24
Estimation of test sensitivity and specifi city 24
Serological tests 25
Testing using pooled samples 26
Observation of clinical signs and productivity as a diagnostic test 27
Testing in multiple laboratories 27
Use of molecular techniques for confi rmatory testing
and diagnosis 27
Guide for Aquatic Animal Health Surveillance iii
Contents
Chapter 6 Sampling considerations for surveillance 29
General considerations 29
Sampling strategies 29
Non-probability sampling methods 30
Probability sampling 32
Clustering of disease and selection bias 33
Cluster and multi-stage sampling 33
Summary of valid sampling for disease and production 34
Sampling units 35
Sample size considerations 35
Chapter 7 Flow of information and tools/methods 38
Data and information fl ow 38
Registration of units 38
Collecting health data and information 38
Recording health data 40
Flow of information through the system 41
Reporting from laboratories 43
Chapter 8 Data management 44
General considerations 44
Diagnostic laboratory sources of data 45
Under-reporting of data in voluntary systems 45
Data validation 45
Detection of new diseases 45
Disease frequency estimation 46
Chapter 9 Statistical aspects 47
Expertise required 47
Quantifying uncertainty 47
Statistical inference 47
Statistical hypothesis testing 47
Errors in statistical hypothesis testing 47
The power of the statistical hypothesis test and sample size 48
Statistical estimation 48
Bayesian statistical inference 48
Assumptions 49
Surveillance to support claims of disease freedom 49
Design prevalence 49
Sensitivity and power of the surveillance system 50
Analysis of data 51
FreeCalc 51
Bayesfreecalc 54
Other data sources 55
Surveillance to describe disease occurrence 56
Estimating disease prevalence using imperfect diagnostic
tests 57
WinPEPI 58
Temporal distribution of disease in a population 58
Surveillance for detection of new diseases 59
iv Guide for Aquatic Animal Health Surveillance
Contents
Chapter 10 Responsibilities and resources 60
Roles and responsibilities 60
Capacity building 62
Allocation of resources 63
Human resources 63
Infrastructure 64
Financial resources 64
Incentives 65
Chapter 11 Response to surveillance information 66
Information dissemination 66
International reporting 66
Eradication 66
Zoning 67
Evidence collection and outbreak investigations 67
Research 67
Aquatic animal health management practices 68
Modifi cations to the surveillance system 68
Health certifi cation and quarantine 69
Diagnostics 69
Contingency plans 69
Risk analysis 70
Policy and legal frameworks 70
Chapter 12 Monitoring and evaluation 71
Flexibility of surveillance 71
Sensitivity and specifi city of surveillance programmes 71
Component testing 72
Timeliness 73
Cost effi ciency 73
Ability for external audit and verifi cation 74
Chapter 13 Special design considerations for surveillance of wild,
ornamental and sessile aquatic organisms 75
Wild populations 75
Ornamental aquatic animals 76
Sessile organisms 77
Chapter 14 Improving evidence to support the design and performance
of surveillance systems 79
Evidence-based policy decisions 79
Considerations for assessment 79
Coordination, responsibilities and funding 80
Confl ict with end-users 80
Appendices 81
1 Establishing a passive surveillance system 82
2 One-stage structured survey (farm certifi cation) 90
3 Two-stage structured survey (national freedom) 94
4 Spatial sampling and the use of tests with imperfect specifi city 98
5 Example record sheet for aquatic animal health offi cers 101
6 Example formats of pond level information records (partial
‘pond book’) 103
Guide for Aquatic Animal Health Surveillance v
Contents
References and further reading 107
Software 108
Index 109
Notes 115
vi Guide for Aquatic Animal Health Surveillance
Acknowledgements
The OIE gratefully acknowledges the work of the members of the OIE ad hoc Group on
Aquatic Animal Health Surveillance in the preparation of this Guide. The principal authors
are Dr Flavio Corsin, Dr Marios Georgiadis, Dr K. Larry Hammell and Dr Barry Hill. In addition,
thanks are due to Drs A. Cameron, J. Jarp and E. Peeler for their work in preparing the OIE
Manual of Diagnostic Tests for Aquatic Animals, parts of which appear in this Guide, and to
Drs C. V. Mohan, A. H. McVicar and E. Peeler for their work peer reviewing the manuscript.
Finally, the OIE appreciates the technical and secretarial support of Drs Gillian Mylrea and
Nathanaelle Donay (OIE Headquarters) in the preparation of this Guide.
Guide for Aquatic Animal Health Surveillance vii

Foreword
For over 40 years the mandate of the World Organisation for Animal Health (OIE) has
included aquatic animals. Mindful of its role as a reference standard-setting organisation
of the World Trade Organization (WTO), the OIE constantly encourages Members to meet
their obligations regarding their OIE Membership and the implementation of OIE standards
in line with the WTO Agreement on the Application of Sanitary and Phytosanitary Standards
(the SPS Agreement). The ability of veterinary services or other competent authorities to
substantiate their reports of the animal health situation in their territory by conducting sound
surveillance programmes is essential to safeguard trade in animals and animal products.
This Guide has been prepared for the OIE by an expert ad hoc Group on Surveillance for
Aquatic Animal Health, which I appointed on the recommendation of the OIE Aquatic
Animal Health Standards Commission. The members of this group (Dr Flavio Corsin,
Dr Marios Georgiadis, Dr K. Larry Hammell and Dr Barry Hill) are world-renowned experts
on the subjects treated in the Guide.
The purpose of this Guide is to provide information and guidance on the design and
evaluation of surveillance systems for aquatic animal diseases. The diseases are principally,
but not exclusively, those listed in the OIE Aquatic Animal Health Code (Aquatic Code).
This detailed guidance supports implementation of the surveillance standards set out in the
Aquatic Code and will be invaluable to OIE Members, and others, in implementing effi cient
surveillance systems for obtaining information on the situation and occurrence of aquatic
animal diseases, including evidence to support self-declaration of freedom from a particular
disease. This will also enable veterinary and other competent authorities to better comply with
the OIE Aquatic Code standards, including obligations for disease reporting, early detection
and rapid response to adverse events, and thereby reduce the risk of spread of aquatic
animal diseases through national, regional and global trade in live aquatic animals and their
products.
The emphasis throughout this Guide is on surveillance for diseases and pathogens of
farmed aquatic animals, but many of the concepts and approaches apply equally to wild
populations. However, while some guidance is given on disease surveillance in wild aquatic
animal populations, extensive guidance for this specialised subject is beyond the scope of
this fi rst edition of this Guide. The topic of wild aquatic animal disease surveillance may
be considered for inclusion in future revisions, depending on feedback from OIE Members.
I would like to thank the experts from the ad hoc Group who generously contributed their
time and their extensive knowledge in preparing this excellent Guide.
Dr Bernard Vallat
Director General
OIE
Guide for Aquatic Animal Health Surveillance ix