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Glossary & References / Book List / B493 - Terrestrial Animal Health Code Sixteenth Edition / Appendix 3.8.7:
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APPENDIX 3.8.7.
Introduction
This
Appendix defines the principles and provides a guide for the surveillance
of foot and mouth disease (FMD) in accordance with Appendix 3.8.1 [GENERAL GUIDELINES FOR ANIMAL HEALTH SURVEILLANCE] applicable
to countries seeking recognition from the OIE for freedom from FMD, either
with or without the use of vaccination. This may be for the entire country
or a zone within the country. Guidance
for countries seeking reestablishment of freedom from FMD for the whole
country or a zone within the country,
either with or without vaccination, following an outbreak,
as well as guidelines for the maintenance of FMD status are provided.
These guidelines are intended to expand on and explain the requirements of
Chapter 2.2.10. [See: Book Ref. 493 - Terrestrial Animal Health Code Sixteenth Edition
- full text provided]. Applications to the OIE for recognition of
freedom should follow the format and answer all the questions posed by the
“Questionnaire on FMD” available from the OIE Central
Bureau. The
impact and epidemiology of FMD differ widely in different regions of the
world and therefore it is impossible to provide specific guidelines for
all situations. It is axiomatic that the surveillance strategies employed
for demonstrating freedom from FMD at an acceptable level of confidence
will need to be adapted to the local situation. For example, the approach
to proving freedom from FMD following an outbreak
caused by a pig-adapted strain of FMD virus (FMDV) should differ
significantly from an application designed to prove freedom from FMD for a
country or zone where African buffaloes
(Syncerus caffer) provide a potential reservoir of
infection. It is incumbent upon the applicant country to submit a dossier
to the OIE in support of its application that not only explains the
epidemiology of FMD in the region concerned but also demonstrates how all
the risk factors are managed. This should include provision of
scientifically-based supporting data. There is therefore considerable
latitude available to Member Countries to provide a well-reasoned argument
to prove that the absence of FMDV infection (in non-vaccinated
populations) or circulation (in vaccinated populations) is assured at an
acceptable level of confidence. Surveillance
for FMD should be in the form of a continuing programme designed to
establish that the whole territory or part of it is free from FMDV
infection/circulation. For
the purposes of this Appendix, virus circulation means transmission of
FMDV as demonstrated by clinical signs, serological evidence or virus
isolation. General
conditions and methods 1.
A surveillance system in accordance with Appendix 3.8.1 [GENERAL GUIDELINES FOR ANIMAL HEALTH SURVEILLANCE]
should be under the responsibility of the Veterinary
Authority. A procedure should be in place for the rapid collection
and transport of samples from suspect cases of FMD to a laboratory for FMD
diagnoses as described in the Terrestrial Manual. 2.
The FMD surveillance programme should: a.
include an early warning system throughout the production,
marketing and processing chain for reporting suspicious cases. Farmers and
workers who have day-to-day contact with livestock, as well as
diagnosticians, should report promptly any suspicion of FMD. They should
be supported directly or indirectly (e.g. through private veterinarians or
veterinary para-professionals) by
government information programmes and the Veterinary
Authority. All suspect cases of FMD should be investigated
immediately. Where suspicion cannot be resolved by epidemiological and
clinical investigation, samples should be taken and submitted to an approved
laboratory. This requires that sampling
kits and other equipment are available for those responsible for
surveillance. Personnel responsible for surveillance should be able to
call for assistance from a team with expertise in FMD diagnosis and
control; b.
implement, when relevant, regular and frequent clinical inspection
and serological testing of high-risk groups of animals, such as those
adjacent to an FMD infected country or zone (for example, bordering a game
park in which infected wildlife are present). An
effective surveillance system will periodically identify suspicious cases
that require follow-up and investigation to confirm or exclude that the
cause of the condition is FMDV. The rate at which such suspicious cases
are likely to occur will differ between epidemiological situations and
cannot therefore be predicted reliably. Applications for freedom from FMDV
infection/circulation should, in consequence, provide details of the
occurrence of suspicious cases and how they were investigated and dealt
with. This should include the results of laboratory testing and the
control measures to which the animals concerned were subjected during the
investigation (quarantine, movement stand-still orders, etc.). Surveillance
strategies 1.
Introduction The
target population for surveillance aimed at identifying disease
and infection should cover all the
susceptible species within the country or zone
to be recognised as free from FMDV infection/circulation. The
strategy employed may be based on randomised sampling requiring
surveillance consistent with demonstrating the absence of FMDV
infection/circulation at an acceptable level of statistical confidence.
The frequency of sampling should be dependent on the epidemiological
situation. Targeted surveillance (e.g. based on the increased likelihood
of infection in particular localities or
species) may be an appropriate strategy. The applicant country should
justify the surveillance strategy chosen as adequate to detect the
presence of FMDV infection/circulation in accordance with Appendix 3.8.1 [GENERAL GUIDELINES FOR ANIMAL HEALTH SURVEILLANCE]
and the epidemiological situation. It may, for example, be appropriate to
target clinical surveillance at particular species likely to exhibit clear
clinical signs (e.g. cattle and pigs). If a Member Country wishes to apply
for recognition of a specific zone
within the country as being free from FMDV infection/circulation, the
design of the survey and the basis for the sampling process would need to
be aimed at the population within the zone. For
random surveys, the design of the sampling strategy will need to
incorporate an epidemiologically appropriate design prevalence. The sample
size selected for testing will need to be large enough to detect
infection/circulation if it were to occur at a predetermined minimum rate.
The sample size and expected disease prevalence determine the level of
confidence in the results of the survey. The applicant country must
justify the choice of design prevalence and confidence level based on the
objectives of surveillance and the epidemiological situation, in
accordance with Appendix 3.8.1 [GENERAL GUIDELINES FOR ANIMAL HEALTH SURVEILLANCE].
Selection of the design prevalence in particular clearly needs to be based
on the prevailing or historical epidemiological situation. Irrespective
of the survey design selected, the sensitivity and specificity of the
diagnostic tests employed are key factors in the design, sample size
determination and interpretation of the results obtained. Ideally, the
sensitivity and specificity of the tests used should be validated for the
vaccination/infection history and production class of animals in the
target population. Irrespective
of the testing system employed, surveillance design should anticipate the
occurrence of false positive reactions. If the characteristics of the
testing system are known, the rate at which these false positives are
likely to occur can be calculated in advance. There needs to be an
effective procedure for following-up positives to ultimately determine
with a high level of confidence, whether they are indicative of
infection/circulation or not. This should involve both supplementary tests
and follow-up investigation to collect diagnostic material from the
original sampling unit as well as herds which may be epidemiologically
linked to it. The
principles involved in surveillance for disease/infection
are technically well defined. The design of surveillance programmes to
prove the absence of FMDV infection/circulation needs to be carefully
followed to avoid producing results that are either insufficiently
reliable to be accepted by the OIE or international trading partners, or
excessively costly and logistically complicated. The design of any
surveillance programme, therefore, requires inputs from professionals
competent and experienced in this field. 2.
Clinical surveillance Clinical
surveillance aims at detecting clinical signs of FMD by close physical
examination of susceptible animals. Whereas significant emphasis is placed
on the diagnostic value of mass serological screening, surveillance based
on clinical inspection should not be underrated. It may be able to provide
a high level of confidence of detection of disease if a sufficiently large
number of clinically susceptible animals is examined. Clinical
surveillance and laboratory testing should always be applied in series to
clarify the status of FMD suspects detected by either of these
complementary diagnostic approaches. Laboratory testing may confirm
clinical suspicion, while clinical surveillance may contribute to
confirmation of positive serology. Any sampling unit within which
suspicious animals are detected should be classified as infected until
contrary evidence is produced. A
number of issues must be considered in clinical surveillance for FMD. The
often underestimated labour intensity and the logistical difficulties
involved in conducting clinical examinations should not be underestimated
and should be taken into account. Identification
of clinical cases is fundamental to FMD surveillance. Establishment of the
molecular, antigenic and other biological characteristics of the causative
virus, as well as its source, is dependent upon disclosure of such
animals. It is essential that FMDV isolates are sent regularly to the
regional reference laboratory for genetic and antigenic characterization. 3.
Virological surveillance Virological
surveillance using tests described in the Terrestrial
Manual should be conducted: a.
to monitor at risk populations; b.
to confirm clinically suspect cases; c.
to follow up positive serological results; d.
to test “normal” daily mortality, to ensure early detection of
infection in the face of vaccination or in establishments
epidemiologically linked to an outbreak. 4.
Serological surveillance Serological
surveillance aims at detecting antibodies against FMDV. Positive FMDV
antibody test results can have four possible causes: a.
natural infection with FMDV; b.
vaccination against FMD; c.
maternal antibodies derived from an immune dam (maternal antibodies
in cattle are usually found only up to 6 months of age but in some
individuals and in some species, maternal antibodies can be detected for
considerably longer periods); d.
heterophile (cross) reactions. It is
important that serological tests, where applicable, contain antigens
appropriate for detecting antibodies against viral variants (types,
subtypes, lineages, topotypes, etc.) that have recently occurred in the
region concerned. Where the probable identity of FMDVs is unknown or where
exotic viruses are suspected to be present, tests able to detect
representatives of all serotypes should be employed (e.g. tests based on
nonstructural viral proteins – see below). It
may be possible to use serum collected for other survey purposes for FMD
surveillance. However, the principles of survey design described in this
Appendix and the requirement for a statistically valid survey for the
presence of FMDV should not be compromised. The
discovery of clustering of seropositive reactions should be foreseen. It
may reflect any of a series of events, including but not limited to the
demographics of the population sampled, vaccinal exposure or the presence
of field strain infection. As clustering may signal field strain
infection, the investigation of all instances must be incorporated in the
survey design. If vaccination cannot be excluded as the cause of positive
serological reactions, diagnostic methods should be employed that detect
the presence of antibodies to nonstructural proteins (NSPs) of FMDVs as
described in the Terrestrial Manual. The
results of random or targeted serological surveys are important in
providing reliable evidence that FMDV infection is not present in a
country or zone. It is therefore essential that the survey be thoroughly
documented. Countries
applying for freedom from FMD for the whole country or a zone where
vaccination is not practised In
addition to the general conditions described in Chapter 2.2.10. [See:
Book Ref. 493 - Terrestrial Animal Health Code Sixteenth Edition
- full text provided], a Member Country applying for recognition of
FMD freedom for the country or a zone
where vaccination is not practised should provide evidence for the
existence of an effective surveillance programme. The strategy and design
of the surveillance programme will depend on the prevailing
epidemiological circumstances and will be planned and implemented
according to general conditions and methods in this Appendix, to
demonstrate absence of FMDV infection, during the preceding 12 months
in susceptible populations. This requires the support of a national or
other laboratory able to undertake identification of FMDV infection
through virus/antigen/genome detection and antibody tests described in the
Terrestrial Manual. Countries
or zones applying for freedom from FMD where vaccination is practised In
addition to the general conditions described in Chapter 2.2.10. [See:
Book Ref. 493 - Terrestrial Animal Health Code Sixteenth Edition
- full text provided], a Member Country applying for recognition of
country or zone freedom from FMD with
vaccination should show evidence of an effective surveillance programme
planned and implemented according to general conditions and methods in
this Appendix. Absence of clinical disease in the country or zone
for the past 2 years should be demonstrated. Furthermore,
surveillance should demonstrate that FMDV has not been circulating in any
susceptible population during the past 12 months. This will require
serological surveillance incorporating tests able to detect antibodies to
NSPs as described in the Terrestrial Manual.
Vaccination to prevent the transmission of FMDV may be part of a disease
control programme. The level of herd immunity required to prevent
transmission will depend on the size, composition (e.g. species) and
density of the susceptible population. It is therefore impossible to be
prescriptive. However, the aim should, in general, be to vaccinate at
least 80% of the susceptible population. The vaccine must comply with the Terrestrial
Manual. Based on the epidemiology of FMD in the country or zone,
it may be that a decision is reached to vaccinate only certain species or
other subsets of the total susceptible population. In that case, the
rationale should be contained within the dossier accompanying the
application to the OIE for recognition of status. Evidence
to show the effectiveness of the vaccination programme should be provided. Countries
or zones re-applying for freedom from FMD where vaccination is either
practised or not practised, following an outbreak In
addition to the general conditions described in Chapter 2.2.10. [See:
Book Ref. 493 - Terrestrial Animal Health Code Sixteenth Edition
- full text provided], a country re-applying for country or zone
freedom from FMD where vaccination is practised or not practised should
show evidence of an active surveillance programme for FMD as well as
absence of FMDV infection/circulation. This will require serological
surveillance incorporating, in the case of a country or a zone
practising vaccination, tests able to detect antibodies to NSPs as
described in the Terrestrial Manual. Four
strategies are recognised by the OIE in a programme to eradicate FMDV
infection following an outbreak: 1.
slaughter of all clinically affected and in-contact susceptible
animals; 2.
slaughter of all clinically affected and in-contact susceptible
animals and vaccination of at-risk animals, with subsequent slaughter of
vaccinated animals; 3.
slaughter of all clinically affected and in-contact susceptible
animals and vaccination of at-risk animals, without subsequent slaughter
of vaccinated animals; 4.
vaccination used without slaughter of affected animals or
subsequent slaughter of vaccinated animals. The
time periods before which an application can be made for re-instatement of
freedom from FMD depends on which of these alternatives is followed. The
time periods are prescribed in Article 2.2.10.7 [See: Book Ref. 493 - Terrestrial Animal Health Code Sixteenth Edition
- full text provided] In all circumstances, a Member Country re-applying for country or zone freedom from FMD with vaccination or without vaccination should report the results of an active surveillance programme implemented according to general conditions and methods in this Appendix. The use and
interpretation of serological tests (see Figure 1)
The
recommended serological tests for FMD surveillance are described in the Terrestrial
Manual. Animals
infected with FMDV produce antibodies to both the structural proteins (SP)
and the nonstructural proteins (NSP) of the virus. Tests for SP antibodies
to include SP-ELISAs and the virus neutralisation test (VNT). The SP tests
are serotype specific and for optimal sensitivity should utilise an
antigen or virus closely related to the field strain against which
antibodies are being sought. Tests for NSP antibodies include NSP I-ELISA
3ABC and the electro-immunotransfer blotting technique (EITB) as
recommended in the Terrestrial Manual or
equivalent validated tests. In contrast to SP tests, NSP tests can detect
antibodies to all serotypes of FMD virus. Animals vaccinated and
subsequently infected with FMD virus develop antibodies to NSPs, but in
some, the titre may be lower than that found in infected animals that have
not been vaccinated. Both the NSP I-ELISA 3ABC and EITB tests have been
extensively used in cattle. Validation in other species is ongoing.
Vaccines used should comply with the standards of the Terrestrial
Manual insofar as purity is concerned to avoid interference with
NSP antibody testing. Serological
testing is a suitable tool for FMD surveillance. The choice of a
serosurveillance system will depend on, amongst other things, the
vaccination status of the country. A country, which is free from FMD
without vaccination, may choose serosurveillance of high-risk
subpopulations (e.g. based on geographical risk for exposure to FMDV). SP
tests may be used in such situations for screening sera for evidence of
FMDV infection/circulation if a particular virus of serious threat has
been identified and is well characterised. In other cases, NSP testing is
recommended in order to cover a broader range of strains and even
serotypes. In both cases, serological testing can provide additional
support to clinical surveillance. Regardless of whether SP or NSP tests
are used in countries that do not vaccinate, a diagnostic follow-up
protocol should be in place to resolve any presumptive positive
serological test results. In
areas where animals have been vaccinated, SP antibody tests may be used to
monitor the serological response to the vaccination. However, NSP antibody
tests should be used to monitor for FMDV infection/circulation. NSP-ELISAs
may be used for screening sera for evidence of infection/circulation
irrespective of the vaccination status of the animal. All herds with
seropositive reactors should be investigated. Epidemiological and
supplementary laboratory investigation results should document the status
of FMDV infection/circulation for each positive herd. Tests used for
confirmation should be of high diagnostic specificity to eliminate as many
false positive screening test reactors as possible. The diagnostic
sensitivity of the confirmatory test should approach that of the screening
test. The EITB or another OIE-accepted test should be used for
confirmation. Information
should be provided on the protocols, reagents, performance characteristics
and validation of all tests used. 1.
The follow-up procedure in case of positive test results if no
vaccination is used in order to establish or re-establish FMD free status
without vaccination Any
positive test result (regardless of whether SP or NSP tests were used)
should be followed up immediately using appropriate clinical,
epidemiological, serological and, where possible, virological
investigations of the reactor animal at hand, of susceptible animals of
the same epidemiological unit and of susceptible animals that have been in
contact or otherwise epidemiologically associated with the reactor animal.
If the follow-up investigations provide no evidence for FMDV infection,
the reactor animal shall be classified as FMD negative. In all other
cases, including the absence of such follow-up investigations, the reactor
animal should be classified as FMD positive. 2.
The follow-up procedure in case of positive test results if
vaccination is used in order to establish or re-establish FMD free status
with vaccination In
case of vaccinated populations, one has to exclude that positive test
results are indicative of virus circulation. To this end, the following
procedure should be followed in the investigation of positive serological
test results derived from surveillance conducted on FMD vaccinated
populations. The
investigation should examine all evidence that might confirm or refute the
hypothesis that the positive results to the serological tests employed in
the initial survey were not due to virus circulation. All the
epidemiological information should be substantiated, and the results
should be collated in the final report. It is
suggested that in the primary sampling units where at least one animal
reacts positive to the NSP test, the following strategy(ies) should be
applied: a.
Following clinical examination, a second serum sample should be
taken from the animals tested in the initial survey after an adequate
interval of time has lapsed, on the condition that they are individually
identified, accessible and have not been vaccinated during this period.
Antibody titres against NSP at the time of retest should be statistically
either equal to or lower than those observed in the initial test if virus
is not circulating. The
animals sampled should remain in the holding pending test results and
should be clearly identifiable. If the three conditions for retesting
mentioned above cannot be met, a new serological survey should be carried
out in the holding after an adequate period of time, repeating the
application of the primary survey design and ensuring that all animals
tested are individually identified. These animals should remain in the
holding and should not be vaccinated, so that they can be retested after
an adequate period of time. b.
Following clinical examination, serum samples should be collected
from representative numbers of cattle that were in physical contact with
the primary sampling unit. The magnitude and prevalence of antibody
reactivity observed should not differ in a statistically significant
manner from that of the primary sample if virus is not circulating. c.
Following clinical examination, epidemiologically linked herds
should be serologically tested and satisfactory results should be achieved
if virus is not circulating. d.
Sentinel animals can also be used. These can be young, unvaccinated
animals or animals in which maternally conferred immunity has lapsed and
belonging to the same species resident within the positive initial
sampling units. They should be serologically negative if virus is not
circulating. If other susceptible, unvaccinated ruminants (sheep, goats)
are present, they could act as sentinels to provide additional serological
evidence. Laboratory
results should be examined in the context of the epidemiological
situation. Corollary information needed to complement the serological
survey and assess the possibility of viral circulation includes but is not
limited to: ·
characterization of the existing production systems; ·
results of clinical surveillance of the suspects and their
cohorts; ·
quantification of vaccinations performed on the affected
sites; ·
sanitary protocol and history of the establishments
with positive reactors; ·
control of animal identification and movements; ·
other parameters of regional significance in historic FMDV
transmission. The
entire investigative process should be documented as standard operating
procedure within the surveillance programme.
Fig. 1. Schematic
representation of laboratory tests
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