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CONTROL OPTIONS for Stopping the FMD Virus Spreading

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Introduction and General Information

In most countries, Foot-and-Mouth Disease is a controlled or scheduled disease and its control is primarily in the hands of government policy-makers; the approach to disease control must be considered within local regulations and legislation. This section describes the general principles of control which can be applied.

These general principles of control are in specific reference to CONTROL OF THE VIRUS. The issues associated with Local Economy and International Trade are discussed in Costs and Consequences of FMD and its Control.

Where FMD is endemic, or there are very great risks of its introduction, general prophylactic vaccination is a recommended means of control (B496).

It is essential, in an area where vaccination against foot-and-mouth disease does not occur, for countries to be prepared to cope with the worst possible scenario. FMD is a devastating disease but, with forward planning, vital decisions can be made very quickly thereby enabling people (epidemiologists, veterinarians, slaughters, Army support for logistics, public communications), equipment, disinfectants, vaccines etc. to be mobilised. SPEED OF DECISION-MAKING IS CRUCIAL IN LIMITING SPREAD OF THE VIRUS. (J70.17.w1; D35.w1 - Strategy for Emergency Vaccination against Foot and Mouth Disease (FMD) Report of the Scientific Committee on Animal Health and Animal Welfare - full text provided)

Advance preparation includes:

  • Preparation of scenarios for the response to infection in different types of husbandry.
  • Validation of prepared scenarios by use of simulation exercises.
  • Preparation of a National Contingency Plan for dealing with an outbreak of foot-and-mouth disease.
  • Ensuring that a vaccine bank is available as an emergency and immediately available source of vaccine, combined with a formalised arrangement with a commercial supplier to provide more vaccine if required.

The National Contingency Plan should have pre-defined policy on a variety of scenarios, which should cover all aspects of the four "Critical Stages" of disease defined below. This Wildpro volume has been developed to support government departments preparing for or dealing with a FMD outbreak and does not supersede prepared National Contingency Plans, which MUST BE AVAILABLE AND CONSULTED DURING AN OUTBREAK.

It is important to recognise that the course of each outbreak will be different, therefore "decisions about the most effective control procedures need to take account of such variability." (B495.6.w6 - full text provided)

  • Rapid decision making is important, since early control measures can have large impacts on the final size of an epidemic. (B495.9.w9 - full text provided)
  • Disease control could be substantially advanced if it was possible to identify infected farms while they were incubating the disease, before the onset of clinical signs. (B495.9.w9 - full text provided)

Note: Countries frequently have legislation in place to deal with FMD outbreaks, which must be consulted.

European Legislation is detailed in LEU6 - COUNCIL DIRECTIVE 2003-85-EC of 29 September 2003 on Community measures for the control of foot-and-mouth disease which permits the use of emergency vaccination as an adjunct to the control and eradication measures. (LEU6 - W19.Sept07.w1 - full text provided)

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The Choices of Policy for Dealing with an Outbreak of FMD in an area previously FMD-free

Each country is listed by the Office International des Epizooties (OIE) within one of the following six categories:
  • FMD free country where vaccination is not practised
  • FMD free country where vaccination is practised
  • FMD free zone where vaccination is not practised
  • FMD free zone where vaccination is practised
  • FMD infected country
  • FMD infected zone

See FMD Import and Transport Restrictions and refer to the Terrestrial Animal Health Code Sixteenth Edition Chapter 2.2.10 Foot and Mouth Disease (W31.Sept07.w2)  for full details of OIE requirements for Country Status with respect to Foot-and-Mouth Disease.

OVERALL POLICIES in general use in countries or zones which are FMD-free

In "FMD-free without vaccination" countries or zones:

"Stamping Out" WITHOUT vaccination

  • Culling and Disinfection of all infected animals and dangerous in contacts: This allows a return to "FMD-free without vaccination" country or zone status "3 months after the last case, where stamping out and serological surveillance are applied in accordance with Appendix 3.8.7." (W31.Sept07.w2)
"Stamping Out" with Emergency Vaccination
  • "Stamping out" (see 1. above) with Emergency Vaccination (e.g. Ring Vaccination) and subsequent slaughter of vaccinated animals: This allows a return to "FMD-free without vaccination" country or zone status "3 months after the slaughter of all vaccinated animal where a stamping out policy, emergency vaccination and serological surveillance are applied in accordance with Appendix 3.8.7." (B493.2.2.10.w1 [(Terrestrial Animal Health Code Sixteenth Edition Chapter 2.2.10 Foot and Mouth Disease - full text provided], W31.Sept07.w2)
  • "Stamping out" with Emergency Vaccination (Ring Vaccination or Mass Vaccination as appropriate) and without subsequent slaughter of vaccinated animals: This allows a return to "FMD-free without vaccination" country status "6 months after the last case or the last vaccination (according to the event that occurs the latest), where a stamping-out policy, emergency vaccination not followed by the slaughtering of all vaccinated animals, and serological surveillance are applied in accordance with Appendix 3.8.7., provided that a serological survey based on the detection of antibodies to nonstructural proteins of FMDV demonstrates the absence of infection in the remaining vaccinated population." (B493.2.2.10.w1 [(Terrestrial Animal Health Code Sixteenth Edition Chapter 2.2.10 Foot and Mouth Disease - full text provided], W31.Sept07.w2)
Routine prophylactic vaccination, with or without "stamping out"
  • Policy of last resort - after all others have been unsuccessful: gain "FMD-free with vaccination" status after there has been no outbreak of FMD for the past 2 years. "To qualify for inclusion in the list of FMD free countries where vaccination is practised, a country should:
    1. have a record of regular and prompt animal disease reporting;
    2. send a declaration to the OIE that there has been no outbreak of FMD for the past 2 years and no evidence of FMDV circulation for the past 12 months, with documented evidence that:
    a) surveillance for FMD and FMDV circulation in accordance with Appendix 3.8.7. is in operation, and that regulatory measures for the prevention and control of FMD have been implemented;
    b) routine vaccination is carried out for the purpose of the prevention of FMD;
    c) the vaccine used complies with the standards described in the Terrestrial Manual."

    (B493.2.2.10.w1 [( Terrestrial Animal Health Code Sixteenth Edition Chapter 2.2.10 Foot and Mouth Disease - full text provided, W31.Sept07.w2)], W31.Sept07.w2)

In "FMD-free with vaccination" countries or zones:

Emergency vaccination with "stamping out"
  • This allows a return to "FMD-free with vaccination" country status:
    • "3 months after the slaughter of all vaccinated animals where a stamping-out policy, emergency vaccination and serological surveillance are applied in accordance with Appendix 3.8.7."; or
    • "6 months after the last case or the last vaccination (according to the event that occurs the latest), where a stamping-out policy, emergency vaccination not followed by the slaughtering of all vaccinated animals, and serological surveillance are applied in accordance with Appendix 3.8.7., provided that a serological survey based on the detection of antibodies to nonstructural proteins of FMDV demonstrates the absence of infection in the remaining vaccinated population." (B493.2.2.10.w1 [(Terrestrial Animal Health Code Sixteenth Edition Chapter 2.2.10 Foot and Mouth Disease - full text provided], W31.Sept07.w2)
Emergency vaccination without "stamping out"
  • This allows a return to "FMD-free with vaccination" country status "18 months after the last case, where a stamping-out policy is not applied, but emergency vaccination and serological surveillance in accordance with Appendix 3.8.7 are applied, provided that the serological surveillance based on the detection of antibodies to nonstructural proteins of FMDV demonstrates the absence of virus circulation." (W31.Sept07.w2)
Routine prophylactic vaccination, with or without "stamping out"
  • Regain "FMD-free with vaccination" status after there has been no outbreak of FMD for the past 2 years. "To qualify for inclusion in the list of FMD free countries where vaccination is practised, a country should:
    1. have a record of regular and prompt animal disease reporting;
    2. send a declaration to the OIE that there has been no outbreak of FMD for the past 2 years and no evidence of FMDV circulation for the past 12 months, with documented evidence that:
    a) surveillance for FMD and FMDV circulation in accordance with Appendix 3.8.7. is in operation, and that regulatory measures for the prevention and control of FMD have been implemented;
    b) routine vaccination is carried out for the purpose of the prevention of FMD;
    c) the vaccine used complies with the standards described in the Terrestrial Manual."

    (B493.2.2.10.w1 [(Terrestrial Animal Health Code Sixteenth Edition Chapter 2.2.10 Foot and Mouth Disease - full text provided], W31.Sept07.w2)

SPECIFIC POLICY DECISIONS THAT MUST BE MADE

1) Which animals to slaughter?

  • It is generally agreed that all actively infected and dangerous contact animals should be slaughtered within an eradication policy. This is referred to as a "Stamping-Out" policy. In identifying "dangerous contact animals", local knowledge is essential; it is important to consider the probability of disease transmission taking into account such factors as wind direction, time since possible exposure and actual distance between groups on animals.
  • Large scale "Stamping-Out" may not be acceptable to a country which has no significant export trade, is not wealthy and simply needs to keep producing animals and meat domestically, albeit at a reduced rate.
  • Exceptions to slaughter within a "Stamping-Out" policy could possibly be considered for individual animals vitally important to the continuation of their species.
  • Widespread "Stamping-Out" may not be feasible where Critical Stages 3 and 4 (see definitions below) of viral spread have been reached, due to the large number of animals involved.

2) Which animals to vaccinate?

  • No vaccination - it is NEVER absolutely necessary to vaccinate animals to control a FMD outbreak. However, the government of the country concerned must then be prepared to slaughter an extremely high percentage of susceptible animals (including wildlife) that are likely both to become affected and to pass the disease to another individual. In addition, countries which trade as part of a Trading Group may not be allowed to use vaccines without official permission of the overall governing body, e.g. in the European Union.
  • Individual (Small Group) vaccination - may be employed for important animals e.g. genetically ("Dolly" the sheep, species of conservation importance etc.); due to human bonding (elephants etc.); local "knowledge" passed through subsequent generations of animals (e.g. hefted sheep).
  • Emergency vaccination:
    • Ring vaccination - limited "one-off" vaccination of all susceptible animals (cloven-hoofed) in a limited "at risk" area.
    • Mass vaccination - limited "one-off" vaccination of all susceptible animals (cloven-hoofed) in a country.
    • N.B. Both "suppressive" vaccination (followed by slaughter of vaccinated animals) and "protective" vaccination (where it is intended that vaccinated animals should continue alive) may be used. (LEU6 - W19.Sept07.w1 - full text provided)
  • Routine prophylactic vaccination - regular vaccination of all animals in a region (undertaken where the disease is endemic, particularly in wildlife which cannot be fully vaccinated).

3) Which quarantine policies to implement? (depends on vaccination policy) (See: Quarantine and Disinfection)

  • Quarantine measures must be imposed sufficient to prevent the movement of animals which are or may be infected.
  • Quarantine (movement restrictions) and Disinfection are recognised to be an important part of any "stamping out" or other slaughter programme and must be rigorously implemented.

4) Which surveillance policies to implement? (depends on vaccination policy) (See: Diagnosis, Surveillance and Carriers)

  • During a disease outbreak, epidemiological monitoring is important both for tracing the origin of the outbreak and for determining the animals which are likely to be infected. Epidemiological studies in a Foot-and-Mouth Disease outbreak may include tracing back from the first known case in order to try to determine the source of the infection (time, place and original virus source) and tracing forward of animals which may be at risk, using data such as animal, person and vehicle movement records and models of possible airborne spread.
  • The forms of surveillance required will vary depending on the situation (e.g. animals affected, presence or otherwise of a free-living reservoir species) and may change considerably during the course of an outbreak and in response to particular events or new information.
    • Clinical, virological, and serological surveillance all may be used. (W31.Sept07.w3)
  • Note: The OIE, in its Terrestrial Animal Health Code Sixteenth Edition (updated 2007), sets out the principles of surveillance and provides a guide for surveillance, including information on surveillance strategies required for a country to regain FMD-free status following an outbreak of the disease. (B493.2.2.10.w1, W31.Sept07.w3) See B493.App3.8.7.w2 (Terrestrial Animal Health Code Sixteenth Edition Appendix 3.8.7 Surveillance - full text provided, W31.Sept07.w3)] for further details on serological surveillance.
    • In recent years, serological tests have been developed, and validated for cattle, for distinguishing vaccinated animals from those which have been infected. These tests for non-structural proteins allow a faster (six months, compared to the previous 12 months) return to FMD-free status following emergency vaccination, if appropriate vaccines and serological testing are employed, without vaccinated animals being slaughtered. (B493.App3.8.7.w2, W31.Sept07.w2, W31.Sept07.w3)
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Factors to be considered

Whilst cost benefit analyses and public acceptance are important, the main factors to be considered in choosing a control policy should be those affecting speed of control of the disease, together with consideration of minimization of impacts on animal welfare and production, and reducing negative impacts on the rural and wider community (J249.91.w2). 

In essence, the aim of control programmes is to reduce the effective reproduction ratio R, that is, to ensure that the average number of individuals infected by each infected individual is below one, so that the epidemic declines. (B495.6.w6 -full text provided)

  • Criteria for the use of emergency vaccination in the European Community: "The decision to apply emergency vaccination would be based on a number of criteria including the species and density of animals in the area, the predicted risk of airborne spread, the economic consequences for trade, and environmental and welfare considerations and public opinion". (J70.12.w1)
FACTORS AFFECTING VIRAL SPREAD

There are a number of factors affecting the likely spread of FMD Virus in an outbreak. These depend on the virus strain characteristics, susceptible species present, and external factors:

  1. Virus sub-type and strain (which affects level of excretion, pathogenicity for different species etc.)
  2. Likelihood of airborne transmission (affected by e.g. virus strain, species infected, meteorological conditions).
  3. Whether the origin can be traced and subsequent in contact animals traced.
  4. Whether infected premises are localised or if there are many separate outbreaks by the time the outbreak is recognised.
  5. Number, density and species of susceptible animals within region affected.
  6. Direct and indirect contacts between premises (movements of animals, movements of vehicles etc.)
  7. Number and species of free-ranging susceptible wildlife involved throughout region.
  8. Geographical constraints on control programmes.
  9. Capacity of the authorities to execute culling and disposal programme quickly enough to contain the disease.
  10. Ability of authorities to implement and maintain effective movement controls, including border controls (particularly where adjacent countries have active Foot-and-Mouth Disease).
FACTORS AFFECTING COMPLIANCE AND EFFECTIVENESS

"Stamping out", quarantine and surveillance without vaccination should ONLY be used as the sole means of control if the logistical capacity of the Government Department controlling the disease AND the support of the public is sufficient that the criteria below are met, AND a small, single primary focus with all dangerous contacts has been identified and isolated. If any of these criteria are NOT met - the virus is likely to spread. Ring vaccination would normally be the next move and, if agreed, should be instigated with immediate effect:

  1. all susceptible animals and dangerous contact animals (including wild cloven-hoofed animals) due to be culled can be slaughtered and the bodies disposed of within 24 hours in a manner that will not encourage air-borne spread (i.e. disposed of "on site" and other than (i.e. not) burning on open pyres)
  2. movement of all persons vehicles and animals can effectively be stopped for 21 days within an appropriate radius (minimum 3 km radius in the EU) of the infected premises and as determined by geographical, administrative, ecological and epizootiological factors. (Other than those persons essential for disease control, who must then effectively disinfect and not risk contact with susceptible animals (or other persons / animals able to carry the virus on to other susceptible animals) for at minimum 48 hours (5 days is frequently recommended)).
  3. infected premises can be effectively cleaned, disinfected and left fallow for an appropriate length of time (usually three months) ()
  4. surveillance for virus persistence within animals and the environment can be effectively carried out through use and monitoring of sentinel animals and through serological survey and virus testing of susceptible animals (including wild cloven-hoofed animals) within an appropriate radius (10 km in EU) of infected premises and as determined by geographical, administrative, ecological and epizootiological factors. 

(D35.w1, J3.151.w5, J13.64.w1, J112.25.w5, W19.17Dec1992, W19.Sept07.w1 - COUNCIL DIRECTIVE 2003-85-EC of 29 September 2003 on Community measures for the control of foot-and-mouth disease - full text provided, B495.6.w6 -full text provided

Note: "Ideally, a situation in which the decision to vaccinate was delayed until the vaccination area encompassed most of the country would be avoided. Indeed there is an opinion that emergency vaccine should be employed as a first, rather than a last, resort." (J112.25.w3) 

However, vaccination can only be used if:

  • An appropriate vaccine is available or can be produced from antigen stores in vaccine banks, in sufficient quantity. 
  • Personnel are available/trained to vaccinate animals in the area in which vaccination is required.
  • Vaccines can be distributed effectively, with appropriate maintenance of the required cold chain.

    (J70.17.w5, J112.25.w4)

FACTORS AFFECTING COST
  1. Likely length of time and extent of export restrictions on animals and animal products during the disease outbreak and after it has been controlled.
  2. Number of farmers and directly dependent industries likely to be affected through animal slaughter.
  3. Effect of quarantine restrictions on the tourist industry and other businesses.
  4. Number of animals likely to have to be slaughtered.
  5. Number of vaccine doses and vaccination teams required.

Note: wider costs to the affected community may also be relevant. See: Assessing the Costs (Actual and Potential) of FMD and its consequences for further details.

FACTORS AFFECTING PUBLIC ACCEPTANCE
  1. The importance of the genetics of the animals involved (breeds, species and subspecies).
  2. Public resistance and logistical restrictions to culling programme (water tables, air pollution, litigation processes which can be exercised, perceived public health risks).
  3. Impact on welfare of animals due to control measures (e.g. related to prolonged movement restrictions).
  4. Public acceptance and understanding of restrictions that will accompany any vaccination programme, and perceived public health risks of products (e.g. milk, meat) from vaccinated animals.
  5. Communication to the public of the economic impacts of different policies and why a particular policy is being used.

(D35.w1, J3.151.w5, J64.21.w31, J64.21.w32, J70.12.w1, J112.25.w3, J249.91.w2, W19.17Dec1992, W19.Sept07.w1)

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Making the decisions

For the most effective disease control, policy decisions should normally be determined by the stage at which the outbreak is detected combined with assessment of the logistical capacity of the Government Department controlling the disease to undertake different potential control measures. The table below details policies usually employed and is based on control measures currently in operation worldwide for each stage of disease outbreak. 

PLEASE NOTE: National Contingency Plans should have pre-defined policies on a variety of scenarios, which should cover all aspects of the four "Critical Stages" of disease defined below. This Wildpro volume has been developed to support Government Departments preparing for or dealing with a FMD outbreak and does not supersede prepared National Contingency Plans, which MUST BE AVAILABLE AND CONSULTED DURING AN OUTBREAK. See: FMD National Contingency Plans (Foot and Mouth Disease Control)

In general, the following may apply:

Guide to normal Foot And Mouth Disease control policy-making when dealing with an outbreak in a country previously free of FMD

Critical Stage* (progression of virus spread) POLICY Outline Definition
CRITICAL STAGE 1 "Stamping out" is necessary. Vaccination is probably NOT necessary The virus has been detected at the first outbreak on one farm or stock-holding (or cluster of local premises) within 24 hours of first signs; 24 hour slaughter and disposal is possible: (i.e. a single primary focus with all dangerous contact animals directly traceable).
CRITICAL STAGE 2 - usually a progression after a "stamping out" policy has not been successful (although an outbreak may already be in "Critical Stage 2" by the time the disease is first detected.) Ring emergency vaccination with "stamping out" would normally be the next move and, if agreed, should be instigated with immediate effect. Multiple outbreaks are occurring in a small number of regions (caused by the virus spreading through the air or movement of animals, including wildlife, or people) and the origin of the virus can still be traced to the original source; 24 hour slaughter and disposal will not continue to be possible unless disease spread is reduced.
CRITICAL STAGE 3 - usually a progression after ring emergency vaccination policy has not been successful More widespread, "Mass" emergency vaccination with "stamping out" should probably be employed. Multiple outbreaks are occurring in a large number of regions and the government department controlling the disease cannot slaughter and dispose of carcasses fast enough to prevent further spread.
CRITICAL STAGE 4 - usually a progression after mass vaccination policy has not been successful Routine prophylactic (preventative) vaccination should probably be employed, at least until sporadic outbreaks cease. "Stamping out" may not be possible in the early stages. Outbreaks of disease are occurring repeatedly throughout the country. Virus is freely circulating within the domestic herds and/or cloven-hoofed wildlife of the region.

* Further descriptions of the "Critical Stages" are given below: DEFINITION: "Critical Stages" of disease

Political and trade constraints on disease control strategy decisions
  • It should be noted that in some outbreaks trade considerations, rather than science-based risk assessments for most effective disease control, appear to have been paramount in decision making (J112.25.w5, J249.91.w2).
    • Until late in May 2002, the regulations set out by the OIE included a large time penalty (12 months after the last case or vaccination) if vaccinate-to-live was used in control of an FMD outbreak in a normally FMD-free country, compared with three months for "stamping out" or if vaccinate-to-kill was used (B495.4.w4 - full text provided). Changes in the regulations mean that the time difference is now much reduced (six months after the last case if vaccination and serological surveillance, including non-structural antibody tests is used, versus three months after the last case/vaccination if either "stamping out" is used or suppressive vaccination is used and vaccinated animals are culled). (W31.Sept07.w2 - Terrestrial Animal Health Code Sixteenth Edition: Chapter 2.2.10 Foot and mouth Disease - full text provided)
  • Countries that trade as part of a "Trading Group" or "Economic Community" may be required to follow regional, not just national, guidelines on acceptable policies. (B495.1.w1 - full text provided)
Requirements for use of emergency vaccination in the EU

Council Directive 2003/85/EC (29th September 2003) gives the following statements regarding the use of emergency vaccination in EU member states (W19.Sept07.w1):

Article 50 Decision on introducing emergency vaccination
1. It may be decided to introduce emergency vaccination where at least one of the following conditions applies:
(a) outbreaks of foot-and-mouth disease have been confirmed and threaten to become widespread in the Member State where such outbreaks have been confirmed;
(b) other Member States are at risk due to the geographical situation of or the prevailing meteorological conditions in relation to reported outbreaks of foot-and-mouth disease in a Member State;
(c) other Member States are at risk due to epidemiologically relevant contacts between holdings on their territories and holdings keeping animals of susceptible species in a Member State where there are outbreaks of foot-and mouth disease;
(d) Member States are at risk due to the geographical situation or the prevailing meteorological conditions in a neighbouring third country where there are outbreaks of foot-and-mouth disease.

2. When deciding on the introduction of emergency vaccination, consideration shall be given to the measures provided for in Article 15 and to the criteria listed in Annex X.

3. The decision to introduce emergency vaccination shall be adopted in accordance with the procedure referred to in Article 89(3).

4. The decision referred to in paragraph 3 to introduce emergency vaccination on its own territory may be requested: 
(a) either by the Member State referred to in paragraph 1(a), or
(b) by a Member State referred to in paragraph 1(b), (c) or (d).

5. By way of derogation from paragraph 3, the decision to introduce emergency vaccination may be taken by the Member State concerned and implemented in accordance with this Directive, after a written notification to the Commission which shall include the specifications provided for in Article 51.

6. If a Member State introduces emergency vaccination in accordance with paragraph 5, that decision shall be immediately reviewed in the Standing Committee on the Food Chain and Animal Health and Community measures shall be adopted in accordance with the procedure referred to in Article 89(3).

7. By way of derogation from paragraph 4, a decision to introduce emergency vaccination in a Member State referred to in paragraph (1)(a) may be adopted in concertation with the affected Member State in accordance with the procedure referred to in Article 89(3) on the Commissionís own initiative, if the condition in paragraph (1)(a) and paragraph (1)(b) apply.

(W19.Sept07.w1)

The Royal Society Inquiry Report - Infectious Diseases in Livestock after the 2001 FMD outbreak in the UK provided the following main recommendations for FMD control in the event of a future outbreak in the UK:

  • that the main objective in dealing with an outbreak must be to ensure that it does not develop into an epidemic. This requires the following basic measures:
    • i. on suspicion of an outbreak the immediate imposition of strict local movement restrictions and biosecurity measures, including the culling of the animal with clinical signs;
    • ii. on confirmation of an outbreak by an OIE Reference Laboratory:
      • the mobilization of the full emergency arrangements including interdepartmental coordination and scientific advisory structure;
      • imposition of a total country-wide ban on animal movement with unambiguous and widely publicised advice on the fate of any animals in transit;
      • rapid culling of all infected premises;
      • identification and rapid culling of all premises where there is a high risk of the disease.
  • where these measures are insufficient to guarantee that the outbreak will be contained, we recommend in addition the early deployment of emergency vaccination; 
  • as a matter of urgency, DEFRA draw up arrangements for a process for the prior registration for vaccination of zoos and rare breed collections;

(B495.9.w9 - full text provided)

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DEFINITION: "Critical Stages" of disease

CRITICAL STAGE 1

The virus has been detected at the first outbreak on one farm or stock-holding (or cluster of local premises) within 24 hours of first signs; 24 hour slaughter and disposal is possible: (i.e. a single primary focus with all dangerous contact animals directly traceable) "Stamping out" is necessary. Vaccination is probably NOT necessary.

  • The full "FMD free" export market can be regained "3 months after the last case, where stamping out and serological surveillance are applied in accordance with Appendix 3.8.7." (W31.Sept07.w2)

This is assuming adequate logistical capabilities (see below). There are few animals and farmers likely to be involved, and very little impact on directly dependent industries including tourism. However the costs of loss of export markets could be large for some countries. If export markets are significant, priority should be given to recovering the export markets as soon as possible. Not vaccinating at this point may increase the risk of virus multiplication but this is probably out weighed by the slight improvement in disease surveillance and the absence of any risk of vaccinating teams spreading infection.

CRITICAL STAGE 2

Multiple outbreaks are occurring in a small number of regions (caused by the virus spreading through the air or movement of animals, including wildlife, or people) and the origin of the virus can still be traced to the original source; 24 hour slaughter and disposal will not continue to be possible unless disease spread is reduced: Emergency ring vaccination with "stamping out" should probably be employed.

This is the situation when the virus is believed to have disseminated beyond the primary focus, dangerous contact animals cannot be traced, and/or aerosol spread has occurred; the number of animals likely to need to be slaughtered may exceed the logistical capacity (see above) or the magnitude of slaughter required may be unacceptable. This stage may be reached quickly (within the first 24 hours of the first case) if it is clear that there has already been viral spread. It is also reached when "stamping out" alone has not been successful.

An outbreak in an area with a high density of stock is difficult to control by slaughter and burial/incineration of carcasses alone. Disposal of large numbers (e.g. tens of thousands) of animals per day poses enormous logistical problems. Emergency vaccination can be used "to prevent the build-up of high levels of circulating virus in susceptible animals close to disease foci" (J70.12.w1).This allows more time to deal with slaughter and disinfection of contaminated premises. The choice of what to do with vaccinated animals can wait until after the disease is contained; in the mean time they can be kept quarantined. Tests have been developed for detecting non-structural antibodies, allowing vaccinated animals to be differentiated from those which have been infected. The OIE Terrestrial Animal Health Code Sixteenth Edition (2007) takes this into account. The OIE now allows the following options:

  • "Stamping out" with Ring Vaccination and subsequent slaughter of vaccinated animals: return to "FMD-free without vaccination" country status "3 months after the slaughter of all vaccinated animal where a stamping out policy , emergency vaccination and serological surveillance are applied in accordance with Appendix 3.8.7." (B493.2.2.10.w1 [( Terrestrial Animal Health Code Sixteenth Edition Chapter 2.2.10 Foot and Mouth Disease - full text provided], W31.Sept07.w2)
  • "Stamping out" with Ring Vaccination and without subsequent slaughter of vaccinated animals: return to "FMD-free without vaccination" country status "6 months after the last case or the last vaccination (according to the event that occurs the latest), where a stamping-out policy, emergency vaccination not followed by the slaughtering of all vaccinated animals, and serological surveillance are applied in accordance with Appendix 3.8.7., provided that a serological survey based on the detection of antibodies to nonstructural proteins of FMDV demonstrates the absence of infection in the remaining vaccinated population." (B493.2.2.10.w1 [( Terrestrial Animal Health Code Sixteenth Edition Chapter 2.2.10 Foot and Mouth Disease - full text provided], W31.Sept07.w2)

CRITICAL STAGE 3

Multiple outbreaks are occurring in a large number of regions, and the government department controlling the disease cannot slaughter and dispose of carcasses fast enough to prevent further spread: Emergency mass vaccination with "stamping out" should probably be employed.

This stage is reached when Ring Vaccination has not been successful.

The priority with Emergency Mass Vaccination is to prevent the virus becoming endemic - that is cycling continuously in the region. This is of particularly relevance in trying to ensure that any free-ranging cloven-hoofed wildlife do not become infected as these may allow the virus to continue to circulate and re-infect domestic stock. It is unlikely that "FMD disease free without vaccination" status could be regained quickly, due to the continuance of outbreaks initially. However, once the disease is under control, development of serological tests which can distinguish between vaccinated and infected animals can allow return to FMD-free status within six months is surveillance is adequate, rather than the 12 months previously required by the OIE:

  • The full "FMD free" export market may be regained "6 months after the last case or the last vaccination (according to the event that occurs the latest), where a stamping-out policy, emergency vaccination not followed by the slaughtering of all vaccinated animals, and serological surveillance are applied in accordance with Appendix 3.8.7., provided that a serological survey based on the detection of antibodies to nonstructural proteins of FMDV demonstrates the absence of infection in the remaining vaccinated population." (B493.2.2.10.w1 [(Terrestrial Animal Health Code Sixteenth Edition Chapter 2.2.10 Foot and Mouth Disease - full text provided], W31.Sept07.w2)

CRITICAL STAGE 4

Outbreaks of disease are occurring repeatedly throughout the country. Virus is freely circulating within the domestic herds and/or cloven-hoofed wildlife of the region: Routine prophylactic vaccination should probably be employed, at least until sporadic outbreaks cease. "Stamping out" may not be possible in the early stages.

This stage is reached when all other attempts at control have not been successful. Disease eradication should continue to be pursued and should be possible, unless there are free-ranging wildlife acting as carriers from which the virus cannot be eliminated.

It is unlikely that "FMD-free without vaccination" status could be regained for a number of years.

  • "To qualify for inclusion in the existing list of FMD free countries where vaccination is not practised, a country should:
    1. have a record of regular and prompt animal disease reporting;
    2. send a declaration to the OIE stating that:
    a) there has been no outbreak of FMD during the past 12 months;
    b) no evidence of FMDV infection has been found during the past 12 months;
    c) no vaccination against FMD has been carried out during the past 12 months;
    d) no vaccinated animal has been introduced since the cessation of vaccination;
    3. supply documented evidence that:
    a) surveillance for both FMD and FMDV infection in accordance with Appendix 3.8.7. is in operation;
    b) regulatory measures for the prevention and control of FMD have been implemented.
    The country will be included in the list only after the submitted evidence has been accepted by the OIE
    ." (B493.2.2.10.w1 [(Terrestrial Animal Health Code Sixteenth Edition Chapter 2.2.10 Foot and Mouth Disease - full text provided], W31.Sept07.w2))
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Use of Epidemiological Modelling

  • "Mathematical modelling describes the dynamics of infection through time and/or space. (J21.73.w4)
  • "Mathematical models of epidemics are sets of equations that describe the spread of infection." (B495.6.w6 -full text provided)

Epidemiological modelling can be used descriptively, i.e. following an outbreak, to describe how the outbreak developed and the effects which different control methods appeared to have on the outbreak. Modelling can also be used predictively, to consider how a disease is likely to spread and the probable effects of different control methods.

Various types of models are available and a number of complex computer programs have been developed for modelling the epidemiology of infectious diseases. Models need to describe the type of interactions which may occur, and to specify the rate at which each interaction occurs (B495.6.w6 -full text provided).

Epidemiological models can be very useful tools to assist in making decisions regarding different control options; they can help to identify "factors and values that effectively influence control and prevention strategies" (J3.160.w2) and they could be used to help develop the most effective vaccination strategies for use in FMD outbreaks (B495.8.w8 -full text provided). However, "by their nature mathematical models are simplified abstractions of complex processes" (B495.6.w6 -full text provided) and it is important also to acknowledge their limitations, which include:

  • Inherent limits of the models.
    • Different models make different assumptions and may give different results.
    • A given model may be more accurate for large scale versus small scale, or vice versa.
    • Deterministic models (which consider only average behaviour) (B495.6.w6 -full text provided) "are of limited use to predict a quantified outcome in one outbreak since any one epidemic does not follow an average pattern: it is a "one off" (J21.73.w4).
    • Stochastic models "contain and produce variability" (J21.73.w4). These models tend to be more realistic than deterministic models, but have an added level of complexity, and the inclusion of chance "sometimes compromises some other aspect of realism" (B495.6.w6 -full text provided)
  • Accuracy and completeness (quality) of data entered into the models.
    • "Key factors and global data may be known, when a index case is discovered it is a real challenge to know which numerical values to give to each of the known variables." (J112.25.w5)
    • If data for sensitive rates (those having a large impact on the modelling process) are poor, more data are needed. (J21.73.w4)
    • Different modellers may make different assumptions and input different data (e.g. time until vaccination would start, speed of vaccination, speed of protection afforded by vaccination, time to slaughter, costs of vaccination, costs of slaughter & clean up) and may therefore give different results regarding effectiveness and cost-benefit.
    • Data may be inadequate when, for example, the disease situation is changing very rapidly, also when multiple means of transmission/transport of infective agents are possible (and should be included in the model).
    • Note: "The exact mechanisms of local spread are unknown" (B495.3.w3 - full text provided).
      • In 2001 in the UK, "80% of transmissions were classified as 'local spread' without the actual mechanisms of transmission being known." (B495.6.w6 -full text provided)
  • Questions posed to the models.
    • Models can be used to ask a variety of questions (e.g. what will happen if we employ X, Y or Z control options) and to compare the answers. However, if a given question is not posed (i.e. the model is not asked, what would happen if we did this?), then obviously the model will not provide an answer regarding that control option.
  • Differences between control measures suggested and what can be achieved in practice, and the effects of those differences.
  • Maintenance of the model, and ease of use (or otherwise).
    • "The computational implementation of each model needs to be kept up to date and functioning, to be properly documented, and to have an easily used interface." (B495.6.w6 -full text provided)

(B495.3.w3 - full text provided, B495.6.w6 -full text provided, J3.152.w4, J9.421.w1, J9.440.w1, J9.445.w1, J9.445.w2, J13.64.w3, J21.73.w4, J112.25.w5, J473.2.w1, V.w5)

Note: 

  • Lessons learned from descriptive modelling after an outbreak should be used to inform predictive modelling for subsequent outbreaks.
    • For example, predictive modelling used to determine control policy in the UK during the 2001 FMD outbreak led to the use of the novel control methods of contiguous culling (slaughter of all susceptible animals on premises contiguous to Infected Premises (IPs) and 3 km radius culling of pigs and small ruminants around IPs) (J9.413.w2, J22.292.w1, J22.294.w2). Descriptive modelling carried out later showed that the outbreak peaked before these control measures were instigated, that longer distance spread continued after they were instigated, and that the novel culling strategies were not effective or efficient in disease control (as indicated by various measures, including the low areal attack rates for contiguous premises and the very small number of IPs identified among the farms culled under these strategies), while the traditional policies, focusing on rapid slaughter of animals on IPs, strict biosecurity, and tracing and veterinary assessment of Direct Contacts (including contiguous premises, where appropriate) from the IPs, were effective and efficient (J3.154.w4, J3.155.w3, J3.155.w4, J3.156.w3, J3.156.w4).
  • Each outbreak has unique elements, combined in a unique manner. 
    • The 2001 FMD epidemic in the UK was very different from that 1967-68 or that in 2007. (B494.5.w5 - full text provided, B494.7.w7 - full text provided, D36, J3.149.w8, W66.Sept07.w9)
    • "It must be recalled that any new outbreak in our countries represents a new situation, sometimes difficult to anticipate from the average past outbreaks on which we have been trained. It should be seen as a unique situation, difficult to generalise." (J112.25.w5)
  • Models are most likely to be useful when they use an integrated team approach, drawing on as many as possible of the appropriate disciplines (field and laboratory-based veterinarians, mathematical modellers, meteorologists, statisticians, economists etc.) (J3.160.w2).
  • Results of models must be interpreted.
    • Simulation models give results as "distributions that reflect the uncertainty and variability in the information provided" (J13.64.w3).
    • It is important to remember that even with very good data, the use of models to predict epidemic processes is not an exact science. (J21.73.w4)
  • "A valid model should be true for data not used in the modelling process." (J21.73.w4)Models must be validated (as far as is possible) using data from different outbreaks not used in the original model construction (B495.6.w6 -full text provided). 
  • "The model should not be considered complete until sensitivity analysis is used to identify the rates that have a large impact on the modelling process." (J21.73.w4). Sensitivity analysis is essential so that the extent to which models they depend on uncertain parameters is understood (B495.6.w6 -full text provided).
  • Local knowledge should be used as well as epidemiology and modelling tools. (B495.9.w9 - full text provided)
Models of Airborne Spread

Models of airborne spread, based on actual meteorological data and calculated or estimated (depending on how much is known about excretion of a particular virus strain) virus production data, can be used to inform:

  • Where additional surveillance is required (e.g. on large dairy units under a probable virus plume). (J3.140.w6, J19.124.w2, J112.25.w5)
  • Where emergency vaccination (e.g. ring vaccination or protective emergency vaccination) should be employed, to minimise the chance that the area chosen is inadequate to prevent further spread outside that area. (D36.Para198)
  • Where preventative slaughter may be required (e.g. for a large pig farm very likely have been infected, to prevent excretion of large quantities of virus which may infect further farms downwind). (J19.124.w2, J112.25.w5)
  • As with other modelling, results may vary considerably depending on data entered and on model assumptions (e.g. average concentration of virus versus allowing for short-lived high concentrations of virus; whether or not topography is included in the model) (J3.152.w4).
  • For further information see: Use of Models of Airborne Spread for Foot-and-Mouth Disease (Techniques)
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Authors & Referees

Authors Suzanne I Boardman BVMS MRCVS, Dr Debra Bourne MA VetMB PhD MRCVS
Referee Dr Debra Bourne MA VetMB PhD MRCVS, Suzanne I Boardman BVMS MRCVS

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