Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

Animal Health ManagementManaging animal health for trade

Author: Dr Mary-Louise Penrith.

Licensed under a Creative Commons Attribution license.

CONTROL OF ANIMAL DISEASES TO SUPPORT ANIMAL PRODUCTION AND TRADE Animal disease control measures to support production and trade fall into two main categories: those measures required to deal with emergency situations created by the outbreak of a serious transboundary disease that was not previously present in the affected country or area, and those required to prevent diseases that are endemic from having deleterious effects on either livestock production or trade.

Control of endemic livestock diseases

Animal production in developing countries, particularly in Africa, is often severely constrained by the presence of animal diseases that cause high mortality, like peste des petits ruminants (PPR), ASF and Newcastle disease (ND), or result in poor performance, like the tick-borne diseases and trypanosomosis. The result may be a lack of animals to satisfy the country’s own needs as well as the lack of a surplus to export. Concerns are also raised about zoonotic diseases, which are more easily transmitted under conditions of close contact between humans and animals and where milk and meat are handled and consumed without being processed in any way that will destroy pathogens.

Vaccination of cattle against anthrax, South Africa (photograph courtesy of Anabela Manhiça, Mozambique Institute for Agricultural Research)

1 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

In sub-Saharan Africa, a number of serious transboundary diseases (FMD, RVF, PPR, CBPP, contagious caprine pleuropneumonia, bluetongue, sheep and goat pox, African horse sickness (AHS), ASF, ND, to name a few) are present endemically, usually in several countries. For some of these, particularly those in which maintenance of the agent occurs in wild animals, like FMD and ASF, eradication at least in the short term is not a realistic option. In order to trade in livestock commodities, these countries are required to adopt control measures that will convince trading partners that livestock commodities originating from these countries pose no more than an acceptable level of risk for transmission of endemically present transboundary diseases.

Routine disease control

Routine disease control activities are aimed at attaining or maintaining good animal health status and supporting animal production.

Routine disease control activities may include:

Programmes for control and/or eradication of specific diseases

Vaccination campaigns (procurement, storage, distribution)

Monitoring the results of disease control activities

Provision of treatment/clinical services by the state

Routine surveillance for diseases including changes in epidemiological patterns.

Control (managing the disease) and eradication (eliminating the disease) programmes require the participation of the livestock owners. Such programmes may be compulsory or voluntary, depending upon the nature of the disease and the available resources. Diseases that are frequently the target of sustained control programmes are erosive diseases that affect production and/or are zoonoses like brucellosis, bovine tuberculosis, rabies, tick-borne diseases and trypanosomosis, as well as transboundary diseases like FMD, contagious bovine pleuropneumonia (CBPP), and the swine fevers. Depending upon the disease, approaches include testing and slaughter of positive animals, vaccination, and vector control. All of these activities have cost implications, and in order to be successful must be well planned and implemented. Before embarking on a control programme, it is important to identify the target population and then to decide upon a strategy that will be both effective and achievable with the available resources. It will be necessary to determine what laboratory diagnostic capacity is available to support the programme if laboratory tests are involved. The wide spectrum of laboratory techniques described for each disease in the OIE Manual for Diagnostic Tests and Vaccines may not be available in the local laboratory!

2 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

Vaccination campaigns need careful planning and management. Most vaccines are fragile and require that the cold chain be maintained from manufacture to administration to the animal. Even so-called thermostable vaccines are usually thermotolerant but will not withstand prolonged storage at high temperatures. The procurement process for vaccines should ensure that they are delivered well in advance of their expiry date, in a way that will ensure maintenance of the cold chain. They should be stored in such a way that the recommended temperature (usually 2-8°C) is reliably maintained. Arrangements must be made to ensure that the vaccines can be kept cold throughout the distribution and administration process. Vaccines that have spent a hot day in an uninsulated container on the back of a vehicle in the sun are not likely to be effective and the whole effort will have been wasted. On the other hand, allowing liquid vaccines to freeze will usually render them ineffective.

Vaccination of dogs against rabies, Catuane, Mozambique

Whatever the nature of a control programme, monitoring its progress is extremely important and the monitoring strategy should be built into the programme from the beginning. Effective monitoring will permit identification of problems and enable changes of strategy to resolve them, and will also enable programmes that are clearly not working to be modified or abandoned. After control has been achieved, a surveillance programme should be maintained in order to intervene early at any sign of resurgence of the disease.

The provision of treatment and clinical services by government veterinarians when this is not linked to official control programmes is a matter for debate. In countries where no or very limited private veterinary services are available, or where a large proportion of the livestock producers are subsistence farmers who cannot afford private services, interventions by government veterinarians may be necessary. There is no doubt that the provision of primary animal health

3 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

care enhances the image of state veterinarians and creates an opportunity to improve disease surveillance. Various attempts have been made to distinguish between “public” and “private” goods in the provision of veterinary services, the former involving animal diseases that are a threat to public health or the national economy, for example highly contagious diseases, while the latter refers to diseases that are in the farmer’s own interests to control. Greater private sector involvement has been advocated, but the practicality of this will of course depend upon the availability of private veterinary service providers as well as the ability and willingness of livestock producers to pay for the services. The provision of primary animal health care by trained community animal health workers (CAHWs) is an option that has proved beneficial when properly managed. Well trained CAHWs, who are members of the communities they serve, have proven invaluable in remote areas and among nomadic pastoralists who would otherwise have no access to veterinary services. They can also make significant contributions to surveillance for disease, as has been demonstrated in a study in northern Tanzania.

State-sponsored dipping programmes provide opportunities for surveillance and vaccination, South Africa

Options for managing endemic transboundary animal diseases to support trade in livestock commodities

As indicated above, the SPS Agreements of the World Trade Organisation are designed to prevent importing countries from unfairly using non-tariff trade barriers, e.g. risk of importing an

4 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

unwanted animal disease, unless they can demonstrate that the risk posed by the imports is real and does not already exist within their borders. This means that they may not discriminate against countries that have an equivalent health status, but does not prevent them from prohibiting imports from countries that have a less satisfactory status in terms of serious livestock diseases. The requirement that an exporting country should have the same animal disease status as the importing country is widely accepted in industrialised countries. Since most of these are free from all of the serious transboundary animal diseases, it could theoretically be impossible for countries where one or more of those diseases occurs endemically to access the advantageous markets for livestock products afforded by the industrialised countries. In response to the need to provide market access for developing countries, the SPS Agreement recognizes the principle of equivalence, which permits export from countries that are not free of certain diseases provided that they can satisfactorily demonstrate that the commodities pose no more than an acceptable level of risk. In practical terms, this means that the commodities should originate from an area that is free of the specified disease/s, or should be demonstrably unable to transmit the specified infectious agent/s.

The OIE recognises geographical zones that are free for FMD, rinderpest (now globally eradicated), CBPP, AHS, PPR and CSF. Countries can also apply for a rating for the level of risk that they pose for BSE. In some SADC countries zonal freedom from FMD without vaccination has been achieved by using fences to effect physical separation between African buffalo and domestic livestock combined with buffer zones with vaccination and observation. The principle that a zone can be free of a specific disease with vaccination is accepted and is applied in Brazil, but to achieve freedom with vaccination it is necessary to be able to distinguish between vaccinated and unvaccinated animals. This is currently difficult for FMD within the SADC region, since the test used to distinguish between vaccinated and infected animals is regarded as insufficiently sensitive for the SAT virus types, but purification of the antigen used in vaccine production has greatly increased the sensitivity of the assay.

It has been accepted by the OIE that for certain diseases it will be virtually impossible to achieve geographically free zones, for example ND and avian influenza. A “new” concept, compartmentalisation, has been proposed, in which a production unit may be recognised as being free of a specific disease, allowing export of livestock commodities originating from that unit to take place. The concept is based on strict biosecurity of the unit, which applies also to the feed source, transportation of animals for slaughter, and the slaughter facility. Once a compartment has achieved official recognition by the competent veterinary authority (the OIE does not provide official recognition for compartments) of freedom from one disease, this status can obviously be extended to other diseases. It is recognised that the control measures that countries like Kenya and South Africa adopted for pig farms not long after ASF was identified as a disease entity in the first half of the last century effectively resulted in compartmentalisation of pig farms. The guidelines for zoning and compartmentalisation are defined together in the TAHC and there is a chapter on the application of compartmentalisation.

5 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

The commodity-based trade approach acknowledges that it may be difficult if not impossible for many developing countries with endemic transboundary diseases to achieve country or zonal freedom in the short term and that compartmentalisation will initially, at least, apply only to a few commercial producers able to achieve a high level of biosecurity in their production units. In spite of initial concerns that acceptance of commodity-based trade might reduce the impetus to eradicate transboundary diseases which is the stated aim of the OIE, it is increasingly accepted that if sub-Saharan Africa is to benefit from its livestock resources in ways that could change lives there has to be an alternative that will improve their access to global markets. Lack of competitiveness in terms of livestock numbers, quality and resources has been cited as likely to exclude sub-Saharan African countries from global livestock markets, but these impediments may be susceptible to change once trade in livestock commodities actually becomes possible because there are no longer definitive bans on particular areas.

Managing animal disease emergencies

Definition of an animal disease emergency

An animal disease emergency refers to any change in the status of a disease that can have potentially disastrous consequences in terms of animal health, human health, and/or the national economy.

Objectives of animal disease emergency management

Managing an animal disease emergency, which usually implies an outbreak of a highly contagious disease, is never easy, even with the best contingency plans in place and all the resources needed to implement them. Success can never be assured, because in the end the outcome depends not only on the actions of the veterinary department but also on the behaviour of producers and traders, which in spite of legislation may be impossible to monitor and control. It is therefore imperative to prevent disease emergencies as far as possible by ensuring good surveillance for animal diseases and identifying and managing risks, for example the management of airport and harbour swill.

If, in spite of all efforts to prevent it, an animal disease crisis occurs, the objectives of managing it include some or all of the following:

Limiting damage to livestock production when a disease emergency occurs

o Economic losses to livestock producers

o Economic losses in the satellite sectors – loss of trade, jobs

o Economic losses at national level – costs of importation to replace locally produced product, loss of export trade

6 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

Protecting public health

Protecting the environment

The Food & Agriculture Organization of the United Nations (FAO) has developed, under the EMPRES (Emergency Prevention System for Transboundary Animal and Plant Pests and Diseases) Programme (http://www.fao.org/ag/againfo/programmes/en/empres.html), a tool known as Good Emergency Management Practice (GEMP), available on CD and on the FAO/EMPRES website as a multi-media programme. It promotes the concept of a Code of Practice in dealing with animal disease emergencies.

GEMP in animal health is defined as follows: ‘the sum total of organised procedures, structures and resource management that lead to early detection of disease or infection in an animal population, prediction of the likely spread, prompt limitation, targeted control and elimination with subsequent re-establishment of verifiable freedom from infection in accordance with the International Animal Health Code’ [http://www.fao.org/AG/AGAInfo/programmes/en/empres/gemp.html]. The details of GEMP are covered in other modules.

Practical approach to resolving disease emergencies

Key issues that need to be explored when preparing a strategy for dealing with disease emergencies:

Identification of problem areas and risk factors (i.e. factors that place the success of disease emergency management measures at risk)

Identification and training of key personnel (include people outside animal health services)

Integration of stakeholders in disease emergency management

Awareness campaigns

Resources for animal disease emergency management

A variety of resources are required for managing animal disease emergencies:

Information

o Information about the disease

o Background information about livestock numbers and distribution and production systems

o Information from field services

7 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

o Information from laboratory services

Human resources

Financial resources

Infrastructure, equipment, supplies

Appropriate contingency plans and Standard Operating Procedures (SOPS)

Failure to have one or more of these resources in place is likely to lead to failure to contain the disease emergency.

Information

The veterinary department should have access to up-to-date reference works on infectious and parasitic diseases, in order to understand the aetiology and epidemiology, as well as how to confirm the diagnosis. The OIE Manual for Diagnostic Tests and Vaccines, available on the OIE website (www.oie.int) provides basic information about each disease as well as details on the samples required for diagnosis. However, not all of the disease descriptions contain sufficient information about the epidemiology to be adequate for each disease as it occurs in different parts of the world. One way of ensuring ready access to information is to incorporate it in the contingency plan. When preparing the contingency plan (see GEMP and other modules on disease control), the introductory chapter should describe all the important aspects of the disease, and should be updated as necessary, using the most up-to-date reference works available.

A database giving the most up-to-date livestock figures available, with distribution maps and some information about production systems is invaluable for planning actions and identifying high risk areas.

Information from the field services in the affected area and also in unaffected areas is crucial for planning the response in both.

The contingency plan should contain the information about what diagnostic tests can be performed by the laboratory and what type of samples are required, but contact with the laboratory is essential to ensure that there are no obstacles to the performance of the diagnostic tests (for example lack of reagents, equipment not functional, or absence of crucial staff members), and if there are problems, what alternative arrangements have been made to overcome them.

8 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

Human resources

The contingency plan will have identified the human resources required for implementation. The emergency team, which will usually include members of the state veterinary service as well as the laboratory, is of vital importance in the first response to investigate the outbreak and initiate an epidemiological inquiry. Assistance may be required from other departments, for example extension officers, police and army officers, and the media. The necessary mechanisms to enlist their services should be in place to avoid bureaucratic delays. Their activities will need to be coordinated through a Joint Operations Committee or equivalent.

Lack of the necessary human resources is a serious constraint for control of disease emergencies. Often the veterinary services of developing countries are thinly spread. It is important that the contingency plan should specify who is responsible for what, and should also indicate who will substitute officials who are unavoidably not available when the emergency happens. Contact details for the emergency team members should be readily accessible, preferably at the front of the contingency plan, and updated as necessary.

It must also be recognised that a disease emergency takes priority over all other activities, and that undesirable as it may be, it offers animal health officers a unique opportunity to gain experience that should not be missed in favour of some routine activity that can be interrupted without serious consequences.

Financial resources

An emergency fund should be available for dealing with animal disease crises, from which the necessary funds can be released rapidly. Ensuring that such a fund exists is an important responsibility of the veterinary services, who should supply the technical inputs that will convince the decision-makers of the importance of rapidly accessible finance.

A mechanism for rapid release of such funds is vital. It is understandable that in government organisations measures for release of funds are often cumbersome in order to ensure that all the correct authorisations are in place. In the case of an emergency fund, arrangements must be in place to ensure that there is no question of waiting for an indispensable signature while the diseases sweeps unchecked across the country.

Infrastructure, equipment and supplies

The provision of infrastructure is with some exceptions not within the capability of the veterinary services, but it is important that the contingency plan should identify any shortcomings in this respect and propose ways in which they may be overcome.

Equipment includes vehicles and sampling equipment, including the means to keep the samples in a good state of preservation until they reach the laboratory. If stamping out of animals is to be

9 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

part of the control plan or there are large numbers of dead animals to be disposed of safely, earth-moving equipment may be required. The contingency plan will specify the equipment needed.

Supplies will include protective clothing, disinfectants, and any other consumables (specimen jars, preservatives, swabs, etc.).

Contingency plans and Standard Operating Procedures

These should be available and should be relevant to the situation in the country. They should also be tested, preferably by performing simulation exercises, and updated and modified as necessary. The GEMP guidelines of FAO/EMPRES include a concise summary of the nature and structure of contingency plans.

In addition to the resources mentioned above, the following are important resources:

Discipline and good practice at all levels in the livestock industry

Political will

Achieving these through dialogue and education must be part of the long-term strategy of the veterinary services, since, if they are not in place when an animal health crisis occurs, the consequences will inevitably be severe.

Conventional approaches to disease emergencies

The conventional approach to a disease emergency created by the outbreak of a highly contagious disease has traditionally been to eradicate it by stamping out, i.e. the compulsory slaughter of all infected and in-contact animals, sometimes of all the animals of the affected species within a defined area or radius. The slaughtered animals are destroyed by some process that prevents their consumption and dissemination, usually deep burial or burning or both. This is accompanied by quarantine of the affected area or areas, with strict movement control of animals and products out of the area. Disinfection of infected premises follows slaughter, and restocking is permitted after a prescribed period. In order to obtain their cooperation, livestock owners are usually compensated for the animals slaughtered. After discovery of a focus, the veterinary authorities attempt to trace back any movements into and out of the area that occurred before measures were applied, and to stamp out any other potential or actual foci that are detected in this way.

10 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

Eradication by stamping out. Stamping out results in many carcasses for disposal by burning or burial

Until recently, this was the approach advocated by international organisations such as the OIE, the FAO and the EU. Increasingly, however, a combination of strengthening of public opinion against the mass killing of animals, the undoubtedly serious environmental implications of the disposal of vast numbers of carcasses, and the enormous expense involved are making it necessary to explore other options. A further reason to explore other options is the fact that expensive stamping out operations often fail to contain the outbreak and cause more damage to producers than the disease itself, particularly in developing countries.

Reasons why conventional control measures fail

In order to succeed, control measures such as quarantine, movement control and stamping out have to be applied immediately and rigorously, since the objective is to contain the agent within the designated area or cordon, and the escape of even one infected animal may foil that purpose. It is extremely difficult under any conditions, but particularly with limited resources, to apply measures sufficiently rigorously to ensure containment within the focus.

Factors that contribute to the failure of measures are the following:

11 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

Failure of the early warning system, so that the “index” case is not the first case, and other foci of infection exist elsewhere undetected. Tracing back animal movements may result in the discovery of these foci or may fail to do so, depending on the level of cooperation of the population and also their level of information.

Tardiness of response, giving time for spread of the infection. Producers who know that drastic measures are going to be applied are likely to take advantage of any lapse of time to sell as many animals as possible.

Failure of movement control. When an outbreak of disease occurs, and in particular when the method of controlling it is compulsory slaughter, the incentive for owners to move animals to avoid the control measures is usually stronger than the ability to prevent animal movement. Road blocks, if efficiently operated, will prevent at least overt movement of animals along the roads, but these do not offer the only way out of the infected area. Furthermore, there are reasons why road blocks cannot always operate efficiently. Firstly, the sheer volume of road traffic in most countries makes it impractical to thoroughly search every vehicle that passes. Much of the philosophy of outbreak control is based on the measures developed for rinderpest, which among domestic livestock primarily affects cattle. Cattle are large and visible, but the smaller species and parcels of meat are much easier to conceal. Secondly, in developing countries where officials are poorly paid, the incentive to allow animals to pass may be greater than the incentive to prevent them.

Road blocks are not always effective in preventing movement of animals and animal products

Inefficient disposal of carcasses of infected animals. Particularly if large numbers of animals are involved, disposing of carcasses can present serious problems. Incineration of carcasses is

12 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

recommended but the costs are high if the process is to be effective. Deep burial, accompanied by treatment with quick lime, is the alternative. Either way, a suitable site for disposal must be selected, and the immediate focus of infection may not offer the necessary conditions. Moving carcasses is hazardous from the point of view of spreading infection. Furthermore, in poor communities the destruction of large amounts of edible meat is not easily accepted, and in many instances carcasses have been disinterred and consumed or even sold for consumption. Telling people who are in the habit of eating animals that die that eating the meat will endanger their health is unlikely to have any effect, particularly if it rapidly proves to be untrue.

Failure to compensate owners for compulsory slaughter of animals. Prompt payment of market-related compensation may provide the necessary incentive for cooperation, particularly if the disease is of such a nature that it is obvious that large numbers of animals are going to die anyway. However, developing countries are often unable to pay compensation at all, let alone at market-related rates. The application of stamping out without compensation or with inadequate compensation is most likely to result in spread of the disease, since it will encourage clandestine movement and sales that, for reasons given above, will be impossible to prevent. Even when adequate compensation is available, problems such as bureaucratic delays in payment will result in future non-compliance.

Factors that prevent resumption of productive farming as soon as possible. These include requirements for excessively long ‘empty’ periods before re-stocking, lack of suitable animals for re-stocking, lack of funds for re-stocking, and unrealistic requirements for resumption of farming activities, for example provision of new housing and infrastructures according to unachievable standards.

Careful consideration is therefore necessary before embarking on an eradication campaign based on stamping out the infection. This should be clearly reflected in the contingency plan. There are circumstances when it may be feasible, for example if the index case is genuinely the index case, the source of the infection is clear (for example, contact with wildlife), and the affected herd or flock is well isolated, with relatively few animals that need to be killed and plenty of space to dispose of the carcasses.

For countries with a significant export market for meat, and therefore a strong incentive to regain disease free status as soon as possible, stamping out may be the only option. However, even in this case, the probability of success must be weighed against that of failure, and a cost-benefit analysis should be undertaken to ensure that the expected revenues from import will offset the cost of the control operation, or that the losses of revenue due to failure to control the outbreak will exceed the cost of control.

If there is a probability that the considerable resources invested in eradicating the outbreak will be wasted because they will fail, alternative control strategies should be considered.

One option is to limit the number of animals that have to be slaughtered by some form of emergency vaccination to contain the disease, usually by ring vaccination around the affected focus. In order to

13 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

regain disease free status, it has been recommended that the animals that were vaccinated should be slaughtered to eliminate them from the population, but the necessity for this is open to question. When stamping out is not an option, for example in the case of rare zoological collections that are not infected, selective vaccination may be permitted. Vaccination of the total population has also been used as an alternative to stamping out, for example in some HPAI-infected countries where it was deemed impossible to achieve the requisite level of stamping out in backyard flocks.

Alternative control strategies

For most diseases, an obvious alternative to eradication by stamping out is vaccination, usually limited to the area around the outbreak, but sometimes considerably wider. Although the costs involved in purchasing and administering the vaccine may be high, the advantage is that the animals, other than those that are infected and die of disease, are available for sale and consumption, and do not have to be disposed of in an expensive and environmentally unfriendly manner.

The decision to vaccinate depends upon the availability of sufficient quantities of an efficacious vaccine, the funds required to pay for it, and the importance of the export market on which vaccination may have a negative effect. Another factor that contributes is the perception that vaccination as a means of control is an admission of defeat, will result in large numbers of carriers of the disease, and ensure that the disease becomes endemic. The fact that vaccination has played a central role in the eradication of rinderpest is apparently overlooked. Insistence upon the importance of “disease freedom without vaccination”, in other words the demonstrable absence of infection, has induced in many countries a reluctance to vaccinate that does not take local conditions into account, including the need to keep a fragile economy dependent upon livestock production alive and even to ensure household food security.

The obvious disadvantage of vaccination as an outbreak control measure is the fact that antibodies take some time to develop and attain protective levels, usually about two weeks after the first vaccination. This means that all efforts to contain the infection inside the focus must be made during the critical period, and, as indicated above, this may be very difficult to achieve.

Concern about the effect of vaccination on exports will naturally depend on the importance of the export market. Reluctance to import vaccinated animals or their products stems from the fact that until recently it was not possible to distinguish between antibodies resulting from vaccination and those resulting from infection. The development of marker vaccines offers a way to overcome this problem in the future, but for most diseases marker vaccines are not yet available, and progress in this field is hampered by the negative attitude of highly developed countries to vaccination, even in the face of serious outbreaks. However, this may change as eradication by stamping out becomes less and less acceptable. A simulation study performed after the 1997/1998 outbreak of CSF in the Netherlands, which was brought under control by stamping out of affected and neighbouring unaffected herds, concluded that emergency vaccination would have been the best option, with the advantage of sparing healthy pigs.

14 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

The perception that vaccination encourages a carrier state and merely serves to disguise circulating infection is unfortunate, and ignores the important contribution that vaccination has made to disease control and even to eradication. Certainly the use of vaccination implies that either the infection or the risk of infection is known or suspected to be present. The infection, or risk of it, does not result from the vaccine, since the overwhelming majority of vaccines are based on pathogens that have been rendered incapable of causing disease, and reversion to virulence is extremely unusual, although it has been recorded in rare instances. Animals protected by vaccine, when exposed to natural infection, are usually unable to shed infective amounts of the pathogen and thus do not infect other animals, unless vaccination has not been effective or a breakdown of immunity occurs for some reason. Effective vaccination permits normal production to continue in the presence of infection and, in spite of misgivings on the part of trading partners, the derivatives of such animals pose little realistic risk for transmission of disease. In populations in which a high level of immunity is maintained by vaccination, and in the absence of reservoirs of infection in wildlife or vectors, the disappearance of the pathogen, resulting in eradication of infection, is a real possibility. In the case of diseases for which reservoirs exist in wildlife populations, the risk of infection will always be endemic, but with proper protection of domestic livestock, including by effective vaccination, there is no reason why the disease itself should become endemic in domestic animals. There are, however, requirements for successful vaccination, such as the suitability of vaccines (able to protect against the agent causing the outbreak), quality of vaccines, and a delivery system that ensures that the majority of the target population of animals will be effectively vaccinated; this usually includes respect for the cold chain. Vaccination as a disease control tool is dealt with in greater detail in a dedicated module.

The decision to vaccinate as an emergency control measure therefore depends not only upon cost and feasibility, but also on whether eradication of the infection without vaccination is a realistic and feasible option.

Sometimes vaccination may not be possible, either due to costs, or, in the case of some diseases, e.g. ASF, the lack of a vaccine. In these cases, given that large-scale eradication by stamping out is also not feasible, alternative measures must be considered.

In principle, the aim of emergency control measures is to reduce the size of the susceptible population as rapidly as possible. Both stamping out and various vaccination strategies have precisely this aim. Other ways to reduce the susceptible population include the supervised sale for slaughter of healthy animals through official outlets as rapidly as possible, and the protection of unaffected herds by the institution of biosecurity measures that will prevent contact with the pathogen.

15 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

Permanent isolation of pigs in accredited farm, African swine fever control area, Limpopo province, South Africa

With pathogens that require direct contact for transmission, such as ASF virus, which will be used as an example here, protection of animals through simple but strict biosecurity measures that require the full cooperation of the owner will effectively remove such animals from the susceptible population. These measures when applied to ASF consist of maintaining the pigs confined, strictly limiting access to the herd, disinfection of clothing, footwear, and hands for people who have to have contact with the pigs, not feeding swill unless it has been boiled for at least 30 minutes, and avoiding any other practices that might result in infection. These include sharing boars, equipment, feed sacks, and anything else that could possibly be contaminated. If the owners of affected herds are agreeable, slaughter of the remaining in-contact animals should be undertaken. Compensation in the form of nucleus breeding stock is more economical than monetary compensation, and is usually acceptable to owners. The sale of carcasses or meat from infected herds is not acceptable, but owners can be permitted to use some of the meat for own consumption provided that it is thoroughly cooked. Under some circumstances, pigs that have apparently survived the outbreak may be allowed to live, although not to leave the farm, since animals that recover fully from ASF apparently do not become long-term carriers. Such pigs might remain infective for up to a month after recovery, and they should remain on the farm and not be slaughtered or their meat disseminated for at least three months to ensure that they do not infect other pigs.

The same principles apply to other diseases that rely on direct transmission or where airborne transmission is possible only over short distances. If a long-term carrier state is known or suspected to exist, as is the case for many bacterial diseases (e.g. bovine, tuberculosis, bovine brucellosis, glanders)

16 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

animals known to have been exposed to infection that survive the outbreak should be slaughtered, or at least separated and subjected to testing and slaughtered if infection is confirmed.

Creating awareness during an animal health crisis

Livestock producers need to be informed as quickly as possible when their animals are at risk owing to an outbreak of a highly contagious disease. The most effective way to reach as many people as quickly as possible is via the public media (radio, television, newspapers). In this way the public will also be informed so that they will understand measures such as road blocks that may in some way affect them. This should be followed up by the dissemination to producers and other stakeholders in the industry of more detailed information on how to protect animals and on the measures that are to be applied. For this purpose the help of the agricultural extension services can be enlisted. Commercial farmers may be able to be contacted through producer organisations; the existence of farmer organisations at all levels is extremely helpful for disease control support.

The message should be clear, simple and easily understood, and not unnecessarily alarmist. It must also be technically correct and truthful. As indicated above with regard to the safety of meat from dead animals for human consumption, at least some of the producers will have sufficient knowledge to recognize untruths, and the entire message will then lose all credibility.

Pig farmers receive a pamphlet with photographs to assist in recognising African swine fever and a poster with simple instructions as to how to prevent it (Ivory Coast)

17 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

Raising awareness about highly contagious diseases of animals should not only happen in response to an emergency. Awareness about diseases is essential for good surveillance, and, if an emergency occurs, it makes the public awareness campaign much easier, because there is a foundation of knowledge on which to build. Theoretically, at least, if sufficient awareness has been created, animal disease emergencies should be very rare events indeed.

Recovering from an animal disease emergency

The actions required in recovering from an animal disease emergency are the following:

Re-stocking after extensive losses due to mortality and/or control measures. The Terrestrial Animal Health Code of the OIE proposes “infective periods” for diseases during which re-stocking should not be undertaken, usually based on double the maximum incubation period of the disease. In practice, re-stocking should not commence until it is fairly clear that the outbreak is over in that particular area. However, the imposition of unrealistically long bans on re-stocking is unacceptable and can lead to the collapse of the sector, since people have to make a living and are likely to turn to other activities if they cannot resume farming within a reasonable period. The use of sentinel animals at no more than 10% of the normal stocking rate may be recommended to avoid serious losses if an error of judgement has been made and infection is present. Sentinel animals should be fully susceptible, and should be observed for a period that exceeds the incubation period of the disease. If at the end of that period the animals have neither developed clinical signs nor antibodies, the premises can be regarded as safe. The selection of sources of animals for re-stocking should be careful, particularly in developing countries where donors may offer animals. The animals should be from a source that is guaranteed to be free of unwanted diseases, and should be of a breed and type suitable for the farming system. The replacement of indigenous breeds with high quality exotic breeds with nutritional and management requirements that are far beyond the means of the recipient to provide will not be helpful and will compound the losses suffered during the outbreak. Such animals are also prone to disasters such as death as a result of eating toxic plants through lack of previous experience of them.

Risk mitigation: it is important to try to identify the cause/s of the outbreak in order to prevent recurrence due to the same cause. If the actual cause can be pin-pointed and eliminated, that is certainly the first prize. Very often it is not possible to determine with precision the exact cause of the outbreak, and very often as well the apparent cause is not the real cause, which will then be overlooked. It is therefore helpful to examine the circumstances under which the outbreak occurred and to decide whether they can be improved to reduce the probability of further outbreaks. This will probably involve intensifying awareness on the part of producers and stakeholders so that, even if they are not able to alter the system within which they operate, they are able to eliminate high risk factors, for example by boiling swill, reducing contact with wildlife, or improving biosecurity in general.

18 | P a g e

Livestock Health, Management and Production › Animal Health Management › Managing animal health for trade

Building on lessons learned: this is an ongoing process that involves working with stakeholders to achieve better prevention and control, and identifying and rectifying weaknesses in the system (for example by improving surveillance, exerting better control over the fate of waste from ports of entry and abattoirs, intensifying communication with stakeholders, repairing fences, or revising vaccination programmes).

19 | P a g e