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Risk Analysis In Veterinary Science

Dr P. G Marais

Grootfontein Agricultural College, Middelburg, 5900 Cape Province, Republic of South Africa

 

 

Introduction

Risk analysis is not a new discipline, the concept actually has a long record of application in areas of engineering and economic activity, but nonetheless its application in area of animal health is a recent phenomenon. Its origin goes back to the "Dunkel Proposal" under the General Agreement on Tariffs and Trade (GATT).

As from 1 January 1995, GATT is to set up the World Trade Organisation (WTO), and the Dunkel Proposal is to be incorporated in the text of the Agreement on the implementation of sanity and phytosanity measures, which inter alia lays down the principles of risk analysis, regionalisation, harmonisation, equivalency and transparency.

The increasing globalisation of trade in livestock and animal products increases the chances of the spread of diseases. In response to this prospect of trade deregulation there is now an imperative need to establish mechanisms which can be used to speed up international trade but at the same time protect the animal health situation of the countries involved.

Food borne disease is generally recognized as a major human health problem and an important cause of decreased economic productivity in both developed and less developed countries. Despite this, there is very little information available on the true level of exposure of specific populations to potential hazards, particularly in the case of bacterial diseases transmitted by consumption of meat and meat products. Attempts to quantify human health risks consequent to exposure to food borne hazards largely rely on extrapolation of information gained from individual disease outbreak investigations to the population at large.

In the case of meat hygiene, the qualitative recognition that unseen microbiological and chemical contamination rather than grossly apparent abnormalities are now the most important sources of hazards to human health. This has led to increasing demands for a more systematic regulatory approach to combat these hazards. In particular, dependence on traditional meat hygiene programs that focus the large majority of resources on routine ante- and postmortem inspection is now recognised as being inadequate.

A wider recognition of the high level of complexity of food safety issues and increasing demands from consumers for maximum protection are other factors forcing regulatory authorities to adopt a more systematic and scientific approach to meat hygiene. Commensurate with these changes, protection of food from contamination, spoilage, and adulteration is no longer limited to being primarily a domestic issue; regulatory authorities must respond to increasing demands for facilitation of international trade.

According to the International Animal Health Code (IAHC) of the OlE (7):

'The principal aim of import risk analysis is to provide importing countries with an objective and defensible method of assessing the risk associated with the importation of animals, animal products, animal genetic material, feedstuffs, biological products, and pathological material The analysis should be transparent in order that the exporting country may be provided with a clear and documented decision on the conditions imposed for importation, or refusal of importation. Import risk analysis is preferable to a zero-risk approach because it provides a more objective decision, and enable Veterinary Administrations to discuss any differences in conclusion which may arise concerning potential risks.’

 

Risk analysis approach in imports of animals and animal products

Risk analysis is based on an amalgam of scientific and technical information, and social and political policy decisions. Thus it is an applied rather than a theoretical science. The elements of risk analysis are risk assessment (RA), risk management (RM), and risk communication (RC).

RA is the primary scientific process and is regarded as the estimation of the likelihood (probability) and severity (magnitude) of harm or damage resulting from exposure to hazardous agent or situations. In the ideal situation, the RA process would be restricted to the "value-neutral" (non-normative) assessment of purely objective scientific data generated from alternative courses of action.

Scientific value judgements and policy choices are inevitably involved at some decision points in the RA process. Thus scientific experts assembling RA data should be guided by clear policy directives when any value judgements affecting the outcome of the RA are made. Determining this "RA policy" is an interactive process and examples of decision points where policy guidelines are necessary are:

- range of hazards included in the primary hazard identification,

- judging the scientific adequacy of the data set that is available,

- treatment of uncertainty,

- and deciding on the statistical basis for the standard of proof.

RM is concerned with development and selection of policy options for the purpose of decision-making, and the implementation of the regulatory programme that is developed from the RA. The options that are considered may be quantified solely in economic terms and RM decisions made according to some risk balancing standard, e.g., the risk-cost benefit analysis producing the highest benefit/cost ratio.

However, RM decisions often have to be made in the face of significant scientific uncertainty and the values that are considered may not be reduced to monetary values alone. Relevant social criteria concerned with issues of "equity and ethics" include standards of health, technological feasibility, social concerns, and politics.

Risk managers must make a choice about what is an "acceptable" level of risk. The simplest technique is a risk-cost-benefit approach in those situations where all RM options can be reduced to, and quantified in, economic terms. Risk analyses involving human values will require use of other methodology such as threshold, comparative, "zero-risk", or as-low-as-reasonably achievable (ALARA) risk standards. Additionally, RM decisions in animal health import risk analysis are likely to depend on the trustworthiness of information likely to depend on the trustworthiness of information gathered in another country on an on-going basis, focus on means of reducing risks associated with imported animals or animal products, and be limited to estimating the probability of the hazard being realised rather than including an estimation of the severity of such an outcome.

Recognition of RC is a vital part of the risk analysis process. The results of RA and RM need to be effectively communicated both within and between regulatory authorities and to the public.

In discussing risk analysis, it should be recognised that while uniform principles of RA and RM can be pursued, uniform conventions (such as levels of statistical significance) are not necessarily advisable in deciding what level of proof is acceptable for policy purposes. As an example, it may be appropriate to rely on "most likely" estimates of risk when evaluating a chemical that is essential to a beneficial societal activity (e.g., use of radio nuclides in medicine), whereas a "worst-case" estimate may be appropriate when evaluating a nonessential chemical.

 

Why risk analysis in meat hygiene?

Meat hygiene programs are primarily engaged to ensure that meat and meat products are "safe and wholesome". In the case of raw meat, this is only a qualitative measure of freedom form hazards to human (and animal) health. Postmortem meat inspection cannot guarantee freedom from all grossly detectable abnormalities, and sampling programs have limited ability to detect randomly occurring violative levels of chemical residues and contaminants. More importantly, some degree of inadvertent microbiological contamination is inevitable in the slaughterhouse environment. In broad terms, the major "hazards" detectable at postmortem meat inspection are identified during observation of tissues. Following removal of the most important hazards, incremental benefits decrease as the level of inspection intensity increases. The optimum usage of postmortem inspection occurs when the incremental gain in benefits (in the broadest sense) equals the incremental increase in costs. Thus the optimal use of inspection resources does not eliminate all hazards, but removes all-important hazards and ensures that any residual hazards are minor in nature and exist at a prevalence that constitutes a "negligible" risk to the consumer.

A well-designed RA model can provide a quantitative basis for comparative evaluations, thus delivering scientifically appropriate information for RM decisions. The four analytical steps of the general health RA model can be suitably modified:

Selection of sampling parameters are RA policy decisions that are primarily scientific value judgements. Samples must be representative of the population to which the conclusions are to relate and must include enough samples to enable definite conclusions to be reached as to the consequences of any change in inspection procedures. The level of residual risk that is not addressed by the model also depends on sample size.

Other RA policy decisions include the statistical choice for comparison of the outcomes of different inspection procedures. Some studies have used tests of statistical significance to decide on equivalent performance but although superficially attractive, they provide only limited information on the comparative performance of the procedures. The most rigorous approach upon which to base RA decisions is to consider the worst cases included in the confidence intervals for the non-detection rates for each procedure.

Decision-making criteria (RM) for establishing an acceptable level of risk for postmortem meat inspection programmes may be complex. With the realisation that even high-intensity routine inspection procedures are neither 100% sensitive nor specific. It is not technically feasible nor cost-effective for current meat inspection systems to eradicate all potential hazards from fresh meat produced for human consumption. Thus a "zero risk" approach to RM is inappropriate.

An important issue in RM is a consideration of scenario trees for meat and meat products. The scenario tree starts with an initial event and charts the functions that can affect the outcome of the initial event. Construction of a scenario tree collectively describes the risk model, and calculation of the likelihood of each of the risk scenarios (and their aggregation into an overall quantification of risk) can be achieved by several statistical methods. The use of probability density formats is gaining in acceptance and in this case, quantification of each scenario parameter depends on expressing each numerical value as a probability curve against all possible values. PC software programmes such as @RISK (Palisad Corporation, New York) can use more elemental probability distributions, e.g., triangular distributions based on minimum most likely and maximum estimates, to carry out iterative calculations for RA.

The problems associated with formal analysis of the risk of food borne microbiological disease are very different to risk analysis of food borne chemical hazards.

If an uncritical assumption is made that a human health hazard exists because of the presence of particular contaminating microflora, it would be tempting to try and characterise that risk by exposure assessment. One approach would be to construct a numerical dose-response curve for each potential pathogen that may be present in the final product and attempt to characterise risk in these terms. However, experience in ecological RA would suggest that irrespective of the difficulty in gaining the quantitative data, developing this additive organism-by-organism approach would be very difficult. In the case of meat, the biological interactions in the microflora that occur after the product leaves the slaughter- or packhouse are not able to be quantified with any certainty and as stated above, prediction of exposure should not automatically lead to an assumption of a human health risk.

Notwithstanding the problems mentioned above, microbiological hazards in food can be subjected to a formal risk analysis process, with data generally being generated from clinical and epidemiological studies in humans, and surveillance. The best probability estimates would come from a "perfect" epidemiological study on the human population of interest at the range of doses or exposures of interest. Unfortunately, such studies rarely exist. Estimates of risk derived from epidemiological studies are therefore often quantified in terms of relative risk or attributable risk.

Development of quantitative microbiological RAs is in its infancy but will probably increase in the future: this may lead to establishment of more meaningful microbiological criteria in terms of human health risks. The choice of a human health endpoint is very different for microbiological hazards compared with chemical ones and this would be an important RA policy decision in a theoretical quantitative microbiological RA. Possible outcomes of microbiological contamination are true exposure, infection, disease, or death.

Currently, RAs for microbiological hazards in fresh meat and fresh meat products are very unlikely to be able to draw on equivalent quantitative data to that described above for specific pathogens of animal health importance. The absence of detailed knowledge on the prevalence and specific zoonotic potential of the wide range of bacterial species commonly found as inadvertent contaminants on fresh meat, coupled with very limited dose-response data for those pathogenic strains known to be transmitted to humans by digestion, makes microbiological RA for public health hazards a difficult proposition.

Current risk analysis of microbiological hazards is primarily inhibited by lack of information and lack of a detailed conceptual framework. However, these problems are not intractable and national initiatives to address these issues in the general area of food safety are underway. Several countries have recently

embarked on studies to gather microbiological baseline data on dressed carcasses as a first step to provide quantitative input to a "risk analysis" approach to meat hygiene. Development of a substantial conceptual framework is a prerequisite for successful microbiological risk analysis.

 

Qualitative aspects of risk

The notion of risk involves both the possibility of loss or injury and the degree of probability of such a loss. Risk, therefore, implies damage, and it can be expressed as:

Risk = f (uncertainty, damage)

If hazard is defined as "a source of danger", then, risk can be symbolically expressed as:

Risk = f(hazard/safeguards)

Risk includes safeguards, is never zero and can be made as small as one likes by increasing safeguards Calculation of something as "unrestricted risk", therefore, particularly in the case animal health risk, appears an abstraction that does not seem to have a great relationships both with the actual world and with risk analysis as defined in the specialized literature. When "unrestricted risk" calculation are applied to large volumes of commodities Risk Estimate (URE) appears a "fuzzy set method" of calculating and expressing prevalence.

In fact, risk depends, quantitatively, on, what you know, what you do not know and what you do and what you do not do.

 

Quantitative definition of risk

Taking into account the basic concepts, one can define risk, from the quantitative point of view, as a set of triplets:

i. What can happen = scenario (si).

ii. How likely is it that it will happen = likelihood (pi.)

iii. If it does happen what are the consequences = consequences (xi )

Therefore, more formally, risk (R) is the set of triplets defined as:

 

R= {( si , pi , xi )

Where,

si  = a scenario identification or description;

pi = the probability of that scenario;

xi = the consequence of that scenario (i.e. the measure of damage).

 

If scenarios are arranged in order of increasing severity of damage (x1 ≤ X2 ≤ X3 ≤ …< XN ), one can calculate the cumulative probability adding from the last scenario (Pi ), that can be described with a staircase function of ( xi ,  Pi ). Given that one speaks of "categories of scenarios" one can draw a smoothed curve through the staircase and thus obtain a risk curve.

Risk, therefore, is probability and consequences. It follows that it cannot be described by a single number but as a function of ( xi Pi ) that is at least, by one curve.

Within the concept of risk described above the notion of URE (Unrestricted Risk Estimate) as an expression of "risk" is difficult to accept, because it does express neither the probability of consequences occurring, nor a credible scenario. It seems only a pure number.

Moreover, risk cannot be spoken as either acceptable or unacceptable in isolation, but only in combination with the cost and benefits relative to that risk management. In fact risk and risk analysis are always part of decision-making processes where the optimum mix of cost and benefit and risk is the endeavour. It should also be recognized that, in relation to any hazard, risk can be made as small as one wants according to the amount of safeguards one is going to apply to prevent it.

Risk, furthermore, is never acceptable, although obviously must sometimes be accepted. In any case, the acceptance of risk is one of the most volatile subjects both within countries and in international agreements. The expression of "Acceptable risk" should, therefore not be used within the context of animal health and animal health products and the expression "Accepted risk' should be used, instead. The level of risk accepted should be clearly defined and documented.

 

Risk analysis approach in imports of animals and animal products

Risk analysis relative to animals and animal products, therefore, should be based on the following assumptions:

The method for risk assessment suggested by the OlE

The sole method suggested by the IAHC of the OlE for risk assessment is based on calculation of the Unrestricted Risk Estimation. The latter is the probability of the occurrence of at least one outbreak of a given disease following the importation of a given quantity of either live animals or animal products. If this probability is lower than a given threshold 51, importation is permitted without any restriction, if it is higher than a second threshold 52>51, importation is not permitted. Finally, if the probability is between 51, and 52, importation is allowed only if safeguards measures are adopted.

The suggested method is, in fact, a very simplified method to calculate risk considering only one scenario in which no safeguard measures are adopted. Of all possible triplets able to identify each point of the risk function, furthermore, it, takes into account only the probability and not the consequences, i.e.: damage.

Unrestricted Risk Estimate (URE), therefore, seems to be an oversimplification that appears to be an exponential function of the number of units imported. I n other words the increase of units imported make the risk increase very rapidly to high level, to the point of overcoming the 52 threshold, irrespective of the fact that one might have a very low infection/disease prevalence in the exporting Country.

In Figure 2 the variation of URE as function of the number of outbreaks occurring in the exporting Country is reported, while in Figure 3 the same variation is calculated as function of the number of animal imported.

 

In the example the disease chosen is Foot & mouth disease (FMD) and the exporting Country has a population of 10000000 bovines and an average of ten animals in each herd. FMD was chosen to be able to use the same parameters used by Morley (1993), however the same curves would be generated in case of any disease or infection. It should be stressed, furthermore, than in a situation of free trade one has to assume, by definition, that in any given Country, in any given moment, the possibility of at least one unidentified infection/disease outbreak, cannot be excluded. In the example, in case of a single unidentified outbreak in the exporting Country, the importation of only 100 animals (nAIUS) would result in an URE of 2.4 x 10-5 . The latter is a value higher than those usually considered acceptable by Countries currently using the OlE method to calculate risks due to import.

 

Conclusions

To analyze and manage risks is a traditional activity of veterinary medicine. The "new" international policy in trade of animals and animal products, however, requires radical changes. Veterinary services in this type of activity have used, traditionally, only qualitative assessment. They must now introduce also quantitative methods, based upon rigorous scientific principles, and they must also document the logical process followed in their qualitative evaluations. The objective of these changes is to reduce, or ideally, eliminate, as far as possible, inconsistencies in decision processes relating to the definition of safeguard against risks deriving from international trade of animals and animal products.

Risk assessment is a component of risk analysis. It is a provisional technique which, starting from experimental data and observations, tries to estimate probability and damages, linked to a given scenario, in a purely deductive mode. Risk curves are an essential tool for risk assessment. These are generated with the aim of describing a series of scenarios in which, to the identification of a series of hazards, correspond different possible safeguard measures. For each scenario series a series of curves is generated to compare the different scenarios by quantifying risks a priori.

Risk assessment, according to the OlE suggested method, is based on the estimate of risk associated to a single factor (i.e. risk of importing FMD by frozen meat from Argentina). The use of the OlE suggested method several shortcomings, especially when applied to large volume of commodity trade in such circumstances it is virtually inapplicable if one wants to assure free trade of animals as required by present international agreements. OlE suggested risk assessment method, in its present formulation, has not only a very limited value as a decision tool, but has some conceptual inadequacy.

Quantitative risk assessment methods are, however, necessary to assure a harmonic development of international animals and animal products trade. They also appear necessary to improve resource management both in the planning and in the evaluation stages of veterinary activity. A promising method seems to be the use of risk curves to comparatively evaluate various scenarios describing both hazards and safeguards measures avoiding excessive and dangerous oversimplifications. This appears to be also more coherent with veterinary service need. It allows, in fact, the comparison of different strategies of risk management, each represented by a scenario category and consequently at least by a risk curve. Difficulties in the interpretation of the semantic value of the functions describing risk, however, persist also with this type of method.

Concrete reduction of uncertainty in risk assessment is possible only if one uses factual data. These can be generated only by a correct scientific analysis of the information produced by epidemiological surveillance systems.

Studies of association between risk factors and sanitary problems would be particularly useful because they generate factual data that can be used to evaluate risk assessment methods and safeguard measures scientifically.

When trade takes place within free trade areas, as for example within the European Union, it is very difficult to define the exact limits of national and international trade. In this case the management of risks, due to animals and animal products trade, is only one of the components to be taken into account, within the general strategic choices made to safeguards against sanitary problems. In particular one should not forget that the new international animal and animal products health policy provides for regionalization. In other words within a Country one can create circumscribed areas with sanitary level different from the rest of the national territory and for which particular rules apply. This policy can have devastating effects for those Regions or Areas representing a risk higher than the remaining Country territory. They, in fact, would not be able to trade not only at the international but also at the national level.

There is little doubt that the possible use of this type of techniques has been grossly underestimated within the context of international animal and animal product trade. In fact problems, both at the international and within free trade zones, are not only those linked to exotic diseases, in other words, to rare phenomena, but also those due to diseases, infections, contamination present with various occurrence rates in the territory of all trading partners.

 

Published

Veterinary Congress, Cedara, 1995