Chapter 4

Epidemiologic/Economic Tuberculosis Studies and Bioeconomic Research Considerations

The design of a program to eradicate or control disease must consider both the size and distribution of economic costs and benefits as well as noneconomic political and cultural factors that affect public and private decision making. The discussion in this chapter reviews applications of bioeconomic modeling in order to evaluate alternative disease management strategies and also considers concerns (about animal welfare, for example), which are difficult to express in economic terms.

DISEASE CONTROL: ERADICATION AND OTHER END POINTS

When instituting a disease control strategy, the ultimate objectives of the program must be noted while taking into account the current disease status as well as the environmental (both economic and biologic) situation. The objective of disease control per se usually is to maintain the disease at or below its current level, to reduce the incidence of disease below some specified target level, or to reduce progressively the frequency of the disease until eradication is achieved. Eradication, which implies the extinction of the disease (organism), has physical and geographic dimensions that extend from the individual farm to the state, national, continental, and global levels. Eradication also has a species component. For example, it might be appropriate to aim for eradication of a disease in one species, while in another species (depending on environmental issues, endangered species designation, etc.) disease control may be the objective. Obviously, if the presence of the disease in one species can affect the control efforts in the other species, then a rationalization of control activities in both species may be needed.

In general, the tools or methods available to help reduce the frequency of disease include mechanisms to detect the disease (surveillance programs, such as skin testing for tuberculosis); mass vaccination; management practices such as local quarantine and animal movement restrictions (for example, no movement without a negative-test status); vector/reservoir control; cleaning and disinfecting contaminated areas; and treatment or slaughter of reactor and sometimes exposed animals (Schwabe, 1984). As the disease frequency decreases, the program may need to be modified; for example, by ceasing vaccination if it affects disease detection, increasing the movement restrictions on the species of concern between low- and high-prevalence areas, and implementing a depopulation program in which all exposed animals, not just reactors, are slaughtered.

Historically, it has been recognized that to achieve eradication, nondiseased reactor and exposed animals may have to be sacrificed in order to prevent “hidden disease” (false-negatives) from initiating new foci of infection. A justification for this depopulation, beyond the limitations imposed



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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM Chapter 4 Epidemiologic/Economic Tuberculosis Studies and Bioeconomic Research Considerations The design of a program to eradicate or control disease must consider both the size and distribution of economic costs and benefits as well as noneconomic political and cultural factors that affect public and private decision making. The discussion in this chapter reviews applications of bioeconomic modeling in order to evaluate alternative disease management strategies and also considers concerns (about animal welfare, for example), which are difficult to express in economic terms. DISEASE CONTROL: ERADICATION AND OTHER END POINTS When instituting a disease control strategy, the ultimate objectives of the program must be noted while taking into account the current disease status as well as the environmental (both economic and biologic) situation. The objective of disease control per se usually is to maintain the disease at or below its current level, to reduce the incidence of disease below some specified target level, or to reduce progressively the frequency of the disease until eradication is achieved. Eradication, which implies the extinction of the disease (organism), has physical and geographic dimensions that extend from the individual farm to the state, national, continental, and global levels. Eradication also has a species component. For example, it might be appropriate to aim for eradication of a disease in one species, while in another species (depending on environmental issues, endangered species designation, etc.) disease control may be the objective. Obviously, if the presence of the disease in one species can affect the control efforts in the other species, then a rationalization of control activities in both species may be needed. In general, the tools or methods available to help reduce the frequency of disease include mechanisms to detect the disease (surveillance programs, such as skin testing for tuberculosis); mass vaccination; management practices such as local quarantine and animal movement restrictions (for example, no movement without a negative-test status); vector/reservoir control; cleaning and disinfecting contaminated areas; and treatment or slaughter of reactor and sometimes exposed animals (Schwabe, 1984). As the disease frequency decreases, the program may need to be modified; for example, by ceasing vaccination if it affects disease detection, increasing the movement restrictions on the species of concern between low- and high-prevalence areas, and implementing a depopulation program in which all exposed animals, not just reactors, are slaughtered. Historically, it has been recognized that to achieve eradication, nondiseased reactor and exposed animals may have to be sacrificed in order to prevent “hidden disease” (false-negatives) from initiating new foci of infection. A justification for this depopulation, beyond the limitations imposed

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM by the detection system, is that most diseases have a complex natural history. Whereas the majority of disease may arise from identifiable sources, some disease occurrences happen for other, often unknown, reasons. This could include aberrant forms of the organism, unusual methods of spread, or the structure or nature of specific animal enterprises. For example, as noted earlier, large herds may have different epidemiologic features than smaller herds, or disease control in herds located in one type of terrain may be more difficult than in similar herds in a different environment. Another reason for using depopulation is that although a test and slaughter program may be capable of achieving an eradication goal, a depopulation program may offer considerable savings in the total number of animals sacrificed, in time, and in money. Finally, given the limitations of the disease detection process at the individual animal level, there may be no reasonable alternative to depopulation to ensure that the last vestiges of disease have been removed. In principle, determining if and how a disease should be controlled is a straightforward task. In practice, however, there are numerous difficulties, primarily because of uncertainties about the biologic and economic effects of the disease and of the impact of the various control strategies. Depending on the disease and the existing environment, a thorough bioeconomic analysis should help decide whether control efforts can be effectively and efficiently mounted by the affected farms or industries themselves, or if a more widespread government program is needed. If a government program is appropriate, a thorough analysis should help decide on the nature, intensity, and end point of the program(s). MODELING AS AN AID TO DECISIONS ABOUT CONTROL Combining economic and epidemiologic methods has proved to be successful in providing guidelines and decision-making criteria for animal health programs (McInerney et al., 1992). One method, modeling of disease processes, will be stressed here. Bioeconomic animal disease simulation models, a combination of epidemiologic and econometric models, have been used primarily to determine the benefits and costs associated with a number of alternative disease control strategies as part of animal health programs directed against diseases such as brucellosis, tuberculosis, screwworm, and foot and mouth disease (Dijkhuizen et al., 1991; Dijkhuizen, 1992). Paramount to the success of any bioeconomic model is the accuracy with which the epidemiologic coefficients reflect the actual characteristics of the disease within the specific livestock industry. If a valid and representative epidemiologic model has been established, then the effects of the baseline program and of alternative control programs can be simulated. Epidemiologic models are mainly designed to simulate (1) the incidence, prevalence, and spread of infection; (2) the impact of these on the demographics and productivity of the species of concern; and (3) the effects of control program components on the level of infection and related physical losses. Anticipated benefits from disease control include reductions (changes) in physical losses of meat and milk (or other animal products) associated with the alternative programs compared to the baseline program. Most epidemiologic models consider the probability of an animal (or herd) becoming diseased, the biologic impact of the disease in that herd/animal, and the impact on other components of the industry. The model should take into account the expected variability in these parameters depending on the nature of the enterprise, the local environment and any variation over time (for example, cyclical or seasonal patterns). Some epidemiologic models are deterministic and essentially give the same result every time the model is run with the same start-up parameter values. Other

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM models are stochastic and, hence, more realistic in that they allow random variation in the parameter values to influence the outcome. Econometric models are designed to determine the economic impact of changes in physical losses of animal products on consumers, producers, and related industries. In principle the point is to estimate the economic losses caused by the disease and to estimate the costs and effectiveness of the control program(s). This allows examination of the benefits of alternative control strategies per dollar spent on disease control. In most instances it is desirable to identify who (for example, the individual farmer, the industry, or society) bears the costs and who receives the benefits from the control efforts. Often, determining the program costs is a straightforward, if not tedious, task requiring a complete listing and valuation of the materials, components, and activities involved in the program. The impact of the control strategy on the individual producer, as well as on the industry and society (for example, production efficiency, trade constraints, demand/supply balance, public health implications, increased management costs, etc.) is more difficult to estimate but should also be considered under the “costs” heading. In addition, because control and eradication programs may require many years to achieve their objective, some form of discounting future costs and benefits is needed. Thus, good bioeconomic models can calculate the discounted value of the change in benefits (discounted economic value of change in physical losses) and program costs associated with alternative control programs to facilitate the estimation of net change in benefits, change in program costs, and benefit/cost ratios for determining economic acceptability of the programs analyzed. As mentioned earlier, it is often difficult to estimate precisely the effects of control strategies. Hence, data from pilot studies, data from similar program in other areas, expert opinion, and results of other simulation models can be helpful for initial estimates. Initial models may be imperfect, but good models should be sufficiently flexible to allow structural changes in the model, allow updating of the data base with more current data, and allow the evaluation of new strategies for disease control. APPLICATIONS TO BOVINE TUBERCULOSIS Numerous epidemiologic/economic studies have been conducted for a variety of animal diseases during the last two decades. Although there were previous references to “the economic effect of bovine tuberculosis” and general statements as to the effectiveness of the control/eradication program, no thorough economic evaluations were conducted prior to 1970. Hence, the bioeconomic studies of bovine tuberculosis reviewed in this report, include studies by the USDA (1970) and governments in Canada (1979), Australia (1987), and Ireland (1991). U.S. Bovine Tuberculosis Study One of the earliest bioeconomic models for bovine tuberculosis was developed by Kryder, Roswurm, and Beal in 1970. As a basis for comparing gains attributable to various kinds of disease control programs, their analysis began by estimating what the spread of bovine tuberculosis might have been had there been no federal eradication program in 1970 and subsequently. This estimate of

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM baseline infection, extrapolated from 1970 through 2010, was compared to the bioeconomic model's predictions of the effects of four alternative eradication strategies: the 1970 state-federal cooperative program; the 1970 program but with the percentage of infected herds depopulated increased from 40 to 95 percent; the 1970 program with the disease detection rate at 50 percent annually; and the 1970 program with both detection and depopulation rates increased. In the model, slaughter surveillance was the method for detecting infected herds, and it was assumed that adequate funding would be available for the specified levels of surveillance and depopulation. In the model, beef and dairy herds were each divided into eight herd-size groups ranging from 1 to 4 cows up to 200 cows or more for the dairy herds; beef herd categories ranged in size from 1 to 9 cows up to 500 cows or more. The number of infected herds and number of infected cows by herd size were estimated. The construct of the model assumed that spread of bovine tuberculosis was caused by infected cattle from tuberculosis-infected herds being purchased and placed in noninfected herds; it did not include the possibility of spread from fence-line contact of cattle or contact of cattle with other infected species. A formula for estimating the probability of purchasing one or more infected cows during the year, by herd size, was developed. The model took into account herd management practices such as replacement (cull) rates, source replacement ratio (number of herds or sources from which replacements were purchased), probability of purchasing infected replacements, and clean-up rates. Infected herds were partitioned by duration of infection, ranging from 1 to more than 3 years. The average number of infected cows was then calculated by herd size and year of infection. Economic losses were classified as (1) losses at slaughter, (2) processing costs, and (3) farm losses. Reactors at slaughter were classified as condemned (12 percent), retained (45 percent), and neither retained nor condemned (43 percent). Condemned carcasses were assessed a loss of $247 per carcass. Retained carcasses were each assessed a $10 loss due to condemnation of parts of the carcass. Carcasses neither condemned or retained were not assessed a loss. A $25 processing cost was assessed on all reactors. Farm losses caused by bovine tuberculosis included (1) a 10 percent milk production loss per year, (2) a calf weaning weight loss of 20 percent due to early culling, and (3) replacement loss due to purchasing additional cattle to cover the increased number culled. Comparing the model's results across different assumptions about the rate of disease detection and the extent of subsequent depopulation, the analysis demonstrated the benefits from checking the spread of bovine tuberculosis over the period 1970 to 2010. With no eradication effort the baseline infection rate rose from 0.08 percent of the national beef and dairy herd at the start of the period to more than 5 percent by 1995. The 1970 program was projected to have achieved eradication by 1995, with a cost/benefit ratio of 7.81 compared to the no-program baseline. If depopulation rates were more than doubled, eradication was expected by 1986, providing even greater gains, compared to the baseline, with a cost/benefit of 9.13. With enhanced disease detection (but no increase in depopulation) under the 1970 program, eradication was projected by 1983, yielding a cost/benefit of 8.53 compared with the no-program alternative.

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM With both enhanced detection and more aggressive depopulation, eradication was predicted to occur in 1979, with a cost/benefit of 10.45. In the context of contemporary concerns about the potential for increase in the prevalence of bovine tuberculosis, the usefulness of the Kryder et al. (1970) model is limited because it does not consider the more recent emergence of Mexican cattle imports and of farmed exotics as disease threats. Moreover, the economic structure of both the dairy and the beef cattle industries has changed markedly in the past 25 years. These changes imply the need to reevaluate the model 's characterization of both its epidemiological and economic features. Further, the model's assumption of sufficient financial resources, public or private, to implement any of the eradication program alternatives may well not be valid in today's more constrained fiscal environment. At the same time, the model's results do show the relative gain in the benefit/cost ratio as disease detection improves and as depopulation is pursued more aggressively, enabling the eradication goal to be reached more quickly. Canadian Bovine Tuberculosis Study Almost a decade after the U.S. study, Canada completed a benefit/cost analysis of alternative bovine tuberculosis eradication programs (Agriculture Canada, 1979). At that time, the prevalence of tuberculosis was very low in Canada (< < 1/1000 cattle), and the Canadian government was pursuing a test and slaughter program with the objective of national eradication. The analysis compared the existing program's benefits and costs to those expected with no eradication effects at one extreme and with depopulation at the other extreme. The underlying model was based on the Beal and Kryder APHIS brucellosis model developed in 1977 as described in an APHIS paper entitled “The Stratified Triple Binomial Herd-to-Herd Disease Population Model in Cost-Benefit Analysis.” This APHIS model contained three basic components: estimation of the probability of purchasing infected animals; estimation of the probability of spread from farm to farm via contact (fence-line spread); and estimation of the probability of detecting disease through the Market Cattle Test (MCT)--the slaughter surveillance--program. The model divided Canada into five regions based on geographic location, surveillance program effectiveness, producers' characteristics, and animal infection levels. Beef and dairy sectors were analyzed separately. Physical losses were estimated on a per-infected-animal basis and then aggregated on a regional and national basis. Economic losses were evaluated at 1975 prices over a 35-year simulation period with cow numbers and herd size structure being held constant. Often it is the case that data on testing frequency, results, and confirming diagnoses on potentially infected animals are not aggregated in a way that permits straightforward estimates of population disease rates. This lack of systematic data collection currently characterizes the situation in the El Paso milkshed and posed problems for the 1979 Canadian analysis. In these circumstances, subjective judgement and extrapolation from other data sets is required. For example, in the Canadian case, the number of nonreactor infected cases per million cattle was estimated to have declined from 84 in 1967-1968 to 16 in 1977-1978. These were converted into estimates of the number of infected herds; 158 in 1967-1968 and 35 in 1977-1978. Then, based on the adjusted number of herds placed under quarantine, it appeared that about 24 to 25 percent of previously undetected infected herds were quarantined each year.

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM To demonstrate the range of assumptions needed to initiate a bioeconomic disease model, the ten factors that were estimated for the Canadian analysis are cited below. It was estimated that 25 percent of undetected infected herds were found each year. The number of “base” infected herds by duration (< 1 to > 3 years) of infection was estimated to be 44 for 1977-1978. The prevalence of infection in infected herds, by duration, ranged from 6 percent to 33 percent. The model assumed an inverse relationship between prevalence and herd size. The clean-up rates of herds by duration were estimated to be between 60 and 67 percent for test and slaughter, 80 to 100 percent for depopulation, and 0 percent for no program. It later turned out that the clean-up rate assumptions were crucial to the model outcomes (that is, the results depended heavily on these assumed values). The number of source herds for purchases was estimated using the number of purchases. The cull rate per herd was set at 30 percent for dairy and 20 percent for beef cattle. The proportion of a herd purchased as outside replacements, by agreement of the study group, was set at 10 percent. The number of cattle with gross lesions traced to herds of origin (market cattle-testing rate) was set at 54 percent to indicate that 54 percent of infected herds would be found each year by the market cattle-testing program. Only 5 percent of animals with “lesions” were actually infected (demonstrating the relatively poor predictive value of a lesion at slaughter). Based on the assumptions about the probability of detecting infected herds, larger herds had a higher detection rate than small herds. The probability of farm-to-farm spread in the absence of purchases of infected cattle was estimated to be 30 percent (that is, 10 infected farms would spread infection to 3 adjacen farms each year). A regional test factor reflecting the effort to prevent the purchase of infected animals ranged from 0 = maximum effort to 100 = no effort. In the model, this parameter was set at 50 for depopulation, 60 for test and slaughter, and 90 for no program. The above estimates were further categorized, as necessary, based on herd size and cattle type. Producer costs associated with tuberculosis were estimated based on the Kryder et. al. (1970) methodology. For dairy cattle there was an assumed 10 percent loss in milk production, 20 percent loss in calf production, and a 15 percent loss from premature culling. For beef cattle, a 20 percent loss in calf production and a 20 percent loss from premature culling were assumed. Additional losses were calculated based on portions of culled cows condemned (retention loss) and whole-carcass condemnations. These losses were partitioned into losses per reactor animal and losses per nonreactor infected animal for modeling purposes. Total costs for each of the three programs were estimated based on salaries, operation costs, capital costs, grants and contributions, and compensation (with the latter adjusted for the lowered costs associated with no quarantine). There did not appear to be any consideration of “on-farm” producer costs as a result of the program. In summary, the results favored the depopulation program. The no-program alternative was predicted to result in a higher infection rate in Canada than existed in the 1920s prior to initiation of control efforts (4.5 percent of cattle infected). The test and slaughter program was predicted to achieve national eradication in 16 years compared to 6 years for the depopulation program. The

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM discounted benefit cost ratios for test and slaughter were 21:1 and for depopulation 34:1 in comparison to no program. As is the case with the 1970 U.S. model, the 1979 Canadian effort has somewhat limited applicability today because of changes in sources of disease threat and industry structure, as well as increasingly severe constraints on public financial support for eradication efforts. However, the two models are comparable in their finding that, given the decision to eradicate bovine tuberculosis, adoption of a strategy of depopulation is preferred to one of test and slaughter as evidenced by consistently higher benefit/cost ratios. Indeed, APHIS reaffirmed depopulation as the major thrust of the USDA eradication program because it represents “the only assurance that a focus of tuberculosis has been eliminated” (U.S. Department of Agriculture, Animal Plant Health Inspection Service, Veterinary Services, 1990). Australian Bovine Tuberculosis Study In the 1980s the Australian government considered whether to advance its efforts to eradicate bovine tuberculosis from the southern part of the country, where it had been quite successful, to the more remote northern part. To inform this decision, Stoneham and Johnson (1987) analyzed the potential costs and benefits of the extended campaign as well as the alternatives for providing financial assistance to producers as a means of inducing participation. The status of the tuberculosis campaign in Australia as of June 1985 revealed that 0.2 percent of the herds were infected (347 herds) with an area prevalence (percent of all animals tested that were infected) of 0.0115 percent. Highest tuberculosis infection rates were reported in the Northern Territory, where 28 percent of the herds were infected with an area prevalence of 0.15 percent. Western Australia and Queensland had the next highest herd infection rates of 0.43 percent and 0.37 percent, respectively. The numbers of infected herds reported in the Northern Territory was 148 and 142 in Queensland. The potential reservoirs of bovine tuberculosis infection in Australia are cattle, buffalo, wild hogs, and deer, with cattle being the chief source. A major problem facing eradication efforts in northern Australia was the cost of mustering (gathering or rounding up) cattle for the required number of tests within a given time frame. Although the program provided financial assistance for routine mustering of cattle for testing or destocking, additional mustering and handling costs associated with presenting cattle for testing or destocking were to be borne by producers. Analysis of cash flows generated by northern beef properties revealed that many producers in the most difficult “mustering” country would be unable to meet the additional costs associated with the eradication program and remain viable. For example, costs of completing eradication over the northern areas were estimated to be $200 million of which $94 million would be assessed to the industry under the current program. Thus doubts existed about the ability of northern beef producers to meet the costs inherent in the existing testing program. The authors of the report stated that the most important potential benefit of continuing the eradication campaign was the protection of export market access for Australian beef. Potential loss of the U.S. market was estimated to cost the beef industry and the nation approximately $3.5 billion. The exclusion from a major overseas market would result in dislocation of the beef industry and impose high social costs on Australia. Two broad options were evaluated regarding the future of the Australian tuberculosis campaign: (1) continue with the objective of eradication or (2) change the campaign objective to

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM control. As noted, the first option faced a major difficulty because tuberculosis eradication costs were expected to rise rapidly as the campaign moved into northern Australia. Consequently, if a total eradication campaign were to be successful in the north, changes would have to be made in the assistance arrangements. The second option presented potential problems for the tuberculosis-free areas of Australia, which could be reinfected by cattle from the northern areas if the disease were not eradicated. Protecting clean areas would require severe restrictions on cattle movements from the north, which would also affect the traditional movement of slaughter cattle from the north to the south. In addition to these two program options, the authors investigated different methods of financially assisting the producers with the costs incurred in the program. In particular, they proposed a lump sum payment to producers from the government, a recommendation based on a least-cost analysis of disease control strategies on individual farms. The analysis showed that “if the risk of losing access to a major market is greater than one chance in 25, then eradication should be pursued.” In contrast, if the risk of major market closure were less than 1 in 25, then the campaign should not proceed to full eradication. As the risk to total or partial market closure was considered to be small, the conclusion was to discontinue the eradication program in the northern territories. Despite the recommendations of the study, the Australian cattle industry rallied against any slackening of eradication efforts, effectively increasing its share of the program cost burden. Currently, the tuberculosis control effort continues to rely on the skin test for disease detection and is nearing its original goal--namely, national eradication of bovine tuberculosis. The Irish Bovine Tuberculosis Study A benefit cost analysis of the Irish Bovine Tuberculosis Eradication Scheme (Sheehy and Christiansen, 1991) presents an interesting alternative approach to a bioeconomic evaluation of disease control programs. The Irish eradication program began in 1954 and was deemed close to being successful in 1965. Unfortunately, approximately 30,000 reactors per year (in approximately 6,000 herds) continued to be found in a population of about 7 million cattle (158,000 herds); hence, a reexamination of the program from a biologic and economic viewpoint was conducted. The recent Irish program, known as ERAD, is an intensive test and slaughter campaign. All herds are tested annually, and herds at high risk are tested more frequently. The interpretation of skin test results varies across the risk categories, with the more severe interpretation, designed to increase sensitivity, used in high-risk herds. Other aspects of ERAD include an extended period of restricted cattle movement to and from infected herds, compulsory disinfection of infected premises, removal of badgers if they are deemed to be the source of the outbreak, and owner education about the program. The alternative schemes investigated compared both more and less intensive test and slaughter programs than ERAD. The two extremes--herd depopulation after proving the presence of M. bovis and no program at all--were not considered. The most intensive program considered would feature all tests being conducted by government veterinarians, animal movement control with testing prior to movement, rapid derestriction of “singleton” (single reactor) herds, zoning of the country according to tuberculosis prevalence with inter-zone movement control, and

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM “insurance” contributions required by the individual producer, the level to be determined according to the producer-controllable risk. The least intensive program would minimize testing beyond the one-herd test per year, derestrict reactor herds more easily, reduce the effort on depopulation, and leave disinfection of infected premises to the individual producer. The responsibility for the annual herd test would be devolved to the herd owner. No cattle movement would be permitted without both the annual herd test and individual premovement tests (also the responsibility of the owner). In a sense, clear ongoing tuberculosis testing would be the basic requirement for any trade as an annual herd test is required (as it is now) by the European Community. Crucial to the economic analysis was knowledge of the impact of different eradication and control strategies on the prevalence of tuberculosis. As is often the case, such knowledge was not available. On the biologic side, estimates of key parameters used in this study included 10,000 cattle per year infected from wildlife; 5,000 false-negative cattle per year; 10 to 15,000 reactors missed per year because of imperfect testing; and 0.1 percent (10 to 12,000 cattle) false-positive reactors. As background to the results, it must be appreciated that in Ireland there is a wildlife reservoir of tuberculosis, primarily in badgers but also in deer. Badgers are widespread across Ireland and have close contact with cattle as they live in fence rows and bush next to cattle pastures. The level of infection in badgers (estimates are approximately 10 to 12 percent) poses a major problem and prevents near-term eradication of bovine tuberculosis. Other salient factors affecting program results include test errors (false-negatives, false-positives), extensive movement of cattle, and poor producer attitudes toward the disease and the program (these latter features have been common to almost all national eradication efforts). Based on discounted current values, over the next 20 years, a less intensive program aimed at control of bovine tuberculosis appeared to be a logical choice, entailing ongoing costs amounting to 2.5 percent of the annual revenue from bovine products. The fact that must be faced in Ireland (as in New Zealand) is that eradication of the disease cannot succeed given the entrenched wildlife reservoir and the close contact of that reservoir with cattle. Thus, at present, the Irish retain eradication as a long-term goal while employing a least-cost program of control for the foreseeable future. Both the Australian and the Irish analyses considered the potential contribution of vaccines and more accurate tests to the effectiveness of an eradication or control campaign. Vaccines for cattle and for wildlife (especially important in the Irish case) would help check the spread of disease and also require accommodation in test design to allow discrimination between vaccinated and field-infected animals. The development of such vaccines and more accurate tests was viewed as a long-term proposition by both the Australians and the Irish, requiring international cooperation. So while recognizing the potential for gains in the efficacy of control strategies, the studies concluded these improvements could not be relied on as part of near-term program design.

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM CONCLUSIONS FROM BIOECONOMIC MODELS Eradication of bovine tuberculosis can be achieved through test and slaughter programs as well as depopulation programs. Analyses based on bioeconomic models of disease transmission and control in the United States and Canada shows that the highest benefit/cost ratios, the greatest net benefits, the lowest accumulated industry losses, and the lowest accumulated total program costs are likely to occur if known infected herds are depopulated. Both analyses assumed that, along with depopulation, disease surveillance would permit detection of 90 percent of lesioned cattle at slaughter with successful traceback to the farm of origin. Conclusions about the superiority of depopulation were the same in both studies despite differences in the time periods under consideration and in disease prevalence rates and industry structure. When eradication is feasible, as it is in the absence of an established reservoir of disease in the wildlife population, aggressive depopulation can provide larger gains to society than does a less intensive test and slaughter program. Depopulation's superiority is attributable to the earlier achievement of the eradication goal, which results in lower program costs over time and reduced losses from disease. Based on the U.S. and Canadian studies of the 1970s, then, one might conclude that aggressive depopulation would be the best approach for the United States today. However, as has been noted, significant changes in biological and economic (as well as noneconomic) conditions since the 1970s point to the need for revision of the analytical models to support public and private decision making. Critical aspects of change that should be incorporated in any revision are discussed below. In particular, the robustness of the assumption about adequacy of financial support for aggressive depopulation needs to be explored because the 1970s analyses showed an advantage to relatively aggressive depopulation programs compared to test and slaughter programs, given adequate incentives are provided for producer cooperation. Given the persistent, low level of bovine tuberculosis infection in the U.S. cattle industry since the 1970s, the key question for future program direction is whether to continue to focus on control, aimed at eradication at some time in the future, with current levels of funding for depopulation or to mount an all-out effort to eradicate bovine tuberculosis from the beef and dairy industries as well as the farmed Cervidae/Camelidae herds. Revised bioeconomic models could be formulated to estimate costs and benefits for various program options such as the current program combined with various levels of herd depopulation, the current program with various levels of increased slaughter surveillance efficiency and varying levels of herd depopulation, or complete and immediate depopulation of all infected herds. Partial budgeting, which has often been used for analyzing various enterprises within medium to large firms, might be used as a complement to the kind of bioeconomic modeling that has been discussed here. Partial budgeting could be useful for analyzing the consequences of alternative herd health management practices and/or potential consequences of depopulation in the short run--for example, for individual dairy operations in the El Paso milkshed area. Such studies are less costly than large bioeconomic simulation models but are limited with respect to analyzing the impacts of spread between herds or among regions and generally are not designed for analyses that include a large number of factors.

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM Funding and Indemnities To a considerable degree, the success of any eradication or control strategy depends on the adequacy of compensation for producers whose animals, infected or not, must be slaughtered. The bioeconomic models reviewed here maintained the assumption of funding adequacy in supporting results showing the superiority of depopulation. However, in the current constrained fiscal climate, the availability of sufficient public resources is questionable. Recent experience with the U.S. State-Federal Cooperative Bovine Tuberculosis Eradication Program has brought to light the unwillingness of considerable numbers of producers to participate when federal funds were unavailable or could not cover the full cost of depopulation. Federal funding for the U.S. eradication program averaged $3.4 million per year for the period 1987 to 1991. Funds for depopulation of large dairy herds under quarantine in 1991 (18,000 head) were not sufficient to cover all eligible producers. Even when funds were available, indemnity rates did not meet the cost of replacement dairy animals. Additional costs not included in the indemnity schedule, even if replacements were purchased, involve interruptions in the milk output per cow depopulated (for 30 to 60 days prior to resumption of full-line production), lost wages of dairy employees, and loss of owner revenue to meet current financial obligations. If Kryder and colleagues' 1970 estimated dairy farm losses are adjusted to represent 1992 prices and economic conditions, the farm loss per infected (or depopulated) dairy cow would be a minimum of $250 per cow. Further, if such losses are adjusted for the net value of milk output disruptions per cow while replacements are being purchased ($45 per month),1 interest costs on borrowed funds to meet financial obligations, and cost of transporting and order buying ($74 per head),2the current minimum loss per depopulated dairy cow would be $369 per cow. For a 1,500 head dairy cow operation operating at 92 percent of capacity, this loss translates into a $514,620 minimum indemnity under the current program to accommodate depopulation. Since indemnity is a key issue in either a test and slaughter or a depopulation program, identification of some basic principles of a workable indemnity scheme would be useful. In Canada, these principles have been enunciated (J. Kellar and M. Koller, Agriculture and Food, Ottawa, personal communication, 1992) and are summarized below. Assistance should be provided to the owner in replacing animals removed as a result of the program. 1   The value of milk output disruption was calculated using the following assumptions: (1) a milk price of $.14/pound, (2) daily production of 55 pounds/cow, (3) 30.42 days/month, (4) adjustment for culling (0.33 percent) and production cycle (10/12 or 0.833 percent), (5) 92 percent capacity utilization rate, and (6) variable plus fixed costs at $.10/pound of production. The net value of production per month per cow = gross value minus cost. Net value = 0.14[(55 × 30.42 × 0.725 × 0.92)] − 0.10[(55 × 30.42 × 0.725 × 0.92)] = 156.23 − 111.60 = $44.63. Net value does not include interest on investment cost and insurance. 2   Transportation and order-buying costs were approximated as follows: transportation costs of $2/mile, for a 48,000 pound capacity truck hauling 40 cows (average weight 1,200 pounds) 1,000 miles = $2,000 or $50/cow. Order-buying costs were assumed to be $2/hundred weight = $960 or $24 per cow.

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM The level of compensation must not make it profitable to have the disease. The level of compensation should be sufficient to encourage reporting the disease. The value of the diseased animal, the exposed animal, and the infected herd need to be judiciously evaluated. Compensation for potential future losses or lost income should not be included. The level of compensation should not be so onerous to the government that it causes the program to falter. Obviously, consideration of these six principles leads to a balancing of costs and benefits. In the Canadian situation, the maximum payable indemnity was $1,800 Cdn per animal; although with recovery of slaughter value, the actual payout per animal removed during the peak years of depopulation (1977 and 1978) was $385.00 Cdn. In the United States, flexible indemnity rates, based on milk production records for those dairies undergoing depopulation, would appear to be a method for establishing equitable indemnity rates. Revisions to bioeconomic models, or perhaps partial budgeting, might be employed to evaluate the sensitivity of a producer's willingness to participate with the level of indemnity provided. Whether depopulation is mandatory, as in Canada, or voluntary, as in the United States, any publicly funded indemnity program is unlikely to provide full compensation to affected producers. Consequently, an effective eradication program will require financial participation by producers, either explicitly in the form of insurance premiums or implicitly through absorption of the noncompensated costs of depopulation. Industry-wide insurance schemes pool risks, while cost absorption is essentially self-insurance; the choice between them depends on a variety of factors, including industry size and structure as well as producers' attitudes about risk bearing. If public funds cannot be expected to provide full indemnification to producers for slaughter, adequate participation in any kind of eradication strategy becomes problematic. The question of who should pay (if taxpayers do not foot the entire bill) depends largely on who is affected by the presence of the disease and who benefits from its eradication. In the case of bovine tuberculosis, owners of herds (beef, dairy, or Cervidae) and those who work with the live animals or after slaughter, have the most direct stake in disease management, either for economic or for health reasons. Less directly affected are those in the general public who are at risk of consuming products from infected animals or of coming into contact with those who, in turn, may have handled infected livestock. Bioeconomic models that allow identification of the size and distribution of costs and benefits to the various groups can assist in making private and public policy decisions about the assignment of financial responsibility. Public Health The bioeconomic models reviewed here focus largely on the size of economic costs and benefits of eradication to livestock producers. However, there are public health issues that warrant consideration as well. As mentioned, there are documented risks to those working in animal husbandry, livestock transportation, slaughter, rendering, veterinary care, postmortem diagnosis, and research (Diehl, 1971; Meissner et al., 1974; Robinson et al., 1988; Georghiou et al., 1989; Fanning and Edwards, 1991; Dalovisio et al., 1992). In addition, a recent survey showed that 35 percent of the dairy families sampled said they drank raw milk (Rohrbach et al., 1992). Another health concern is triggered by the levels of tuberculin positivity in rural migrant workers (Centers for Disease

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM Control, 1989), which may not be necessarily, attributable to M. bovis. Testing laboratories are currently using DNA probe technology, which does not differentiate between M. tuberculosis and M. bovis; hence, they are reporting results as “M. tuberculosis complex.” Furthermore, the institution of a treatment regimen and subsequent prognosis in humans is not dependent on precise differentiation beyond M. tuberculosis complex. Thus it is possible that the actual incidence of human M. bovis infections is currently underestimated in the United States. This is cause for concern particularly because a case of M. bovis infection in a human could theoretically serve as an indicator of previously unrecognized infection in animals. Another, less traditional route of human exposure to bovine tuberculosis is attributable to a significant increase in the number of privately owned indigenous and exotic ungulates (Lanka et al., 1990). The privately owned collections include large hunting preserves that contain free-ranging herds, drive-through game parks, conventional-type ranches and farms raising elk and deer for venison or llamas as pets and pack animals, and traveling or roadside petting zoos. In some instances, these enterprises have acquired tuberculosis-infected or susceptible animals through public auctions, private sales, or trading. Outbreaks of M. bovis in zoo and game park collections are well documented (Towar et al., 1965; Pattyn et al., 1967; Himes et al., 1976; Jones et al., 1976; Mann et al., 1981; Himes et al., 1982; Frolka, 1989; Bush et al., 1986; Bush et al., 1990; Cranfield et al., 1990; Thoen, 1990). A variety of situations exist in which infected animals may come in contact with the general public, particularly children, the greatest risks perhaps being those operations where humans can feed or touch animals. Currently, federal regulations do not address this potential tuberculosis concern. More broadly, gains to human health as a result of efforts to eradicate bovine tuberculosis have been estimated by Roberts (1986), who examined the human health protection benefits of the U.S. program by evaluating what might have occurred if no federal program had been instituted in 1917. In this analysis the four most likely pathways of human exposure to bovine tuberculosis listed were (1) aerosol contamination of the barn and air system, (2) cuts and abrasions on the hand of slaughterhouse or processing plant workers, (3) aerosol contamination from the carcass, and (4) consumption of meat and meat products. Roberts estimated that in the absence of a U.S. bovine tuberculosis program, 120,030 infected beef carcasses would have resulted annually, in excess of the average annual 95 carcasses condemned for the 5-year period 1975 to 1980. Because of tuberculous cattle entering the human food chain, it was estimated that between 48,000 and 120,030 humans might be infected per year, of which 2,400 to 12,003 would actually develop clinical disease symptoms requiring treatment. Further, 144 to 720 of the individuals developing clinical disease symptoms might die. (These biologic estimates were needed as a basis for the subsequent economic estimates.) Roberts consulted with others and estimated a schedule of medical treatment costs and lost wages as a result of illness or death that would have occurred to humans from the disease. The total estimated economic benefits to humans ranged from $33 million to $309 million annually during the 5-year period 1976 to 1980. Medical cost savings from the program were estimated to range from $14 million to $72 million. Wage benefits in the absence of illness or death from bovine tuberculosis ranged from $18 million to $237 million, annually. A contemporary public health concern stems from the presence of immunosuppressive conditions (AIDS, chemotherapy, antirejection drugs, and steroid therapy) that increase an individual's susceptibility to tuberculosis. These conditions exist in the general population as well as in the previously mentioned occupational risk groups and result in an increasingly susceptible

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM population (Dankner et al., 1993). In summary, public health risks are related to changes in the makeup of the human population and its susceptibility as well as developments in the livestock industry, fluctuations in the nature and rate of animal importations, the emergence and growth of various types of enterprises involving species susceptible to tuberculosis, and the increased mobility of both animals and humans. Industry Structure Changes in the structure of the livestock industry over the past 25 years have important implications for the design of an effective eradication strategy. These changes, listed below, may be reflected in either or both the epidemiology of bovine tuberculosis and the economic costs of livestock production and disease control. The average size of dairy herds continues to increase. The number of potentially infected steers imported from Mexico has increased. The number of captive cervids and nontraditional ungulates, some of which originated in Europe and New Zealand, has increased dramatically. A brief discussion follows of the trend toward larger herds and of other factors that may lead to the increased possibility of disease transmission. Implications of increases in Mexican cattle imports and in farmed exotics have been discussed elsewhere in this report (and see U.S. Department of Agriculture, Animal Plant Health Inspection Service, Veterinary Service, 1992). The trend in livestock production throughout the United States is toward fewer herds of increasing size. The large milksheds of California and the El Paso, Texas, area stand out as dramatic examples. Technological developments in animal science related to production management such as feed analysis, computerized ration formulation, microchip-controlled feed supply, and climate-controlled environments have resulted in increased animal densities in larger herds. These developments have led to more commingling among animals within herds. The development of new technologies in animal genetics and reproduction, market imperatives for higher quality products and enhanced productivity, and readily available methods of safe, cheap, reliable animal transportation have resulted in movement of animals into and out of herds on an almost daily basis. These developments also contribute to increased within-industry specialization, best exemplified in the dairy cattle industry where the milk producer may contract out the specialized task of rearing replacement heifers. Such specialization results in a constant flow of animals between the two herds. If the contracted producer is also raising heifers for other milk producers, then all become linked to one another in terms of disease potential. Another trend in husbandry that contributes to increased contact among animals is enterprise diversification. Beef ranchers may raise bison and elk along with their cattle for recreation or profit. Dairy farmers may raise a few deer for the same reasons. Pig farmers may raise some wild boars for a specialized market. Horse owners may take on some llamas as a novelty or companion or pack animal. North American zoos, most of which have been established within the past century, are reaching their capacity because of space constraints as existing populations are maintained longer due to improvements in nutrition, reproduction, and husbandry. At the same time, zoos have exhausted the use of some of their genetic lines and need to dispose of inbred animals and bring in new lines.

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM The end result is a surplus of animals that is either traded between institutions or moved out into the secondary dealer market and a myriad of private collections. A consequence of these industry dynamics is that intraherd and interherd contact and therefore disease spread opportunities exist at much higher levels than before. The term “national herd” is taking on an increasingly literal meaning, not only as it relates to populations of certain species, but also as it relates to all species of animals raised and cared for by humans. Environmental Protection Over the past 2 decades, society's increasing concern about protection of the environment has complicated the problem of disposal of animals infected with bovine tuberculosis. As the options for disposal are reduced, costs to the producer or processor are increased. The success of either a depopulation or test and slaughter strategy will be affected by the costs of disposal, where any increase could translate into a component of any indemnity payment. Indirect costs of disposal may be associated with restrictions on the operation of slaughterhouses, rendering plants, and meat packers. In an ideal world, infected and exposed animals would be safely delivered to a nearby slaughterhouse or diagnostic laboratory and subjected to a detailed inspection. In the slaughterhouse, carcasses meeting the required inspection standards and disposition criteria would be released for human consumption. Carcasses and tissues not fit for human consumption would be safely removed to a nearby rendering plant for proper processing and decontamination and subsequent safe recycling into protein supplements in animal feeds or organic fertilizers. In the diagnostic laboratory, carcasses and tissues would be safely removed to a nearby incinerator or rendering plant for proper disposal. All infectious material would be rendered innocuous; environmental contamination would be minimized and recycling maximized. The reality is considerably different. Given the availability of nondiseased and nonexposed animals, meat packing plants are increasingly reluctant to process infected and exposed animals. Rendering plants, which are competing against suppliers to the animal feed manufacturing industry, have recently had to deal with product safety questions relative to bovine spongiform encephalopathy and salmonella infections. Renderers share the concerns and reservations of the meat-packing industry about processing tuberculosis-infected and -exposed animals. As access to packing and rendering plants for disposal of conventional livestock becomes increasingly difficult, other means of disposal must be pursued. On-farm slaughter and disposal of infected and exposed animals may be necessary where water tables permit burial. Where water tables preclude burial, burning could be considered. However, the potential aerial pollution associated with this incineration will considerably restrict the availability of this form of disposal. Where nearby slaughter, rendering, burial, or incineration are not available options, live animals or their carcasses may have to be transported considerable distances to facilitate disposal. Their safe transportation will require compliance with various environmental legislation and other guidelines surrounding the handling of hazardous materials and biomedical waste. International Trade Beyond domestic public health and environmental concerns, increases in the volume and integration of international trade (as under the North America Free Trade Agreement or the potential

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM new terms of the General Agreement on Tariffs and Trade) may require accommodation on the part of a disease control strategy. Movement of animals and animal products internationally ultimately depends on mutual agreements regarding animal health and food safety requirements between the importing and exporting countries. For example, to assist in international trade, the Paris-based Office International des Epizooties (OIE), with 116 member countries including the United States (Food and Agriculture Organization, 1991), has prepared an International Zoo Sanitary Code. This code is updated regularly and specifies uniform definitions and standardized notifications of health status, recommended rules of trade for lists of diseases, recommended norms for diagnostic techniques and biologics, and model international certificates approved by OIE. Another function of OIE is to examine various animal diseases and determine their international significance. Bovine tuberculosis is among the “list B” diseases--communicable diseases considered to be of socioeconomic and/or public health importance within the country and significant in the international trade of livestock and livestock products (Food and Agriculture Organization, 1991). Countries consult OIE when they want to assess their domestic policies in the global scene or negotiate conditions for trade in animals and animal products. The establishment of free-trade zones--such as those created by the North American Free-Trade Agreement (NAFTA)--are changing the way countries conduct commerce in the international marketplace. Through these agreements, trade barriers are being removed and any remaining justifiable restrictions, such as health status, are being scrutinized for comparison to international norms as represented by the OIE code. Whereas in the past, countries may have simply refused to import certain animals or products on the basis of a disease risk, they are now challenged to manage the risk and find a way to let the trade occur without jeopardizing the health of the domestic population. In such an environment the United States will have to negotiate agreements that deal with the risk of importing or exporting tuberculosis-infected or -exposed animals. This is obviously pertinent to the current situation in which a high percentage of beef carcasses with tuberculous granulomas detected at slaughter in the United States are from steers imported from Mexico. As the importing country, the United States is faced with choosing between two strategies: it can either manage the risk through certification demands at source and post-entry restrictions, which will be met with resistance because they impede trade; or it can minimize the initial risk of introduction by taking steps to assist in the control and eradication of the disease at source, which requires a political will and expenditure of resources. In any event, the design of a domestic disease control strategy must take trans-border considerations into account. Again, bioeconomic models built to reflect the position of the United States in world livestock trade can assist in identification of program alternatives. Recognizing the changing circumstances of livestock production, revisions of the 1970s' bioeconomic models for the United States have been attempted. For example, Dietrich and colleagues (1978), working with the National Brucellosis Technical Commission (NBTC), designed a bioeconomic simulation model that used both an epidemiologic model and a sector equilibrium econometric model. The NBTC simulation model expanded on the Beal and Kryder model by (1) further delineating the United States into eight regions; (2) allowing for affected herds to move into a “quarantine status,” infected and detected, or an undetected infected status; (3) allowing the disease to spread between beef and dairy herds; and (4) allowing for quarantine release while still infected, as occurs on a limited basis. More recently, Dietrich and colleagues (1985) updated and redesigned the NBTC model. In this model (BRUSIM), the contiguous 48 states were delineated into 16 regions based on brucellosis infection, herd-size distribution, method of operation, trading patterns, and effectiveness of brucellosis control. The epidemiologic model specified major bovine brucellosis

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM program components as market cattle testing (MCT), first point of concentration testing, adjacent herd testing, secondary epidemiologic tracing, postquarantine testing, and private or owner testing. In addition to these, the USDA has conducted an in-depth epidemiologic review of risk factors for bovine tuberculosis, which should be studied for its relevance to current issues and as a major source of background data on tuberculosis in the United States (U.S. Department of Agriculture, Animal Plant Health Inspection Service, Veterinary Services, 1992). Animal Welfare Public concern for animal welfare is another factor--critical but difficult to capture in bioeconomic models--that may influence the design and execution of a disease control program. Some animal protection activists accept the need for use of certain animals for food and fiber and for some recreational activities, insisting only that the animals be treated as humanely as possible. Others involved with animal rights believe that exploitation of animals, even for food, fiber, and recreation, should be minimized, if not eliminated. Various animal protection groups in the United States are seeking modifications to, and in some instances the outright curtailment of, many practices long considered acceptable and integral to animal agriculture--both on- and off-farm practices (Becker, 1992). Some facets of the eradication program that may incur animal welfare considerations include hot-iron face branding, chemical and physical restraint, transportation conditions and methods, slaughter requirements and procedures, the destruction of endangered or unusual species in zoos and private collections, and the timing of all of these activities relative to breeding season, pregnancy, parturition, and the nursing period. Current and future bovine tuberculosis eradication programs should be able to withstand the scrutiny of a responsible evaluation for humane animal handling and treatment issues. Wildlife Although somewhat outside the scope of traditional bioeconomic models of animal disease, the disposition of free-roaming wildlife raises significant ecological and environmental concerns for any eradication strategy. Two roles for free-roaming wildlife can be identified. In the first role, the primary significance of the species is as a vector. The wildlife species in question, by becoming infected and excreting the organism, serves to readily transmit the infection to other species of animals and other geographical populations. In the second role, the species' primary significance is as a reservoir in which the disease can perpetuate itself. As examples, wildlife species have emerged as significant elements of the bovine tuberculosis eradication programs in the United Kingdom and New Zealand. Both countries have experienced widespread reinfection problems associated with persistent infections in wildlife vectors. The European badger (Meles meles) (Cheeseman et al., 1989; McInerney, 1986) has become a reservoir for M. bovis in the United Kingdom, serving as a continuous source of reinfection for cattle herds and potentially other species, both free-roaming and farmed, and possibly even humans. In New Zealand, the infected brush-tail possum (Trichosurus vulpecula) populations have become the single largest obstacle to the eradication of bovine tuberculosis in that country (Hellstrom, 1989; Collins et al., 1986; Davidson, 1976; Livingstone, 1992). The possum, in turn, has contributed to the emergence of other wildlife vectors in New Zealand including feral deer (Hellstrom, 1989).

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM North America's wildlife fauna consists of many species, including close relatives of the European badger and brush-tail possum, which could serve as vectors should they become infected. There is currently no evidence to support the suggestion that active wildlife vectors exist here; however, isolated instances of infection in “dead-end” hosts have been reported (Levine, 1934; Beli, 1962; Friend et al., 1963). Evaluation of the potential impact of wildlife vectors should consider that many of the efforts put forward to address badger and possum problems have met with objections from animal protection organizations, as well as environmental protection and public safety advocates. Under certain conditions, infection introduced into a wildlife population has been established, creating an active reservoir, as in the axis deer of Hawaii (Sawa et al., 1974) and as currently exists in the bison of Wood Buffalo National Park in Canada (Connelly et al., 1990). The disease threat to free-roaming wildlife posed by farmed animals has assumed an added dimension in recent years as free-roaming herds and their management have expanded and evolved and as the farming of nontraditional species has increased (Thorne et al., 1992). Agencies and organizations associated with the protection and promotion of wildlife as well as groups representing hunters have expressed numerous concerns about the impact that game farming can have on the health and viability of free-roaming herds (Lanka et al., 1990). Although these concerns may encompass such issues as habitat encroachment and gene pool preservation, a number of diseases and parasite infestations--including tuberculosis--have been identified as threats to North American wildlife either through the escape of infected captive animals or over-the-fence contact. Education Finally, an important although largely intangible aspect of an effective disease control program has to do with the level of understanding about the disease. Over the past 75 years the success of the tuberculosis eradication program has reduced the prevalence of the disease and placed most people at least two generations away from knowledge of the disease and experience with its impact in both humans and animals. Today it is unlikely that any beef or dairy producers have seen clinical cases of the disease in cattle or know people who have contracted the disease. The same applies to the associated industries; most veterinarians have not had direct experience with the disease, and slaughterhouse workers and inspectors are increasingly unfamiliar with actual cases. These sociological and cultural factors support the contention that knowledge about bovine tuberculosis among those who need to know is deficient. Only one APHIS public service information pamphlet on bovine tuberculosis (U.S. Department of Agriculture, 1982) is available, and it is in need of revision. The Brucellosis Technical Commission appointed in 1976 to review eradication of brucellosis in the United States was faced with a similar problem regarding knowledge and attitudes of producers. A random sample of Texas beef and dairy producers was interviewed and it was clear that their knowledge base was inadequate (Yetley, 1978). Sources of information, their perceived reliability, and related factors such as income and educational levels and language proficiency of the audience, need to be clearly identified. Although human tuberculosis is currently receiving increased publicity, it is doubtful that many producers are aware of distinctions between M. tuberculosis and M. bovis infections. Ultimately, a new initiative pursuing selective public and producer education will be needed to complement the current program. In addition, extensive continuing education initiatives are indicated for professionals such as regulatory personnel on whom the success of eradication depends. The U.S. Animal Health

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LIVESTOCK DISEASE ERADICATION: EVALUATION OF THE COOPERATIVE STATE–FEDERAL BOVINE TUBERCULOSIS ERADICATION PROGRAM Association could play a large role in the future, as it has in the past, in promoting greater awareness of the threat of bovine tuberculosis as well as the options for its management.

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