Management actions are “tools” that can be used to reduce the risk of brucellosis transmission and to mitigate the effects of infection in the Greater Yellowstone Area (GYA). This chapter provides a brief overview of various approaches that have been used and are available for stakeholders in managing the risk of Brucella abortus transmission. These management tools can and will need to be used in combination as part of an active adaptive management approach.
One way to affect change would be to provide incentives for action. In the context of managing brucellosis, it could take the form of incentivizing cattle producers either to undertake risk mitigating efforts and decisions or to adjust the time or location for allowing cattle to graze on public or private lands. These two options are discussed in more detail in Chapter 8. Two other tools include (1) adjusting governmental fixed rate and placement date approaches to public grazing and (2) an insurance approach to help protect producers against damages. These are also discussed briefly in Chapter 8 and are expanded on below.
2.1 Adjusting Governmental Fixed Rate and Placement Date Approaches
Public efforts could be better aligned to encourage certain outcomes. One option would be to compensate cattle producers whose herds become infected in direct proportion to their risk mitigation efforts. A producer could be compensated by the government in “full” if they provide evidence that they have implemented a set of “best management practices” for reducing brucellosis risk. Conversely, if a producer is able to provide only partial evidence of “good faith behavior,” then only some proportion of compensation would be available (e.g., if a producer in the GYA elected to not fence off their haystacks, they may then be eligible for only a proportion of the compensation level deemed available for brucellosis based testing and damages). Indemnity claims have been used for other diseases—the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (USDA-APHIS) has regulations to specify conditions for payment of indemnity claims for low pathogenic avian influenza (LPAI)—and a similar approach could also be considered as a possible tool for brucellosis. However, care will need to be taken as the core role of indemnity compensation is to encourage timely and complete reporting by reducing the economic incentive to censor information on disease events.
The establishment of public grazing fees and cattle placement dates also warrants further consideration. Parcels vary in risk depending on their location, the presence or absence of elk, and the time of year. Currently, the fixed rate (updated annually) and entry date for federal grazing makes no consideration of brucellosis risks (Rimbey and Toreel, 2011). For example, one parcel next to an elk feedground with no fences will be riskier than another that is further away with fences; however, the federal grazing rate for both parcels is the same even though the brucellosis exposure risk is different across the two parcels. This is a classic example of an economically inefficient, fixed rate pricing program that fails to reflect the different impacts public grazing has on broader brucellosis risks in the area. The committee acknowledges the political challenges that may arise with a differential grazing rate system, yet the fixed rate approach fails
to account for risks and external costs. Even if a differential pricing system is infeasible upon further assessment, it will be essential to restrict or adjust the placement and removal dates to reflect parcel-specific brucellosis risk. If cattle were allowed to graze on “high risk” public lands with earlier placement remaining available on “lower risk” parcels, producer actions would more directly internalize brucellosis risks currently not captured by the fixed pricing and entry date system. To date, risk categorization of public lands has yet to be clearly defined and a risk assessment is clearly needed. (See Box 7-1 for an example of land managers using a risk assessment to reduce contact between Sierra Nevada bighorn sheep and domestic sheep.)
Federal land management agencies could stipulate risk reduction “best management practices” in exchange for the privilege of using public land grazing allotments. Although an individual producer may not view these practices as necessary or cost-effective, reducing risk of transmission between elk and cattle in the GYA is in the public interest. Therefore, this would be another area where policies could be used to incentivize best practices. By considering additional private incentives, it may be possible to encourage private action to better align with the broader public interest.
Insurance for livestock diseases provides monetary relief to producers, as some losses—business interruption, welfare (feeding and care) costs for animals, and loss of markets—are not currently eligible for U.S. government indemnification (Grannis et al., 2004). Insurance premiums subsidies could be tied to evidence of implementing best management practices, a concept reflected in USDA’s recent adjustments to highly pathogenic avian influenza indemnity payments to poultry producers (USDA-APHIS, 2016). For example, producers in the GYA could be eligible for an insurance premium discount if they wait until late June to place cattle on public lands when the risk from elk is lower. Although the concept of an insurance program is sound, there are a host of challenges to making it viable, including knowledge gaps in accurately assessing risk, whether there is sufficient interest by producers, and the government’s capacity to administer and subsidize premiums (Goodwin and Smith, 2013; Reeling and Horan, 2014). Also, livestock producers tend to implement even less costly risk management strategies than expected (Goodwin and Schroeder, 1994; Pennings and Garcia, 2001; Wolf and Widmar, 2014). Information is currently lacking to assess the viability of either a new insurance program or an alternative compensation program. Insurance programs are not prevalent in livestock disease prevention programs, but indemnity programs are (Hoag et al., 2006; USDA-APHIS, 2016).
Efforts to feed wildlife can range from individual efforts (such as backyard birdfeeders and baiting on private property to aid in hunting) to state-sponsored programs that feed large ungulates across the western United States (Smith, 2001; Sorensen et al., 2014). Supplemental feedgrounds for elk and bison in Wyoming are some of the largest-and-longest operating efforts. The originalintent of feedgrounds was both to buffer against starvation in severe winters (as traditional winter feed areas had been developed into cattle ranches) as well as to limit the losses of hay on private properties due to elk (Smith, 2001). A third reason for the feedgrounds is to reduce the likelihood of disease transmission by maintaining a separation between elk and cattle. However, counter to that purpose, supplementalfeeding increases elk and bison aggregations and facilitates brucellosis transmission within these populations (NRC, 1998; Cross et al., 2007). Although the intent is to minimize the chance of spillover to cattle, feedgrounds may exacerbate the problem by increasing seroprevalence in elk, not only in the southern GYA but also in other portions of the GYA. While there are aesthetic or philosophical arguments for or against the feedgrounds, this report confines the examination of feedgrounds to their role in either facilitating or limiting the spread of brucellosis both within and between host species as well as their potential role in the future management of brucellosis.
Supplemental feedgrounds have exacerbated brucellosis in elk and bison, facilitated the spread of brucellosis across the GYA, and increased the risk for the introduction of other diseases (such as chronic wasting disease [CWD] or bovine tuberculosis). Brucellosis isolates taken from elk and livestock outside of Yellowstone National Park (YNP) had genetic ancestors from the feedgrounds rather than bison from Yellowstone (Kamath et al., 2016). Although the current genetic data suggest that the supplemental feedgrounds likely sparked several outbreaks in distant elk populations, the rare dispersal events between populations are unlikely to maintain the high seroprevalence of the disease currently observed in many free-ranging elk populations (Cross et al., 2010a). Despite the potential drawbacks of feedgrounds, they do provide some management opportunities. First, the number of cattle outbreaks in counties with supplemental feedgrounds appears to be no higher than in areas without supplemental feedgrounds (Brennan, 2015). This suggests that feedgrounds may contribute to maintaining spatial separation between cattle and elk even though they exacerbate disease in the elk population. Second, feedgrounds make elk more accessible either for vaccination or for capture in corral traps or darting from the ground. Feedgrounds could thus be used as a test case for management action. One example is for sterilizing elk that are likely to abort (presumably young age seropositive females that may be in their first or second pregnancy), which would slow the transmission of brucellosis and subsequently reduce elk seroprevalence over time.
Ecologically oriented management actions may also help mitigate feedground associated problems. Feeding elk later in the spring tends to be associated with higher seroprevalence: an additional 30 days of feeding was associated with a two- to three-fold increase in seroprevalence, as abortions and calving are more likely to occur in the spring (Cross et al., 2007). However, the winter population size at the feedgrounds was not a significant predictor of seroprevalence, which may be due to an interaction between density and timing of transmission; if so, transmission occurring later in the spring would be less dependent on feedground elk density in the winter (Maichak et al., 2009). These results have prompted the Brucellosis-Habitat-Feedground Program at the Wyoming Game & Fish Department (WGFD) to attempt to implement a test program of ending the feeding season earlier on some feedgrounds to test the causal link between the length of the feeding season and the resulting elk seroprevalence. Even if this management action is successful, it is potentially not without trade-offs. Even if elk seroprevalence declines, it is unclear whether cattle risk may be reduced because additional elk-cattle contact outside of the feeding season may occur. Thus, there may be short-term risks of local elk-cattle spillover around the feedgrounds prior to realizing the potential long-term benefits of reduced elk seroprevalence. Feeding hay in a more widely distributed
style is another approach that has been shown to markedly reduce elk-fetus contacts (Creech et al., 2012). This treatment is being implemented on several feedgrounds, but it remains to be seen whether it results in reduced elk seroprevalence.
At the time of the 1998 NRC report, brucellosis was limited to bison and the Wyoming supplemental feedgrounds, and therefore a recommended phase-out of the feedgrounds appeared to be a means toward wide-scale disease reduction in elk. This is no longer the case as elk populations distant from both bison and elk appear to maintain the infection, and management actions on feedgrounds are unlikely to have ramifications for distant elk populations (e.g., Montana elk, as well as the Cody and Clarks Fork regions of Wyoming) given that the disease is already present in those populations. However, reductions on the feedgrounds may be beneficial for reducing potential spread to other regions, such as northeastern Utah where another supplemental feedground operates. Several nongovernmental organizations have argued for the complete phasing out of supplemental feedgrounds for a number of reasons, including CWD. If this were to be considered, feeding could first be curtailed at the most cattle-sensitive feedgrounds with the expectation that elk would move to less sensitive feedgrounds prior to a complete phaseout. As noted above, feedground closures are likely to have short-term costs due to the potential for increased elk-cattle contact while the seroprevalence in elk remains high, yet the long-term benefits could include reduced elk seroprevalence. Feedgrounds appear to mitigate some of the cattle risk locally while enhancing disease risks across the ecosystem (for B. abortus, CWD, and other diseases).
The concentration of elk and bison on supplemental feedgrounds has been associated with a number of diseases in addition to brucellosis, which led to a recent court case against the U.S. Fish & Wildlife Service (USFWS) for allegedly failing in its mandate to promote “healthy” wildlife (Defenders of Wildlife et al. v. Salazar, U.S. App. D.C., No.10-1544). More than half of the adult male elk that die on the National Elk Refuge (NER) annually were infected with scabies, while only 5% of surviving adult males showed clinical signs (Smith and Anderson, 1998). In addition, the management units with feedgrounds had variable calf ratios, indicating no clear support for generally higher ratios in areas with supplemental feedgrounds (Foley et al., 2015). Elk attending the feedgrounds had higher fecal glucocorticoids (FGCs)—hormones associated with stress—than elk that were on native winter ranges (Forristal et al., 2012). These FGCs also appeared to be correlated with the local density of elk at each site. Although glucocorticoids are known to be immunosuppressive, it remains undetermined how these levels of FGCs relate to other factors such as disease susceptibility, survival, or recruitment. Meanwhile, results from the analysis of Brucella isolates suggest that the feedgrounds are the likely source for elk infections in other areas of the GYA, with the exception of the Paradise Valley in Montana (Kamath et al., 2016).
Finally, CWD is often a major point of discussion with supplemental feeding programs (Smith, 2013). CWD is a transmissible spongiform encephalopathy that infects elk, mule deer (Odocoileus hemionus), white-tailed deer (O. virginianus), and moose (Alces alces) (Williams and Young, 1980; Williams, 2005). It can be transmitted by direct contact or indirectly via the deposition of prions in feces, saliva, and urine in the environment. Several studies suggest that these prions persist in the environment for years (Miller et al., 2004; Mathiason et al., 2006). While the prevalence of CWD in free-ranging elk tends to be much lower than in either white-tailed or mule deer, the supplemental feedgrounds may represent a worst-case scenario that is more similar to the high potential for rapid spread in captive elk herds where prevalence can be quite high. CWD may have dramatic effects on the elk populations visiting the supplemental feedgrounds, but those effects are likely to occur over long timescales (e.g., 20-40 years) (Wasserberg et al., 2009; Almberg et al., 2011).
Hunting is often cited as the foundation for the system of wildlife management in North America (Heffelfinger, 2013). Unhunted wild ungulate populations—particularly in the absence of predators or other natural mortality factors—often overpopulate their habitat to a point that negatively impacts forage production, causes detrimental changes in the ecosystem, reduces ungulate carrying capacity, and causes conflicts with humans (e.g., agriculturallosses and vehicular accidents) (Conover, 2001). When ecosystem--
level effects are seen, reproduction may decrease and mortality increase due to competition for remaining resources (McCullough, 1979). Hunting is sustainable as long as off-take does not exceed reproductive and survival capacity of the next generations. Overhunting was the cause of severe depletion (elk deer, antelope, bighorn sheep) and near extinction (bison) of many game species in North America in the late 19th century (Heffelfinger, 2013).
The distribution and abundance of wildlife can be changed by manipulating hunting pressure and its spatial distribution (Conner et al., 2007). Public hunting can be used to alter numbers of free-ranging wild ungulates (deer, elk, antelope, and bison), population densities, and sex ratios (Heffelfinger, 2013). However, public hunting is not a precise tool and has significant limitations when targeting specific populations, particularly if target animals are not easily identifiable in the field or are not on accessible lands. Despite initial enthusiastic cooperation by hunters, efforts to use hunting to reduce or eliminate chronic wasting disease in white-tailed deer in Wisconsin failed due to several factors, including waning enthusiasm for the program and too little progress in reducing infection rates (Jennelle et al., 2014). This demonstrates how hunting can be a limited tool for disease reduction purposes.
4.1 Hunting and Disease Control in the GYA
The management of wildlife is primarily the legal responsibility of state and federal governments, and hunting of wildlife generally falls under the jurisdiction of state wildlife management agencies (Krausman, 2013). Each state sets seasons and bag limits on a herd-by-herd basis through Herd Management Plans (HMPs) (MDFWP, 2015; WGFD, 2015). The results of the previous year’s harvest, field observations, and marking studies (otherwise known as the marked capture/recapture index) of selected herds are used to set HMP goals (MDFWP, 2015). There are instances in which hunting is allowed on federal parks and refuges. A limited elk hunt is allowed at the eastern edge of Grand Teton National Park (Consolo-Murphy, 2015). Elk and bison are taken by hunters on the NER, which is managed by the USFWS. YNP does not allow hunting. Hunting access is allowed on most Bureau of Land Management (BLM) and U.S. Forest Service (USFS) lands and a large portion of the GYA, while hunting on private lands is managed by their owners.
Hunting could be used to reduce disease transmission risk by reducing elk populations in areas where prevalence of brucellosis is relatively high, where incidence of infection appears to be increasing, and where there is greater risk of contact with cattle. Increasing the proportion of female elk harvested yearly can help reduce elk herd numbers and the number of potentially infectious females. Late-season antlerless hunts could also reduce the number of female elk numbers and proportion of infected females, decrease the herd growth rate, and possibly break up dense aggregations of elk. This has been done to some extent in Wyoming. However, it is difficult for hunters to identify and specifically target brucellosis-infected elk or bison. There are also temporal (e.g., seasons), physical (e.g., weather, terrain), and legal (e.g., private lands) barriers that may limit the effectiveness of hunting as a disease-control tool. A significant barrier to wider applications of hunting for brucellosis management is the complex land ownership pattern that results in elk refugia forming on unhunted private lands during hunting seasons. Informational outreach, incentives, and a case for hunting as a disease-control tool may need to be made.
When disease transmission is correlated with host density as it is with brucellosis, disease agents may be unable to persist if densities are lowered beyond a critical threshold. In wildlife systems, however, those thresholds are difficult to define and there is countervailing evidence that merely decreasing elk population size alone may not decrease seroprevalence enough to warrant management changes (Lloyd-Smith et al., 2005; Cross et al., 2010b; Proffitt et al., 2015).
A secondary benefit of hunting in areas where elk populations exceed herd management goals could be to ensure against catastrophic winter kill in years of extreme weather. Hunting is a management tool to be used with caution because increasing hunter tags at a broad regional scale may shift elk distributions to areas of limited hunter access and thus intensify conflict on private lands or drive elk to unhunted (refuge) private lands.
Blood samples can help track brucellosis exposure, and hunters are often willing to collect blood samples from harvested animals to assist wildlife management agencies. The quality of samples and the
accuracy of location information have unfortunately been less than optimal for hunter-collected blood samples provided to WGFD. The Montana Department of Fish, Wildlife & Parks has ceased using hunter-collected blood samples in favor of samples collected from elk captured for marking and herd studies. But, as seen with recent cases of brucellosis on the Montana-Wyoming border near the Bighorn Mountains, targeted hunter sampling (as opposed to general sampling) could help in monitoring brucellosis at the DSA border and just beyond.
4.2 Economic Considerations
Hunting and harvesting elk and bison (and other wildlife) in the Greater Yellowstone Ecosystem is a source of income for individuals and small businesses (USFWS, 2012). Many in Idaho, Montana, and Wyoming would even consider access to public lands for hunting a right, and the view the harvesting of an elk (or a deer, an antelope, and, to a lesser extent, bison) as a yearly necessity for food security. Native Americans have the legal right to harvest wildlife under various treaties (Organ, 2013). Although no hunting occurs within the boundaries of YNP, bison culls and hunts do occur when bison move out of YNP and into the Gardiner Valley and along the western YNP boundary. Bison that are not part of YNP herds are hunted on public and private lands in Montana and Wyoming.
State game and fish departments derive a significant portion of income from hunting, with elk hunting revenue being one of the largest single sources of revenue for the game and fish departments in Idaho, Montana, and Wyoming (Heffelfinger, 2013). In 2009, there were 62,620 elk-hunting licenses sold in Wyoming, which resulted in $8,649,005 in license sales alone, approximately 50% of revenue for WGFD. The cost to WGFD was $638 per animal, with net income to WGFD of $1,765 per animal. During the hunting season, hunters use the full array of local business services and amenities (such as gas, food, lodging, sporting goods and equipment). In 2006, 762,000 people spent a total of $1.1 billion to take part in wildlife associated recreation in Wyoming (USFWS, 2012). Of these, 84% reported participating in wildlife watching, 13% participated in hunting, and 3% indicated other (undisclosed). Of the money spent, 44% were trip-related expenses (e.g., fuel, hotels). The committee received public comments from ranchers in the GYA who are part-time hunting guides and derive significant income from these activities, and ranchers also noted that they charge access fees to allow hunters on their property. It is interesting to note that for Wyoming in 2010, the aggregate gross value of cattle ranching for the entire state ($1.24 billion) is only slightly higher than the amount spent on wildlife-related recreation ($1.1 billion) (USDA-NASS, 2010). Nationwide, the money generated by regulated sport hunting and the incentives it provides for wildland conservation is generally credited with being the primary reason for the recovery of elk, antelope, and deer populations and—to a lesser degree—bison in the last century (Heffelfinger, 2013). Therefore, a major reduction in elk numbers for brucellosis control could potentially be in direct conflict with the interests of state game and fish departments.
Intense hunting activities involving brucellosis-infected bison or elk could elevate the public health risk if carcasses and offal are not removed. Approximately 50% of the bison that leave YNP enter the Gardiner, Montana, area in late winter and are subject to intensive hunting pressure in a relatively small geographic area. Testimony and photos were provided to the committee during a public comment session noting instances in which bison carcasses were left in close proximity to populated and public areas. The failure to remove carcasses and “gut piles”—including the lymphoid organs and reproductive tracts of animals—constitutes a potential health risk to the public, domestic livestock, and companion animals. Timely removal and proper disposal of post-harvest animal remains could also help build public support for the Interagency Bison Management Plan (IBMP) hunts.
In the past few decades, some prime hunting and ranching lands (particularly in Montana, north and northwest of YNP) have been purchased by individuals who do not support hunting (Haggerty and Travis, 2006). These are often large tracts of land that serve as refuges for elk and complicate efforts to regulate elk numbers by hunter harvest (Haggerty and Travis, 2006; MDFWP, 2015). Elk habituating to use of private protected lands significantly compromises the ability of state wildlife agencies to use hunting as a tool to manage elk numbers.
5.1 Brucellosis Management Action Plans
Brucellosis Management Action Plans (BMAPs) have been developed to consider a wide range of efforts aimed at addressing brucellosis in a more holistic fashion. Many of these BMAPs have been developed to address brucellosis by species (either elk or bison). For example, the Jackson elk herd BMAP states its objectives are to “maintain livestock producer viability, reduce/eliminate dependence of elk on supplemental feed, maintain established elk herd unit objectives, improve range health, and maximize benefits to all wildlife” (WGFD, 2011). A BMAP identifies the pros and cons for various options, including fencing, habitat improvement, conservation easements, and switching from cow-calf operations to stocker operations. The BMAP also acknowledges that for any action, such decisions would be under the purview of various stakeholders, including state agencies and individual producers. Land acquisition and conservation easements would involve buying or long-term leasing of land, with decision authority resting with private landowners; transactions involving WGFD (e.g., conservation easements) would have to proceed ultimately through that state agency (WGFD, 2011).
Land acquisition for winter range outside YNP remains a goal for many stakeholders interested in bison welfare, habitat to support the free-roaming nature of bison, and less invasive management actions. Land acquisition and deactivation of livestock grazing allotments have proven to be successful not only at providing bison with more habitat but also in reducing risks associated with bison-livestock interactions. As has occurred under the IBMP, acquisition of bison winter range is achieved through purchase of grazing rights, easements, or property from landowners and livestock producers, thus providing them with economic compensation.
A BMAP for the Jackson bison herd was developed by WGFD in cooperation with the National Park Service (NPS) and USFWS (WGFD, 2008a). The BMAP outlines efforts to conserve and improve habitats, minimize bison/elk conflicts with adjacent landowners, provide for a feeding program co-managed with WGFD, and a structured framework of adaptive management in collaboration with the WGFD to transition from intensive supplemental winter feeding to greater reliance on natural forage. The BMAP calls for WGFD to work with the Wyoming Livestock Board to keep bison and cattle separated through several actions, such as hazing as appropriate and fencing. It also calls for WGFD to work with managers on the NER and USFS lands to use hunting to maintain a population objective. The BMAP also calls for habitat enhancement, shorter feeding durations, and feeding in fewer years to reduce risk of intraspecies transmission. A bison BMAP has also been developed for the Absaroka Bison Management Area to address the few bison that wander from the YNP herd and exit the eastern boundary of YNP (WGFD, 2008b). This BMAP calls for many of the same management options as in the Jackson BMAP, particularly efforts to maintain separation of bison from livestock. The IBMP has been successful in managing bison, but it is not considered a BMAP as it does not directly address brucellosis.
Livestock producers in the GYA have been working with federal and state management agencies to reduce risks of transmission to their herds. Management efforts are developed as part of herd management plans for the designated surveillance areas (DSAs). For its BMAP, WGFD has suggested management options for fencing the elk and bison herds away from cattle in Wyoming. WGFD has also suggested that the timing of cattle grazing on Bridger-Teton National Forest and Grand Teton National Park grazing allotments be manipulated to achieve temporal and spatial separation of bison and cattle. The same principle would also apply to managing the timing of cattle grazing on allotments throughout the GYA and within DSAs that are permitted by USFS and BLM. The Cody herd BMAP provides management actions to redistribute elk and reduce negative impacts of land ownership on elk distributions and hunter access (WGFD, 2012). These proposed actions include working with landowners to maintain access for hunters to meet harvest objectives (possibly through an incentive program); reducing or dispersing large groups of elk adjacent to and on private lands; and preventing the comingling of elk and cattle during high-risk periods, which requires WGFD to cooperate with landowners to move elk away from cattle. Similar management actions would be useful throughout the broader GYA.
5.2 Biosecurity (Spatial-Temporal Separation)
Biosecurity is defined as “the implementation of measures that reduce the risk of disease agents being introduced and spread” (FAO, 2010). Biosecurity measures are used to prevent the entry of pathogens into a herd or farm (external biosecurity); if a pathogen is already present, biosecurity measures are used to prevent the spread of disease to uninfected animals within a herd (internal biosecurity).1 Biosecurity is one of the most important considerations in preventing brucellosis from getting into a cattle herd, especially given the presence of free-ranging wildlife. Biosecurity measures within the GYA are focused on external biosecurity, specifically the separation of cattle from elk and bison. Examples of practices recommended by state and local agencies include fencing of haystacks, testing cattle prior to adding them to the herd, and not moving breeding stock to risky summer range until after mid-June.
USDA-APHIS conducts National Animal Health Monitoring System (NAHMS) surveys that document the national adoption rates of biosecurity-related practices. The NAHMS surveys consistently find that many biosecurity measures are only partially implemented by producers despite strong, long-standing recommendations from experts. Although there is some available research that investigates necessary biosecurity and security practices for operations outside the GYA (Brandt et al., 2008), little is known about the factors affecting producers’ willingness to implement protective practices because literature related to brucellosis for the GYA is limited. There are estimates on the costs of implementing brucellosis prevention activities on a representative cow/calf-long yearling operation, which provides a break-even analysis from the producer’s perspective (Roberts et al., 2012). However, analysis is lacking that captures a germane discussion of public goods and externalities for the GYA. Furthermore, the actual implementation rate of brucellosis-focused biosecurity practices in the GYA remains unknown.
Cattle producers in the GYA incur additional expenses when implementing biosecurity measures, which they consider costly as “it just makes doing business in this part of the world much harder” (Lundquist, 2014; Rice, 2015). The costs and benefits of implementing a specific biosecurity measure may vary across producers, yet this has not been fully documented. For instance, a producer bordering an elk feedground faces different private benefits while a producer with more “home ranch” summer range options faces lower costs of delaying movement of cattle onto higher-risk, external summer range. Moreover, the impact of a given producer’s actions on other producers is not well documented yet is critical to understand (Peck, 2010). This ties directly to externalities and the need for a broader bioeconomic modeling that considers more than just private aspects of these decisions (see Chapter 8 on bioeconomics).
The Brucellosis Eradication Program formerly relied on a state-by-state approach (defined by geopolitical areas and boundaries) for classifying brucellosis status in the United States. States with no cases of brucellosis in livestock (zero prevalence) for at least a year with documented surveillance were classified as Class Free states. Interstate movement requirements and associated testing costs to producers became less burdensome as a state’s status was upgraded (9 CFR Part 78, 2006). This approach worked wellbecause there was an incentive for livestock producers to work with states to eliminate brucellosis and thus reduce or eliminate costs associated with testing. All 50 states were briefly recognized as free of brucellosis in 2008. It was then recognized that the identification of only a few cases of brucellosis in livestock in a small geographic area, such as the GYA, could result in loss of Class Free status for the entire state. Increased testing costs associated with loss of status would then be unnecessarily and inefficiently borne by all producers, even though the majority of the cattle herds resided in low-risk areas of the state far from the risk of infection. Politically challenging surveillance and disease-control approaches were often quickly implemented in an effort to regain statewide Class Free status.
DSAs were introduced by USDA-APHIS in a 2009 concept paper as a zoning approach for addressing brucellosis and were implemented in a 2010 interim rule (USDA-APHIS, 2009; 75 Federal Register 81090 ). Aregionalization approach that defines brucellosis risk areas and is consistent with World Organisation for Animal Health standards creates several advantages, including the ability to focus resources specifically in high-risk areas and increased flexibility in modifying the boundaries of the disease management area to reflect changes in risk while still assuring trading partners of the brucellosis-free status for the remainder of the country.
The success of the DSA concept relies on at least two important surveillance streams. First, it is dependent on adequate surveillance in wildlife. The DSA encompasses areas with endemic brucellosis in wildlife populations; thus, surveillance on the DSA perimeter will need to be adequate to delineate the area of risk to livestock species and determine the appropriate boundaries for the DSA. With financial support from USDA, state wildlife and animal health agencies cooperate to conduct surveillance in wildlife. Second, the concept of zoning relies on sufficient surveillance to detect brucellosis in livestock within and leaving the DSA. Adult breeding cattle are tested as they leave the DSA or as they change ownership within the DSA, but there are exceptions in some states for livestock consigned to slaughter.
State animal health agencies are responsible for designating the boundaries of their DSA and describing their rationale via a Brucellosis Management Plan (BMP) that is subsequently approved by USDA. Idaho, Montana, and Wyoming have BMPs, yet they have varied approaches in meeting these two critical surveillance needs. DSA testing requirements have led to the disclosure of 16 herds with brucellosis in the GYA since the DSAs were implemented. Each of the GYA states has consequently adjusted its DSA boundaries at least once since initial designation because of seropositive elk. The lack of uniformity in how states conduct surveillance, determine appropriate expansion of DSAs, and enforce DSA boundaries may be a hindrance to rapid identification and adequate mitigation of infection. As previously mentioned in Chapter 5, these and other gaps in the management of animals leaving the DSA will need to be addressed for the regionalization approach to be effective in addressing brucellosis (USAHA, 2012).
Testing and removal of brucellosis seropositive animals is a critical component of a strategy for eliminating brucellosis from an affected population. Test and remove is one of many tools that has been used in a variety of ways and to various degrees of success; however, it is rarely effective if used alone. To reduce the possibility of transmission, seropositive animals in an affected population would need to be removed from the herd and maintained separately from negative animals, or removed to either slaughter, research, or to a properly monitored quarantined feedlot, if available. The failure to remove seropositive animals likely results in continued transmission and an inability to control the disease. A major factor to reduce exposure and transmission of brucellosis is detecting and removing infected cows prior to parturition (Nielsen and Duncan, 1990). High-risk animals, such as exposed bred heifers, are sometimes removed as part of a brucellosis elimination strategy to ensure that they do not seroconvert and continue to spread the disease. In addition, highly susceptible seronegative animals are sometimes maintained separately to prevent exposure and subsequent infection.
In livestock populations, testing and removal alone without any other disease mitigation efforts—and especially testing and removal without consideration of the time of calving and abortion—has not proven to be an effective strategy (Caetano et al., 2016). However, testing and removing seropositive animals is an effective tool when property utilized as part of a disease-control or elimination strategy. Three major strategies have been demonstrated to be effective tools to control brucellosis in livestock when used in combination with other tools: (1) strict biosecurity at the farm level, including herd management to minimize the risk of contact with viable Brucella (such as calving management, separating replacement heifers and managing them as a separate unit, increasing biosecurity so as to protect herds from purchasing infected animals or becoming infected from community herds, and utilizing cleaning and disinfecting when appropriate to minimize environmental contamination); (2) vaccination; and (3) testing and removal programs (Pérez-Sancho et al., 2015).
In the United States, considerable progress was made toward eliminating brucellosis from cattle by replacing blind test and slaughter methods of the 1970s with the development of individual herd plans (Adams, 1990). These herd plans included the use of additional disease mitigation actions such as vaccination and separation of high-risk animals to reduce transmission and limit exposure of naïve animals. Vaccination alone is insufficient to eradicate brucellosis, but it increases resistance to infection and it reduces both the risk of abortions and the excretion of Brucella (European Commission, 2009). The key to success, however, is to test and rapidly remove infected animals before they have the opportunity to continue to transmit the disease (PAHO, 2001).
In some countries, when the prevalence of brucellosis is high or socioeconomic resources are limited, mass vaccination is the most suitable tool for the initial control of the disease (Pérez-Sancho et al., 2015). In those cases, systemic and mandatory vaccination is used to reduce infection rate to a level where testing and removal can then be used to eradicate the disease. For brucellosis, it is estimated that 7-10 years of systemic vaccination are necessary to achieve this objective (PAHO, 2001).
In several cases with both privately and publicly owned bison herds, a testing and removal strategy has been used in combination with other management actions to eliminate brucellosis. In combination with vaccination, the test and remove strategy has been effectively used for brucellosis in bison in the following six cases:
- Test and removal, combined with vaccination, was previously used in YNP in the early 1900s and reduced the seroprevalence of bison from 62% to 15% in 2 years (Coburn, 1948).
- In 1961, the Henry Mountain bison herd in Utah was declared free of brucellosis after a 2-year disease eradication campaign that utilized test and removal. This herd originated from YNP bison in 1941 and had a peak seroprevalence rate of approximately 10% in 1961 (Nishi, 2010). Recent research has shown that the Henry Mountain bison herd represents a genetically important subpopulation of the YNP-based metapopulation. This herd meets the YNP standard of no detectable cattle introgression, but it is also free of brucellosis (Ranglack et al., 2015).
- In 1973, the Custer State Park bison herd in South Dakota was declared free of brucellosis after a 10-year disease management program from 1963 to 1973. That herd had a peak seropositive rate of 48% in 1961. A combination of annual vaccination of calves and yearlings, test and removal, and herd size reduction were utilized (Nishi, 2010).
- In 1974, the Wichita Mountain National Wildlife Refuge bison herd in Oklahoma went from 3% seropositive to free of brucellosis after an 11-year disease management effort. A combination of test and removal, population reduction, isolation of select groups, and vaccination of calves up until 1973 were utilized to free the herd of brucellosis (Nishi, 2010).
- In 1985, the Wind Cave National Park bison herd in South Dakota went from a high seropositive rate of 85% in 1945 to brucellosis free after a disease management effort conducted from 1964 to 1985. A combination of whole herd and calfhood vaccination and test and removal were utilized (Nishi, 2010).
- In 2000, a privately owned bison herd in South Dakota was released from quarantine after a 10-year effort to eliminate brucellosis from the herd. This was accomplished by a combination of testing and removal of positive animals together with herd management to reduce exposure and transmission. The main herd of older, chronically infected animals was depopulated in January 1999. Younger, uninfected animals from calf crops were separated, intensely vaccinated with RB51, tested, and retained on the ranch to rebuild the herd (USAHA, 2000).
None of the cases above, however, are comparable to the bison herds in the GYA, and those situations did not involve affected elk populations. Data are limited on the use of test and removal alone or in combination with other methods. Hobbs and colleagues (2015) forecasted the effects of annually removing 200 seropositive bison using a Bayesian model that included uncertainties associated with a number of important parameters. Removal of seropositive bison was one of the few management actions likely to reduce
seroprevalence in the short term: from 55% to 14% over 5 years, although the credibility interval was still large, ranging from 0.12% to 57% in the fifth year (Hobbs et al., 2015).
In elk, the Muddy Creek pilot project was conducted from 2006-2010 to assess the use of test and removal to reduce prevalence of brucellosis in elk attending a Wyoming feedground. Data from that study showed that capturing nearly half of available yearling and adult female elk attending a feedground, testing for B. abortus, and removing those that test positive can reduce antibody prevalence of brucellosis in captured elk by more than 30% in 5 years. However, once the pilot project ended, the seroprevalence of brucellosis in elk on the feedgrounds resurged (Scurlock et al., 2010).
A variant of testing with the intention of lethal removal is test and quarantine. A bison quarantine pilot project was initiated in 2005 to determine whether it was feasible to qualify animals originating from the YNP bison herd as free from brucellosis. This project used the concept of separating seronegative, young animals so as to minimize exposure, with testing and removal. A majority of those animals were subsequently declared brucellosis-free and were moved to other locations, including to two Native American rangelands.
Vaccination is proven to prevent or mitigate infectious diseases. A number of highly efficacious commercial vaccines exist against bacterial diseases for use in cattle, including against Leptospira borgpetersenei serovar Hardjo-bovis, as well as vaccines for humans, such as those against bacterial meningitis, tetanus, and Haemophilus influenza B. Vaccines have been shown to be an effective tool to control the spread of brucellosis when combined with management practices. Adult cattle can be safely vaccinated with conventional Brucella vaccines via a primary or boosting dose, and cattle may be pregnant when vaccinated. This has been shown to be efficacious and to increase the immune response as measured using in vitro tests. In wildlife, development of oral vaccination strategies would be preferable to ballistic or needle injection, and a limited number of studies have shown promise.
9.1 Improving Cattle Vaccines
Cattle vaccines to date have been designed to protect against B. abortus-induced abortion and not against infection. Many of the brucellosis concerns in cattle could potentially be resolved by improving cattle vaccines for resistance to infection even under high dosage challenge conditions and even when herd immunity is compromised by comingling with infected wildlife (bison and elk). In the long run, an effective vaccine to protect against infection could reduce the legal, political, and financial costs associated with brucellosis in cattle. Improvements would be needed for adult vaccines (for both primary immunizations and booster doses for previously vaccinated cattle) and therapeutic vaccines that boost or retrain immune responses of animals already infected with Brucella (Wright, 1942). If it were possible to develop a vaccine that would not only prevent abortion but also prevent infection in cattle, the need for wildlife vaccines may be less paramount. Comprehensive delivery of vaccines may be a particular challenge that could be avoided if cattle vaccines were sufficiently improved.
9.2 Delivery Systems for Brucellosis Vaccination of Wildlife
Vaccinating wildlife can be challenging. Vaccines have been delivered to elk by needle immunization and biobullets, but they have been ineffective. Elk are widely dispersed and mobile, and many herds—including some that are infected at a high rate—do not concentrate on accessible feedgrounds in the winter. Even if an efficacious vaccine were available for elk, vaccinating elk populations in the GYA is infeasible in the absence of a novel method for delivering the vaccine (beyond biobullets or darting). Progress toward a feasible delivery system along with developing efficacious vaccines for elk will both be critical. A recent modification of Komarov’s bullets has been made and was shown to induce both antibody and cellular responses in cattle and bison with no detrimental effects (Denisov et al., 2010). While it can be delivered
from 100 meters, the safety range is 40-60 meters which may not be feasible for all terrains found in the GYA (Denisov et al., 2010).
Oral vaccines have been suggested to better stimulate mucosal immunity because exposure to brucellosis is generally through the mucosa. The gut mucosa regularly samples antigens from the intestinal lumen via dendritic cells embedded within the epithelium or via specialized microfold cells. Brucella antigens are then picked up and delivered to the mucosal and systemic immune systems to stimulate anti-vaccine immunity. Thus, oral vaccines may be more effective at preventing infection than parenteral administration of the vaccine. The administration of B. abortus strain 19 (S19) vaccine by oral vaccination proved to be equally as effective as subcutaneous vaccination in protecting pregnant heifers from Brucella-induced abortion (Nicoletti and Milward, 1983; Nicoletti, 1984). Cattle have been immunized orally with B. abortus strain RB51 (RB51) as a model for wildlife. When RB51 was mixed with feed and fed to beef heifers, which were then bred and exposed to a challenge dose of 107B. abortus strain 2308 organisms, it was shown that there was protection from abortion in 70% of the vaccinates but only 30% of the unvaccinated controls (Elzer et al., 1998). Microspheres composed of eggshell-precursor protein of Fasciola hepatica (Vitelline protein B) have been used to orally vaccinate red deer (Cervus elaphus elaphus) with RB51. This was shown to induce a good cellular immune response, as measured by lymphocyte proliferation assays, as well as to induce an antibody response (IgG) (Arenas-Gamboa et al., 2009b). Following challenge with another vaccine strain (S19), there was reduced bacteria in the spleens of vaccinates. A similar study using alginate microencapsuled S19 organisms to immunize red deer also showed a cellular immune response (Arenas-Gamboa et al., 2009a). Less considered is uptake of brucellae in the tonsils following exposures of the head and neck mucosa (Suraud et al., 2008). Vaccination of the tonsils may improve protection against Brucella infections. Thus, the development of oral and mucosal vaccination strategies for wildlife are promising.
The use of sterilization and contraceptives as a tool for wildlife management is controversial. Although it cannot prevent infection, sterilizing bison or elk early in life could prevent them from breeding, becoming pregnant, and if they are also infected with brucellosis, aborting and exposing cattle or other wildlife. Surgical sterilization of cattle (spaying heifers) has been a procedure used by stockmen for years to reduce or prevent transmission of brucellosis in cattle herds. Surgically spaying wild elk and bison is infeasible, but nonsurgical reproductive control via contraception may be feasible. Contraception of bison as a potential means to slow brucellosis transmission in wildlife may be more effective than testing and removal (Ebinger et al., 2011). Ebinger and colleagues (2011) posit that in social species that form groups, sterilized individuals essentially create herd immunity similar to effective vaccination efforts. On the other hand, when seropositive individuals are removed from the population, the social group may reform and bring susceptible individuals into greater contact with the remaining infectious individuals, thereby reducing herd immunity and increasing the potential for a strong resurgence of disease (Ebinger et al., 2011).
USDA-APHIS has recently conducted research on the possible use of a gonadotropin-releasing hormone (GnRH) antagonist vaccine (GonaCon™) as a method of inducing sterility in bison and elk (Rhyan, 2015). Earlier efforts using a zona pellucida vaccine were deemed ineffective (Kirkpatrick et al., 2011). Experimental trials with GonaCon™ in elk were under way as of the writing of this report. Information provided by USDA indicated that GonaCon™ has been approved by the U.S. Environmental Protection Agency (EPA) for use in deer and wild horses (Rhyan, 2015). In most species, GonaCon™ provided 2-3 years of sterility and the animals were anestrus (did not come into breeding condition). However, 5%-15% of animals became permanently sterile (up to 5 years), adjuvants caused some injection site reactions (abscesses), and protection was not 100% (Rhyan, 2015).
GonaCon™ has been better tested in bison than in elk. From 2002-2008, five vaccinated captive bison in Idaho did not calve while a small number of control bison calved 75% of the time (Rhyan, 2015). Bison that were in mid-to-late pregnancy when first vaccinated calved normally. A dose-response study showed that a high dose of GonaCon™ was 86% effective, low dose was 50% effective, and the medium dose
between those levels (Rhyan, 2015). In field trials with free-ranging bison in southern Colorado, there were mixed results: GonaCon™ vaccinated cows had 7 calves while unvaccinated cows had 24 calves. A field trial at Corwin Springs examined rates of infection and abortion in 20 vaccinated and 20 control bison cows exposed to brucellosis, and GonaCon™ appeared to be effective at significantly reducing abortion and birthing of infected bison calves (Rhyan, 2015). Another set of trials at Corwin Springs with 15 vaccinates and 15 controls had mixed results. In the first year, 75% of controls became pregnant while 20% of vaccinates did; in the second year, 77% of controls became pregnant while only 13% of vaccinates did; in the third year, 90% of controls became pregnant but so did 36% of vaccinates (Rhyan, 2015).
No large, free-ranging wildlife population in North America has ever been successfully managed using contraception. Modeling studies for wild horses suggests that even highly effective contraceptives can at best only slow population growth (Garrott et al., 1992; Gross, 2000; Ballou et al., 2008). Contraception conjures up the notion of manipulation that may unacceptable to the public. By decreasing reproduction, it could also be seen as decreasing future hunter harvest and potentially jeopardizing their acceptance. The management of elk inside national parks is under the jurisdiction of the NPS and outside national parks is under the authority of state wildlife management agencies. It is unclear whether state agencies or the NPS would allow experimental use of GnRH vaccines in free-ranging elk as part of brucellosis management efforts. With limited information available on GonaCon™ and other contraceptive approaches at the writing of this report, they would currently not be considered as a viable management option.
There are a number of mechanisms by which both scavengers and predators are likely to affect the distribution and abundance of elk as well as the transmission and prevalence of brucellosis. Scavengers and predators play a valuable role in suppressing the spread of brucellosis, as B. abortus is known to survive for weeks or months under typical GYA winter conditions and for up to 6 months if protected from sunlight (Stableforth, 1959). For the most part, the efficacy of predation and scavenging to alter brucellosis dynamics is unknown and untested. In the absence of healthy predator populations, however, elk may exceed management objectives, particularly in regions with limited hunter access (Haggerty and Travis, 2006; Cole et al., 2015). In this scenario, managers could consider further restricting the tag limits on predators or increasing the tag limits for elk. This would likely be a contentious decision, and it remains to be determined whether the benefits associated with fewer elk would be offset by the additional livestock losses that are likely to coincide with increasing predator populations in localized areas.
USDA-APHIS’s Wildlife Services removes coyotes from many regions across the country at the request of individual landowners. Coyotes are categorized as predators and can be shot or trapped in Idaho, Montana, and Wyoming without a license. However, coyotes are a major scavenger of aborted fetuses, and they are likely to reduce transmission rates both among elk and between elk and livestock (Maichak et al., 2009). Coyote hunting is unregulated; thus, it is unknown how many coyotes are removed annually and whether restricting coyote harvest would have any beneficial effect on brucellosis transmission. Again, this management tool is likely to incur a direct trade-off for the producer in the form of additional calf losses.
Several different avenues could be explored with respect to trained dogs (Wasser et al., 2004). First, in localized areas such as winter feedlines, dogs could be used by producers to investigate an area for fetuses daily prior to bringing cattle out. Because this would create a significant risk to the dog for becoming infected with brucellosis, the dogs would need to be muzzled to prevent ingestion or be trained to find abortions in an area and to stay a safe distance away. In addition, dogs have been used in some cases to detect certain forms of cancer in humans (Cornu et al., 2011). If detection dogs could be used pen-side to detect actively infected elk, bison, or cattle, this would facilitate more targeted test-and-remove or sterilization approaches.
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