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Introduction and General Information

Culling
  • Removal of infected animals, which may be a source of infection to other individuals, from the population is a well-recognised tool in the control of infectious diseases.
  • It has been recognised for many years that a high population density tends to increase transmission of diseases. (B126)
  • Reducing the population of susceptible individuals below the level required for a disease to persist is a recognised tool for management of disease in wild animal populations. (B127.12.w12, J64.21.w9, D109.w1)
  • Depopulation is rarely used for the control of disease in free-living animals but is used more commonly in control of disease in domestic animals, particularly in the control of highly infectious diseases. (B127.12.w12)
    • Depopulation is one of two measures available for the control of CWD in captive deer and elk herds which may have CWD (the other being quarantine with testing). (B209.17.w17, P10.67.w1)
    • Depopulation and/or herd reduction is also an option in the control of CWD in free-living populations of deer and elk.
      • "Computerised epidemiologic modeling indicates that early and aggressive intervention through population reduction offers the best chance to prevent establishment of new endemic foci." (N8.18.w8)

Processing and Disposal of Carcasses

It is known that certain parts of carcasses of cervids infected with CWD contain high levels of infectivity. Although the role, if any, of carcasses in the transmission of this disease between cervids is not known, it is reasonable to minimise the potential for transmission of the disease via carcasses, by restricting movement of carcasses and ensuring that non-edible portions of carcasses are disposed of in an appropriate manner.

In disposing of carcasses of cervids which have been diagnosed with, or may have, CWD it is important to remember the recommendations of the World Health Organization:

  • "No part or product of any animal which has shown signs of a TSE should enter any food chain (human or animal). In particular:
    • - All countries must ensure the killing and safe disposal of all parts or products of such animals so that TSE infectivity cannot enter any food chain;" (W244.09Apr2002.CWD1 - Recommendation 4)

Because it is not possible to state categorically, from the scientific evidence presently available, that CWD does not infect humans or domestic animals, it is recommended that precautions are taken to minimise the risk of exposure of humans and domestic animals to material from deer or elk known to be infected with CWD. 

  • It is prudent also to take practical measures to minimise any potential exposure of humans and domestic animals to the CWD agent in tissues from deer or elk which do not appear to have the disease and a number of recommendations have been made to minimise this risk.

(J64.21.w17, D126, W244.09Apr2002.CWD1)

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Which animals to cull in an outbreak

In captive facilities:

Depopulation:

  • Depopulation is one of the two options available for the management of CWD in captive populations, the other being quarantine. (N8.18.w8, D109.w3)
  • Depopulation may be appropriate in situations where it is believed that more than a few animals within a herd are likely to be infected with CWD.
    • In Canada whole herds of farmed elk have been depopulated when CWD has been detected in a herd. (P41.18.w1)
    • In Saskatchewan, Canada, a herd of elk on a game farm was depopulated in response to a singe case of CWD. (B294.10.w10)
  • Both animals which are officially part of the captive herd and publicly-owned cervids which are present on the property should be culled.
  • The preferred option identified in the APHIS Revised Draft CWD Program Plan (June 2001) is for the whole herd to be culled (depopulation) if a single animal is identified as being CWD-positive. (W30.23May02.CWD1)
  • Following detection of CWD in a single seven-year-old bull elk in Korea, which had been imported from Canada, all cervids on the farm were destroyed and tested for CWD (no other positive animals were found). (J27.64.w1)

Culling of selected animals:

  • A possible alternative, in which the herd would be quarantined, would involve culling and testing of selected animals within the herd, followed by monthly inspections of the herd by State or Federal personnel with suspect animals being removed from the herd and tested for CWD. (W30.23May02.CWD1)
  • When a herd is not known to be CWD-positive, but some animals on the premises are known to have been on a premises on which CWD has now been identified, within a set period of time before the disease was identified on that premises, it may be appropriate to cull and test those animals for CWD, with the remainder of the animals being quarantined until the results of the testing are known.
    • This option was used in elk farms in Alberta, Canada, with quarantine in the "trace forward" herds (herds that had received one or more cervids in the 36 months prior to CWD detection) being lifted when test results showed that all the trace-forward animals were CWD-negative. (W428.27Mar03.CWD1)

In free-ranging populations:

  • Live-sampling with euthanasia of CWD-positive animals (test and slaughter program):
    • For maximum efficacy, test and slaughter programs depend on being able to inspect every animal in a population, identify each individual, detect infected individuals using a test with high sensitivity and specificity, remove infected individuals and prevent contact between uninfected individuals and those which have not yet been tested. (B127.12.w12)
      • Because of practical limitations test and slaughter programs are "of limited value for disease management in free-ranging animals." (B127.12.w12)
    • The development of a live test (tonsillar biopsy) for antemortem detection of CWD makes live testing followed by euthanasia of CWD-positive deer a theoretical possibility.
    • This would require, for each individual animal, live capture (trap or remote injection), anaesthesia and tonsillar biopsy, followed by maintenance in captivity until the test result was available, or attachment of a radiocollar to allow subsequent tracking and shooting of infected individuals.
    • This method cannot be considered as a practical option for application to free-ranging populations.(J40.66.w1)
    • This technique may be appropriate for research purposes in limited areas where public hunting and culling is not feasible and may be applicable in some strictly localised situations. (D118)
    • It is important to remember that even deer testing negative cannot be guaranteed not to be infected, as the tonsils may not contain detectable PrPCWD in the early stages of infection. (J40.66.w2)
  • Targeted removal of sick animals
    • Targeted removal of sick animals showing clinical signs compatible with CWD is likely to remove from the population some animals which are infectious and may therefore reduce the amount of infective material available and the spread of the disease. (D114.III.w3, B127.12.w12, D118)
    • Targeted removal of sick animals also contributes to surveillance operations (targeted surveillance) and provides necropsy material and material for research. (D114.III.w3). 
    • It should be recognised that data from Colorado and Wyoming demonstrate that, on its own, selective culling of clinical suspects is insufficient to reduce the prevalence of CWD in endemic populations. (J40.66.w1, J64.21.w17, N8.18.w8)
    • Selected culling may be more effective as a tool for preventing new endemic foci from becoming established, if new areas of infection can be detected sufficiently early. (J40.65.w1, J40.66.w1, J64.21.w17)
  • Targeted removal of animals considered likely to spread the disease by natural movements.
    • Data from the current literature, as well as simulation modelling, suggests that the main way in which CWD is likely to spread from an infected area to other populations outside that area is by the normal movements of deer, particularly dispersal of yearling bucks. The median (most common) dispersal movements are probably about 5-10 miles although in the Midwest movements as long as 130 miles may (rarely) occur. (D109.w3)
    • Targeted removal may be used to reduce this subset (yearling males) from the population. (D110.w3)
  • Population reduction (herd reduction)
    • Reducing the population density is a recognised method for disease control and is based on the idea that infectious disease is density dependent: reducing the population density is considered likely to reduce the transmission of the disease and therefore its prevalence. (B127.12.w12, B127.13.w13)
    • Localised population reduction is being used experimentally in areas of high CWD prevalence in Colorado with the aim of reducing both transmission and the likelihood that infected animals will migrate to adjacent areas. (J40.66.w1, J64.21.w17, N8.18.w8, P40.1.w34, D118)
      • The efficacy of this management strategy may be diminished by the effects of historic migration patterns and characteristic social behaviours of some deer and elk populations. (J40.66.w1, J64.21.w17)
    • Localised population reduction may be more effective as a tool for preventing new endemic foci from becoming established, if new areas of infection can be detected sufficiently early. (J40.66.w1, J64.21.w17)
      • Localised population reduction will be used in Wyoming in the event of a new focus of infection being detected outside the endemic area, to attempt eradication of the disease in the new area. (D114.III.w3)
      • Population reduction of white-tailed deer around the core CWD affected area has been chosen as part of the management plan for control of CWD in Wisconsin. (D109.w4)
    • Population reduction may be used in areas in which CWD is not yet present, with the aim of reducing the potential for the disease to become established. (P40.1.w40, D110.w3)
    • Generalised population reduction in endemic areas may be used, with the intention of reducing transmission and prevalence of the disease. (D118)
      • The degree of population reduction that is required to reduce transmission of the disease is not known, however a considerable reduction in population density may be required. (D118)
      • It is important to recognise that population reduction must be maintained for several years in order to determine whether it is effective in decreasing prevalence of CWD. (D118)
  • Depopulation
    • Depopulation involves the removal of all animals in an area/facility or, in the wild, reduction of the population to very low levels.
      • This is the most extreme form of host manipulation for the purposes of disease control. (B127.10.w10)
      • Depopulation may be appropriate in a situation where a new disease has been discovered in a local area; this may prevent dispersal of potentially infected animals to other areas. (B127.10.w10)
    • Depopulation would be expected to facilitate CWD control by removal of infectious animals, reducing the population density in the area and reducing the accumulation of the infective agent in the environment (which may be shed by live animals and leached into the environment from carcasses). (D109.w5)
    • Complete depopulation in an area may be extremely difficult; the effort required to remove individuals from the population increases substantially once the population has been reduced to a low level. (D109.w3)
    • Depopulation of free-living cervids in an area may, depending on the size of the area and the initial population, require several years of effort to be effective. (D109.w5)
    • Depopulation of white-tailed deer in the core CWD affected area has been chosen as part of the management plan for control of CWD in Wisconsin. (D109.w4)
    • In Colorado, culling may be directed to "hot spots" of high CWD prevalence identified by surveillance. Such culling would be likely to reduce the potential exposure of cervids in the surrounding area to the disease agent. (D118).
    • In Michigan, depopulation may be used if CWD is detected in one or more free-ranging cervids:
      • During active surveillance in an area (five miles radius) around a privately-owned captive cervid facility (deer or elk farm), if such is discovered. (D119)
      • During active surveillance in an area (five miles radius) around an initial detected CWD-positive free-living cervid. (D119)
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Factors affecting effectiveness of culling for CWD control

In captive facilities:
  • If selected culling is combined with quarantine and surveillance, the effectiveness of the program will depend on the ability of surveillance methods to detect the disease so that all CWD-positive animals are removed from the herd.
  • There should be no reasons why it is not possible to depopulate a herd in a captive facility.
  • The disease may recur in a facility if:
    • Repopulation is premature;
    • Effective disinfection has not been carried out;
    • The facility is in an area in which CWD is present in the wild population and stringent measures to prevent wild cervids coming onto the property are not in place.
    • Repopulation is carried out using animals which are not from a herd certified to be CWD-free. 

In free-ranging populations:

  • Historic migration patterns and social behaviours may reduce the effectiveness of wholesale reduction of population density in controlling CWD. (N8.18.w8)
  • Surveillance limitations may delay detection of newly-infected free-ranging populations for years after the disease has been introduced. (N8.18.w8)
Factors which may affect the effectiveness of depopulation as a disease control strategy include: 
  • The size of the proposed area targeted for depopulation. Depopulation becomes more difficult as the size of the area over which depopulation is required increases. (D109.w5)
  • The geographical distribution of the disease (whether the area depopulated fully contains a CWD focus). If infected deer exist in the population immediately outside a depopulated area reinfection of the area may be expected within a short time period. (D109.w5)
  • Willingness of hunters to hunt in a proposed depopulation zone. (D109.w5)
  • Willingness of landowners to allow hunters or shooters sent by the relevant State agency to shoot on their land (if some landowners do not allow shooting such areas could act as refuges for deer, which could allow the disease to persist in the area). (D109.w5)
  • Resources available to the relevant wildlife agency. (D109.w5)
It is important to consider also that:
  • It is not known how long it would be necessary to keep an affected area free of deer to ensure local eradication of CWD. (D109)
  • Information from a CWD model (J40.65.w1) suggests that in the wild (unlike in captive situations where deer are highly concentrated) infection from contaminated environments "is relatively unimportant in sustaining CWD epidemics." (D109)
  • Criteria for removing an area in the wild from depopulation status have not yet been established. It may be relevant to compare with the captive situation, where five years with surveillance for CWD of all juvenile and adult deer which die during that time appears to be becoming accepted.)
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Techniques of culling animals

In captive facilities:
  • Shooting.
  • Normal slaughter methods used on deer farms.
  • Euthanasia: for depopulation programs individuals may be sedated with xylazine followed by intravenous injection of a euthanasia solution or use of a captive bolt.

In free-ranging populations:

For free-ranging deer populations the main way in which deer are culled is by shooting. This may be carried out by members of the public (hunters, landowners), by personnel of the agency responsible for the culling or by sharpshooters specifically employed for this purpose.

If culling operations are to be combined with surveillance operations it is necessary that the deer or elk NOT be killed by a head shot as the brain stem and/or tonsils and/or retropharyngeal lymph nodes (all found in the head) are required for diagnosis.

Hunting by members of the public, including landowners:

  • A major way in which depopulation and heard reduction efforts may be carried out is by encouraging increased hunting of deer by the public in the required area. 
    • Hunting is the preferred method for management of cervid herd populations and herd densities. (D117, D126)
    • "Public hunting is believed to be the most effective method of herd reductions due to the large number of hunters and their access to both public and private lands in an IHZ [Intensive Hunting Zone]." (D109.w5)
  • Ways in which harvesting of deer by the public may be increased include (the following examples are based on the actions proposed in the Wisconsin DNR's Environmental Impact Statement (D109.w5)):
    • Extending the hunting season.
    • Provision of unlimited and free hunting tags for deer.
    • Provision of unlimited "earn-a-buck", whereby a hunter who has harvested an antlerless deer may then shoot a buck, without a requirement to get a buck tag first, and where there is no limit to the number of bucks which may be earned in this way.
    • Either-Sex regulation - allowing hunting of deer of either sex when the population drops below a determined limit (for the Wisconsin IHZ, when the overwinter deer population is reduced to five or less deer per square mile of deer habitat).
    • State Park Seasons: allowing hunting in designated State parks and other State-owned properties, normally closed to deer hunting, during defined seasons. This would not be considered appropriate for e.g. parks in urban areas.
    • Relaxation on firearm restrictions, for example allowing the use of rifles in areas in which these are not normally allowed.
    • Provision of Landowner Permits, allowing landowners and their guests to hunt deer on their property, with exemption from normal hunting licences and the regular deer hunting season.

Culling by agency personnel and sharpshooters:

  • Further ways in which harvest may be increased include
    • Use of Agency shooters, on State-owned lands and, with permission, on private lands. 
      • Such shooters may be allowed to shoot over bait and from vehicles.
    • Use of aircraft to spot, rally or drive deer and, where appropriate permission was granted, for harvesting of deer.
  • The use of highly trained individuals is particularly important in areas where there may be increased human safety concerns related to discharge of long-range firearms.

Live capture and euthanasia:

  • This is an extremely inefficient method.
    • It is very labour intensive;
    • Pre-baiting for up to a week is required before trap placement in order to begin attracting deer.
    • It is likely to be successful only in late winter and early spring when food is scarce and cervids may be food-stressed.
    • In areas with alternative food sources available, even in late winter and early spring, it is difficult to entice deer into traps.
    • Some deer will never enter a trap although others may do so more readily. Therefore trap success is likely to decline to zero while a proportion of the local population is still present (i.e. it is unlikely that all local individuals will be captured)
  • Confinement in a live trap may be less humane than shooting, due to stress associated with confinement of a free-living animal as well as the possibility of self-injury and even death while struggling within the trap
  • Live trapping and euthanasia may be of use in strictly limited situations where the cervid population is small and use of firearms is not practical for example in small urban parks.

    (D109.w5, D118)

Use of chemical toxicants (poisons):

  • Chemical toxicants are relatively low in cost and labour and are widely utilised for the control depopulation of rodent pests but less commonly for other species.
  • Chemical toxicants are rarely used for large vertebrates.
  • There are no EPA-registered toxicants available for use on white-tailed deer.
  • Use of chemical toxicants would involve risks to non-target species, both primary poisoning (eating of baits) and secondary poisoning (ingestion of contaminated carcasses by predators and scavengers).
  • Sublethal dosages could occur in both target and non-target species, with associated animal welfare concerns.
  • Perceptions that poisoning is inhumane would make their use highly controversial; many landowners probably would not allow use of chemical toxicants on their land.

    (D109.w5)

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Recommendations for processing of deer and elk carcasses

Details of recommendations and regulations may vary between States and it is important that any hunter contacts the relevant state wildlife agency regarding the recommendations and regulations for the State in which they are hunting and, if different, the State to which they will be transporting the carcass or parts of the carcass.

Recommendations for hunters:

The following precautions have been suggested for hunters when hunting, field dressing and processing (butchering) deer or elk from areas where CWD is found:

  • Do not shoot, handle or consume any animal that appears to be sick or is acting abnormally.
  • Wear latex or rubber gloves when field dressing deer or elk carcasses.
  • When butchering (processing) the carcass, bone out the meat. Do not saw through bone, and avoid cutting through the brain or spinal cord (backbone).
  • Avoid/minimize the handling of brain and spinal tissues.
  • Liberally trim gunshot areas involving the spinal cord. 
  • Use a separate saw/knife for removing the head and/or antlers. 
    • The saw blade used for removing the head and/or antlers could be used also for cutting up the carcass for disposal after boning out the meat. (W437.10Apr03.CWD1)
    • The saw blade should be disposed of after use. (W437.10Apr03.CWD1)
    • If saving the skull cap attached to the antlers, soak it in a 50-50 bleach and water solution for an hour (keep the antlers out of the bleach). W437.10Apr03.CWD1
  • Wash hands and instruments thoroughly after field dressing/butchering is completed.
  • A separate knife should be kept for butchering deer and not used for other purposes. this knife should be disinfected thoroughly after use. See: CWD CONTROL: CWD Quarantine and Disinfection (Overview of Techniques) specific section - Disinfection of knives and other implements. (J40.66.w1)
  • Avoid consuming brain, spinal cord, eyes, spleen, tonsils and lymph nodes of harvested animals, particularly those from areas where CWD is known to be present..
    • Lymph nodes should be removed intact and discarded.
  • Avoid consuming the meat from any animal that tests positive for CWD
    • A World Health Organization Report (WHO Consultation on Public Health and Animal Transmissible Spongiform Encephalopathies: Epidemiology, Risk and Research Requirements) noted that "there is currently no evidence that CWD in Cervidae is transmitted to humans" but recommended that "no part or product of any animal with evidence of CWD or other TSEs should be fed to any species (human, or any domestic or captive animal)." (W244.09Apr2002.CWD1)
  • If the deer or elk is commercially processed, it should be processed individually, without meat from other animals being mixed together.
  • If samples have been taken from the carcass for surveillance purposes, it is recommended that the meat from the carcass is stored frozen until the result of the testing is known.

(B209.17.w17, J64.21.w17, D114.V.w5, P10.67.w1, P40.1.w32, W402.24Mar03.CWD1, W425.27Mar03.CWD5, W426.27Mar03.CWD1, W437.10Apr03.CWD1, W443.26Mar03.CWD)

Detailed instructions for processing a deer using boneless cutting procedures are provided in the publication "Processing Your Deer" - (W437.10Apr03.CWD1).

"Strong bleach (diluted 50:50 with water to give a final concentration of 2.7% active ingredient sodium hypochlorite) should be used to sanitize utensils and equipment coming in contact with the specific tissues listed above." (W443.26Mar03.CWD1)

Recommendations for meat processors:

  • Wear latex, vinyl or rubber gloves when processing carcasses and change gloves between carcasses.
    • Wear rubber gloves when removing the head/antlers. (W443.26Mar03.CWD1)
  • Avoid or minimise handling of brain, spinal cord, eyes, spleen, lymph nodes and major nerve complexes.
  • Use a separate saw/knife for removing the head/antlers.
    • If removing antlers, use a saw which is designated just for that purpose and dispose of the blade after use.
  • Discard major lymph nodes: these will be removed if all fat and connective tissue is removed from the meat.
  • Do not cut through the spinal column or split down the midline and avoid using a saw.
  • Trim liberally around gunshot areas involving the spinal cord (W443.26Mar03.CWD1)
  • Bone out the meat.
    • Possibly request that boned-out meat should be submitted for processing. (W420.27Mar03.CWD5)
  • Dispose of the inedible portions of the carcass in a safe manner as recommended by State regulations.
    • In Wisconsin the hide, brain and spinal cord, eyes, spleen lymph nodes, bones and head should be sealed in plastic bags and sent to a legal disposal agent as designated by the Department of Agriculture, Trade and Consumer Protection. (D115)
  • Keep carcasses separate and keep processed meat and trimmings from each carcass separate and identified: each hunter should receive products back produced only from their own game animal.
  • Clean and sanitise with bleach tables, utensils and equipment used in processing between carcasses.
    • Use a 50:50 strong chlorine bleach and water solution. (To give a final concentration of 2.7% sodium hypochlorite). (W443.26Mar03.CWD1)
    • Wipe down tables/countertops and let them dry.
    • Soak knives and other utensils for one hour.
    • Further dilute the bleach solution before disposing of it down a drain.
  • Keep accurate records of the owner, species of animal, condition of the carcass/meat, weight, date the carcass/meat was accepted, date of processing and recipes used.
  • Try to keep ground-mixed products separate whatever the batch size (sausage, "slim-jims", hamburger)
  • Where appropriate (where CWD surveillance operations are being conducted), encourage hunters to get their carcasses checked.
  • If storing meat until CWD test results are available work with the owners to dispose of meat from CWD-positive animals in an appropriate manner.
  • More aggressive actions which could be taken include only processing deer/elk which have been tested for CWD and found to be negative, processing game animals in separate facilities, not processing game from CWD-endemic areas or not processing these species at all.(W443.26Mar03.CWD1)

(B209.17.w17, J64.21.w17, P10.67.w1, D115, W420.27Mar03.CWD5, W443.26Mar03.CWD1)

Recommendations for Taxidermists:

  • Wear latex, vinyl or rubber gloves when processing carcasses. (B209.17.w17, J64.21.w17)
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Disposal of non-edible portions of individual deer and elk carcasses

Regulations or recommendations for the disposal of non-edible portions of deer and elk carcasses should be developed. (D126
  • Details of recommendation may vary between States and it is important that any hunter contacts the relevant state wildlife agency regarding the recommendations and regulations for the State in which they are hunting and, if different, the State to which they will be transporting the carcass or parts of the carcass.

For information on transport of carcasses see: CWD CONTROL: CWD Import and Transport Restrictions (Overview of Techniques) specific section - Recommended "Best Practice" for Deer and Elk Carcass Movement

Traditionally deer have been gutted in the field at the site of harvest and the internal organs left for scavengers, while butcher waste (head, bones, any internal organs not removed in the field) have been taken to rendering plants or sent to local landfill sites with other trash. (D109.w10). 

In Wyoming the following recommendations are made for individuals processing their own deer:

  • For hunters intending to process their deer within the endemic area "we recommend that you bag the head and spine and dispose of them in an approved landfill within the endemic area." (W425.27Mar03.CWD5)
  • For hunters intending to process their deer outside the endemic area either entirely or needing to quarter the carcass to pack it out,  "we recommend that you remove the head and spine and leave them at the site of the kill." (W425.27Mar03.CWD5)
  • It is emphasised that "It is illegal to dump carcasses on public or private land." (W425.27Mar03.CWD5)
  • Bones, hide and head should be disposed of "in the appropriate location at landfills." (W426.27Mar03.CWD1)

In Minnesota its is recommended that bones and offal should be disposed of through rendering, burial, incineration or landfill. (D121)

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FDA regulations regarding use of material from animals with CWD

On November 12 2002 the FDA announced that "the Agency will not permit material from Chronic Wasting Disease (CWD)-positive animals, or animals at high risk for CWD, to be used as an ingredient in feed for any animal species." (W380.24Mar03.CWD2)

Animals considered to be "at high risk" would include (W380.24Mar03.CWD2):

  • Animals from CWD-positive captive herds;
  • Free-ranging animals from the CWD-endemic area in Colorado and Wyoming
  • Deer from the CWD eradication zone in Wisconsin;
  • "Deer from any areas designated around any new foci of CWD infection that might be identified through surveillance or hunter harvest testing".

(W380.24Mar03.CWD2)

It was stated further that "animal feed or feed ingredients on the market that incorporate this material should be recalled or otherwise removed from the marketplace." (W380.24Mar03.CWD2)

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Large-scale carcass disposal and Implications

"The primary goal of carcass disposal is to prevent spread of the disease agent to other animals through environmental contamination." (B36.4.w4)

In designing a disposal program for carcasses of cervids which may be infected with CWD it is essential to consider the physical and biological properties of the CWD agent as well as the incomplete knowledge of the specific mechanisms of natural transmission of CWD, the lack of a rapid diagnostic test and the lack of practical analytical methods for sampling air, water or soil for the infective agent of CWD. (P40.1.w43)

  • "The causal agents of the TSEs are collectively recognized to have the potential for extended survival in the environment and to be resistant to many, but not all, processes that are traditionally used for the inactivation of conventional microorganisms." (P40.1.w43)

  • "Without an effective, rapid postmortem test, carcass disposal will remain a major element in increased surveillance or population reduction efforts. Rapid and accurate testing will permit presorting of carcasses for their most effective disposition. Federal funds may be used to purchase or lease capital-intensive equipment for disposal to be made available to States and other entities as needed." (D110.w3)

There is no single best choice for disposal of CWD-infected cervid populations and there is no "zero-risk" option. (P40.1.w43)
  • The method of disposal chosen will depend on the number of carcasses for which disposal is required, local conditions, available resources and both local and state regulations. (P40.1.w43)
  • Outreach will be required to the general public, other regulatory agencies and within the home agency to provide information on the method chosen. (P40.1.w43)

Methods which may be used for carcass disposal include:

Burial at an uncontrolled site:

  • This provides excellent capacity.
  • There is a relatively low cost.
  • There is no or very low inactivation of the agent.
  • There is a potential concern regarding water contamination and quality.
  • There are concerns regarding environmental contamination.
  • This was eliminated as an option for Wisconsin. 

(P40.1.w43)

  • In Minnesota burial of carcasses that have tested positive for CWD is not considered to be an appropriate option. (W414.10Apr03.CWD1)

Landfilling in a modern, engineered and regulated site:

  • Modern landfill sites include engineered liners, caps and leachate and gas collection systems.
  • Landfill sites provide excellent capacity for carcass disposal.
  • Relatively low cost - this is more cost effective than dedicated rendering with controlled disposal, incineration or alkaline digestion. 
  • It is accepted that there is no or very low inactivation of the agent in landfill sites, at least in the short to medium term.
    • It is not known how long natural degradation would take for complete inactivation of the CWD agent.
  • There is a potential concern regarding water contamination and quality.
  • Standard landfills have been chosen as the primary method for disposal of carcasses testing as CWD-negative in Wisconsin. (D109.w10)
  • It would be possible to build a landfill site (to modern specifications) specifically for disposal of deer carcasses, with the extracted leachate being solidified on-site and returned to the landfill (i.e. a closed system).
    • Such sites could be chosen and designed but constructed only if needed, for CWD or other disease control operations. (D109.w10)

(P40.1.w43, D109.w10)

A detailed analysis has been made of the risks associated with disposal of deer in landfill sites, based on the situation in Wisconsin:

  • The analysis considered the risk of the following potential primary pathway for movement of CWD infective agent: carcass to landfill to leachate to wastewater treatment plant to sludge to farm field to ingestion by humans or deer. (D112.w1)
  • The main conclusions were that:
    • It is not possible at present to make a quantitative or semiquantitative assessment of the risk due to too many unknown factors such as the quantity of infectious agent present in a deer carcass and the dose required for infection. (D112.w5)
    • "It is reasonable to conclude that while absolute numbers relating to human health risk cannot be generated, the available knowledge about CWD and other TSEs suggests that landfilling of CWD-infected deer does not pose a significant risk to human health." (D112.w5)
    • "It is deemed likely that the risk of spreading CWD among Wisconsin's deer population by landfill disposal of infected carcasses is quite small." (D112.w5)

An Analysis of Risks Associated with the Disposal of Deer from Wisconsin in Municipal Solid Waste Landfill (D112) -

In Minnesota, while the recommended method of disposal for carcasses of cervids known to be CWD-positive is by incineration above 1,100F, landfilling in approved sites is considered to be an "acceptable, safe and practical" alternative. (W414.10Apr03.CWD1)

In Michigan deer/elk heads collected for testing will be disposed of in landfill sites until CWD is detected in the state, but by incineration once the disease has been detected. (D119)

Dedicated rendering with controlled disposal:

  • Rendering involves cooking of animal tissues at specific temperatures for set time periods, to produce water, tallow (fats) and meat and bone meal (the protein portion).
  • Rendering involves some level of inactivation of the agent and may reasonably be expected to reduce infectivity by 10-100 fold however studies using BSE and scrapie agents indicate that TSE agents can survive rendering to some degree. (D109.w10)
  • Controlled disposal would be required since the tallow and meat-and-bone-meal could contain infectious agent and could not be marketed for fertiliser or animal feed.
  • There are potential concerns regarding water contamination and quality. If water from the process contained solids the agent could "stick" to this. Potential infectivity in wastewater could be reduced by filtering solids from the wastewater before discharge.
  • The use of this option may be limited by refusal of rendering plants to accept cervids (as happened in Wisconsin following the discovery of CWD in the area). (D109.w10)

(P40.1.w43, D109.w10)

Incineration:

  • Incineration provides the potential for complete inactivation if temperatures are sufficiently high.
  • A controlled furnace may be used with a primary and secondary combustion chamber (examples are pathological incinerators and incinerators used at per crematoria). 
    • These units are generally expensive, have a limited throughput (thus are unsuitable for handling of large numbers of carcasses) but do effectively meet the temperature criteria for inactivation of the TSE agents.
    • These units have been chosen for the disposal of visibly sick deer and those testing CWD-positive in Wisconsin. (D109.w10)
    • These units are being used also for the disposal of deer killed by collision with vehicles, butcher waste and heads of deer collected for sampling in Wisconsin. (D109.w10)
  • Air curtain destroyers are a sub-type of incinerator consisting of an open topped pit or combustion box, fueled with wood,  with a fan mounted along the length of the box to provide both oxygen and a curtain of air over the top of the box thus preventing escape of smoke and unburned particulates from the box.
    • These are less expensive and of higher capacity but are less controlled than other methods of incineration. Temperatures in excess of 600C can be achieved and maintained (with fluctuations) but excellent operator skills are required to maintain throughput, high temperatures and minimise smoke production.
  • There may be concern regarding potential airborne dispersal of the CWD agent.
    • The air curtain is disrupted during loading operations and by wind and rain, which allows smoke to escape

(P40.1.w43, D109.w10)

Digestion - high temperature, high pressure alkaline hydrolysis:

  • Tissue digestion is more properly described as high pressure alkaline hydrolysis.
    • This involves the use of pressurised sodium hydroxide or potassium hydroxide solution, at high temperatures (about 150C), to hydrolyse proteins to peptides and amino acids. (D109.w10)
  • Excellent agent inactivation.
  • Low throughput capacity.
  • Resultant liquid has a high biological demand and low pH therefore requires specialised handling.
  • Potential concern regarding water contamination and quality.

(P40.1.w43)

Associated techniques linked from Wildpro
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Further research

For effective management of CWD it will be necessary to undertake research into:
  • The effect of animal density on CWD prevalence and transmission. (D117)
  • The effects of animal movement (including migration and dispersal) and behaviour on CWD transmission and spatial distribution. (D117, D121)
  • The effects of intensive culling on dispersal of cervids. (D118)
  • Methods of carcass disposal. (D110)
  • The relative risks to wild cervids from disposal of offal and bones in landfills. (D118)
  • Raw antler velvet is a product unique to the farmed cervid industry; it may be necessary for this product to be evaluated specifically for the presence of PrPCWD. (J64.21.w17)

N.B. Results of research must be distributed effectively if they are to be of benefit to agencies responsible for disease management. See: CWD CONTROL: Education and Communication for Chronic Wasting Disease (Overview of Techniques)

Associated techniques linked from Wildpro

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Authors & Referees

Authors Dr Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referee Suzanne I Boardman BVMS MRCVS (V.w6), Chris Brand (V.w52), Dr Terry Kreeger (V.w49), Dr Julie Langenberg (V.w50), Bruce Morrison (V.w48), Michael Samuel (V.w53), Scott Wright (V.w54)

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