Planning, Management of Chronic Wasting Disease Outbreaks in Wisconsin Science of a Transmissible Spongiform Encephalopathy (TSE) and Management Options for Disposal

By Joseph W. Brusca

Wisconsin Department of Natural Resources

3911 Fish Hatchery Road Madison, WI 53711

Phone (608) 275-3296


Prepared for the Symposium on Composting Mortalities and Slaughterhouse Residuals

Portland, Maine

May 24-25, 2005

In February 2002 the Wisconsin Department of Natural Resources (WDNR) through routine sampling of wild white-tailed deer, learned that the herd in the southern portion of the state had contracted CWD.  This was the first evidence of CWD infecting a free-ranging herd east of the Mississippi River. Colorado and several other western states have been involved with managing CWD infected elk and mule deer for years in both wild and captive herds.  As of April 2005 CWD has been documented in free-ranging cervids in 10 states and 1 Canadian province and in captive reared cervids in 10 states and 2 Canadian provinces. TSE was well known in the devastating outbreak of Mad Cow Disease in Europe.  TSE infected sheep in the form of scrapie has been common knowledge for decades. TSE also infects humans in the form of Creutzfeldt-Jakob Disease.

WDNR embarked on a very aggressive program to contain and eliminate CWD though several approaches. The first was to define the extent of CWD in the wild herd by sampling 40,000 animals of an estimated herd of 1.5 million in 2002.  In addition, owners of captive herds were required to sample any animal that was killed or died on the farm.  The results of that initial sampling indicated the geographic distribution of CWD was limited in the wild herd to an area of approximately 625 square miles in the southwest portion of the state.  Several captive herds were also identified as having infected animals.  The second strategy was to significantly reduce the concentration of wild deer in an area in what became known as the Disease Eradication Zone or DEZ to 5 deer per square mile.  Deer density varies in this part of the state with the average of 40 deer per square mile.

Several teams were formed to cope with the strategy and operations of managing the disease.  One of those teams was tasked with disposal of unwanted carcasses and CWD infected animals.  The Initial strategy was to dispose of carcasses in an engineered landfill.  Although this was the preferred alternative, it was quickly dropped from consideration in response to a flurry of media attention.  Because of the persistence of prions in the natural environment, only two alternatives emerged as being acceptable to elected public officials.  One was incineration and the other chemical digestion.  Both of these alternatives had standing in the scientific community as acceptable treatments because the protein molecule chain was broken which has the effect of inactivating the prion. The problem faced in Wisconsin in 2002 was the throughput capacity of these alternatives would not be able to treat the large number of carcasses that were going to show up at our collection stations starting with the archery season in September.  The Carcass Disposal Team developed bid proposals for handling carcasses and waste products from the fall hunt. We expected to generate waste from removal of heads for CWD sampling, butchered waste from hunters and meat processors, car killed deer and unwanted carcasses.  What developed was a “frost and toast” option where carcasses were sampled and held in refer units (16 refrigerated semis) until test results allowed for sorting of positive and negative animals.  This option was selected because the disease prevalence among all deer sampled in the DEZ was approximately 1.5-%.  All negative animals could be landfilled.  All CWD tested positive animals, butchered waste, heads and car-killed deer would be incinerated at a licensed pet crematorium.  The 2002 season generated over 1.1 million pounds of waste (about 9,000 deer equivalents) at a disposal cost of $1 million.

In 2003 WDNR drafted legislation to allow for indemnification of publicly owned sewer plants and sanitary landfills that accepted DEZ harvested deer.  The state legislature failed to act on the measure.  The 2003 season was similar to the first with the “frost and toast” option selected as the preferred alternative with carcasses stored in refrigerated semis and sorting after test results were made available.  The majority of the untested and positive tested waste went to Stericycle incinerators. A second option became available late in the fall season.  The University of Wisconsin Veterinarian Diagnostic Lab (UWVDL) housed and operated a chemical digester purchased by USDA. The amount of waste handled through incineration and chemical digestion amounted to 633,000 pounds at a cost of $512,000 (including storage and sorting tested carcasses). Although the DEZ was expanded in response to the discovery of additional positive deer (1,153 square miles) the volume of waste was reduced by an increase in the number of deer retained by hunters during the 2003 deer season.

In 2004 the DEZ was expanded again to encompass additional positive deer along the Illinois border and portions of the Southeast Region of the State.  A food pantry program was initiated so hunters could donate negative tested animals.  The UWVDL digester took over the lion share of disposal needs with the crematorium used as backup.  To date 382,000 pounds of waste were disposed of through chemical digestion and incineration.  Over 200,000 pounds of venison were donated to food pantries.  State contract costs for disposal and the pantry program amounted to $380,000 for the 2004 season.

CWD Waste Disposal Alternatives Analysis

Incineration is one of two scientifically accepted methods to inactivate prions.  The incineration standard developed in Europe for Mad Cow Disease was complete combustion of the waste in the primary burn chamber at temperatures maintained at 1600 degree Fahrenheit with a secondary burn chamber and retention of 1 second of emissions at a similar temperature.

The second accepted method is chemical digestion.  The standard for operating the digester at UWVDL is adding an equal amount of water (by weight) plus a 28% solution of potassium hydroxide to an adjusted pH of 10.5-11.5. The temperature is raised to 305 degrees F and maintained for 4 hours in the pressurized vessel.  The capacity for each cycle of the digester is 4000 pounds of waste tissue. The effluent is trucked to the Madison Metropolitan Sewage District for disposal.

Composting is an effective method of volume reduction.  However, the temperatures reached in compost operations are not effective in inactivating the prion resulting in a disposal problem of residual materials and remediation of the site once the facility is closed.

Rendering is another effective method of volume reduction.  USDA promulgated rules that effectively removed rendering as a waste disposal alternative from a CWD designated area.  The cost liability should a CWD positive animal go though the rendering process limited the industry to a dedicated plant. The cost of setting aside and operating a dedicated facility and the problem of wastewater disposal and end products eliminated this option from consideration because rendering is not consider effective in inactivating the prion.  This approach was considered conservative by the industry since there has been no scientific evidence that CWD can cross over to cattle or humans.

Air Curtain Destructors were considered because of the initial low cost & throughput capacity.  This option did not meet the incineration standards for maintaining temperature and there is no secondary burn chamber.  The operation of ACD requires excellent control of start up and shut down procedures.

A dedicated landfill was given serious consideration.  A request for proposal was sent out to design, construct and operate an engineered site with an artificial liner, leachate recirculation and lysimter monitoring system.  The proposed site would have a capacity for 100,000 carcasses in a 4-phased configuration. The proposed site would be placed on state-owned property.  The concept was abandoned because of time constraints and political fall out of exempting the siting process from local zoning.

Recommendations for Disposal of Waste from a CWD-Affected Area

Considering cost, worker safety issues, logistics, capacity to handle waste volumes and environmental considerations the author recommends disposal of untested waste from a CWD-affected area in a sanitary landfill.  Waste sources would include carcasses, heads, butchered waste and car killed deer. Our experience in handling waste is that workers are at risk from physical injuries and pathogens from carcasses that are poor condition.  The WDNR prepared a risk analysis of the fate of prion in a landfill that can be found on the following web site:

The analysis concluded that the risk associated with landfilling prions in an engineered site would pose minimal risk to spreading the prion through waste waster treatment plant’s solids spreading program.  Placing the waste in the upper lifts of the fill allow for ample exchange capacity for the prion (prions are highly hydrophobic) to adhere to clay and waste particles before the prion encounters the leachate collection system.  The sewer plants that treat leachate have little risk associated with prions entering the treatment system.  Sewer plants that accepted landfill leachate and the concern by these plants that CWD waste would jeopardize their land spreading programs was the key issue in landfills refusing to accept CWD waste.  The state of Wisconsin continues to work on indemnification legislation that would eliminate the financial risk for sewer plants and landfills that accept waste from CWD affected areas.

Relative Cost of CWD Waste Disposal Alternatives

Costs do not reflect storage, handling and transportation fees which are considerably higher for the incineration and chemical digestion options when looking at large volumes of waste. Costs are in dollars per ton.

LANDFILL: $35-70



Hunting season 2002 2003 2004
Square miles in DEZ 625 1153 1634
Harvest for the season 9509 13694 15,600
No. of deer retained by hunters 4009 (42%) 10694 (78%) 12,750 (82%)
No. of deer disposed 5500 3000 650
No. of deer donated to food pantry program 0 0 2200
Total amount of waste generated for disposal (in tons) 688 316 307
Total cost of disposal contracts $1,032,669 ($1500/ton) $512,000 ($1620/ton) $237,000 ($771/ton)
Total cost of pantry program 0 0 $143,000