Disposal of Prion-Contaminated Wastes from 

Veterinary Laboratories

 

 

Dr. Donal O’Toole, Wyoming State Veterinary Laboratory, University of Wyoming

 

Safe disposal of prion-contaminated wastes became an issue for veterinary laboratories after a link was established between bovine spongiform encephalopathy (BSE) in European cattle and variant Creutzfeldt-Jakob disease (v-CJD) in people.  The two most common transmissible spongiform encephalopathies of animals in the United States are scrapie (sheep and goats), and chronic wasting disease (mule deer, white-tailed deer, and elk).  There is no evidence that scrapie or CWD are zoonotic diseases. 

 

Most veterinary laboratories dispose of tissues and prion-contaminated wastes by incineration, alkali hydrolysis, or a combination of both.  A small amount of prion-contaminated wastes, chiefly blood and fragments of tissue, enter necropsy drains during post-mortem examinations.  Most of this material is processed at publicly owned treatment works.  The insoluble, hydrophobic character of prions results in binding to particulates at all times – little or none remains in suspension.  Currently there is no way to test for prions in wastewater.

 

Recently, Region 8 of the Environmental Protection Agency addressed the issue of laboratory disposal of potentially contaminated wastes in meetings with diagnosticians, state veterinarians, and wastewater managers.  EPA region 8 prepared a draft policy (Discharges of Laboratory Waste to Publicly Owned Treatment Works (POTWs); January 10 2003) under the Industrial Pretreatment Program.  This region has declared its intention to impose strict controls on the discharge of prion-contaminated materials from veterinary laboratories.  In one instance, EPA Region 8 issued a cease-and-desist order to a Colorado Division of Wildlife necropsy facility that was testing deer for CWD.  Such a policy, if strictly enforced, will impose considerable costs on veterinary laboratories.  It may have impacts on current surveillance of hunter-harvested and sick deer that is necessary to establish the extent of CWD.  The cost of routine necropsies on cervid species that die of all causes in CWD-endemic areas will be increased.  The EPA has yet to perform a risk assessment to establish whether it is scientifically justified to impose a complete ban on prion-contaminated wastes in the sewer system.  A risk assessment performed in England in the context of BSE estimated that, with worst case assumptions, an individual would have to consume 2 liters/day of tap water for 45 million years to have a 50% chance of infection1  The cost of retrofitting veterinary laboratories to comply with the regulations is likely to be several hundred thousand dollars per laboratory.

 

Even in the absence of data that CWD and scrapie are transmissible to people, given current public and regulatory concerns it will be prudent for veterinary laboratories to develop the capability to capture and inactivate prion-contaminated wastes, particularly from necropsy floors.

 

1:  Gale, P, Young, C., Stanfield, G, Oakes, D.: 1998, Development of a risk assessment for BSE in the aquatic environment.  J Appl Microbiol 84: 467 – 477.