General Environment Changes, Cleaning and Disinfection

• There is the potential for CWD to be transmitted via a contaminated environment; disinfection of the environment is an important consideration for this disease.
• To date efforts at disinfection of sites which have been heavily contaminated have been unsuccessful. It is unclear what factors may have been responsible for these failures.
• For disinfection of implements that may have been contaminated, such as knives used in butchering deer, sodium hypochlorite (household bleach at greater than 2% free chlorine, diluted one part bleach to four parts water, at room temperature for one hour) or sodium hydroxide (caustic soda, soda lye, at 38 g per litre of water at room temperature for one hour) are recommended as disinfectants.
• It should be noted that there are considerable concerns regarding the complete assurance of decontamination of objects which may have become contaminated with TSE agents (for this reason it has been suggested that surgical instruments used in operations involving the brain, spinal cord or eyes of persons known or suspected to have CJD should be discarded).

Limited data on other TSE diseases is provided in literature reports below the information on CWD. Information on these diseases within the "Chronic Wasting Disease of Deer and Elk" volume of Wildpro is provided for comparative purposes and is not intended to be comprehensive.

• In one captive breeding facility: depopulation, removal of soil to a depth of one foot (30 cm), plowing of the ground, spraying of hypochlorite (Clorox) over the whole area and leaving the facility empty for one year. The disease reappeared following repopulation of the facility with deer and elk. The source is unclear. [It is not known whether one or more of the animals which were used to repopulate the facility was infected when brought into the facility or whether the disinfection used had been insufficient]. (J237.43.w1). 
• The Kremmling Research Facility and the Foothills Wildlife Research Station were depopulated, sprayed at an application rate of 1,000 ppm with a 65% active chloride solution by mobile sprayer and by helicopter and an external fence, eight feet (2.44 m) high, was constructed before reintroduction of big game cervids was begun with 12 elk calves for hand rearing. Materials for the construction of the elk rearing units were acquired from dismantled pens from the Fort Collins Research Center [what if any disinfection was employed on these pens prior to their use was not stated]. [It is not known whether one or more of the animals which were used to repopulate the facility was infected when brought into the facility or whether the disinfection used had been insufficient]. (N9.1985.w1, N9.1986.w1)
• Depopulation and disinfection (Fort Collins facility, Colorado). All deer and elk were killed and buried on site, the soil was turned, the structures and pastures were sprayed repeatedly with calcium hydrocloride and the area kept cervid-free for a year before restocking with elk calves hand-reared using evaporated milk but no other sources of animal protein. Two of 12 animals developed CWD at three to four-and-a-half years old. The source of infection was unknown; it is possible that the calves were already latently infected on arrival as they had been collected from a region in which cases of CWD were recognised subsequently.(J64.11.w3)
• CWD recurred in a facility following complete depopulation and subsequent repopulation with animals from a certified CWD-free herd. (P41.18.w1)
• Sodium hypochlorite may be used for disinfection (household bleach, greater than 2% free chlorine, 280 ml in 720 ml of water at room temperature, for one hour). This solution may be corrosive to metal utensils (J40.66.w1)
• Sodium hydroxide may be used for disinfection (caustic soda, soda lye, at 38g in one litre of water at room temperature for one hour). This solution may be corrosive to metal utensils (J40.66.w1)
• In Canada, for premises where environmental contamination is thought to have been only minimal (only one or two clinical cases, over a short period of time, with the affected animal(s) probably having acquired the infection elsewhere), the measures taken for disinfection have included scraping off soil and manure to a depth where the soil is undisturbed, or deeper if an affected animal spent a considerable length of time in one place, with new material added to form a barrier over the remaining soil. All facilities and equipment exposed to clinically-affected animals are cleaned of organic material before being disinfected by soaking for one hour in sodium hydroxide or sodium hypochlorite. The removed soil/manure is buried to ensure no access to animals. (P41.18.w1)
• "A major concern with CWD is the potential for indirect transmission through contamination of the environment through excretions, secretions, or the decomposition of infected animal carcasses. Management plans need to provide for decontamination as research provides tools and approaches." (D110.w3)
• The approach for adequate cleaning and disinfection of premises contaminated with CWD agent is not known, nor have techniques been developed to measure the level of CWD agent in the environment." [2003] (P50.1.w7)

Other TSE Diseases

• "Prions are inactivated by 1N NaOH, 4.0 M guanidinium hydrochloride or isocyanate, sodium hypochlorite (2% free chlorine concentration), and steam autoclaving at 132°C for 4.5 h. It is recommended that dry waste be autoclaved at 132°C for 4.5 h or incinerated. Large volumes of infectious liquid waste containing high titers of prions can be completely sterilized by treatment with 1N NaOH (final concentration) or autoclaving at 132°C for 4.5 h. Disposable plasticware, which can be discarded as a dry waste, is highly recommended. Because the paraformaldehyde vaporization procedure does not diminish prion titers, the biosafety cabinets must be decontaminated with 1N NaOH, followed by 1N HCl, and rinsed with water. HEPA filters should be autoclaved and incinerated." (D131)

Scrapie:

• Control and eradication of scrapie is hindered by "lack of knowledge on how to properly rid a natural environment of scrapie contamination.". (J64.11.w4)
• On a number of occasions it has been shown with sheep flocks that depopulation followed by restocking has, after a period of time, resulted in reappearance of scrapie and a progressive increase in incidences thereafter. It was noted that this was the case particularly with lowland farms using intensive grazing rather than with sparsely stocked hill farms "on which the chance of contracting infection from the pasture would be much reduced." (J35.96.w1)

Creutzfeldt-Jakob Disease (CJD):

• It has been recommended in the UK, due to the difficulty of complete assurance of decontamination, that instruments which have been used in neurosurgery or ophthalmology of patients with known or suspected CJD, or at risk of developing CJD (e.g. individuals who have previously received cadaveric human growth hormone or dura mater), should be destroyed rather than decontaminated and re-used. (B297.6.w6)