Chronic Wasting Disease (CWD)

What are Prion Diseases?

• Transmissible spongiform encephalopathy (TSE)

  • Transmissible- can be spread 

  • Spongiform- looks like a sponge 

  • Encephalopathy- conditions that affects bran function 

• Caused by a misfolded normal cellular prion protein- PrP^c -> PrP^Sc (infectious form)

  • Increased beta sheets

Common Prion Diseases

• Humans- Creutzfeldt-Jakob Disease (CJD)

• Ovines- Scrapie (sheep)

• Bovines- Bovine Spongiform Encephalopathy (BSE) “Mad Cow Disease”

• Felines- Feline Spongiform Encephalopathy 

• Cervids- Chronic Wasting Disease (CWD)

Species Affected by CWD

History of CWD

• 1979: U.S. established endemic zone 

• 1981: first case outside of the U.S.& first case in a wild herd population

CWD Signs

• Incubation time: 3 months - 4 years 

  • Varies depending on route of exposure or infectious dose 

• Observations based off captive animals 

• Easier to detect signs in deer compared to elk because of their natural behavioral patterns 

  • Elk tend to not show how much they’re sick compared to deer 

• Early signs: Dullness in eyes and diminished alertness 

• Progressive neurodegeneration- build-up of prions form sponge-like holes in brain tissue 

• Late-stage Clinical Signs: 

  • Weight loss

  • Behavioral changes 

  • Lowered head 

• Variable Signs: (may not be seen in every case)

  • Sialorrhea- excessive drooling 

  • Ataxia- loss of coordination, stumbling 

  • Polydipsia- excessive, persistent fluid intake 

    • More common in deer than elk 

• Signs last weeks to months before becoming fatal 

  • Slow progressing disease

Transmission

• Horizontal transfer between cervids 

  • Direct and indirect contact 

  • Protein sheds in secretions/excretions and decaying carcasses 

• Prions may persist in environment up to 15 years

  • Because of extra beta sheet folding, they are much harder to destroy  

• Vertical transmission also possible 

• Most-commonly reported in animals 3-7 years old 

  • Because signs take so long to show up

CWD Transmission

Transmission 2

• Risk for Livestock? 

  • Cattle only developed disease after intracerebral inoculation (directly into brain)

  • Not after oral or contact exposure to CWD infected deer

    • Not a risk for livestock, have their own version of the disease 

• NOT zoonotic 

  • Humans exposed through consumption of infected meat products- no major outbreaks

Prevalence

• Dense free-ranging populations: up to 30%

• Captive: up to 100%

Diagnosis

• 31 approved labs 

• Immunohistochemistry (IHC)

  • Gold-standard

• ELISA 

  • Faster and cheaper 

  • Typically used for surveillance 

• Western Blot 

• Lymph nodes or brainstem collected for testing 

  • Many guides online for how hunters should collect samples 

• Currently no widespread testing for live animals

Treatment and Prevention

• No treatment or vaccines available 

  • Extremely robust prions 

    • Resistant to heat, bleach, enzymes, etc.

    • *bleach works as a surface decontaminant 

• 100% fatal 

• Prevention strategies: Federal + State Level 

  • Regulating movement of captive cervids 

  • Proper disposal of carcasses 

  • Monitoring movement of free-ranging herds 

  • Regulatory testing 

  • Depopulation

Management: USDA-APHIS CWD Voluntary Herd Certification Program (HCP)

• Cooperative effort between APHIS, state agencies, and cervid owners 

• Goal: prevent spread of CWD between states 

• National interstate movement requirements for cervids 

• Herd Certification Program (HCP): 

  • Fencing regulations 

  • Individual animal IDs

  • Inventory and testing of animals that die (>12 months) for any reason 

• 28 participating states

State Agency Management:

• History 

• How to test 

  • Where?

  • Sample collection guides 

  • CWD test results 

• Hunting Regulations and Carcass Disposal Requirements 

• Management zones with special restrictions/regulations 

• Monitoring Programs 

• Initial Detection of CWD: 

  • Majority from hunter-harvested samples 

  • Secondary-testing suspected CWD animals 

• Initial responses to CWD: 

  • Communication: public service announcements, education, stakeholder meetings

  • Mandatory testing of deer harvested in designated zones 

  • Increased regulations of deer movement, baiting/feeding, and deer hunting 

• Management 

  • ~50% of agencies began localized culling in affected area 

    • May have increased harvest opportunities for culling of free-ranging herds 

  • Privately owned herds may be provided compensation

State Agencies Managing without CWD:

• Nevada has NEVER had a reported case of CWD 

• Extensive resources online to ensure prevention of CWD in their state 

• Implementing stricter regulations when CWD cases appear close to their state border

Texas Impacts

• 1st discovered in Texas in 2012 in free-ranging mule-deer

• Severe Economic Impacts on: 

  • Ranching 

  • Hunting 

  • Wildlife management 

• Monitoring and Prevention 

  • Education programs 

  • Free CWD Sample Kits

 Why is this Important?

• Inconsistent management strategies across states 

  • Hard to work together for nationwide prevention 

  • Every state has their own ideas on how to monitor CWD

• Population Level Impacts 

  • 100% fatal, no treatment, no vaccines 

• Economic Impacts:

  • Decreased hunting demand where CWD spikes 

    • Decreased tourism revenue from nonresident deer hunters 

    • Less money for conservation and management 

  • Captive cervid Herds 

    • Animal loss 

    • Private hunting operations