Chronic Wasting Disease - Harley

What are prion diseases?

1. Transmissible spongiform encephalopathy (TSE)

   1. Transmissible - can be spread

   2. Spongiform - looks like a sponge (makes hold in brain tissue)

   3. Encephalopathy - conditions that affects brain function

2. Caused by a misfolded normal cellular prion protein

   1. PrPc —> PrPsc

HIstory

1967: CWD 1st discovered in CO research mule deer herd, mistaken for malnutrition

1978: CWD confirmed a TSE

1979: found in CO and WY captive facilities, endemic established

1981: CO - 1st case in wild elk

2001: Wild WTD in South Dakota - spreading outside endemic zone in US

2025: 36 states with reported CWD

Common prion disease

1. Humans - creutzfeldt-jakob disease (CID)

2. Ovines - scrapie

3. Bovies - Bovine spongiform encephalopathy (mad cow disease)

4. Felines - Feline spongiform encephalopathy

5. Cervids - chronic wasting disease (CWD)

Species affected by chronic wasting disease

1. White-tailed deer

2. Elk

3. Mule deer

4. Moose 

5. Caribou

6. Muntjac (only experimentally infected)

CWD signs

1. Incubation time: 3 months - 4 years

   1. Varies depending on route of exposure or infectious dose

2. Observations based off captive animals

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

4. Early signs: dullness in eyes and diminished alertness

5. Progressive neurodegeneration – build-up of prions form sponge-like holes in brain tissue

6. Late stage signs:

   1. Weight loss

   2. Behavioral changes

   3. Lowered head

7. Variable signs

   1. Sialoorhea

   2. Ataxia

   3. Polydipsia

8. Signs last weeks to months before becoming fatal

Transmission

1. Horizontal transfer between cervids

   1. Direct and Indirect contact

   2. Protein sheds in secretions/excretions and decaying carcasses

2. Prions may persist in environment up to 15 years

3. Vertical transmission also possible

4. Most-commonly reported in animals 3-7 years old

5. Risk for livestock?

   1. Cattle only developed disease after intracerebral inoculation

   2. Not after oral or contact exposure to CWD infected deer

6. NOT zoonotic

   1. Humans exposed through consumption of infected meat products – no major outbreaks

Prevalence

1. Dense free-ranging populations: up to 30$

2. Captive up to 100% 

3. Quite a lot

Diagnosis

1. 31 approved loans

2. Gold standard: immunohistochemistry (IHC)

3. ELISA

   1. Faster and cheaper

   2. Typically used for surveillance

4. Western Blot

5. Lymph nodes or brainstem collected for testing

6. Currently no widespread test for live animals

Treatment and Prevention

1. No treatment or vaccines available

   1. Extremely robust prions

2. 100% fatal

3. Prevention strategies: Federal + state level

   1. Regulating movement of captive cervids

   2. Proper disposal of carcasses

   3. Monitoring movement of free-ranging herds

   4. Regulatory testing

   5. Depopulation

Management: USDA-APHIS CWD voluntary herd certification program (HCP)

1. Cooperative effort between APHIS, state agencies, and cervid owners

2. Goal: prevent spread of CWD between states

3. National interstate movement requirements for cervids

4. Herd certification program (HCP):

   1. Fencing regulations

   2. Individual animals IDs

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

State agency management:

1. Initial detection of CWD:

   1. Majority from hunter-harvested samples

   2. Secondary – testing suspected CWD animals

2. Initial responses to CWD:

   1. Communication: public service announcements, education, stakeholder meetings

   2. Mandatory testing of deer harvested in designated zones

   3. Increased regulations of deer movement, baiting/feeding and deer hunting

3. Management

   1. ~50% of agencies began localized culling in affected areas

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

State agencies managing without CWD:

1. Nevada has never had a reported case of CWD

2. Extensive resources online to ensure prevention of CWD in their state

3. Implementing stricter regulation when CWD cases appear close to their state border

Texas Impacts

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

2. Severe economic impacts on

   1. Ranching 

   2. Hunting

   3. Wildlife management

3. Monitoring and prevention

   1. Education programs

   2. Free CWD Sample Kits

Why is this important?

1. Inconsistent management strategies across states

   1. Hard to work together for nationwide prevention

2. Population level impacts

3. Economic impacts

   1. Decreased hunting demand

   2. Decreased tourism revenue from nonresident deer hunters

   3. Less month for conservation and management

4. Captive cervid herds

   1. Animal loss

   2. Private hunting