Chronic Wasting Disease (Professor)

Other TSEs: Scrapie

• Prototype 

  • Sheep & Goats 

  • Transmitted via fetal fluids (unique)

    • Most transmission occurs at birth 

    • Main route of transmission 

  • Causes pruritis, tremors, incoordination death

    • Pruritus: itchy  

  • 1st described in 1732 

  • Genetic resistance virtually complete

Other TSEs: Bovine Spongiform Encephalopathy

• Cattle 

  • Transmitted via consumption of ruminant protein 

    • Sheep &/or goat protein

  • Causes changes in behavior, abnormal posture, incoordination, death 

  • 1st observed 1984, described 1986

  • Genetic resistance? Not complete, may be partial

BSE

• Remains a significant “driving force” behind TSE panic 

• Only TSE known to be Zoonotic 

• Linked to vCJD

Human TSEs

• Creutzfeldt-Jakob Disease (CJD) -> normal, human disease 

  • Variant (CJDvar) linked to BSE

  • T-bone steak, vertebral (spinal cord) 

• Kuru (Papua New Guinea)

  • These tribes practiced cannibalism 

• Fatal Familial Insomnia 

  • Travels along genetic lineages 

• Others 

• All fatal 

• Genetics plays some role

Other TSEs:

• Transmissible Mink Encephalopathy 

  • Ranched mink; food-borne; 1947

  • Don't have this issue anymore 

• Feline Spongiform Encephalopathy 

  • Domestic & Captive Wildlife; food link, 1990 

• Exotic Ungulate Spongiform Encephalopathy (various other names)

  • Kudu, Nyala, Gemsbok, Eland, Oryx, Watusi; food link, 1990s 

• All fed ruminant proteins

• Other cervids susceptible to CWD:

  • Sika deer 

  • Red deer 

  • Axis deer 

  • Fallow deer may not be susceptible, more distantly related

  • All natural cases of CWD have been in cervids (deer family)

Early Signs of CWD

• Very subtle 

• Minor changes in behavior 

• Increased risk of trauma, predators 

  • Even if you can't see signs 

• Rough hair coat 

• CWD is SLOWLY progressive

Prevention of CWD

• No vaccines available; disease is inevitably fatal to infected cervids 

• Preventing exposure prevents disease (importation of cervids from CWD endemic areas) 

  • Live or dead 

  • If you have the brain and spinal cord, can still infect 

• Can’t stop natural migration

Genetic Resistance to CWD

• Some genotypes of deer and elk have a level of resistance to CWD 

  • May need a higher dose, may live longer once they get CWD

• Resistance genotypes may be less likely to become infected. If infected, disease course is protracted. All animals eventually die

Abundance of Caution

Most human health organizations advise against consuming meat from animals with a known TSE or from animals with neurologic signs

How CWD kills Cervids

• Direct mortality 

• Indirect mortality (more animals die from this)

  • Hunters 

  • Predators 

  • Trauma (HBC)

  • Secondary infections 

  • “Control” programs

Studies in WY & CO

• Cautionary tale 

  • Probably does have a population effect on deer and elk 

• CO & WY probably have had CWD for 20+ years before any other state 

• MAY indicate what might happen with other populations 

• Notably, some populations in CO/WY doing fine w/ CWD 

• NOT predictive

Table Mesa, CO Study

• Non-hunted Mule Deer population 

  • Problems with them overpopulating, hard to control them 

• Abundant habitat 

• High prevalence (41% males; 20% females)

• 1988-2006 declined 45%

• CWD associated with decline-but CASUAL relationship not proven 

• CWD dramatically reduced life expectancy 

  • Negative deer- 5.2 years 

  • Positive deer- 1.8 years 

• Mt. Lion Predation 4x higher for CWD+

Glenrock, WY study

• Hunted WTD population 

• High prevalence (29% males; 42% females)

  • Prevalence increasing 

• Well established herd, previously known for trophy bucks

Population Growth Rate (ƛ)

• Multiply by last year's population

• If ƛ=1 population is stable 

• If ƛ>1 population is growing 

• If ƛ<1 population is declining

Glenrock, WY results

• ƛ=0.8960 

• 10.4% annual population decline

• If nothing change will go extinct in 48 years 

  • Things can/will change

Are Glenrock, WY results due to CWD?

• Positives 4.5x more likely to die each year 

• ƛ=0.8960

  • ƛ for CWD neg=1.07 

  • ƛ for CWD pos=0.6805

• While above doesn't prove decline is due to CWD, it does indicate that w/o CWD population grows, w/ CWD population declines 

Will CWD impact cervid populations in TX?

• No evidence of large-scale impacts 

  • Yet?

• Many variables 

  • Animal density 

  • Genotypes 

  • Species 

  • Soil 

    • Especially Montmorillonite Clay, binds prions and keeps them available for animals to ingest 

  • Other diseases 

• No way to predict- but it is possible that there will be population impacts

How to minimize environmental contamination

• No CNS from endemic areas to new areas 

  • Bone out- or remove brain/spinal cord 

• Remove live sources of CWD prion 

  • Sacrifice known positives 

  • Sacrifice high-risk animals 

  • Require sequential live-animal tests on potentially-exposed cervids