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Prion Diseases. CMED 526/EPI 526 - May 6 th , 2009 Robert Harrington, DVM, PhD USDA – Agricultural Research Service UW – Dept. of Comparative Medicine rdhdvm@u.washington.edu. Transmissible Spongiform Encephalopathies~Prion Disease. NORMAL. ABNORMAL. PrP c. PrP d. -helix rich.

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Prion Diseases

CMED 526/EPI 526 - May 6th, 2009

Robert Harrington, DVM, PhD

USDA – Agricultural Research Service

UW – Dept. of Comparative Medicine

rdhdvm@u.washington.edu


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Transmissible Spongiform Encephalopathies~Prion Disease

NORMAL

ABNORMAL

PrPc

PrPd

-helix rich

-sheet rich

Prusiner, et al.


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PrP Conversion

PrPd

PrPc

Heterodimer


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TSE Pathogenesis

  • Transmission occurs by oral route

  • PrPd localizes to regional lymphoid tissue

    • Transient in some species

  • Migration to central nervous system

    • Retrograde along nerves

    • Blood-borne transport

  • Accumulation in brain with subsequent neurodegeneration


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Diagnosis

  • Postmortem

    • Microscopic pathology

    • Immunohistochemistry

    • ELISA, Immunoblotting

    • Bioassay

  • Antemortem

    • Same techniques as above applied to:

    • Brain biopsy

    • Tonsil, lymph node, third eyelid biopsy, or rectal

    • ? Blood test ?


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Histology

Figure 3: Photomicrographs illustrating increased diameter and density of vacuoles in TME positive IC recipient (top row, a, b, c), as compared to CWD positive IC recipient, (middle row, d, e, f) and absence of lesions in CWD negative IC recipient (bottom, row, g, h, i). Left column = cerebral cortex, middle column = hippocampus, right column = thalamus. All sections stained with hematoxylin and eosin. Bar=100 µm.


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Immunohistochemistry


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Western blot


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Animal Prion Disease

  • Scrapie - sheep, goats

  • Chronic Wasting Disease (CWD) - deer, elk, moose

  • Bovine Spongiform Encephalopathy (BSE) - cattle

  • Transmissible mink encephalopathy (TME) - mink

  • Feline spongiform encephalopathy - large & domestic cats

  • Spongiform encephalopathy of captive ungulates - exotic hoof-stock in zoological parks


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Human Prion Disease

  • Sporadic

    • Creutzfeldt-Jakob disease (CJD)

  • Familial (genetic)

    • Familial CJD

    • Gerstman-Straussler-Scheinker Syndrome (GSS)

    • Fatal Familial Insomnia (FFI)

  • Acquired by transmission

    • Kuru

    • Iatrogenic CJD (neurosurgical instruments, dura mater grafts)

    • Variant CJD (vCJD)


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Human PrP Mutations

Jackson, G S et al. Mol Pathol 2001;54:393-399


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Transmission Within Species

vertical and horizontal

in utero, fetal fluids, fetal membranes

COMMON

horizontal

Oral (urine, feces, or blood?)

Foodborne

Direct only through bite wounds

UNCOMMON

Foodborne (MBM)

No direct transmission

from cow to cow

Foodborne, blood,

tissue transplant, HGH, instruments


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Species Barrier Concept

  • Transmission within a species may occur readily

  • Barrier between species limits transmission

    • Inefficient transmission

    • Extended incubation times

    • Low or non-existent rate of disease

  • Serial passage

    • Required to overcome species barrier

    • Progressive reduction in incubation time

    • Increased rate of disease


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Transmission Between Species

SOURCE → → → → → → HOST ROUTE


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Recognition of BSE

  • Late 1985: Unusual neurologic disease in UK cattle

  • Insidious onset

    • Irritabilty, agression

    • Motor system impairment (ataxia)

    • Difficulty in rising (e.g. “downer cow”)

    • Decreased milk production

    • Wasting

    • Death

  • Predominantly dairy cattle

    • Feeding practices

    • Relative herd age

  • Neuropathology similar to Scrapie

    • Vacuolation, PrPd, astrocytosis, Scrapie associated fibrils


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Cause of BSE

  • Ruminant tissue in food chain

    • Meat and bone meal (MBM)

    • Scrapie

    • Sporadic BSE in cattle

  • Alternative theories

    • Human tissue?

    • Toxin?

    • Environmental?

    • Other?


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BSE Epidemic

  • ~180,000 cumulative cases in UK

  • Peaked at 37,000 cases per annum in 1992

  • Recycling of ruminant tissue in food chain implicated

  • Progressive decline with introduction of feed bans


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(mammals)

Transmissible Spongiform Encephalopathy as a Zoonotic Disease, Brown, P., et. al. ILSI, March 2003


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Spread of BSE Epidemic

  • 1990: Domestic BSE detected in Switzerland, imported cases in Portugal

  • 1999: 7 other EU countries with domestic BSE

  • Jan 2000 to Oct 2002: 11 additional EU countries

  • 2001: BSE detected in Japan

  • 2002: BSE detected in Israel

  • 2003: BSE in Canadian cow


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BSE in the United States

  • 30-40 million cattle slaughtered/year

  • 1997: ban on feeding US cattle meat-and-bone meal

  • 3 cases to date - RARE!

    • 2003: 6.5yo dairy cow imported from Canada

    • 2004: 12yo beef cow born and raised in Texas

    • 2006: 10yo beef cow in Alabama uncertain origin

    • Were there previously unrecognized cases?


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BSE in the United States

  • 2003: Additional measures post WA BSE case

    • “downer” cattle excluded from human consumption

    • Ban on SRM from animals >30 months of age from human consumption

    • Ban on mechanically-separated meat


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New variant CJD

  • Unusual form of neurologic disease in teenagers and young adults

  • Spongiform encephalopathy

  • Neuropathology not consistent with sporadic forms of CJD

  • Stimulus for US National Prion Disease Center


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Percent distribution of non-iatrogenic# UK vCJD and US CJD deaths, by age group, 1995-2005

+

# Excludes blood transfusion-associated vCJD and pituitary hormone- or dural graft-associated CJD

* UK vCJD deaths, including UK-related nonresident cases, 1995-2003 (Will, RG; personal communication, 2004)

** US CJD deaths, 1995- 2001.


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Western Blots

Jackson, G S et al. Mol Pathol 2001;54:393-399


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BSE-vCJD Link

  • New variant disease that differs from classical CJD

    • Similarities to BSE

    • Geographically related to areas of BSE

    • Hypothesis: consumption of contaminated beef products

  • Epidemiologic curve

  • Animal challenge studies

  • Molecular biology


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BSE and vCJD

Hilton, 2006. J of Pathology, 208:134


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Goldfarb, L. G. Microbes and Infection 4 (2002) 875-882


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Animal Challenge Studies

  • BSE → primates ≈ vCJD → primates

    • Similar lesions and biochemistry

  • Transgenic mice

    • BSE → humanized mice

    • vCJD → bovinized mice

    • Lesions, biochemistry of BSE ≈ vCJD regardless of mouse type

    • Both differ from sCJD


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Western Blots

Jackson, G S et al. Mol Pathol 2001;54:393-399


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Continuing US Cattle Surveillance

  • USDA National Veterinary Services Laboratory

    • AAVLD certified labs, refer positives to NVSL

  • If 1 case per 1 million slaughter then 95% CI requires:

    • All slaughters = 2,995,731

    • Suspect cattle = 40,000 (neuro signs, fallen, “downers”)

    • 45,803 samples in 2007

    • Meets OIE “controlled risk” classification

  • National animal ID system


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Continuing US Human Surveillance

  • National Prion Disease Center

    • Established 1996

  • Monitoring for unusual trends in mortality data

  • ↑ # of autopsies in US, ↑ # of referrals

  • CJD monitoring in CWD endemic areas


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CWD to Humans?

  • CJD flatline in endemic areas

  • Challenge studies indicate natural transmission is unlikely

    • Cattle

    • Mink

    • Humanized Tg mice


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CWD risk reduction?

  • Hunting

    • Avoid endemic areas

    • Test animals in effected areas

  • Consumption

    • Don’t eat brain, nerves, spleen, lymph nodes, or eyes

    • Avoid composite foods (sausage, head cheese)


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Conclusion

  • Prion diseases vary by species, distinct differences

  • TSE transmission usually limited to within a species

  • Only Scrapie and CWD are readily transmissible

  • Species barrier limits transmission between species


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Questions?


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Do you think this study supportsthe association of beef consumption as a primary risk factor for development of vCJD?


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Did the study authors take adequate measures to address the limitations to the study design?What other measures could they have considered?


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Are there other ways that the question of risk factors for vCJD may be addressed?


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