Part II: Transmissible Spongiform Encephalopathies TSEs With special emphasis on bovine spongiform encephalopathy BSE

1. 1 Part II: Transmissible Spongiform Encephalopathies (TSEs) With special emphasis on bovine spongiform encephalopathy (BSE) and variant Creutzfeldt-Jakob disease (vCJD) Ben Sun, DVM, MPVM

2. 2 Transmissible Spongiform Encephalopathies (TSEs) Infectious fatal neurodegenerative disorders Transmissible agent unknown Most widely accepted theory is that TSEs are caused by a modified form of a normal cellular glycoprotein called a prion protein

3. 3 Prions Normal protein (PrPc) in mammals, coded for by the PRNP gene PrPSc same primary structure but structurally aberrant Resistant to proteases and other agents PrPSc converts PrPc to PrPSc Accumulation of PrPSc in CNS causes disease Little is known about prion infectivity in peripheral tissues

4. 4 Prions Smaller than most viral particles HIGHLY resistant to heat, UV light, ionizing radiation, disinfectants Causes no detectable immune or inflammatory response Has not been observed microscopically

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11. 11 Prion diseases of humans Sporadic (>85%) Creutzfeldt-Jakob disease (CJD) Sporadic fatal insomnia Genetic (<15%) Familial CJD (fCJD) Gerstmann-Str�ussler-Scheinker syndrome (GSS) Fatal familiar insomnia Environmental / Iatrogenic (<1%) In about 85% of CJD patients, it occurs as a sporadic disease with no recognizable pattern of transmission. In 5-15% of patients, there is an inherited mutation of the prion protein gene. These inherited forms include GSS and fatal familial insomniaIn about 85% of CJD patients, it occurs as a sporadic disease with no recognizable pattern of transmission. In 5-15% of patients, there is an inherited mutation of the prion protein gene. These inherited forms include GSS and fatal familial insomnia

12. 12 Environmental/Iatrogenic CJD Kuru � ritual cannibalism of deceased relatives New variant CJD (vCJD) Contaminated human growth hormone Grafts Cornea Dura mater Contaminated equipment EEG electrodes Neurosurgical instruments

13. 13 Sporadic CJD (CJD) Rapidly progressive, fatal neurodegenerative disease Age at onset is 55-75 y.o. (median 68 y.o, mean 61 y.o.) Incidence of 1 � 1.5/million per year ~300 cases per year in the U.S. 6000 cases worldwide Great mimicker � resembles many other diseases

14. 14 Animal TSEs Bovine spongiform encephalopathy of cattle (aka Mad Cow Disease) Scrapie of sheep and goats Chronic wasting disease of deer and elk (in western U.S.) Transmissible mink encephalopathy Feline spongiform encephalopathy

15. 15 Diagnostics for TSEs No test is highly sensitive or specific Only definitive test is post-mortem pathology Criteria developed for clinical diagnosis of probable vCJD Confirmation requires neuropathology Only definitive test is post-mortem pathology

16. 16 BSE Progressive degeneration of the nervous system Affected cattle show Nervousness and aggression Incoordination Death Incubation period is 2-8 years No antemortem test

17. 17 Origin of BSE Still unclear, but� Appears to have originated from scrapie, an endemic TSE recognized since mid-18th c. Rendered carcasses of livestock (including sheep) fed to cattle as protein-rich nutritional supplement In 1980, change in rendering process allowed etiologic agent to survive

18. 18 Origin of BSE (continued) Cattle were infected through ingestion Cattle carcasses were recycled through rendering plants, amplifying the cattle-adapted pathogen First verified case of BSE in the UK in 1986; outbreak peaked in 1993 In the end > 180,000 infected cattle Slaughter of 4.5M cattle >30 months old Preemptive slaughter of 4.5 million cattle over 30 months of agePreemptive slaughter of 4.5 million cattle over 30 months of age

19. 19 BSE epidemic curve in the U.K.

20. 20 BSE to other species BSE infected tissues and meat-and-bone-meal fed to exotic zoo ungulates and cats TSEs identified in these species Feline spongiform encephalopathy BSE can therefore cross species barrier Could it infect humans?

21. 21 Protective measures in the U.K. Ban on ruminant protein in ruminant feed (1988) Ban on specified bovine offal (SBO) in animal feed (1990) SBO: brain, spinal cord, spleen, thymus, tonsil, part of intestinal tract Pre-emptive slaughter of 4.5 million cattle >30 months of age Exclusion of animals >30 m.o. from food chain Surveillance unit to monitor CJD (1990) (SBO includes brain, spinal cord, spleen, duodenum to rectum of intestine, thymus and tonsil) banned from cattle feed in 1989(SBO includes brain, spinal cord, spleen, duodenum to rectum of intestine, thymus and tonsil) banned from cattle feed in 1989

22. 22 Link to vCJD In 1995, the CJD Surveillance Unit was notified of 3 cases of CJD Patients were 16, 19 and 29 y.o., which is younger than sporadic CJD patients Neuropathologic examination revealed amyloid plaques which occur in only 5-10% of sporadic CJD By January 1996, additional cases identified and distinctive clinical syndrome was beginning to emerge

23. 23 BSE link to vCJD Spatial-temporal clustering of vCJD Transmission of BSE to macaques looked like vCJD pathologically (Nature 1996;381:743-4.) Western blot analysis of prions from 10 vCJD patients and BSE cases had similar molecular characteristics distinct from prions from other types of CJD (Nature 1996;383:685-90.)

24. 24 vCJD Young age at onset Early psychiatric symptoms Absence of periodic electroencephalographic activity Comparatively prolonged illness Believed due to ingestion of beef products contaminated by nervous system tissue

25. 25 Sporadic CJD vs. vCJD

26. 26 Incubation period Unknown From iatrogenic CJD (transmission from human growth hormone), incubation is 13 years Could potentially see many more cases of vCJD

27. 27 vCJD surveillance As of December 1, 2003, 153 cases in the world 143 from the U.K. 6 from France 1 each from Canada, Ireland, Italy and the U.S. (the U.S. case lived in the U.K. prior to moving to U.S.) All cases have history of exposure to country with BSE

28. 28 Where has BSE been identified? France Portugal Germany Spain Switzerland Netherlands Belgium Republic of Ireland Japan Israel Denmark Italy Canada (2003) United States (2003) Others

29. 29 Protective measures in the U.S. BSE surveillance system Downer / neurologic animals tested (~20,000/yr) BSE made notifiable Ban on mammalian protein in ruminant feed (FDA regulation, 1997) Ban on importation of live ruminants and high-risk products (including all rendered products) from BSE-affected countries Ban blood donations from anyone who has been in the UK for a cumulative period of =6 months during 1980 to 1996

30. 30 vCJD surveillance in the U.S. Death certificate information Actively investigate possible CJD/vCJD cases CEIP CJD surveillance project (<55 y.o.) National Prion Disease Pathology Surveillance Center at Case Western Reserve University (CDC and American Association of Neuropathologists) Performs special diagnostic tests including post-mortem tests

31. 31 Active surveillance for CJD in CA California Creutzfeldt-Jakob Disease Surveillance Project Mortality review of death certificate data Follow-up investigation of medical records in CJD-related deaths in persons under 55 years or who have a possible environmental or unusual source of exposure For 1996-2000 18 CJD-related deaths were identified No evidence of vCJD

32. 32 Passive surveillance for CJD in CA Health care providers and local Health Officers asked to report < 55 years old Clinical history suspicious for vCJD History of deer or elk consumption from area with CWD Known high-risk iatrogenic exposure

33. 33 BSE in the U.S. December 23, 2003, the USDA announced a presumptive diagnosis of BSE in cow from Washington state Samples taken December 9 as part of BSE surveillance system BSE confirmed by international reference laboratory in Weybridge, England on December 25

34. 34 BSE-positive cow Cow imported from Canada in 2001 6.5 years old, so born before ban on ruminant-derived protein Is this an isolated case? Where are the other cows in the herd that was imported from Canada? Where are her offspring?

35. 35 Protective measures in response to U.S. BSE case Elimination of all downer animals from food chain USDA will withhold �inspected and passed� mark until negative BSE test results are received for any animal tested Specified risk materials (SRM) banned from food chain SRM: skull, brain, trigeminal ganglia, eyes, vertebral column, spinal cord and dorsal root ganglia of cattle > 30 months and distal ileum of the small intestine of all cattle An interim final rule declaring that the Specified Risk Materials, theskull, brain, trigeminal ganglia, eyes, vertebral column, spinal cord anddorsal root ganglia of cattle 30 months of age or older, and the smallintestine of all cattle are prohibited in the food supply. (Tonsils werealready excluded). These prohibitions will be effective immediately uponpublication in the Federal Register.An interim final rule expanding on the prohibition of central nervoussystem tissues in advanced meat recovery products.A final rule to prohibit air injection stunning.A notice announcing that FSIS inspectors will not mark ambulatory cattlethat have been targeted for BSE surveillance testing as "inspected andpassed" until negative test results are obtained.USDA continues to work to develop the details of its BSE surveillanceprogram. This includes determining how samples from high-risk (whichincludes non-ambulatory) animals will be collected at sources other thanslaughter. USDA is working to have access to those animals at renderingfacilities and other establishments. USDA also looks forward to receivingrecommendations regarding the U.S. BSE surveillance program from theinternational review team that is expected to convene later this month[January 2004]. Traceback to herd of origin and herdmates Traceback of cow�s offspring An interim final rule declaring that the Specified Risk Materials, theskull, brain, trigeminal ganglia, eyes, vertebral column, spinal cord anddorsal root ganglia of cattle 30 months of age or older, and the smallintestine of all cattle are prohibited in the food supply. (Tonsils werealready excluded). These prohibitions will be effective immediately uponpublication in the Federal Register.

36. 36 Additional issues Advanced meat recovery (AMR) systems Modify the BSE surveillance system? ~20,000 cattle/year is small proportion Some countries (i.e. Japan) test ALL animals Some countries test proportion (e.g. 5%) of healthy animals going to slaughter Huge economic losses to cattle industry National animal identification system

37. 37 What is the risk?

38. 38 What is the risk? Meat and bones from the lot containing the BSE-positive cow distributed to OR, WA, CA, ID, MT and NV 9 California counties USDA says zero-risk USDA issues voluntary recall of meat Many countries ban American beef

39. 39 What is the risk? Despite >180,000 infected cattle in UK, only 143 cases of vCJD have been identified Species barrier Met / met homozygosity at codon 129 of the PRNP gene in all vCJD patients Unknown infectious dose Presence in muscle? Species barrier provides substantial but imncomplete protection against development of vCJDSpecies barrier provides substantial but imncomplete protection against development of vCJD

40. 40 Prions in skeletal muscle Bosque PJ, et al. PNAS. 2001(99):3812-3817. Mouse skeletal muscle shown to propagate and accumulate prions Varies with PrP gene presence in muscle What is reality in livestock? Premise for new diagnostic test? Glatzel M, et al. NEJM. 2003(349):1812-1820. 8 of 32 vCJD patients had PrPSc in skeletal muscle samples

41. 41 Prions in tongue Prions injected into hamster brains traveled to tongue and accumulated to high levels Rapid neuroinvasion following experimental tongue infection in hamsters Bartz, JC, et al. Journal of Virology, 2003(77): 583-591.

42. 42 Are prions transmissible in blood? Experimental transmission in sheep Positive transmissions occurred with blood drawn at pre-clinical and clinical stages of infection Hunter N, et al., Journal of General Virology. 2002(83):2897-2905. Possible transfusion transmission in human 2003 vCJD patient was transfused with blood from pre-clinical vCJD patient Nature News, December 22, 2003.

43. 43 Other concerns Safe use of medical and surgical instruments, especially those used in neurosurgery and ophthalmic surgery What about vaccines, cosmetics and gelatin? Animal identification scheme so tracebacks are quickly possible Distribution of meat to retail outlets

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48. 48 TSE References http://www.ceip.us/html/cjd.htm http://www.cdc.gov/ncidod/diseases/cjd/cjd.htm http://www.aphis.usda.gov/lpa/issues/bse/bse.html http://www.cjdsurveillance.com/

49. 49 Mad cow questions?