Evaluation of the Potential for BSE in the United States

1. Evaluation of the Potentialfor BSE in the United States Joshua T. Cohen Keith Duggar George M. Gray Silvia Kreindel Harvard Center for Risk Analysis Harvard School of Public Health Hatim Abdelrahman Tsegaye HabteMariam David Oryang Berhanu Tameru Center for Computational Epidemiology College of Veterinary Medicine Tuskegee University

2. What USDA Asked Us to Do • Identify and characterize possible sources for BSE (or a TSE disease with similar clinical and pathologic signs as BSE - will refer to as BSE for brevity) infectivity in U.S. cattle • Identify and characterize pathways for cattle-derived BSE infectivity in the U.S. cattle herd or human food supply • Evaluate implications over time of possible introduction of BSE into US system

3. How We Got Involved • HSPH/HCRA • Group with long history in risk analysis of hazards to human health and the environment • Expertise in methods of risk analysis • Multidisciplinary approach • TU/CCE • Expertise in the integration of quantitative modeling, expert systems and operations research methods in studying the epidemiology of health systems • Strong record of work on animal health issues

4. Our Approach • Understand the science • Describe potential pathways of BSE infectivity to U.S. herd or food supply • Build quantitative model • Characterize the response of the US system BSE

5. BSE Cattle Learning from UK Experience We assume the prevailing hypothesis of UK BSE spread is correct: Scrapie? Feed Rendering Spontaneous?

6. Simulation Overview Infectivity Sources Cattle Population Number Infected Number Clinical Death and Disposal Feed Administered to Cattle Slaughter Disposal Human Food Death and Rendering Rendering and Feed Production Other Uses and Elimination from System Other Protein Sources

7. Important Attributes of Model • Built up from knowledge of science and agriculture system • Probabilistic - results are distributions • Infectivity characterized as cattle oral ID50s • Characterize average situation across the US

8. Key Assumptions

9. Key Assumptions Relationship between time since infection and the fraction of maximal level of ID50s

10. A n t e m o r t e m S t u n n i n g E x s a n g u i n a t i o n D i s p o s i t i o n o f S i c k A n i m a l I n s p e c t i o n B r a i n C h a r a c t e r i s t i c s 3 . 1 . 2 . 2 3 . 1 . 2 . 3 3 . 1 . 2 . 4 3 . 1 . 2 . 5 3 . 1 . 2 . 1 P o s t m o r t e m S p l i t t i n g 3 . 1 . 2 . 6 T i s s u e s t o r e n d e r i n g The Slaughter Process Out Out Out A M R / S p i n a l T i s s u e s f o r C o r d / D R G P o s s i b l e H u m a n 3 . 1 . 2 . 7 C o n s u m p t i o n I n s p e c t i o n 5 . 2 . 1 0 3 . 1 . 2 . 9 P r o c e s s i n g 3 . 1 . 2 . 9 Out Out

11. Analyses • Base Case • Assume BSE not currently present in US • Introduce 10 BSE infected animals (also simulated importation of 1 to 500 BSE infected cows) • Follow for 20 years • Example Risk Management Options • Ban on rendering cattle that die on farm • UK-style “Specified Risk Material” ban • Test with introduction of 10 infected animals and follow for 20 years • Others • Potential for pre ‘89 imports from England to introduce BSE to US • Switzerland • Spontaneous • Scrapie as source

12. Results: Introduction of 10 Infected Cattleafter 20 Years • Few new cases of BSE (mean 2.9, 95th 11) • Primarily through feed ban leaks • 40% of animals predicted to die on farm introduce 96% of infectivity to system • BSE gone within 20 years of introduction • Little infectivity for potential human exposure (mean 35 cattle oral ID50s , 95th 170) • Brain 26% • Beef on bone 11% • AMR meat 56% • Spinal Cord 5% • Conservative assumptions (e.g, no change if case detected)

17. Other Importations

18. Key Uncertainties

19. Results: Risk Management Options • Evaluate 2 potential risk management options - test with 10 imported BSE cows • UK-style ban on specified risk material (brain, spinal cord, etc) in human and animal food • Reduces BSE cases by 80% • Reduces potential human exposure by 95% • Ban on rendering cattle that die on the farm • Reduces BSE cases by 77% • Reduces potential human exposure by 20% • Managing risk upstream makes feed ban compliance less important

24. Imports from England before 1989 • Evaluated potential for 173 (of 334) English imports not known to have been destroyed to introduce infectivity to US cattle and implications • Used information on birth year, export year, animal type and sex, last sighting and more to estimate likelihood and potential magnitude of introductions of BSE infectivity to US cattle feed • Used model to look at new BSE cases if introduction of different sizes did occur

25. Results: Introduction of Infectivity through UK Imports • 82% chance of no introduction • Most introduction give no new cases • Surveillance rules out big introductions • If introduced, is on course for elimination

26. Cumulative Distribution for U.S. Cattle Exposure to Cattle Oral ID50s from Animals Imported from England during the 1980s

27. Cumulative Distribution for the Number of BSE-Clinical Cattle in the Year 2000 for Different Levels of Infectivity Introduced via Import of UK Cattle During the 1980s

28. Other Results: • Switzerland • Test of model plausibility • Reasonably reproduces time course and size of Swiss BSE outbreak • Spontaneous • If true would result in mean of 2 cases per year and <100 cattle oral ID50s to humans over 20 years • Test in absence of feed ban casts some doubt of plausibility of this hypothesis • Scrapie • If transmission possible (no American scrapie can infect cattle) predict mean of 2 BSE cases/yr • <100 cattle oral ID50s to humans over 20 years

29. Summary • We have assessed the potential for BSE/TSE infectivity to spread in the US dairy/beef cattle population and in the U.S. food supply if it were to arise here • We have constructed a simulation model to explore the dynamics of BSE following an introduction and to quantitatively evaluate the relative risk of specific pathways

30. Summary • We find that the US is highly resistant to BSE and any plausible introduction yields few new cases of disease and dies out within 20 years. Human exposure to infectious cattle tissues is quite low • Spread in cattle herd • Mostly due to leaks in FDA feed ban and some maternal transmission • Animals that die on farm with provide greatest infectivity to animal feed system • Potential human exposure • Handling of brain and spinal cord in processing very important • Primary routes of exposure are cattle brain, spinal cord, beef on bone and AMR meat

31. Summary • Cattle imported from UK between 1980 and 1989 have small chance of having put BSE into US herd - would be on the way to elimination if introduced • Our approach supported by ability to reasonably mimic Swiss BSE outbreak • Cross-species transmission of Scrapie or Spontaneous BSE, if real would result in a couple of cases of BSE and fewer than 5 cattle oral ID50s for potential human exposure each year • Our model is useful for evaluating potential further risk management strategies

32. Thank You!