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Canadian and U.S. BSE Risk Steven Anderson, Ph.D, MPP Office of Biostatistics & Epidemiology Center for Biologics Evaluation & Research U.S. Food & Drug Administration TSE Advisory Committee February 12, 2004 Policy questions for BSE in North America

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canadian and u s bse risk

Canadian and U.S. BSE Risk

Steven Anderson, Ph.D, MPP

Office of Biostatistics & Epidemiology

Center for Biologics Evaluation & Research

U.S. Food & Drug Administration

TSE Advisory Committee

February 12, 2004

policy questions for bse in north america
Policy questions for BSE in North America
  • What is the BSE risk for the U.S. and Canada?
    • Part I - Estimating BSE risk: Potential exposure pathways in U.S. and Canada
  • What is the risk for the general U.S. population? What are the implications for the blood supply?
    • Part II – Estimating BSE exposure and risks in the U.S.
part i estimating bse risk potential exposure pathways in u s and canada
Part I – Estimating BSE risk:Potential exposure pathways in U.S. and Canada
  • Imports from BSE countries of:
  • A. Live animals
  • B. Mammalian-derived feed ingredients
      • Meat and bone meal, meals, etc.
  • C. U.S. and Canada – bilateral imports / exports
      • Has implications for movement of potentially infected cattle and contaminated products
  • Focus on imports from:
      • U.K. - since 1980
      • BSE countries - since 1986
potential exposure pathways feed b feed ingredients from bse countries
Potential Exposure Pathways – FeedB. Feed ingredients from BSE countries

U.S.

  • feed meal imports from UK since 1980 – total 81 tons
      • 12 tons in 1981
      • 10 tons in 1984
      • 2 tons in 1985
      • 20 tons in 1989 (Disputed by U.S. authorities)
      • 37 tons in 1997
  • U.S.A. imported ~10,500 metric tons of inedible meat byproducts from 1980-2000 from BSE countries

Canada

  • reported no MBM imports from UK since 1980.
  • Canada imported ~8,523 metric tons of mammalian flours, meals, meat pellets from 1993-2000 from Denmark, Germany, Japan & France.
cattle and beef trade in north america
Cattle and beef trade in North America
  • Considerable movement of animals, feed ingredients, and beef products
  • Trade and production practices similar for each country
  • Import/export could introduce or spread infected animals or contaminated products
conclusions part i estimating bse risk u s and canada
Conclusions Part I: Estimating BSE risk U.S. and Canada
  • Difficult to estimate absolute risk for U.S. and Canada
    • Most potential for introduction of BSE agent would have occurred prior to 1990
    • Potential amount of BSE agent introduced unknown
    • Numerous chance events would be involved over last 10 to 15 years
      • Rendering
      • Fed to other cattle, dead on farm, etc.
  • Imports of live animals and feed materials from BSE countries occurred since 1980 but was small
  • Qualitative estimate of risk predicted to be low but difficult to estimate with certainty
part ii estimating bse exposure and risks for the us population
Part II – Estimating BSE exposure and risks for the US population

Many potential routes for human exposure to beef and bovine products

  • Primary source of potential BSE exposure
  • Food
    • High risk tissues – brain, spinal cord, eyes, dorsal root ganglia, small intestine

Other sources

  • Dietary supplements
  • Medical products – devices, biologics, drugs
ii bse exposure pathways for us population via beef
II. BSE exposure pathways for US population via beef
  • A. Consumption of large amounts high risk tissue (very low probability event)
      • Bovine brain or spinal cord
  • B. Consumption of small amounts high risk tissues in processed foods
      • Advanced meat recovery beef product
      • Ground beef products, beef sausages, hot dogs, processed meat sauces, etc.
ii bse exposure pathways for us population via beef14
II. BSE exposure pathways for US population via beef

U.S. risk

Probability of exposure to infected cow in 2003

  • 1 positive identified – 35 million slaughtered

1 in 35 million (3.5 x 10-7 )

  • Worst case – Based on statistical analysis USDA surveillance (~20,000 tests)

~1 in 1 million (1 x 10-6)

a consumption of large amounts high risk tissue bovine brain
A.Consumption of large amounts high risk tissue: bovine brain
  • Probability of exposure: brain rarely consumed by Americans (100,000 – 180,000 servings)
    • Many servings from low risk cattle – calf brains, etc.
    • Probability infected brain in 2003 3.5 x 10-7 to 10-6
  • Quantity of exposure: assume brain late stage BSE-infected cow 5,000 to 6,500 cattle oral ID50
  • Conclusions:

There is risk of exposure via this route Risk to the U.S. general population is low

b consumption of small amounts high risk tissue advanced meat recovery
B. Consumption of small amounts high risk tissue: advanced meat recovery
  • Advanced Meat Recovery (AMR):
  • Removes remaining meat from carcass, vertebral column and bone by machinery
    • Spinal cord usually removed before process
    • Dorsal root ganglia on vertebral column
  • > 70% of carcasses processed with AMR
  • Process would mix and dilute residual BSE agent present
b consumption of small amounts high risk tissue advanced meat recovery17
B. Consumption of small amounts high risk tissue: advanced meat recovery
  • Machines can process 4,500 to 7,000 lbs bones per hour
  • Represents material from 20 to >35 animals
  • 5 – 10 lbs meat recovered per carcass
  • Estimated as much as 250 million lbs AMR meat produced annually
b consumption of small amounts high risk tissue advanced meat recovery18
B. Consumption of small amounts high risk tissue: advanced meat recovery
  • Probability of exposure: advanced meat recovery (AMR) product consumed frequently
  • Dilution of BSE infectivity throughout a batch of AMR product
  • Probability infected cow in 2003
    • 3.5 x 10-7 to 10-6 annually
  • Amount BSE infectivity present – estimated to be low because of dilution via AMR
    • Estimate ~ < 2 x 10-2(<4 x 10-3 to 2 x 10-2) cattle oral ID50 per average serving
  • Greater than a hundred of servings from each batch of AMR product
b consumption of small amounts high risk tissue advanced meat recovery19
B. Consumption of small amounts high risk tissue: advanced meat recovery
  • Assuming BSE infected animal(s) enter AMR and residual infectivity present in vertebral column:
  • Probability exposure via AMR is low
    • 1 x10-7 to 2 x10-5 per serving beef AMR product per year
  • Probability ofinfection even lower
    • Assuming a species barrier of 1,000
    • Reduction by oral route of >90%
    • Assume ~40% population sensitive - methionine homozygous at codon 129 of PrP
    • Probability of infection would be estimated to be less than < 3 x10-9 (2 x10-10 to 3 x10-9)annually in the U.S.
b consumption of small amounts high risk tissue advanced meat recovery20
B. Consumption of small amounts high risk tissue: advanced meat recovery
  • Conclusions
  • Our preliminary estimates suggest that there is a low risk of human exposure to BSE agent via beef AMR product
  • Probability of human infection even lower
  • There is uncertainty in the estimates and some assumptions were made to estimate the risk
  • Risk to general population and blood supply is low
recent bse risk reduction measures for food supply feed
Recent BSE risk-reduction measures for food supply & feed
  • Should dramatically reduce small BSE risk for U.S.A.
  • Recent USDA measures Dec 30, 2003 prohibit:
    • Use of “downers” for human food
    • High risk tissue in AMR
    • Use of animals >30 months in AMR
  • January 2003 FDA feed ban prohibits:
    • Ruminant blood protein in feed
    • Plate waste, poultry litter
    • Requires dedicated feed processing lines for non-prohibited and prohibited feeds
acknowledgements
Acknowledgements
  • Dr. Sonja Sandberg (OBE)
  • Rene Suarez-Soto (OBE)
  • Dr. David Asher (OBRR)
  • Dr. Rolf Taffs (OBRR)
  • Dr. Pedro Piccardo (OBRR)
  • Others at CBER
factors considered in estimation
Factors considered in estimation
  • Total cattle slaughtered annually
  • 70% - 80% processed via AMMR
  • # animals/batch
  • 5-9lbs AMR per Animal
  • Percentage lost to imports, waste, non-use
  • Conversion lbs to servings
  • Total est AMR meat servings /yr
  • Servings AMR meat contaminated/Total AMR servings per yr
  • And / or
  • Dilution of ID50s from 1 cow in a batch of AMR