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Canadian and U.S. BSE Risk
Steven Anderson, Ph.D, MPPOffice 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
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.
North American beef production statistics
U.S.A. Canada
Total Cattle 96.1 million 13.3 million
Slaughtered 35.7 million 3.6 million
Commercial carcass weight (est)
27 billion lbs ~3.8 billion lbs
Total beef (bone-in) 8.75 million metric tons
908,000 metric tons
% Beef exported ~ 9.8 % > 60%
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 – Live AnimalsA. Cattle Imports from United Kingdom
U.S.A. Canada
Total Animals imported 334 288
Disposition known 161 182
Imports from UK farms with known BSE cases 0 10
Disposition unknown 173 106
BSE positives (1993) cow from U.K.
1
Potential Exposure Pathways – Live Animals A. Cattle Imports from BSE countries
U.S.A. Canada
Total Animals imported 1980 - 2002
1,671 633
Imports Ireland / Europe before 1986 (low risk)
521 298
Total Animals imported from U.K. since 1980
334 288
Other BSE countries since 1986
816 47
Potential Exposure Pathways – Feed B. Feed ingredients from BSE countriesU.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.
C. 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
C. Cattle trade in North America U.S. Cattle imports and exports 1992 to 2002
U.S. Cattle Imports and Exports
0
200,000
400,000
600,000
800,000
1,000,000
1,200,000
1,400,000
1,600,000
1,800,000
1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
Year
Nu
mb
er o
f C
attl
e
from Canada
to Canada
C. Beef trade in North America U.S. Beef imports and exports 1992 to 2002
Beef Imports and Exports1992 to 2002
0
50,000
100,000
150,000
200,000
250,000
300,000
350,000
400,000
1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
Year
Met
ric
Tons
Imports from Canada
Exports to 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
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
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 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
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
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 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 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 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 of infection 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 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 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
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 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