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