# Presentation: 190578

## 

Uday Dessai, MS, Ph.D., M.P.H.
Director, Microbiology Division
Office of Public Health ScienceFood Safety and Inspection ServiceU.S. Department of Agriculture 

**Uday Dessai, MS, Ph.D., M.P.H.**
- Director, Microbiology Division
- Office of Public Health ScienceFood Safety and Inspection ServiceU.S. Department of Agriculture

- Technical Updates to the
- Harvard BSE Risk Assessment:
- FSIS Scenario Analyses

**Notes:**
Chronology to be handed out separately.

## Presentation Overview

- Modeling considerations in the Harvard BSE model
- Known cases of BSE in the United States
- FSIS Scenarios
- SRM removal
- Compliance

## Modeling Considerations in the Harvard BSE Model

- The source of the infectivity (indigenous or external BSE infected cattle) used to initiate the model does not influence model results.
- Model is generally initiated with the hypothetical introduction of 10 BSE infected animals into the United States.

## Modeling Considerations in the Harvard BSE Model

- The potential human exposure expressed as cattle oral ID50s is a cumulative measure over a period of 20 years.
- The model results are in a 3% range for numerical stability.

## Modeling Considerations in the Harvard BSE Model

- To measure the effect of FSIS mitigations, alternative scenarios were compared to the base case. The results are expressed as % reduction in potential human exposure.
- Perfect compliance was assumed in modeling the mitigation scenarios unless stated otherwise.

## Known Cases of BSE in the United States

- First BSE positive case (Washington State): A _6.5 year old_ cow  tested positive in December 2003. This cow was imported into the United States from Canada.
- Second BSE positive case (Texas): A _12 year old_ cow born and raised in the United States, confirmed  BSE positive in June 2005.
- Third BSE positive case (Alabama): A _10 year old_ cow born and raised in the United States, tested positive for BSE in March 2006.

## Known Cases of BSE in the United States: In the Context of Harvard BSE Model

- The revised 2005 Harvard BSE model can be initiated using different hypothetical numbers of BSE infected cattle (1, 10, 500...) to measure the effect of mitigations of interest.
- The revised 2005 Harvard BSE base case scenario predicted ~3.5 new cases of BSE when 10 BSE infected cattle were introduced in the United States.
- The revised 2005 Harvard BSE model does not take into account the current number of BSE cases detected in the United States.

## FSIS Scenarios

- Background/need for FSIS scenarios:
- The revised 2005 Harvard BSE model showed that a ban on use of SRMs has the biggest impact on the spread of BSE among cattle and human exposure.
- The International Review Committee recommended removal of SRMs from cattle ≥ 12 months.

## FSIS Scenarios

- Background/need for FSIS scenarios (continued):
- The 2005 Harvard BSE scenarios considered SRM removal from cattle ≥ 30 months (except for the International Review Committee scenario).
- Potential human exposure to BSE in the United States as a result of less than perfect compliance in SRM removal had not been modeled.
- ______________________________________
- 	Distal ileum and tonsil (both SRMs) are removed from all cattle irrespective of age.

## FSIS Scenarios

-    FSIS modeled the following scenarios that could further strengthen the SRM removal mitigations adopted by FSIS post January 2004.
- SRM removal from younger cattle
- SRM removal from cattle _>_ 24 months and cattle _>_12 months of age
- SRM removal from cattle _>_ 24 months and cattle _>_12 months of age, combined with a ban on non-Ambulatory cattle
- Less than perfect (100%) compliance in SRM removal
- SRM removal compliance from 100% to 95%

## FSIS Scenario: Removal of SRMs from Younger Cattle

| Scenario | Potential Human Exposure |  |
| --- | --- | --- |
|  | Mean ID50s | Reduction from Base Case % |
| Ban on SRMs from Cattle ≥ 30 months (Harvard 2005) | 0.22 | 99.7 |
| Ban on SRMs From Cattle ≥ 24 Months | 0.18 | 99.8 |
| Ban on SRMs From Cattle ≥ 12 Months | 0.18 | 99.8 |
| Ban on Non-Ambulatory + SRMs ≥ 24 Months  | 0.18 | 99.8 |
| Ban on Non-Ambulatory + SRMs ≥ 12 Months | 0.18 | 99.8 |

##  FSIS Scenario:Less than Perfect Compliance in Removal of SRMs 

| Effectiveness of SRM Removal (%) | 100 | 99 | 98 | 95 |
| --- | --- | --- | --- | --- |
| Reduction in Human Exposure from the Base Case (%) | 99.7 | 98.8 | 97.7 | 94.7 |

- The model output indicates that for every 1% drop in SRM removal compliance (from 100% to .. 95%), there is a corresponding 1% increase in potential human exposure to BSE.
- All the other SRM removal scenarios modeled by Harvard and FSIS assumed perfect compliance.

## Concluding Remarks

- Concluding Remarks

- Removal of SRMs from cattle under the age of 30 months did not provide additional benefit to further reduce potential human exposure to BSE.
- The model output shows that for every 1% drop in compliance for removal of SRMs, there was a 1% increase in potential human exposure to BSE.
- 	_______________________________________________ _
- 	Although the hypothetical introduction of 500 BSE infected cattle was for computational convergence and to reduce model run time (~30 days to ~3 days),  the results (% change) for FSIS mitigation scenarios are equally relevant for any number of animals (from 1-500).

## 

Thank you

*Thank you*