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NVAP Reference Guide: Bovine

Spongiform Encephalopathy

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NVAP Reference Guide: Table of Contents

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Preface

Introduction

Control and Eradication

Brucellosis

Johne’s Disease

Pseudorabies (PRV)

Tuberculosis

Transmissible Spongiform Encephalopathies

Scrapie

Bovine Spongiform Encephalopathy (BSE)

Chronic Wasting Disease (CWD)

Poultry
National Poultry Improvement Plan (NPIP)

Avian Influenza (AI)

Exotic Newcastle disease (END)

Equine Disease

Aquatic Animal

Aquatic Animal National Health Plan

Aquatic Animal Health Activities

Animal Health Emergency Management

Animal Health Emergency Management

Emergency Response Structure

National Response Framework (NRF)

National Incident Management System (NIMS)

National Animal Health Emergency Management System (NAHEMS)

Foreign Animal Disease Preparedness and Response Plan (FAD PReP)

FAD Recognition and Initial Response

National Animal Health Emergency Response Corps (NAHERC)

Notifiable Diseases and Conditions

WOAH and International Standards

Cleaning and Disinfection

Importance of Cleaning & Disinfection

Cleaning

Disinfection

Regulation of Disinfectants

Safety

Disease Surveillance

Laboratory Submissions

Animal Movement

Interstate Regulations

Interstate Movement of Cattle, Horses, Swine, Sheep and Goats

Issuing Interstate Animal Movement Documents

International Animal Movement

Issuing International Health Certificates (IHCs) for Live Animal Movement

Common Problems Observed on Certificates for Live Animal Movement
Animal Identification 

Animal Identification

Cattle Identification

Swine Identification

Equine Identification

Sheep and Goat Identification

Fowl Identification

Compliance and Regulations

Appendix

A: 9 CFR PARTS 160, 161, and 162

B: APHIS VS District Offices

C: State Animal Health Officials

D: Forms

E: Other Organizational Information with Contact Points

F: Web Sites

G: Equine Teeth and Aging

Bovine Spongiform Encephalopathy (BSE), widely referred to as “mad cow disease,”

is a chronic degenerative TSE disease affecting the central nervous system of cattle.

It is caused by an abnormal prion protein. It has been identified in two forms:

classical BSE (C-Type) and atypical BSE forms (L-type or H-type).

C-type BSE has been linked to variant Creutzfeldt-Jakob disease (vCJD) in humans,

hence the zoonosis importance of the disease. C-type BSE in cattle results from the

ingestion of cattle feed (i.e. meat-and-bone meal) containing the abnormal prion

protein. Feeding mammalian protein to cattle have been prohibited in the U.S. since

1997. As a result of this control measure C-type BSE cases have not been diagnosed

in the U.S., except for a C-type BSE case in 2003 where the cow originated from

Canada.

The Atypical BSE forms, L- and H-type, occur spontaneously at very low levels in all

cattle populations, particularly older cattle 8 years of age or older and does not

appear to be associated with contaminated feed. Bioassay data support the
hypotheses that these strains are biologically distinct from C-type BSE and might not

pose a risk to humans. In 2015, the World Animal health Organization (OIE) excluded

atypical BSE forms from the classical BSE general risk provisions.   

In 2013, the OIE upgraded U.S. Status for BSE to negligible risk, the highest status

available.

History

BSE was first diagnosed in 1986 in Great Britain. Since then, more than 185,000

cases have been confirmed worldwide. More than 95 percent of these have occurred

in the United Kingdom, but the disease has also been confirmed in native-born cattle

in the following countries: Austria, Belgium, Canada, the Czech Republic, Denmark,

Finland, France, Germany, Greece, Ireland, Israel, Italy, Japan, Luxembourg,

Liechtenstein, the Netherlands, Poland, Portugal, Slovakia, Slovenia, Spain,

Switzerland, and the U.S. 

Five cases of BSE have been identified in the U.S. The first case in 2003 was

confirmed as C-type BSE and the subsequent four cases were confirmed as atypical

BSE forms. The first case was detected in 2003 in Washington State in a 6 year-old

dairy cow imported from Canada. The second, in 2005, was a 12 year-old beef cow

in Texas. The third, in 2006, was a 10 year-old beef cow in Alabama. The fourth, in

2012, was a 10 year-old dairy cow in California. The fifth case, in 2017, was an 11

year-old beef cow in Alabama.  As a result, U.S. beef exports dropped 80% after

2003 and have not yet fully recovered. It was not until May 2017 that China allowed

U.S. beef exports to flow directly to the country since 2003 when the C-type BSE

case was confirmed in U.S.

Clinical Course

Cattle affected by BSE experience progressive degeneration of the nervous system.

Affected animals may display changes in temperament (nervousness or aggression),

abnormal posture, incoordination and difficulty in rising, decreased milk production,

or loss of condition without noticeable loss of appetite. There is no treatment or

vaccine to prevent BSE. The incubation period is from 2 to 8 years. Following the

onset of clinical signs, the animal’s condition deteriorates until it either dies or is
destroyed. This process usually takes from 2 weeks to 6 months.

Etiologic Agent and Tissue Distribution

The agent responsible for BSE has not been completely characterized.  There are a

variety of theories regarding the nature of the agent. The most widely accepted is

that disease is caused by an abnormal prion protein that accumulates in the central

nervous system and causes the normal cellular version of the protein to change

shape such that it can no longer be degraded by the cell, causing the protein to

accumulate and damage the cell. 

The BSE agent is extremely resistant to heat and to normal sterilization processes. It

also does not evoke any detectable immune response or inflammatory reaction in

host animals. In cattle naturally infected with BSE, evidence of disease has been

found only in brain tissue, in the spinal cord, and in the retina. In experimentally

infected cattle, the distal ileum, bone marrow, dorsal root ganglion, and trigeminal

ganglion from experimentally infected cattle were also found to be infective. 

Transmission

BSE is not a contagious disease and therefore is not spread through casual contact

between cattle or with other species. The primary source of C-type BSE infection in

cattle is commercial feed contaminated with the infectious agent. Scientific evidence

shows that feed contamination results from incorporating ingredients (for example,

meat-and-bone meal) that contain protein derived from rendered infected cattle.

Standard rendering processes do not completely inactivate the BSE agent.

Therefore, rendered protein such as meat-and- bone meal derived from infected

animals may contain the infectious agent. The preferred method for disposal of BSEinfected carcasses is alkaline digestion or complete, high- temperature incineration.

Under no circumstances should BSE suspects be used for human or animal

consumption. 

Testing

Currently, there is no validated test to detect the disease in a live animal. BSE

testing is done by examining the obex portion of the brain stem for the accumulation

of abnormally folded prion protein. BSE screening is generally done by enzyme-
linked immunosorbent assay (ELISA) on fresh tissue. BSE can be confirmed by

immunohistochemistry or Western Blot. Histopathology may also be utilized to look

for spongiform changes in brain stem tissue that are characteristic of the TSEs. 

The accumulation of abnormal prion protein material and other changes in brain

stem tissue that are diagnostic for BSE are not apparent in the early stages of the

disease. Thus, the failure to detect BSE is not equivalent to a negative test or the

absence of infectivity. Current testing methods are surveillance tools only. They are

not intended to protect human health or animal health nor can they guarantee food

safety.

Surveillance

BSE surveillance has been conducted in the U.S. since 1990. After the initial case of

BSE was detected in the U.S. in late 2003, APHIS conducted a BSE Enhanced

Surveillance Program from 2004 to 2006. This was a one-time intensive effort to

detect BSE if present at a very low level and to provide information about

prevalence. More than 830,000 animals were tested. Subsequent data analysis

indicated that the prevalence of BSE in the U.S. was very low—less than one infected

animal per million based on a population of 42 million adult cattle.

Beginning in 2006, the BSE Ongoing Surveillance Program was implemented. This

program follows a stringent U.S. standard of detecting one case of BSE per one

million adult cattle with 95% confidence. This standard far exceeds the current

surveillance standards provided by the OIE for the U.S. under BSE negligible risk or

Type B surveillance which is to detect one case of BSE per 50,000 adult cattle with

95% confidence. Both standards are based on a point system that reflects the

likelihood of finding BSE. The BSE Ongoing Surveillance Program focuses on

populations of cattle at higher risk for BSE, including those animals that are 12

months of age and older that display CNS signs and those over 30 months of age

that are condemned on ante-mortem inspection at slaughter and thus are excluded

from slaughter due to poor health status (non-ambulatory, unhealthy, or dead). From

2006 to 2015, the BSE Ongoing Surveillance Program tested approximately 40,000

samples per year. On 2015, the BSE sample collections were reduced to 25,000 per

year. In the last 11 years the U.S. BSE sample collection resulted in point totals that

far exceed both the OIE and U.S. requirements.
Eradication and Control Efforts

Agricultural officials in the United Kingdom and other countries affected with BSE

have taken actions to eradicate or control the disease. These entail prohibiting the

inclusion of mammalian meat-and-bone meal in animal feed; prohibiting the use of

specified risk materials or SRMs (those tissues, e.g., brain and spinal cord, known to

have the highest infectivity) in food, feed, or other products; and destroying animals

showing signs of BSE and other animals at high risk of developing the disease. As a

result of these actions, most notably the imposition of feed bans, the rate of newly

reported cases of BSE in the United Kingdom has greatly decreased. 

In 1997, the U.S. Food and Drug Administration (FDA) implemented regulations that

prohibit the feeding of most mammalian proteins to ruminants, including cattle. This

feed ban is the most important measure to prevent the transmission of disease to

cattle.  In 2008, the ban was strengthened by prohibiting the inclusion of SRMs

(brains and spinal cords from animals 30 months of age or older) in any animal feed.

The 2008 rule also prohibits the use of entire carcass of cattle not inspected and

passed for human consumption, unless the cattle are less than 30 months of age, or

the brains and spinal cords have been removed.  

Public Health Significance

In March 1996, the United Kingdom’s Spongiform Encephalopathy Advisory

Committee (SEAC) announced the identification of 10 cases of variant CreutzfeldtJakob disease (vCJD) in people. These cases had a characteristic clinical and

pathological phenotype that differed from other routinely diagnosed cases of classic

(sporadic) CJD. SEAC concluded, and scientific evidence later confirmed, that these

cases were linked to exposure to C-type BSE before the feed bans were

implemented. It is not known whether atypical forms of BSE (L- or H-type) are

casually linked to forms of human prion diseases.

In the U.S., public or human health protective measures are maintained by both the

Food Safety and Inspection Service (FSIS) and the FDA. The most important public

health protective measure is the removal of SRMs from the human food supply.

Other controls include banning nonambulatory disabled cattle from the human food

chain; prohibiting air-injection stunning of slaughter cattle; requiring additional

process controls in advanced meat-recovery systems; and forbidding the use of
mechanically separated meat in human food. Additionally, protection from BSE and

other disease is achieved through antemortem inspection of slaughter cattle and the

exclusion from slaughter of animals with any clinical signs of neurological disease or

other abnormalities. 

Identifying Affected Animals

The U.S. also maintains import regulations, consistent with the OIE guidelines for

BSE, to prevent BSE from entering the US through imports. Beginning in 1989, APHIS

prohibited the importation of ruminants and most ruminant products from countries

that had identified BSE in native cattle or that were at risk for BSE.

An ongoing, comprehensive interagency surveillance program for BSE has been in

place in the U.S. since 1990. APHIS also supports the FDA’s regulation prohibiting

the use of most mammalian proteins in ruminant feed. Currently, USDA allows the

importation of some animals and commodities under permit or by regulation from

minimal BSE-risk countries. 

Because of the clinical history that can be obtained, samples collected on the farm

from cattle exhibiting symptoms of central nervous system disease are particularly

valuable to the BSE Ongoing Surveillance Program efforts in the U.S. Accredited

veterinarians with proper training can play a key role in the sampling of these

animals and should contact their VS field office for more information. BSE is a

reportable disease. Any suspicious cases should be reported to the APHIS – VS Area

Offices or the State animal health official as a suspected foreign animal disease

(FAD).