Bovine spongiform encephalopathy – Overview

Description

Bovine spongiform encephalopathy (BSE), also known as mad cow disease, is a progressive, fatal disease of the nervous system of cattle. It is a member of a family of diseases known as Transmissible Spongiform Encephalopathies (TSE).

Other TSE include:

• scrapie in sheep and goats
• Chronic Wasting Disease (CWD) in deer, elk and moose
• Creutzfeldt-Jakob Disease (CJD) in humans

Although the exact cause of BSE is unknown, it is associated with the accumulation of abnormal or misfolded proteins (called BSE prions) in the brain of cattle. There is no treatment or vaccine currently available for the disease.

See also: Bovine spongiform encephalopathy (Government of Canada)

How to report

BSE is a federally reportable disease under the Health of Animals Act. It is also a provincially reportable disease under Alberta's Animal Health Act.

All suspected or confirmed cases of BSE in cattle or yaks must be reported by contacting the:

• district veterinarian at your nearest CFIA office
• Office of the Chief Provincial Veterinarian (OCPV) within 24 hours:

Hours: 8:15 am to 4:30 pm (open Monday to Friday, closed statutory holidays)
Phone: 780-427-3448
Toll free: 310-0000 before the phone number (in Alberta)
Fax: 780-415-0810

Clinical signs

Because BSE is a slow developing disease, infected cattle may not show any signs of the disease for up to 5 to 7 years after exposure to BSE prions.

Signs of disease vary but are always progressive and may include:

• nervous or aggressive behaviour
• abnormal posture
• incoordination
• difficulty standing
• weight loss
• decreased milk production

These signs may progress for up to 6 months until the animal dies.

Diagnosis

There is no test to diagnose BSE in live animals. Although a tentative diagnosis may be made based on clinical signs, diagnosis can only be confirmed by microscopic examination of the animal's brainstem after its death.

Immunohistochemistry (IHC) is the international gold standard for confirmatory testing. This procedure takes a few days before results are available.

The CFIA has approved a number of rapid (screening) tests for BSE, which significantly decrease the testing time but must still be performed after death on brainstem tissue.

All tests producing a reaction are confirmed by IHC (and other methods) at CFIA's National and International Reference Laboratory for BSE in Lethbridge, Alberta.

Where it’s found

Alberta

Canada's first case of BSE in a domestic animal was found in May 2003 in a cow from Alberta. In addition to that first case, 13 more BSE cases have been detected in Alberta. The last BSE case was detected in 2015.

For more information, see: Report on the Investigation of the Nineteenth Case of BSE in Canada

Canada

Canada has had a total of 19 cases of BSE in cattle born in Canada. In all cases, the CFIA located the farm of origin, conducted an epidemiological investigation and depopulated cattle of the same birth cohort (those born within 12 months of the infected animal). None of the birth cohorts have tested positive to date.

In each instance, no part of the infected animal entered the human food supply or animal feed chain.

International

Classical BSE was first diagnosed in cattle in the United Kingdom (UK) in 1986, but had probably been present in the country’s cattle population since the 1970s or earlier. According to the World Organisation for Animal Health (OIE) BSE has been reported in 25 countries other than the UK, mainly in Europe, Asia, the Middle East and North America.

How it spreads

BSE is not a contagious disease and cannot be transmitted through animal-to-animal contact: nor are BSE prions present in milk or dairy products.

Research indicates the only risk factor for the spread of BSE is through cattle feeding on meat and bone meal (MBM) derived from BSE-infected cattle and contaminated with BSE prions. Certain tissues of infected animals, so-called specified risk materials (SRMs), are most likely to contain and therefore transmit the BSE prion. According to the OIE Terrestrial Animal Health Code, these tissues include brain, eyes, spinal cord, skull, vertebral column, tonsils and distal ileum. BSE prions are:

• resistant to normal inactivation procedures, such as disinfectants and heat
• not completely destroyed by the rendering process

BSE trade implications

The OIE has developed criteria to classify each country, based upon their risk for BSE. The OIE-BSE Code provides guidelines for other countries to use in determining their import policies.

As a result of the first Canadian-born case of BSE reported in May 2003, over 30 countries placed trade restrictions on beef exports from Canada. Most of these restrictions were since lifted thanks to rigorous BSE control measures that have been put in place in Canada.

On May 27th, 2021, the Honourable Marie-Claude Bibeau, Minister of Agriculture and Agri-Food, announced that Canada has been officially recognized by the World Organisation for Animal Health (OIE) World Assembly of Delegates as a country with negligible risk for BSE. By obtaining this recognition, Canada has achieved the most preferred status under the OIE's 3-tiered categorization system for evaluating BSE risk.

Risk to humans

There is an ongoing need for intervention to manage the risks to human health associated with BSE.

People cannot get BSE. However, BSE is believed to be linked to a fatal but rare human prion disease known as variant Creutzfeldt-Jakob Disease (vCJD). It is believed that the first human cases of vCJD diagnosed in the UK in 1996 resulted from eating cattle tissues infected with the BSE agent.

There is no evidence that people can get vCJD from consuming meat or milk or milk products. No cases of vCJD have been linked to eating Canadian beef and the risk of contracting vCJD in Canada is extremely small.

Alberta's food safety system helps ensure Alberta’s beef and dairy products are safe for consumption. Most beef comes from animals that are less than 30 months of age, before BSE is a problem. In addition, public health is protected by the removal of Specified Risk Material (SRM) from the human food chain.

Prevention and control

Canada has implemented a number of BSE precautions to prevent its spread and protect public health, including making it a federally reportable disease. The Canadian government continually assesses international scientific information as it becomes available and modifies its policies, as required.

An Overview of Canada's BSE Safeguards outlines federal measures implemented since 1990 to limit risks to human and animal health.

Monitoring

Canada has conducted surveillance for BSE since 1993. Surveillance is a measure of the effectiveness of the precautionary processes Canada has implemented since 1990 to prevent the spread of BSE; for example, the ruminant-to-ruminant feed ban implemented in 1997. Alberta has participated in this national BSE surveillance program since 1996.

Surveillance also provides an estimate of the prevalence of BSE in Canada's adult cattle herd. This allows Canada to improve or maintain its status with the OIE and the international community.

Canada's current surveillance testing targets the highest risk animals for BSE as recommended by the World Organisation for Animal Health including cattle over 18 months of age that:

• exhibited neurological signs
• were downers
• were condemned at provincially licensed abattoirs
• were presented for emergency slaughter
• died of no apparent reason

Canada and Alberta BSE Surveillance Program

In 2004, the CFIA announced enhanced targets for BSE testing: 8,000 cattle in 2004, increasing to 30,000 annually. The Canada and Alberta BSE Surveillance Program (CABSESP) was initiated in September 10, 2004 to increase the number of high-risk Alberta cattle tested for BSE as part of Canada's BSE surveillance initiative.

The CABSESP tests cattle from 30 months of age and older that meet the Program Conditions, which are assessed by a certified veterinarian, based on a clinical examination, history and producer records. The program also provides reimbursement to producers for the cost associated with holding the carcass pending a negative test result and for appropriate disposal.

Find out how CABSESP works, and which types of cattle are eligible for the program.

Producer responsibilities

Reporting and surveillance

Beef and dairy producers suspecting an animal is showing neurological signs should contact a veterinarian to diagnose the condition. Cattle suspected of having BSE must be reported to the CFIA.

Producers who believe they have an animal that is eligible under the Canada-Alberta BSE Surveillance Program should contact their local certified veterinarian. Failure by Canada to test an adequate number of these cattle may jeopardize market access of ruminants or ruminant products.

When there is a confirmed case of a disease such as BSE, accurate records become vital for tracing animal movements, animal contacts and finding the herd of origin, offspring, past herd mates and any connection to other herds. The sooner these animals are identified, the sooner the investigation can be completed. The seriousness of one case of BSE is evident. Accurate records are essential to minimize the impact of detecting a case of BSE.

Feed management

Other beef and dairy producer responsibilities include:

• Purchase only feeds identified by retailers or manufacturers as free of SRM. They must check feedbags carefully for the label ‘Do not feed to cattle, sheep, deer or other ruminants’. Such feed may contain material that is prohibited for ruminants. If you mix feed on your farm, ensure that you follow directions and prevent cross contamination of ruminant feeds with feed that is intended for non-ruminants (horses, hogs, poultry).
• Keep records of feed and feed ingredient purchases that include the supplier's name and address, date of purchase, and amount purchased.
• Avoid disposing of old feed in grassing areas.

Livestock traceability

In addition to conducting BSE surveillance on an ongoing basis, Alberta is part of Canada’s national traceability system. The province works closely with industry organizations representing a diverse number of livestock species and poultry.

In Alberta, a robust traceability system is made up of 3 key components:

• premises identification
• animal identification
• animal movement tracking