Chapter 5 - Sampling and Testing
5.4 Prions

This page is part of the Guidance Document Repository (GDR).

Looking for related documents?
Search for related documents in the Guidance Document Repository

The transmissible spongiform encephalopathies (TSEs) are a family of slowly progressive, neurodegenerative disorders affecting humans and animals. The family includes bovine spongiform encephalopathy (BSE) in cattle, Creutzfeldt-Jakob disease in humans, chronic wasting disease (CWD) in deer and elk and scrapie in sheep and goats. The diseases are characterized by a long incubation period and are caused by a misfolded protein called a prion.

Note: All suspect animals displaying clinical signs of neurodegenerative disorders should also be evaluated for rabies virus. Specific procedures are applicable if rabies is suspected and sampling is required.

5.4.1 Bovine Spongiform Encephalopathy (BSE)

5.4.1.1 Introduction

Bovine Spongiform Encephalopathy (BSE) is a progressive, invariably fatal, degenerative neurological disease caused by a misfolded protein (prion), which is extremely resistant to heat, enzymes, and a large range of chemical disinfectants. BSE is a disease that is a major concern to the public and animal health authorities worldwide. The disease agent is believed to be able to infect humans, causing New Variant Creutzfeld-Jakob Disease (vCJD). There is no evidence of horizontal transmission of BSE between cattle, or of vCJD in humans. BSE occurs as a result of dietary exposure to feedstuffs containing meat and bone meal contaminated with the BSE-agent, BSE can only be diagnosed through the detection of the abnormal prion protein in the brain; there is no test to diagnose BSE in live animals.

Canada has only had a few cases of BSE. These cases have been managed in accordance with the World Organisation for Animal Health (OIE) guidelines. As of May 2007, the OIE categorized Canada as a controlled BSE risk country. Our objective is to maintain this status and eventually achieve OIE negligible BSE risk status.

Canada conducts surveillance testing for BSE in targeted high risk bovine categories as recommended by the OIE in its Terrestrial Animal Health Code. The probability of detecting BSE in targeted high risk bovine populations has been documented to be about 20 times greater than in apparently healthy animals. (Refer to section 5.4.1.2.2).

Note: Animals at increased risk of BSE are also at higher risk of being compromised. Therefore, inspectors should evaluate whether the animal may have been unfit for transport, in contravention of Part XII of the Health of Animals Regulations. Additional inquiry may be justified. Refer to Chapter 12 of this manual for additional details.

Since 1990, BSE has been a federally reportable disease in Canada under subsection 5(1) and subsection 5(2) of the Health of Animals Act. Animals displaying behavioural or clinical signs consistent with BSE are required to be reported promptly to the local Animal Health District Veterinarian, who will determine the follow-up actions.

5.4.1.2 Sample selection

5.4.1.1.1 BSE suspect at the abattoir

In accordance with the Animal Health Bovine Spongiform Encephalopathy Manual of Procedures, a BSE suspect case is defined as a bovine of 24 months of age or older exhibiting at least three (3) of the following signs upon clinical examination:

  1. nervous, aggressive or apprehensive behaviour;
  2. abnormal head carriage and/or abnormal posture;
  3. lack of co-ordination (ataxia) or difficulty in turning or rising from a lying position;
  4. poor body condition and/or showing a decrease in milk production;
  5. hesitation at doors, gates or barriers;
  6. increased sensitivity to touch, sounds or sight stimuli;
  7. muscle tremors or trembling.

Any of the following deviations from normal behaviour or appearance during the ante-mortem inspection may indicate BSE and should trigger an in-depth evaluation by a CFIA veterinarian:

  1. locomotor status such as weakness, abnormal head carriage, ataxia, circling, changes in gait;
  2. sensory status such as kicking, blindness, head pressing, head shyness, hypersensitivity to light, touch and noise;
  3. mental status such as apprehension, change in behaviour, abnormal ear position, nervousness, apprehension about passing through entrances, teeth grinding, aggressive behaviour.

If the veterinarian in charge suspects that the animal has BSE, he must consult the local Animal Health District Veterinarian, who will determine whether the animal should be considered a BSE suspect, which follow-up actions are required, and who would be responsible for collecting and submitting the samples. This may include sampling the entire brain when rabies cannot be ruled out.

BSE suspects are to be condemned on ante-mortem inspection and are not permitted to proceed to the slaughter floor or to other areas of the establishment where edible product is processed. The animal is to be isolated and properly euthanized. For sampling purposes, the animal cannot be removed from the premises without CFIA authorisation. Sampling for BSE can be performed at a site other than the abattoir provided:

  1. The Veterinarian in Charge, in consultation with the Animal Health District VeterinarianFootnote 3, determines that rabies is not a concern. This decision is based on the geographic epidemiology of rabies in the area of animal origin and vector species and history of exposure; and
  2. The carcass is transported as dead stock under a permit to convey SRM issued by the CFIA to an approved BSE sampling site; and
  3. A CFIA/ACIA 4206(Requirement to Quarantine and/or Licence to Transport Animals or Things) to detain the carcass in its entirety at the sampling site has been completed and issued.

Refer to Chapter 9 – Emergency situations of this manual for additional details.

5.4.1.1.2 Sample selection - BSE surveillance program

This section deals only with sampling according to the BSE surveillance program. See details in 5.4.1.2.1 above for BSE suspect cases.

BSE is a condition seen in adult cattle of both sexes and all breeds. The long incubation period (mean 4-5 years) dictates that mature cattle be targeted for testing. The typical animal raised and slaughtered for meat is between 18 and 24 months of age and is not old enough for meaningful inclusion in the BSE surveillance program.

BSE abattoir surveillance targets animals in the highest "at risk" categories of adult cattle. Adult cattle aged 30 months and older (OTM) from the following categories shall be sampled for BSE surveillance:

  • found dead, including dead on arrival;
  • non-ambulatory or "downer" cattle;
  • emergency slaughter (i.e. animals killed on the farm and transported under a SRM permit to the slaughter facility); and
  • condemned on ante-mortem inspection for reasons other than neurological signs.

It is imperative that all animals sampled for BSE can be traced back to their farm of origin, if necessary. All identifiers available should be recorded, such as a Canadian Cattle Identification Agency (CCIA) or Agri-Traçabilité Québec (ATQ) tag, a Health of Animals tag, or a Dairy Herd Improvement tag.

When BSE surveillance sampling is to be performed at the establishment level, the CFIA inspector at the abattoir shall gather all required information (see section 5.4.1.2.3 for more details on the requirements)

5.4.1.1.3 Sampling at collection sites other than the abattoir

The slaughter industry is extremely sensitive to the potential perceived adverse market and consumer reaction that may be associated with positive findings on their premises. It is therefore permitted to collect surveillance samples at a sample collection site other than the abattoir.

BSE abattoir surveillance targets animals in the highest "at risk" populations of adult cattle. By definition, these animals are compromised to some degree, therefore any decision to subject these animals to additional transportation has potential to contravene Part XII of the Health of Animals Regulations. Consequently, when an abattoir elects to sample at a site other than the abattoir, these animals must be euthanized and properly marked. If possible, this should be done under the direction of the CFIA. If the Specified Risk Material (SRM) has not been removed, the condemned carcass must be transported as deadstock under a valid CFIA SRM permit (refer to Chapter 17, Annex D of this manual, for more details).

When an operator elects to sample animals for BSE surveillance at a site other than the abattoir, it is an industry decision. Consequently, additional costs related to this activity will be borne by industry.

The CFIA inspector at the abattoir, or the operator, must notify the CFIA inspector at the collection site when BSE surveillance sampling is required.

The following information must be collected on a form CFIA/ACIA 1438 (or an equivalent in-house form) and on form CFIA/ACIA 4206 (Requirement to Quarantine and/or Licence to Transport Animals or Things) or an equivalent in-house form prior to the animal leaving the abattoir:

  • name and address of the owner if available, or auction market, if the animal is from an auction;
  • full description of the animal including:
    • all ear tags;
    • all legible tattoos and brands;
    • production type (i.e. dairy or beef is acceptable); and
    • age (or best estimate of age) in single integers (if the age cannot be reported in single integers, it should be reported as a range based on dentition).
  • description of clinical signs observed at ante-mortem inspection and clinical history if available.

Note that both the carcass transporter and the site where off-site BSE sampling is being performed require a SRM permit issued by the Terrestrial Animal Health Division, as described in Subsection 6.4 (1) of the Health of Animals Regulations.

5.4.1.3 Testing

The CFIA inspector at the collection site (either the abattoir or another site) will be responsible for finalizing the TSE submission and sending it to the laboratory. This information shall be recorded on the LSTS Animal Health Transmissible Spongiform Encephalopathy (TSE) Specimen Submission form (CFIA/ACIA 5420).

It is important to indicate the category of risk (i.e. found dead, non-ambulatory, emergency slaughter, or condemned on ante-mortem inspection for reasons other than neurological signs).

After completion, one copy should accompany the sample to the laboratory and one copy should be retained at the collection site pending confirmation of negative test results.

5.4.1.4 Follow-up

5.4.1.4.1 Carcass detention

In all cases, the carcass and parts (including all inedible parts) of animals tested for BSE (and rabies, as applicable) must be detained pending laboratory test results. It is unacceptable to release any tested carcasses and/or parts for human consumption, animal food, or regular rendering prior to the receipt of test results. The integrity of the sampled carcass(es) and parts must be maintained following BSE sampling (surveillance or disease investigation) in a manner and condition acceptable to the CFIA. If the sampling is done at a site other than the abattoir, then the results should be communicated to the originating establishment for their records. The CFIA will then notify the sampling site operator of the result.

5.4.1.4.2 Carcass disposition

If the laboratory test result is negative, then all restrictions on the carcass and its parts will be removed.

Condemned carcasses in registered establishments shall be disposed of as required in section 54 of the Meat Inspection Regulations, 1990 and described in Chapter 6 of this manual.

The carcass and associated parts from a BSE positive animal should be disposed of by burial at an approved site or destroyed by incineration, or by any method approved by the CFIA for destruction of prions. The operator must have sufficient safeguards in place to ensure that materials derived from any animal that tested positive for BSE is adequately disposed of.

5.4.2 Chronic Wasting Disease (CWD)

5.4.2.1 Introduction

Chronic Wasting Disease (CWD) was first recognized in 1967 in mule deer in Colorado. CWD was first detected in Canada on a Saskatchewan elk farm in 1996. In Canada, CWD exists in free-ranging cervid populations in Alberta and Saskatchewan and has been identified in cervid farms in those two provinces. This disease is a progressive, fatal nervous system disease known to naturally infect white-tailed deer, mule deer, black-tailed deer, moose and elk but is not known to affect other species, or to pose a risk to humans.

Both direct (animal-to-animal) and indirect environmental (animal-to-premises-to-animal) transmission occur in cervids. It is believed that such transmission occurs via shedding of the infectious agent in saliva, urine and feces. The incubation period of CWD, in captive cervids, has been observed to be 16 to 36 months, with an average incubation period of 22 months. No treatment is available for animals affected with CWD and no vaccine is available to prevent infection. CWD is tentatively diagnosed based on clinical signs, but is confirmed by testing of tissue from the affected animal after it is dead.

The clinical signs associated with CWD may be very subtle in the early stages of the disease and thus can mimic other diseases of cervids. CWD should be considered in any cervids over 12  months of age exhibiting signs such as the following:

  • excess salivation;
  • unusual behaviour (including separation from the other animals in the herd);
  • listlessness;
  • depression;
  • aggressive or violent behaviour;
  • neurological signs (including paralysis, difficulty in swallowing, head pressing, ataxia, increased thirst and excessive urination, proprioception deficiencies, and recumbency);
  • weight loss;
  • retention of winter hair coat; and
  • pneumonia.

Clinical signs can last for weeks to months before the animal dies; however, some animals may not show clinical signs except for acute pneumonia. As there is no treatment for CWD, clinical signs progress until the animal dies. Animals are usually three to four years old before clinical signs appear, but signs have been seen in animals as young as 18 months or as old as 13 years.

At the abattoir, all animals deemed as clinical suspects are subject to CWD testing and must be sampled as a CWD suspect. Therefore, any CWD suspect case must be reported promptly to the local Animal Health District Veterinarian to determine the follow-up actions, including appropriate sampling methodology (e.g. sampling the entire brain when rabies cannot be ruled out), and the determination of who would be responsible for collecting and submitting the samples.

Some provinces and territories require CWD testing of all domestic cervids 12 months of age and older that die or are slaughtered. Under these programs, the producer or his representative will collect samples and submit them to a provincial TSE laboratory. In some abattoirs, the sample is collected and submitted by CFIA inspectors on their behalf. Also, samples may be submitted from animals at the abattoir in order to meet certain export requirements.

Current science would suggest that the CWD prion protein does not infect humans; however, clinical trials are ongoing. As such, Health Canada recommends that any tissue that may come from deer or elk with CWD should not be used or consumed by humans.

5.4.2.2 Surveillance sample selection

Under selected provincially mandated surveillance testing programs, all cervids 12 months of age and older that are slaughtered for human consumption must be sampled for testing. It is the responsibility of the producer to ensure that the samples are submitted for testing and the results are communicated to the operator. Sufficient information should be recorded to permit identification of the farm of origin if a traceback should be required.

All cervids that are 12 months of age and older that are dead, condemned at ante-mortem or post-mortem inspection must also be sampled under selected provincially mandated surveillance testing programs. It is the responsibility of the producer to ensure that the samples are submitted for testing.

For testing surveillance samples, retropharyngeal lymph node is preferred in deer (mule deer, white-tailed deer), and brainstem must be tested in elk and other cervids, although both brain and lymphoid tissues are collected and stored until testing (confirmatory, if needed) is completed.

5.4.2.3 Testing

Under selected provincially mandated surveillance testing programs, samples are submitted to TSE Network laboratories for screening. Non-negative samples from the laboratory are submitted to the CFIA reference laboratory by the Animal Health District Office.

5.4.2.4 Follow-up

5.4.2.4.1 Carcass held pending lab results

Carcasses of animals (including all their parts) that are approved for human consumption must be held pending the receipt of laboratory results. The laboratory should be advised by the submitter that the carcass and its parts are held. These cases will be given high priority for laboratory testing.

Because our knowledge of CWD is still incomplete and because of the nature of this hazard, it is deemed unacceptable to release any tested carcasses and parts for human consumption prior to the receipt of test results.

Pending the receipt of CWD results, approved carcasses and parts can be shipped to a federally registered processing establishment with the appropriate controls in place. However, no carcass (including its parts) can be sold outside the federal system (e.g. provincial establishments, retailers, restaurants, etc.) before reception of the negative result. It is the operator's (slaughter and processing establishments) responsibility to ensure control over the identification of each carcass (including its parts) or each lot pending reception of the laboratory results.

Pending laboratory results, inedible parts and carcasses (including dead animals and those condemned at ante mortem inspection) sampled under provincially administered surveillance testing programs must be either detained until the receipt of the test results or disposed of as a positive case in accordance with section 5.4.2.4.2.

The carcass and all associated parts from animal deemed as clinical suspect case must be detained until the receipt of the test results.

5.4.2.4.2 Carcass disposition and disposal

If the laboratory test result is negative, carcasses of animals (including all their parts) that are approved for human consumption can be released and all inedible parts and carcasses (including dead animals and those condemned at ante mortem inspection) can be disposed of as required in section 54 of the Meat Inspection Regulations, 1990 and described in Chapter 6 of this manual.

The carcass and all associated parts from an animal with a positive test result should be disposed of in accordance with the relevant environmental regulations (i.e. by burial at an approved site or incineration), or any method approved by CFIA for destruction of prions. The operator could also elect to send the product to a rendering plant with a dedicated SRM line with the rendered product proceeding to a permitted SRM disposal/destruction site. No compensation under the Health of Animals Act is applicable to any carcasses or products condemned as a result of a positive CWD test.

If the individual identity of a carcass (including its parts) with a positive test result is lost or through further processing, the meat products originating from this carcass are now part of a larger lot, the condemnation shall be broad enough to include all meat products that may have originated from this carcass. Operators should be advised that they assume the risk of condemnation of additional product if they choose not to maintain individual carcass/parts identity until the test results are available.

5.4.3 Scrapie

5.4.3.1 Introduction

Scrapie was first recognized as a disease of sheep in Great Britain and other countries of Western Europe over 200 years ago. Scrapie is a progressive and fatal, degenerative disease affecting the central nervous system of sheep and goats, but is not known to affect any other species. Once an animal appears ill, it will die in one to two months. The disease can spread from animal to animal through direct contact (horizontal and vertical transmission). Infected flocks can experience significant production losses. Over a period of several years, the number of infected animals increases and the age at onset of clinical signs decreases, making these flocks uneconomical. Animals sold from infected flocks spread scrapie to other flocks. No treatment or vaccine is currently available for this disease.

Scrapie was first diagnosed in Canada in 1938 and became a federally reportable disease here in 1945.

Since the scrapie control program only comes into effect when symptoms are noticed and reported, scrapie continues to be endemic in Canada at a low level. The detection of infected animals that are not displaying symptoms requires testing of a statistically valid sample of adult sheep and goats.

Clinical signs of scrapie rarely develop before the age of 18 months and are highly variable. The majority of cases are diagnosed in animals two to five years of age. As many animals do not show overt clinical signs until late in the course of the disease, significant transmission of the scrapie agent occurs prior to any visible indications of disease. Throughout the clinical course of scrapie cases in Canada, wasting and debility, with or without tremors, and lack of coordination are more prominent features.

When present, the predominant nervous signs of scrapie are as follows:

  • tremors and incoordination;
  • a change in mental status (apprehension, teeth grinding, aggression); and
  • altered sensation (pruritus or itchiness, loss of wool, excoriation and inflammation of the skin, nibble reflex, excessive licking).

At the abattoir, all animals deemed as clinical suspects are subject to scrapie testing and must be sampled as a scrapie suspect. Therefore, any scrapie suspect case must be reported promptly to the local Animal Health District Veterinarian to determine the follow-up actions, including appropriate sampling methodology (e.g. sampling the entire brain when rabies cannot be ruled out), and the determination of who would be responsible for collecting and submitting the samples.

Scrapie is not known to be a human health hazard.

5.4.3.2 Surveillance sample selection

In all provincial abattoirs in British Columbia, Saskatchewan, and Manitoba that currently receive inspection by a CFIA inspector (as per a MOU), every sheep and goat 12 months of age and older is to be sampled.

In federally inspected abattoirs in any province, every sheep and goat 12 months of age and older presented for slaughter is to be sampled by a CFIA inspector. This includes all healthy sheep and goats that were slaughtered, died, or were condemned at ante- and post-mortem inspection. Targeted animals must be properly identified.

From each animal, collect the anterior brainstem, including obex, and the retropharyngeal lymph nodes. All tissues are to be submitted frozen.

Ensure that the Canadian Sheep Identification Program (CSIP) eartag number is recorded at the time of sample collection. Place the CSIP tag in the bag with the obex and the retropharyngeal lymph nodes samples so the number can be confirmed to facilitate a traceback investigation in the case of an animal with positive test results.

5.4.3.3 Testing

For surveillance purposes, frozen samples should be held in a freezer and shipped in batches to reduce shipping costs. Monthly shipments or shipment upon collection of 50 samples are recommended. Submit the samples to the lab designated by the Area Animal Health Program specialist responsible for TSE or disease control. Samples may be submitted to CFIA laboratories (Ottawa lab Fallowfield, Lethbridge, St. Hyacinthe) or a TSE network lab approved for scrapie testing, according to Area guidelines. Test results from samples sent to a CFIA lab will be reported on LSTS.

5.4.3.4 Follow-up

5.4.3.4.1 Carcass held pending lab results

The carcass and all associated parts from an animal deemed a clinical suspect case must be detained until reception of the test results.

In the case of non clinical suspect case, it was decided, following discussions between Health Canada and the CFIA in 2008, that when doing random sampling for scrapie surveillance from low risk animals (i.e. healthy slaughter animals) carcasses would not have to be held. As a result, there is no federal requirement to hold edible carcasses pending scrapie test results. As well, there is no need to hold condemned animals derived from non clinical suspect case (carcasses and their parts) or deadstock.

The inedible material derived from non clinical suspect or clinical suspect case tested negative can be disposed of as required in section 54 of the Meat inspection Regulations, 1990 and described in Chapter 6 of this manual.

5.4.3.4.2 Carcass disposition (clinical suspect case only)

The carcass and all associated parts from an animal deemed a clinical suspect case with a positive test result should be disposed of in accordance with relevant environmental regulations (e.g. by burial at an approved site or incineration) or any method approved by the CFIA for the destruction of prions. The operator could also elect to send the products to a rendering plant with a dedicated SRM line, with the rendered product proceeding to a permitted SRM disposal/destruction site.

Date modified: