Chapter 13 – Chronic Wasting Disease Voluntary Herd Certification Program – July 2017
13.6 Appendix 1B: Lymph Node Sampling Procedures – July 2017

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Entire heads may be submitted fresh or frozen to a Canadian Food Inspection Agency (CFIA)-approved laboratory (see Module 13.6, Appendix 1C).

CWD is a reportable disease, and thus if an animal exhibits signs for which CWD is a differential diagnosis, the local CFIA district office can be contacted for sampling.

Samples removed by anyone other than an accredited veterinarian, official veterinarian, a trained and qualified provincial/territorial staff of the VHCP department (e.g. game farm inspectors, etc.) or a CWD certified sample collector (see definition below), or an approved laboratory (or a CFIA veterinarian/inspector) will not be counted as submitted under the Chronic Wasting Disease Voluntary Herd Certification Program (CWD VHCP).

Certified CWD Sample Collector: An individual who has completed appropriate training recognized by his or her regional administrator on the collection and preservation of samples for CWD testing and on proper recordkeeping, and is certified by his or her regional administrator to perform these activities for farmed cervids for the purposes of the VHCP. A certified CWD sample collector may be an accredited veterinarian, an official veterinarian, an approved third party (see definition below) or a cervid farm operator. He/she must operate at arm's length from the owner/cervid farm operator and may not collect samples from his/her own animals. A certified CWD sample collector is responsible for ensuring that, for all cervids presented for sample collection, all identification devices have been verified in situ.

Approved third-party: A party that is not the owner/cervid farm operator, is at arm's length with the owner/cervid farm operator and is approved by the province/territory as an eligible Program deliverer, and who is trained and qualified to deliver certain aspects of the CWD VHCP. Approved third parties may include staff of a provincial/territorial department or agency, a CFIA-accredited veterinarian, an animal health technician who is registered under the appropriate provincial/territorial licensing body and supervised by an accredited veterinarian, and a CFIA veterinarian or inspector.

Both the obex and the retropharyngeal nodes (RPLNs) must be submitted for all farmed cervids tested for CWD under the CWD VHCP.

Visualize the approved identification device in situ prior to removing tissues for testing, record all individual animal identification information on the CWD form, and ensure all identification devices/tag(s) are submitted with the sample to the laboratory.  

Note: Visualization of this technique is available on the training CD entitled "Transmissible Spongiform Encephalopathies: Surveillance and Specimen Collection," published by the CFIA and available from district veterinarians.

Retropharyngeal Lymph Node Harvesting Technique

Recommended tools:

  • medium-sized boning knife;
  • rat-toothed forceps; and
  • scissors (optional).

The following is one suggested removal technique to harvest a set of RPLNs. For orientation, the lymph nodes depicted in this Appendix are the medial RPLNs, and lie deep and between the base of the larynx (windpipe) and the floor of the skull. They are "buried" in an area of whitish connective tissue on either side of the pharynx and upper neck and jaw.

  1. Place the cervid head upside down (dorsal side down), with the nose pointing away from you, and with the foramen magnum facing you, on a clean, disinfected surface (see Figure 6).
    Figure 6 – Cervid head, dorsal side down for correct orientation.

    Figure 6 – Cervid head, dorsal side down for correct orientation

  2. With a medium-sized boning knife, make the first incision, going straight upwards, from just above the foramen magnum to the surface (and through the skin if not skinned) (see Figure 7).
  3. Make a second cut, extending from where the first cut began, staying close to the base of the skull and moving the knife down and to the right as if you were boning out the tissue (see Figure 7).
    Figure 7 – Location of the necessary cuts to access the buried RPLNs.

    Figure 7 – Location of the necessary cuts to access the buried RPLNs

  4. Make the third cut, starting at the same spot above the foramen magnum and going down and to the left, staying close to the skull (see Figure 7).
  5. After pulling back/reflecting the two flaps created, notice an area of white connective tissue and fat on either side of the cut. The RPLNs are fairly large, firm, and encapsulated in the white fibrous tissue (see Figure 8).
    Figure 8 – Location of buried RPLNs.

    Figure 8 – Location of buried RPLNs

    (Photo courtesy of Ministère de l'Agriculture des Pêcheries et de l'Alimentation du Québec [MAPAQ].)

  6. Bluntly dissect out the beige-coloured, firm nodular lymph nodes buried in the white connective tissue, using your gloved fingers and/or a pair of scissors (see Figure 9).
    Figure 9 – Beige RPLNs after dissection from the connective tissue capsule.

    Figure 9 – Beige RPLNs after dissection from the connective tissue capsule

Contact the laboratory to request information on specimen submission (fresh or frozen), and ensure the individual animal's identification devices/tags are submitted with the sample to the approved laboratory.

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