Chapter 13 – Chronic Wasting Disease Voluntary Herd Certification Program
13.6 Appendix 1B: Lymph Node Sampling Procedures
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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.)
Samples removed by anyone other than an accredited veterinarian, provincial staff, or an approved laboratory (or a CFIA veterinarian/inspectorFootnote 5) will not be counted as submitted under the Chronic Wasting Disease Voluntary Herd Certification Program (CWD VHCP).
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 the 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 and TSE veterinary program specialists in the various areas.
Retropharyngeal Lymph Node Harvesting Technique
- medium-sized boning knife;
- rat-toothed forceps;
- 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 (Figure 6).
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) (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 (Figure 7).
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 (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 (Figure 8).
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 (Figure 9).
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 tag is submitted with the sample to the approved laboratory.
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