Three things to keep in mind when submitting samples for Chronic Wasting Disease testing

October 30, 2024

The Texas A&M Veterinary Medical Diagnostic Laboratory, TVMDL, is the only laboratory in Texas authorized by the United States Department of Agriculture to perform testing for Chronic Wasting Disease, CWD. As such, it is critical samples are submitted properly to mitigate potential testing delays.

TVMDL recommends these three best practices to keep in mind when submitting CWD samples:

  • Know your deadline and be proactive
  • Double-check your documents and IDs
  • Beware of invalid sample types
Know your deadline and be proactive

The Texas Parks and Wildlife Department, TPWD, is the regulatory agency that manages and enforces CWD testing requirements. Requirements may apply to hunters, deer breeders, and landowners. It is critical for submitting clients to be aware of the deadline that applies to them and proactively submit samples for testing. Note that you will need to contact the TPWD for the most up to date information on testing requirements.

Clients submitting samples for antemortem immunohistochemical, IHC, testing are strongly encouraged to submit samples at least a month prior to their movement deadline. TVMDL’s average turnaround time for IHC testing is approximately three weeks. However, it’s important to keep in mind that submission sizes vary and can affect the section’s overall turnaround time. It’s not uncommon for TVMDL to receive hundreds of samples in a single submission. As TVMDL works to process and test the larger submissions, smaller submissions submitted later may experience an increased turnaround time. Therefore, early submissions are ideal and reduce the pressure of looming movement deadlines.

Double-check your documents and IDs

It is critical all samples submitted for testing are accompanied by thoroughly completed paperwork. Missing or incomplete forms can delay results as lab staff must spend additional time contacting clients to verify account information before proceeding with testing.

TVMDL recommends deer breeders and non-breeder facilities (e.g. release sites, nursing facilities, veterinary facilities) use the Texas Wildlife Informational Management Services (TWIMS) TVMDL Submission form. This applies to both antemortem and postmortem samples. Step by step instructions can be found in the Deer Breeder Permits and Herd Tracking Instruction Manual.  Deer submitted for necropsy, including field necropsy samples, and CWD testing should have both the TWIMS form and the regular TVMDL submission form (indicating the testing desired) submitted with the samples..

It’s also vital samples are properly labeled to aid in identification. TVMDL recommends labeling cassettes and jars with the TWIMS ID, not farm or ranch IDs. The TWIMS ID is the unique four-character identification number found on the TWIMS form.

If labels are handwritten, avoid using markers as the formalin solution may smear the ink. Instead, use a pencil to label cassettes. Formalin jars can be labeled with pencil or waterproof permanent marker. Additionally, writing the number on the front and back of sample container will decrease the chances of misidentification. Do not write the deer ID on the lid only.

Be aware of invalid sample types

As a reminder, only certified CWD collectors are authorized to collect samples. All accepted samples for each CWD test is listed on the TVMDL website. Be aware when submitting samples, for inadequate or invalid sample types may cause testing delays or insufficient results. In addition, it’s also important to ensure samples are packaged and shipped correctly.

Common sample errors may include:

  • Improper sample packaging
  • Missed location
  • Poor packaging

Package samples properly
When submitting rectal biopsies for antemortem CWD testing, TVMDL recommends enclosing the tissue flat between two sponges within a biopsy cassette. This keeps the tissue flat and easy to process once at the lab. Otherwise, the tissue will curl and increase the process time.

Timely submission of samples is another best practice in mitigating testing delays. If possible, deer owners should submit postmortem samples promptly after death, especially during the summer. Tissues will lose integrity to the point of liquification during exposure to high temperatures making them difficult to identify, confirm location, and test, so clients should submit the sample immediately after locating the carcass.

Ensure accurate sample location
Postmortem samples include the obex and retropharyngeal lymph nodes. The obex contains a microscopic anatomical structure that is necessary to examine in order to render a valid test. The obex is a V-shaped area of the caudal brainstem that is located where it meets the spinal cord. Other sections of the brain that are commonly wrongly submitted instead of the obex include cerebrum, cerebellum and spinal cord.

The retropharyngeal lymph nodes are located in the space behind the pharynx between the mandible and the trachea. Tissues that are commonly wrongly submitted in place of retropharyngeal lymph nodes are tonsils, salivary glands, muscle or fat.

Clients may submit the entire deer head to TVMDL where the samples are harvested or a certified CWD collector can remove the obex/retropharyngeal lymph nodes and submit the samples to TVMDL following the submission guidelines mentioned above. Submission of the head does not guarantee that an adequate sample will be collected since the quality of samples depends on the condition of the head. Please note that submitting the entire head will incur higher shipping cost and collection/disposal fees.

Another common sample issue are rectal biopsies with an insufficient number of lymphoid follicles. This can be due to a number of reasons including host factors, such as age of the animal, or the location of the biopsy sampling. Younger animals have more active immune systems and a greater number of lymphoid follicles in the rectal mucosa. The area with the greatest density of lymphoid follicles is an approximately 1 to 2 cm ring of mucosa just inside the recto-anal junction. In regards to biopsy sampling, a superficial mucosal biopsy or sampling of the non-mucosa skin of the perineum are the most common reasons for insufficient follicles. Rectal samples containing more than 50% skin and an insufficient number of follicles are resulted out as insufficient follicles location. At least half of the sample should be mucosa in order to have a better probability of yielding a valid test result.

Proper packaging practices
Clients must submit samples in tightly sealed formalin jars to prevent leakage. Be mindful that plastic food storage containers are not leak-proof and should not be used to hold samples. Ears may be placed inside the formalin jars if intended to be submitted fixed or bagged separately and not in direct contact with formalin jars if intended to be submitted fresh. Official ID should remain attached to the ear. Fresh ears should be shipped with a cold pack.

In addition, paperwork should be double-bagged, separate from samples to ensure it is protected from unexpected leaks. When possible, use a courier service such as FedEx or UPS to ship samples to TVMDL. This practice ensures samples arrive at the lab quickly and in a testable condition. 

Note that samples sent through the U.S. Postal Service, USPS, often arrive at TVMDL in an untestable condition due to the long in transit times. Because of the lab’s on-campus location, all USPS shipments are sorted through a campus postal hub, which lengthens the in-transit time.    For more information about CWD testing at TVMDL, visit tvmdl.tamu.edu or call the College Station lab at 1.888.646.5623.

Maci Guay

Communications Student Worker
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