Submitting Livestock Samples for Rabies Diagnosis

The rabies laboratory of the New York State Department of Health provides standard shipping containers for the submission of specimens, complete with packing materials and detailed packaging instructions. For the diagnosis of rabies in animals, the preferred sample is the intact head of the suspect animal. Often, it is not practical to send entire heads of livestock (particularly bovines and equines) because of size. Therefore, it is recommended that the clinician remove the appropriate CNS sample for submission for these animals.

While it is possible to confirm rabies infection in livestock by the identification of rabies virus in any portion of the brain, we must examine ample portions of cerebellum and a complete cross-section of the brain stem to reliably reach a negative rabies diagnosis.

Fortunately, it is not necessary to open the cranium in order to remove an adequate sample (recognizable, walnut-size piece) of the necessary CNS tissue, as the hindbrain is accessible through the foramen magnum.

Livestock Brain (see diagram)

1. Sever the head between the occipital bone and the atlas (first vertebra). If the head has been removed with attached cervical vertebrae, these must be removed in order to expose the foramen magnum.
2. Position the head dorsal-side down on a flat surface to access the foramen.
3. Insert a sharp knife with a long, thin blade into the foramen magnum, being certain it is within the dura mater.
4. Using a circular cutting motion (similar to coring an apple) free the brain stem from the meninges. Frequently, a portion of the brain stem will already be protruding from the foramen.
5. Remove the knife, and using a long pair of forceps, gently pull on the brainstem and sever it just inside the foramen with the knife.
6. A useful implement for tissue removal is a spoon/spatula type instrument. One can be made from a long (20 to 25 cm) handled spoon in which the bowl has been ground into an oval shape about 2 cm wide. After the brain stem is removed from the foramen magnum, the spoon can be used to separate the cerebellum from the cerebellar peduncles. Brain tissue is easily cut with this instrument, and it may also be used to coax the cerebellum through the foramen.
7. For satisfactory rabies diagnosis, in addition to a complete cross-section of brain stem, it is essential that all 3 lobes of cerebellum be examined. To achieve this, when extracting tissue through the foramen, be sure to extract copious amounts (a quantity equal to approximately 2 walnuts) of the easily recognizable, highly convoluted cerebellum.

Do not chemically fix the tissue. Preserve by refrigeration, only.

The cerebellum and brainstem samples must be placed in a small, crush-resistant plastic canister or tub, then sent to the lab in the standard New York rabies specimen shipping container according to the provided detailed instructions.