Too often the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) receives samples where there is a concern for rabies testing but the brain tissue submitted is not suitable for testing by the Department of State Health Services (DSHS) in Austin. Usually the problem is an incomplete sample where only half the brain is submitted. Less commonly, the whole brain is submitted, but improperly packaged such that the brain tissue is destroyed by the packing material (i.e. ice packs or other enclosed samples).
The DSHS requires fresh, unfixed brain samples. A complete cross-section of brain is required from two areas. One is mid-way along the length of the cerebrum to pick up the hippocampus and rostral brainstem (Figure 1 & 2, A) while the other is midway at the midpoint of the cerebellum to include the underlying brainstem (Figure 1 & 2, B). The DSHS will perform the test on partial sections of brain, but if the test result is negative, it will be reported out as an unsatisfactory sample.
TVMDL suggests that for small animals where rabies is included in the differential diagnosis list, such as skunks, raccoons, and rodents, to submit the entire head. Small rodents and bats can be submitted in their entirety. TVMDL staff will collect the proper samples for rabies testing and send them to the DSHS lab.
Large animals provide the greatest challenge for submitting a correct sample. They are usually too large for shipping in their entirety to the lab. To satisfy the requirements of the DSHS lab, TVMDL needs the whole brain submitted fresh. Therefore, in situations where rabies is on the differential diagnosis list, TVMDL recommends clients use a technique that will ensure collecting an intact, whole brain in good condition. It should be packaged and shipped on cold packs and protected from damage during shipment. TVMDL suggests double bagging the brain and then placing the bagged brain into a rigid container of some type to prevent it being crushed by other items in the shipment.
The brain must not be exposed to formaldehyde fixatives (including fumes) as this will invalidate testing. To eliminate risk of inactivating the rabies virus, ship the brain separately.
Following these simple guidelines will ensure that the sample you submit for rabies testing will be a valid, diagnostic sample.
For more information on TVMDL specimen shipping guidelines call the College Station laboratory at 1.888.646.5623, the Canyon laboratory at 1.888.646.5624 or visit tvmdl.tamu.edu.
