Bovine tuberculosis (TB) is a contagious, infectious, communicable disease of animals and humans caused by Mycobacterium bovis. It is commonly a chronic, debilitating disease but occasionally may assume an acute, rapidly progressive course. TB is a widespread zoonosis of global magnitude and affects nearly all species of vertebrates. Disease is spread by direct contact, inhalation of droplets expelled from infected lungs, and ingestion of contaminated feed or milk. All accredited veterinarians must immediately report every suspected or diagnosed bovine TB case promptly to both the Assistant District Director and the State Animal Health Official.
Tuberculosis Testing
Diagnosing TB in live animals depends on using an effective testing technique with an intradermal injection of tuberculin obtained through the USDA. Several varieties of tuberculin are produced. However, use only bovine purified protein derivative tuberculin (PPD bovis) licensed by USDA for official testing. See below for tuberculin test requirements for different species of animals.
|
Cattle & Bison | 0.1 mL PPD bovis
| Caudal fold | 72 h +/- 6h |
|
Horses | Not reliable | | |
|
Sheep & Goats | 0.1 mL PPD bovis | Caudal fold
| 72 h
|
|
Swine | 0.1 mL PPD bovis | Base of ear or vulvar lips
| 48 h |
|
Poultry | 0.05 mL avian | Wattle | 48 h |
|
Exotic Bovidae | 0.1 mL PPD bovis | Midcervical | 72 h |
|
Deer, Elk & other Cervidae | 0.1 mL PPD bovis | Midcervical | 72 h |
|
Camelidae | 0.1 mL PPD bovis | Postaxillary region | 72 h |
Because the tuberculin test is based on an immune response, the animal being tested should not concurrently be receiving other medications, vaccinations, or anthelmintic drugs. These agents may temporarily affect the immune system and influence the result of the tuberculin test. This also means that sick animals may not be injected even if they are not being medicated or treated in any fashion. In addition, tail-bleeding is not recommended for other diagnostic procedures at the time of tuberculin-test injection in cattle or bison because tail-bleeding may interfere with test interpretation.
Accredited veterinarians are legally responsible for properly conducting and evaluating the results of tuberculin tests. Therefore, perform the test yourself; do not delegate the responsibility to a technician. For TB testing in species other than cattle or bison (e.g., cervidae), contact the Oregon State Veterinarian's office for additional guidance.
Forms
- Complete VS Form 6-22, Tuberculosis Test Record, or Oregon Electronic Tuberculosis testing form.
- Identify the animal on the form by its official identification
- All cattle and bison tested shall be individually identified by official eartags. Such identification must be recorded in its entirety on the test record at the time of injection and must be confirmed at the time of observation.
- Additional identification (such as bangle tags, non-official metal ear tags, neck chain numbers, tags, brands, horn numbers, and names) should also be recorded on the test record as supplemental information, but must never be used as the sole method of identification.
- When cattle and bison have been tagged with more than one official ear tag, all ear tag numbers must be recorded in their entirety
- The breed, sex, and approximate age in years of each animal tested must be recorded in their entirety on the test record. Abbreviations such as C=Calf or A=Adult are not to be used
- The owner should be informed of the number of animals injected, and advised to restrict them to the premises until the test is completed.
Supplies
Syringe – Use disposable 1.0 mL plastic tuberculin syringe.
Needle – Use a 26 guage, 3/8-inch-long needle; A larger gauge and longer or shorter needle might allow the tuberculin to leak from the injection site. A new needle must be used for each animal.
Tuberculin – Use USDA-Veterinary Services approved PPD Bovis tuberculin. Check the expiration date to be certain that the tuberculin is still valid. Tuberculin is ordered directly from the National Veterinary Services Laboratory. Please refer to
USDA instructions on ordering tuberculin.
Injection of Tuberculin
All cattle and bison tested must be sufficiently restrained to permit careful application of the tuberculin injection(s), correct reading of animal identification, and careful observation and palpation of the injection sites. No test should be applied or observed without having the animal restrained in a satisfactory manner.
- In cattle and bison, injections should be made about 2 to 3 inches distal to the base of the tail. Rest the caudal fold on the forefinger exposing the area outside the hairline in bare skin near the center of the caudal fold.
- Note scars, defects, and anomalies of the skin in this area on VS Form 6-22 so that they will not be confused with possible test reactions at the time of reading.
- Use the caudal fold on either side of the tail; however, note which side you injected.
- Clean the area to be injected, but do not use alcohol because it may be irritating to the skin.
- Grasp the caudal fold between the thumb and index and middle fingers to stabilize it.
- Carefully insert the needle to its full length between the superficial layers of the skin; withdraw it slightly and deposit 0.1 mL of tuberculin.
- A small bleb should appear in the skin at the end of the needle.
Note: it is important to establish a consistent injection technique (i.e., all animals should be injected on the same side of the tail) – particularly when testing large numbers of animals, unless there is some physical abnormality at the injection site.
Reading the Test
The test must be read between 66 and 78 hours after injection (72 hours is optimum). The veterinarian who made the injection must be the veterinarian who reads the test result. Exceptions must be approved in writing by the USDA, Veterinary Services, Assistant District Director. The veterinarian must determine the results of the test by both observation and palpation of the injection site.
- Verify the identification of the restrained animal and raise the tail to exert slight tension on the caudal fold.
- Visually inspect the injection site closely and palpate it carefully to detect changes from the normal. Any swelling, sensitivity, or increase in thickness of the skin is considered to be a positive response to the tuberculin. The size of responses may vary and are not indicative of infectious status. Responses may be small, hard, pea-sized responses, diffuse responses, circumscribed responses, or large responses. If there is doubt about whether a response has occurred, palpate the opposite side of the tail to determine if there is any change from normal. Any observed change should be recorded
- Test observation without palpation is unacceptable.
Recording the Results of the Test
- Record all results on VS Form 6-22 or the Oregon Electronic Tuberculosis testing form.
- Enter “N" (negative) when you observe no change in the tissue at the site of injection.
- Enter “S" (suspect) when you observe or palpate any increase in caudal fold thickness, size, or sensitivity, at the injection site as described above.
Reactions and Interpreting Test Results
Please give ODA a courtesy notification when planning TB testing. This will allow us to plan for possible CFT responders and subsequent CCT testing which will avoid unnecessary delays for you and your clients.
If an animal is exposed to the antigens present in bovine TB, a tuberculin injection results in a delayed hypersensitivity reaction manifested by swelling and induration at the injection site. A positive response usually begins within 8 to 12 hours and peaks about 72 hours after injection.
If the test produces any type of response, immediately notify the Oregon State Veterinarian at (503) 986-4711. The caudal-fold test is used as a presumptive diagnostic procedure, and animals classified as suspect must be evaluated further by the comparative cervical (CCT) test, gamma interferon test, or sent directly to slaughter under permit. In the event any suspects are detected by CFT, the entire herd must be held under quarantine until follow-up CCT testing has been conducted.
Only Federal or State regulatory veterinarians who have had specialized training may conduct the follow up testing using the comparative cervical method. Oregon accredited veterinarians may be given approval by the State Veterinarian to conduct gamma interferon follow up testing on cattle. Follow-up testing must be performed within 10 days of the initial caudal-fold injection in cattle and bison, or the herd owner must wait 60 days (90 days for cervidae) before the follow-up test can be administered. If the CCT or gamma interferon test indicates that the animal is a reactor, all further herd testing is conducted by Federal or State regulatory veterinarians.
In Oregon, a caudal-fold response rate of 0.5 percent or greater should be expected in beef cattle, and a response rate of 1 percent or greater should be expected in dairy cattle. Improper injection or observation techniques may result in true suspects' or reactors' being missed.
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