Caprine Arthritis Encephalitis (CAE) Virus
Caprine arthritis encephalitis (CAE) virus is a member of the small ruminant lentiviruses (also includes ovine progressive pneumonia, or OPP, of sheep), which may lead to chronic disease of the joints, and on rare occasions, encephalitis in goat kids less than six months of age. The CAE virus is intimately associated with white blood cells; therefore, any body secretions that contain blood cells are potential sources of virus to other goats in the herd. Since not all goats that become infected with CAE virus develop clinical disease, it is important to test goats routinely for infection by means of a serologic test that detects viral antibodies in the serum.
WSU-WADDL receives numerous inquiries about CAE virus, how to test for it, and most importantly, how to take steps to control the infection in goat herds. It is important to remember that animal infection status, not clinical disease, is the element of interest in assessing risk factors and designing control programs for CAE virus. We have taken some of the most frequently asked questions and presented them along with some short answers
1. What are the major means of spread of the virus?
The CAE virus is primarily transmitted to kids via colostrum in the first few feedings after birth. Blood (e.g., contaminated instruments such as needles, dehorners, etc, and open wounds) is regarded as the second most common way of spread. Contact transmission between adult goats is considered to be rare except during lactation.
2. May an owner sample goats and send the serum directly to the lab?
The diagnostic laboratory provides services to veterinarians. Although we will test goat serum samples mailed directly from an owner, we strongly encourage goat owners to work with a veterinarian in developing a CAE control program. We will send results to the veterinarian, and also to the owner if requested.
3. What type of sample is needed for CAE testing?
We recommend working with your veterinarian to obtain appropriate samples. Blood should be collected into a 5 or 10 ml. "red-top" clot tube or serum separator tube. Leave the blood at room temperature for at least 1 hour to allow clot formation. We do not recommend separating the serum from the clot prior to shipment. Send blood sample(s) to the lab by overnight mail (FedEx (choose "Standard Overnight" for quickest delivery), UPS, or USPS).
4. How should I ship samples for CAE viral antibody testing?
It is not necessary to individually wrap each tube. The best method is to use padded pouches designed for blood tubes. If you do not have access to these, we recommend using a thick rubber band and grouping your tubes tightly into groups of 7-10 tubes. If you alternate the direction of the tubes they will stay tightly packed. Pack the tubes in a plastic sealable bag with absorbent material in with the tubes, and put another plastic bag around the first. Pack so the box can be dropped from a four foot height without breaking any tubes! An ice pack is recommended if the shipment is expected to take several days in warm weather. If you choose to ship using Federal Express, specify "Standard Overnight Service." Overnight package delivery should be sent to:
1845 Stadium Way
Bustad Hall, Room 155N
Pullman WA 99164-7034
Note that CAE testing is normally performed on Thursdays, so samples must arrive no later than Wednesday afternoon to ensure they will be tested that week. Samples received after Wednesday afternoon will be tested the following week.
5. What documentation should I send with the blood samples?
If submitting for a single animal, complete a WADDL General Accession Form for each submission. If sending blood samples for multiple animals, fill out the WADDL General Accession Form for Multiple Animals. Number the tubes consecutively to match a key sheet with the animal names.
7. How long does it take to get CAE virus serology results?
CAE competitive ELISA (cELISA) tests are normally run once a week, on Thursday morning, with reports going out on Friday. During busy times, the test may be set more than one time per week. However, to be tested on Thursday, samples must arrive by Wednesday afternoon. Test results can be mailed or faxed to the veterinarian and/or owner upon request. Veterinarians also can access laboratory reports electronically. To set up an account to access laboratory reports online, click here. Online access is not yet available for owners that directly submit samples. For security reasons WADDL does not e-mail laboratory results.
8. What does a positive or negative mean?
A positive result means the goat has been infected with the CAE virus and has made antibodies reactive with the CAE antigens used in this test. This goat is regarded as potentially contagious for the virus, especially if lactating. The antibody against CAE is not a protective antibody and infectious virus can still be spread in milk and blood of this goat. As many as 90% of positive goats may be free of clinical signs of the disease, and remain so for years or life. A young goat not infected with CAE virus which has received heat-treated colostrum containing CAE antibodies may also test antibody positive for several months because of passive transfer of maternal antibodies from the colostrum. We recommend re-testing these kids after six months of age to determine their true infection status. A negative result means that this goat is either not infected, or has been recently infected and is producing amounts of antibody too low to be detected. While the latter case does not appear to be common, it is a good reason to retest all negative goats when not in a closed herd. Goats that are negative should be periodically tested (twice a year for the 1st year, and annually thereafter).
9. Can an animal testing positive ever test negative on future tests?
Goats infected with CAE virus are infected for life. Thus a goat tested true positive by the CAEV cELISA test would not later clear the CAE virus infection. Occasionally a very young animal, fed heat-treated colostrum containing CAE antibodies may test positive and later negative from the decline of passively acquired antibodies in the colostrum. In some goats, seroconversion may be delayed for months after exposure. These "silently" infected animals test negative for antibody until the viral infection is activated by stress or other factors. It has not been determined whether these goats were infectious to other goats during the time they harbored the virus but remained seronegative. Lastly, although the CAEV cELISA test is a USDA licensed test showing excellent ability to detect CAE virus antibody true positive results it is not perfect test. The commercial manufacturer of the cELISA test publishes a test specificity of 99.6%, which means 4 in 1000 tests could generated a false positive result that upon retesting could test seronegative.
10. Is there a difference in the types of serology tests available for making a diagnosis of CAE virus infection?
Yes, WADDL has a validated and USDA licensed (cELISA) for CAE virus antibodies. This test is more sensitive (ability to detect true positive animal) than the agar gel immunodiffusion (AGID) test (sensitivity of 85%-90% and specificity of 100%). Values for the CAE cELISA have been set by double testing goat sera by ELISA and a very sensitive research assay, called immunoprecipitation. The positive cutoff score for the cELISA had a sensitivity of 100%, and specificity of 99.6%, which means there is a false positive rate of 4 out of every 1,000 samples tested.
11. Is it okay to drink raw milk containing the infectious CAE virus?
There is NO evidence that the CAE virus is transmissible to humans. However, there are other serious human pathogens which have been transmitted through raw milk. Consult your veterinarian regarding the public health hazards of consuming raw milk.
12. Biosecurity Screen
We recommend this screen for new animals entering the herd and animals producing milk for human consumption. This screen includes Small Ruminent Lentivirus (CAE), Johne's Disease, and caseous lymphadenitis.There is a discount for ordering the screen rather than individual tests.
13. In heat treating colostrum, what times and temperature should I use?
Heat treating colostrum will inactivate the CAE virus and prevent spread from the doe to her offspring. Colostrum from any doe may be heated to between 133 degrees and 138 degrees F (56 to 59 degrees C) and held at that temperature for one hour to inactivate the virus. An accurate thermometer is important. It is recommended to use a water bath or double boiler to regulate the temperature more closely. A large batch may be heat-treated and frozen in small feeding size portions for later use (about one pint per kid). If heated higher than 140 degrees F, the usefulness of the colostrum will be greatly reduced due to denaturing of beneficial proteins, including antibodies to other infectious microorganisms.
14. How often should I test my animals?
Twice a year initially followed by annual testing is suggested for herds which are primarily negative, with testing before kidding recommended. Any new animals brought into the herd should be quarantined and tested twice (at least 30 days apart) before introduction with other negative animals. In addition to CAE infection, new goats should be tested for Johne's disease, as a biosecurity screen (see #12). For herds with both positive and negative animals, negative animals should be tested more often to adjust the milking order so that negative animals are milked first.
15. What should I do if my animal tests positive for CAE?
Because there is a small possibility (4/1000 samples) of a false positive result, it is generally recommended that test-positive animals be re-sampled and re-tested in in 14-30 days. Animals under 6 months of age should not generally be tested, but if a young animal is test-positive, it should be re-tested at 6 months of age because of the potential for influence of maternal antibodies passed from the dam to the kid.
16. Can sheep get CAE? Can goats get OPP?
While the classical strains of CAE and OPP only infect goats and sheep respectively, variants of each virus can infect any small ruminant, including wild small ruminants, such as wild ibex and mouflon.
. If you own both goats and sheep, monitoring for small ruminant lentiviruses should be performed in both species.
17. Is there a vaccine for CAE?
No. It is very difficult to create effective vaccines against retroviral diseases. Several different vaccine types have been experimentally tested, but none have provided adequate protection against CAE infection.
Additional information on CAE virus and other infections of livestock can be obtained by contacting your local veterinarian or the diagnostic laboratory at 509-335-9696, FAX 335-7424.
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