Caprine arthritis encephalitis (CAE) FAQ
Caprine Arthritis Encephalitis (CAE) virus is a lentivirus causing CAE in goats and OPP (ovine progressive pneumonia) in sheep. In goats, CAE may cause chronic disease of the joints, and on rare occasions, encephalitis in goat kids less than six months of age. The virus is intimately associated with white blood cells; therefore, any body secretions which contain blood cells are potential sources of virus to other goats in the herd. Since not all goats that become infected with CAE virus progress to disease, it is important to test goats routinely for infection by means of a serology test which detects viral antibodies in the serum. Hence, goat infection status and not clinical disease, is important in assessing risk factors and designing control programs for CAE virus (Rowe & East, 1997). Below are some of the most frequently asked questions along with some short answers
- 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 and dehorners, 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.
- May an owner sample goats and send the serum directly to the lab?
Although the Veterinary Diagnostic Laboratory at the University of Minnesota will test goat serum samples mailed directly from an owner, we strongly encourage the 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
- What type of sample is needed for CAE testing?
We recommend working with your veterinarian to obtain appropriate samples. Blood should be collected in a "red-top" clot tube or a serum separator tube. Leave the blood at room temperature for at least 1 hour to allow clot formation. Send blood or samples to the lab by overnight mail or second day air (FedEx, UPS, or USPS).
- 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. Pack the tubes in a plastic sealable bag with absorbent material with the tubes, and put another plastic bag around the first. Frozen gel packs should always be added. Please make sure to number the tubes consecutively so that they are easily sorted at the lab.
- What documentation should I send with the blood samples?
Complete a VDL submission form (Ruminant Health Test Chart) for each submission. If sending blood samples from multiple animals, samples should be numbered serially under column “sample #” with ID of each animal printed under column “Animal ID”.
- What tests are available and how much does it cost for testing?
Tests available are AGID and ELISA. Click the links for current fees (per sample) for each test. In addition, there is $10 accession fee per case
- How long does it take to get CAE virus serology results?
The turnaround time for CAE tests is 2-4 business days. CAE competitive ELISA (cELISA) is generally run three times a week (Monday, Wednesday, Thursday) with reports going out on the same day. However, to be tested on indicated days, samples must arrive by previous day afternoon. CAE AGID is run Mondays through Thursdays. Test results are faxed to the veterinarian and/or owner. Veterinarians also can access laboratory reports electronically. Please contact us to establish a secure web log-in (username and password).
- 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).
- 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 initially and later be 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 a perfect test. The commercial manufacturer of the cELISA test publishes a test specificity of 99.6%, which means 4 in 1000 tests could generate a false positive result that upon retesting could test seronegative.
- Is there a difference in the types of serology tests available for making a diagnosis of CAE virus infection?
Yes, our lab 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%). 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.
- 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.
- Biosecurity Screen
We recommend this screen for new animals entering the herd and animals producing milk for human consumption. This screen includes CAE, Johne's Disease, caseous lymphadenitis and Brucella. Tests are priced individually. Our lab offers all of these tests, except caseous lymphadenitis which is outsourced to another laboratory.
- 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°F and 138°F (56°C to 59°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°F, the usefulness of the colostrum will be greatly reduced due to denaturing of beneficial proteins, including antibodies to other infectious microorganisms.
- 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, and Brucellosis 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.
For additional information on CAE virus and other infections of livestock, contact us or your local veterinarian.
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