Caprine Arthritis Encephalitis (CAE) Virus

Caprine arthritis encephalitis (CAE) is a viral infection of goats which may lead to chronic disease of the joints and on rare occasions encephalitis in goat kids less then six months of age. The CAE virus is intimately associated with white blood cells; therefore, any body secretions which contain white 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 routinely test goats for infection by means of a serology test which detects viral antibodies in the serum.

Over the past several years, we have had numerous inquiries about CAE virus, how to test for it, and most importantly, how to take steps to control the infection in goat herds. We have taken some of the most frequently asked questions and presented them 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. Contact transmission between adults goats is considered to be rare except during lactation.
• What does a positive, negative, or suspect result 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 a potential shedder of the virus, especially if lactating. The antibody against CAE is not a protective antibody, and although strong antibody reactions may be detected in the test, infectious virus can still be shed by this goat. As many as 70% of positive goats may be free of clinical signs of the disease, and remain so for years or life. A young goat which has received colostrum containing CAE antibodies may also test positive for several months because of passive transger of maternal antibodies. We recommend retesting these kids between six and nine months of age to determine their 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. This latter case, the false negative, does not appear to be common, but it is a good reason to retest all negative goats when not in a closed herd. Goats that are negative should be periodically tested (annually, if not twice a year). A Suspect result may reflect recently infected goats, young animals who have received colostrum containing antibodies, or animals reacting abnormally in the test. Predictability (or reliability) of test a result is often used to assess the overall accuracy. For the CAE ELISA, the predictability of positive and negative test results id very high. Unfortunately, the ability to predict that a suspect test result represents a true positive or true negative is low, is a very unreliable indicator of whether an individual animal will become positive or negative in the future. Consequently, management decisions based on these values are not valid. There will be no charge for retesting suspect sera submitted between 30 and 90 days after the original samples. Please include the original WADDL number when submitting the follow -up sample.
• Can an animal testing positive ever test negative on future tests? It is unlikely that a CAE virus infected adult goat which has tested positive would ever test negative in the sensitive ELISA test. Occasionally a very young animal , fed heat treated colostrum containing CAE antibodies may test weakly 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 was not determined whether these goats were infectious to other goats during the time the harbored the virus but remained seronegative.
• Is there a difference in the types of serology tests available for making a diagnosis of CAE virus infection? Yes, the Washington Animal disease Diagnostic Laboratory has a kinetic Enzyme Linked Immunosorbent Asay (ELISA) for CAE virus antibodies using detergent disrupted whole CAE virus as the antigen. This test is more sensitive (detects true positive animals) than the Agar Gel Immunodiffusion (AGID) test. Values for the CAE ELISA have been set by double testing goat sera by WLISA and a very sensitive research assay, call immunoprecipitation. The positive cutoff score for our CAE ELISA had a sensitivity of 95.2%, with no false positive results. This is a great improvement over the commercial CAE/OPP AGID test, which had a sensitivity of 56.1% in one study. It is also an improvement over the 90.7% sensitivity of our CAE virus AGID test. We have found no CAE-AGID positive, ELISA negative animals in double testing of over 1,200 samples.
• Is it okay to drink raw milk containing the CAE virus? There is no evidence that the CAE virus can infect humans. However, there are some serious human pathogens which have been shown to be transmitted through raw milk. Consult your veterinarian regarding the public health hazards of consuming raw milk.
• In pasteurizing colostrum, what times and temperatures should I use? Colostrum from any doe may be heated to between 133-138 degrees F (56 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 1 pint per kid). If heated higher than 140 degrees F, the usefulness of the colostrum will be greatly reduced due to denaturing of proteins, including antibodies.
• How often should I test my animals? Yearly 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 before introduction to other negative animals. 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.
• As an owner, may I sample my goats myself and send the serum directly to that lab? The diagnostic laboratory primarily provides services to veterinarians. However, we will test goat serum samples mailed directly from an owner. We suggest that owners provide the name of their veterinarian. We can send results to the veterinarian, and also the owner if requested.
• How should I ship samples for CAE virus antibody testing? We recommend drawing blood into a five or ten ml. "red-top" clot tube or serum separator tube, and immediately sending the packaged samples by overnight mail. There is no need for an ice pack if shipped by an overnight mail service. We do not recommend separating the serum from the clot prior to shipment. Overnight package delivery should be sent to:
  WADDL
  Bustad Hall, Room 155N,
  W.S.U.,
  Pullman, WA 99164.

  The address for post office mail is:
  Washington Animal Disease Diagnostic Laboratory (WADDL),
  P.O. Box 2037,
  Pullman, WA 99165-2037
  An ice pack is recommended if shipment is expected to take several days in warm weather.

• How long does it take to get CAE virus serology results? CAE ELISA tests are generally run once a week, on Thursdays or Fridays. Depending on the day the samples arrive, it may take up to a week to get results. Results can be phoned or faxed to the veterinarian or owner.
• What does it cost for testing at WADDL? Instate (WA) costs are a $10 accession fee per case and $3.00 for each of the first ten samples, then $2. 40 each from 11 on. Costa for out-of-state residents are $10 accession fee and $4.50 each of the first 10, then $3.60 each from 11 on. Please do not send payment with the samples. We will bill the veterinarian or owner directly.
• Are there new test methods on the horizon? Yes, WADDL is working with USDA scientists in the development of a "competitive" ELISA using monoclonal antibodies against the immunodominant CAE virus antigen. This test appears to be both very sensitive and highly specific. Perhaps in the future, polymerase chain reaction (PCR) testing for viral specific nucleic acid will become practical and financially affordable enough for routine testing, especially in goats that have delayed seroconversion.

References:

1. Adams, DS: The meaning of the agar gel immunodiffusion test (AGID) for antibody against caprine arthritis-encephalitis virus (CAEV). Dairy Goat J. 60:17, 1982
2. Adams, DS and JR Gorham, The gp135 of caprine arthritis encephalitis virus affords greater sensitivity than the p28 in immunodiffusion serology. Res Vet Sci 40:157. 1986.
3. LaRue, LH: Serodiagnostic interpretation of CAEV: Pivotal to controlling this caprine pathogen. Vet med (Food-Animal Practice), November 1986. P. 1039.
4. Perk, K. et al: Virological aspects of CAE infection. In Slow Viruses in Sheep, Goats, and Cattle, Comission of the European Communities, 1985.
5. Potter, ME, et al: Unpasteurized milk: The hazards of health fetish. JAMA, 252:2048, 1984.
6. Adams, DS, et al: Transmission and control of caprine arthritis- encephalitis virus. Am J Vet Res 44:1670-1675, 1983.
7. Heckert, RA, et al: evaluation of an enzyme-linked immunosorbent assay for detection of antibodies to caprine arthritis-encephalitis virus in goat serum . Can J Vet Res 56:237-241,1992.
8. Cutlip, RC, et al: Prevalence of antibody to caprine arthritis- encephalitis virus in goats in the United States, JAVMA 200:802, 1992.
9. Knowles, DP, et al: Evaluation of agar gel immunodiffusion serology using caprine and ovine letiviral antigens for detection of antibody to caprine arthritis-encephalitis virus. J Clin Microbiol 32:243-245, 1994.
10. Rimstad. E. et al: Delayed seroconversion following naturally acquired caprine arthritis-encephalitis virus infection in goats. Am J Vet Res, 54: 1858-1862, 1993.
11. Vander Schalie, J, et al: Evaluation of a kinetic enzyme linked immunosorbent assay for detection of c caprine arthritis-encephalitis virus- specific antibodies. J Vet Diagn Invest 6, 30-33, 1994.

These pages were designed by the Computer Science project of the Irvine Mesa Charros 4-H Club by converting information provided by:
Washington Animal Disease Diagnostic Laboratory