CAE Caprine Arthritis Encephalitis : What is CAE...ELISA, AGID and PCR

Discussion in 'Health & Wellness' started by Sondra, Oct 26, 2007.

  1. Sondra

    Sondra New Member

    9,442
    0
    0
    Testing Your Dairy Goat Herd for Caprine Arthritis-Encephalitis (CAE)


    What is CAE? Caprine arthritis-encephalitis (CAE) is a group of diseases caused by caprine arthritis-encephalitis virus (CAEV). Diseases include encephalitis (infection of the brain) in kids, and arthritis in adult goats. Encephalitis usually shows up as a progressive paralysis. Eventually, kids are unable to stand. Signs of arthritis begin with swollen joints and pain on movement. The arthritis develops slowly until the goat is unable to move the affected joints. Other diseases caused by CAEV include mastitis or “hard bag”, pneumonia and wasting. A close relative of CAEV, ovine progressive pneumonia virus (OPPV), causes similar diseases in sheep. Sheep commonly develop wasting and pneumonia. Arthritis is less common in this species than in goats.

    CAEV and OPPV belong to the lentivirus group within the retrovirus family. An important feature of retroviruses is that their genetic material becomes incorporated into the DNA of the infected cell. Once animals are infected with retroviruses, like CAEV, they are permanently infected.

    How do goats become infected with CAEV? The primary means by which goats are infected with CAEV is through the ingestion of virus in the colostrum of infected does. Intrauterine transmission (from the infected doe to her fetuses) of CAEV occurs rarely. There is good evidence that CAEV is transmitted by direct contact with infected goats. This mode of transmission may occur through ingestion of virus in saliva and feces-contaminated feed and water, or by inhalation of aerosolized virus. CAEV is also present in blood and can be transferred through blood-contamination of needles.

    Do goats develop an immune response to CAEV? Yes, infected goats develop antibodies that specifically bind to the CAEV. However, the immune response does not clear the virus infection and the goat remains persistently infected with CAEV for life. The importance of the immune response to CAEV is that it allows us to detect infection. Individual animals may be infected for several months before antibodies can be detected.

    Antibodies to CAEV are transferred to kids that nurse infected does. These antibodies do not protect the kids from infection and are an indication that the kids have probably been exposed to CAEV via colostrum.

    Why should I test my goats? Since there is no cure or vaccine for CAE, controlling the infection relies on removing infected goats. If your herd is not infected with CAEV, testing new introductions will aid in keeping the infection out of the herd. In addition to the loss of animals due to encephalitis and arthritis, CAE infections lead to decreased longevity of goats and decreased milk production. For the dairy herd, elimination of CAEV will increase productivity.

    If you are a purebred or seedstock producer, it is to your advantage to sell CAEV-free goats. Your stock will gain a reputation for longevity, productivity and will not serve as a source of infection for other dairy goatherds.

    What kinds of diagnostic tests are available? CAEV infections can be detected in two ways. The first is by demonstrating the presence of antibodies to CAEV in goat serum. There are 2 diagnostic tests that are commonly used to tell if a goat has antibodies to CAEV, the ELISA and the agar gel immunodiffusion (AGID) tests. The AGID takes 48 hours to complete and cost $5.00 per sample. There are several different ELISA techniques, but ELISA tests usually take 48 to 72 hours. The AGID and ELISA are relatively inexpensive and usually cost $5.00 to 7.50 per sample.

    The second way to detect CAEV is by using a polymerase chain reaction (PCR) test. The PCR for CAEV detects the virus’s genetic material (genome) in the white blood cells present in a sample of blood. The PCR test for CAEV is relatively more expensive at $22 per sample.

    What kind of samples will my veterinarian need to send to the diagnostic lab?
    The AGID and ELISA tests are performed using serum separated from clotted blood. Your veterinarian will collect 5 cc of blood in red-topped blood collection tubes.
    The PCR test requires whole, unclotted blood. Your veterinarian will collect 10 cc of blood in EDTA (purple-topped) blood collection tubes. This test is set up once a week and takes 3 to 5 days to complete.

    Blood and serum should be refrigerated but not frozen, packed well to prevent breakage and sent to the lab by overnight mail service.

    Additional tips for diagnostic tests. If you are planning to test the goats prior to sale, show or export, call your diagnostic lab in advance to obtain their test schedule. Many labs only set up CAE tests once a week. Clear identification of each goat’s sample by name or ID number is important.

    What do test results mean? The majority of CAEV infected goats will be positive by the AGID and ELISA tests and positive on the PCR test. Since CAEV infection is lifelong, goats that are positive should be removed from the herd or segregated as they are a potential source of CAEV infection for other animals.

    Some infected goats are antibody negative and PCR positive. These animals are infected with CAEV, but have not yet developed antibodies. Some individuals may intermittently become antibody negative.

    Some infected goats will be antibody positive and PCR negative. These goats probably have CAEV infected cells in lymph nodes, bone marrow or nervous tissue like the brain. The CAEV in these organs stimulates the immune system to make antibodies. At the time of sampling, however, there may not be any CAEV present in the blood sample and therefore, the PCR test will be negative.

    If antibody or PCR positive goats are found, the herd should be considered CAEV infected. Further testing and control measures are needed to eliminate the infection from the herd.

    Uninfected goats will be antibody negative and PCR negative. If negative animals are found in an infected herd, however, they will need to be retested over several months after separation from CAEV positive goats. Re-testing is needed because of the sometimes-lengthy interval between infection and the appearance of antibodies or virus in blood samples.

    How can CAEV be controlled? Since the main source of CAEV is the colostrum of infected does, positive does should be removed from the herd. If positive does are retained, then their kids should be removed from their dam at birth and fed colostrum from uninfected does or colostrum that has been pasteurized to inactivate any virus present.

    Since the CAEV infection can also be transmitted from CAEV positive goats by other means, goats that have been tested and found positive for CAEV should be well separated from negative goats. Wire fences are not adequate barriers to virus spread. Milking utensils, waterers, feed tubs, tattooing equipment, or needles used in positive goats should not be used in negative groups.

    Some of my goats are positive for CAEV but are completely healthy. Why?
    Most CAE-infected goats will appear healthy. Observable disease only develops in approximately one-third of infected goats, and some symptoms like arthritis may take years to develop.

    Can my goats become infected with CAE from contact with sheep? Sheep become infected with a retrovirus similar to CAEV. The sheep retrovirus most commonly causes ovine progressive pneumonia (OPP) or maedi, and visna (encephalitis). OPPV and CAEV are about 70% similar in some of their genes. Experimentally, OPPV infects kids causing arthritis and pneumonia, and CAEV infects and causes pneumonia in lambs.

    The diagnostic tests described may not differentiate between CAEV and OPPV. Contact the laboratory that you are sending samples to for further information.

    Can humans become infected with CAEV?
    No, humans cannot become infected with CAEV.

    Hana Van Campen
    Colorado State University
    Jim Evermann
    Washington State University
    Veterinary Diagnostic Laboratory Washington Animal Disease Diagnostic Laboratory