DIAGNOSTIC TESTS FOR CAPRINE ARTHRITIS-ENCEPHALITIS AND OVINE PROGRESSIVE PNEUMONIA
By Dr. Hana Van Campen , Colorado State University
As printed in Lab Lines, Volume 5, Number 2 Spring 2001
newsletter of Colorado State University Veterinary Diagnostic Laboratories
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The Viruses—Caprine arthritis -encephalitis (CAE) is a group of diseases caused by caprine arthritis -encephalitis virus (CAEV). Diseases include encephalitis in kids and arthritis in adult goats. Encephalitis usually presents as a progressive paralysis. Signs of arthritis begin with swollen joints and pain on movement. The arthritis may progress until the goat is unable to move the affected joints. Other diseases caused by CAEV include mastitis or “hard bag,” pneumonia, and wasting. Ovine progressive pneumonia virus (OPPV), a close relative of CAEV, causes similar diseases in sheep. Sheep most commonly develop wasting and chronic pneumonia, but encephalitis and mastitis also occur. Arthritis is less common in this species than in goats. Experimentally, OPPV infects kids causing arthritis and pneumonia, and CAEV infects and causes pneumonia in lambs.
CAEV and OPPV belong to the lentivirus genus within the retrovirus family. An important feature of retrovirus replication is that the virus’s genetic material becomes integrated into the DNA of the infected cell. As a consequence, animals infected with retroviruses are permanently infected. “Lenti” means slow and refers to the length of time from infection to the appearance of clinical signs. Most CAEV/OPPV-infected animals do not develop signs of disease. Observable disease develops in approximately one-third of infected goats, and some symptoms (eg., arthritis) may take years to develop.
Immune Response—Infected goats or sheep develop antibodies that specifically bind to the CAEV or OPPV. Although specific, this immune response does not clear the virus infection and the animal remains persistently infected with CAEV/OPPV. Individual animals may be infected for several months before antibodies can be detected. Antibodies to CAEV/OPPV are transferred to kids/lambs via colostrum, but these antibodies do not protect the kids/lambs from infection. Rather, they are an indication that the kids/lambs have been exposed to and are likely to be infected with these viruses.
Transmission—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 but the frequency is unknown. There is good evidence that CAEV also is transmitted by direct contact with infected goats. This mode of transmission is suspected to occur through ingestion of virus in saliva and feces-contaminated feed or water, or by inhalation of aerosolized virus. CAEV also is present in blood, and can be transferred through blood contamination of needles or syringes. Tattooing equipment also is a potential means by which virus can be transmitted. Similarly, OPPV is from sheep to sheep via the respiratory route. Transmission in utero and in feces-contaminated feed have been reported.
Diagnostic Tests Available—CAEV and OPPV infections can be detected in two ways. The first is by demonstrating the presence of virus-specific antibodies in serum. There are two serologic tests for CAEV and OPPV – the agar gel immunodiffusion (AGID) and ELISA-based tests. We perform the AGID test daily and it takes 48 hours to complete.
There are a number of different ELISA-based techniques that detect antibodies to CAEV/OPPV; however, we do not offer these currently. We do perform a polymerase chain reaction (PCR) test for CAEV and OPPV. The PCR detects the virus’ genetic material in white blood cells in a sample of whole blood. The PCR test is set-up once a week and takes 3-to-5 days to complete. None of the diagnostic tests described differentiate between CAEV and OPPV.
Samples Required—The AGID and ELISA tests are performed using serum. A minimum of 5cc of blood should be collected in red-topped blood collection tubes. The PCR test requires 10cc of whole blood collected in EDTA (purple-topped) tubes. Blood and serum should be refrigerated but not frozen, packed well to prevent breakage, and sent to us by overnight mail service.
Additional Tips for Diagnostic Tests—Plan ahead if animals need to be tested prior to sale, show, or export. Call us in advance to obtain the test schedule, or if a large number of samples need to be tested. Clearly identify each goat’s sample by name or ID number.
Test Result Interpretation—The majority of CAEV/OPPV infected animals will be positive by the serologic tests and positive on the PCR test. Some infected goats are antibody negative and PCR positive. These animals are infected with CAEV/OPPV, but have not yet seroconverted. Individual infected animals have been shown to intermittently become seronegative.
Some infected animals will be antibody positive and PCR negative. These animals may harbor CAEV/OPPV infected cells in lymph nodes, bone marrow, or neural tissue. The virus in these organs stimulates the immune system to make antibodies. At the time of sampling, however, there may not be any CAEV/OPPV present in the blood sample, and therefore, the PCR test will be negative. If antibody or PCR positive animals are identified, the herd should be considered to be infected.
Uninfected animals will be antibody negative and PCR negative. If negative animals are found in an infected herd, they will need to be re-tested over several months after separation from positive animals. Re-testing is needed because of the sometimes lengthy interval between infection and the appearance of antibodies or virus in blood samples.
Prevention and Control—Currently, there is no cure or vaccine for CAE or OPP. Preventing infection should be undertaken on a herd/flock basis. If a herd/flock is negative for CAEV/OPPV, any new purchases should be tested prior to their introduction. This method is not foolproof as infected animals may take several months to seroconvert, and some infected animals will be PCR negative.
Positive-test animals should be removed from the herd/flock as they are a source of infection for other animals. The most economical testing procedure is to use serology to detect CAEV/OPPV positive animals for culling. Any remaining negative animals should be tested using the PCR test. Repeated testing is necessary due to the chronic and covert nature of CAEV/OPPV infections. Testing also is useful in surveillance in CAEV/OPPV negative herds.
If, for some reason, it is desirable to retain the offspring of positive dams, the kids/lambs should be removed from the dam at birth and fed colostrums from uninfected does/ewes, or colostrums that have been pasteurized to inactivate these viruses. CAEV/OPPV infections also can be transmitted from animal-to-animal by means other than colostrum. Because of this, test-negative animals should be well separated from any positive animals. Wire fencing is not adequate separation. Milking utensils, feed tubs, needles, etc. used in positive goats or sheep should not be used in negative groups without disinfection or sterilization.
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CAE/OPP testing: AGID—Submit 5cc blood/serum, Fee=$5.00; PCR—Submit 10cc whole blood in EDTA tubes, Fee=$22.
Christine
Dr. Hana Van Campen, Virologist
Colorado State University
Veterinary Diagnostic Laboratory
300 West Drake Rd.
Fort Collins, CO 80526
PHONE: 970-491-1281
FAX: 970-491-0320
EMAIL:
hvancamp@lamar.colostate.eduCAE testing
WSU - WADDL
155N Bustad Hall,
Pullman, WA 99164-7034.
The address for post office mail is
Washington Animal Disease Diagnostic Laboratory (WADDL),
P.O. Box 647034,
Pullman, WA 99164-7034.
An ice pack is recommended if shipment is expected to take several days in warm weather.
509-335-9696
The WSU lab is considered the "gold standard"- they run a kinetic enzyme linked immunosorbent assay (ELISA) for CAE virus).
Pan American Vetinary Laboratories
Ruminant Veterinary Diagnostics
Pan American Vet Labs
166 Brushy Creek Trail
Hutto, Texas 78634
800 856-9655
Ovine Progressive Pneumonia, Caprine Arthritis Encephalitis (CAE), Caseous Lymphadenitis, Paratuberculoiss (Johne's Disease), Brucella ovia/melitensis. Although Pan Am also uses a ELISA test for CAE, it may not be as sensitive as the WSU test.
UC-Davis.......California Veterinary Diagnostic Lab System
West Health Sciences Drive
University of California-Davis
Davis, CA 95616.
(530) 752-7577
Serologic test for CLA, Corynebacterium pseudotuberculosis (Caseous lymphadentitis.)
from BioTracking:
http://www.biotracking.com/biopryn.php$4.00 for CAE test
Here is the report for the CAE test on your samples.
This test looks at the ability of antibodies against CAE in the doe's blood to block binding of a labeled CAE antibody which is added as part of the assay. If there is no antibody to CAE in the sample, it does not compete for, or inhibit, binding of the labeled antibody, and the sample is Negative. If the doe or buck has been exposed to CAE and has an appreciable level of antibody in his or her serum, it will successfully compete for or inhibit binding of the labeled antibody. This results in a high level (greater than 40%) of inhibition which is what is measured in the test.
If the inhibition is greater than 40 percent (% Inhibition > 40), we score the test as Positive. If it is less than 30 percent (% Inhibition < 30), we score the test as negative, and between 30 and 40 percent (% Inhibition = 30 to 40) is scored as Marginal.
The assay is very sensitive, and as such the presence of non-CAE antibodies can result in a positive or marginal score. If a goat has been recently vaccinated, injured, stressed or is ill, the immune system responds to this by producing antibodies specific to the vaccine or injury / illness. These antibodies are produced in such high amounts, or titers, that they can overwhelm the assay and result in a false positive. If you have an unexpected positive score for one of your animals, please call and we can discuss how other health issues may be contributing to a false positive, and steps to take for retesting at a later date when these non-specific antibody titers have decreased.
Marginal result can be an indication of a recent CAE exposure and antibodies are building up in the serum, or this may be the result of a false positive, and non-CAE antibodies which can interfere with the test are increasing or decreasing in titer. In any event, we suggest you wait for 6 – 8 weeks after any vaccinations, injuries or illness symptoms are gone and resubmit for a confirmation.
If you have any questions about the test or the results please don’t hesitate to call or email me.
Thanks
Chuck Passavant PhD
Sr Research Scientist
BioTracking
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