Caprine Arthritis Encephalitis Virus – better known as CAE or Big Knee – was first noticed in 1974, and although nothing was known about it at the time it was recognized as something that was best to be avoided. As more was discovered about it, more control was taken over it through prevention and testing. Now although there is a lot known about CAE, and many preventative measures are being taken, it can still be rather devastating, causing not only loss in the herd, but a drop in production, resulting in loss in income not only for the breeder, but also for those related indirectly to the goat industry, and a bad reputation.
As the name indicates CAE is a virus, and is a member of the lentivirus group which is in the retrovirus family. Retroviruses infect living individuals by incorporating their genetic material with the DNA of certain cells, making it impossible to get rid of. In this case the genetic material (genome) of this retrovirus gets incorporated in the macrophage cell.
CAE is closely related to Ovine Progressive Pneumonia Virus (OPPV) in sheep. Although goats cannot get OPPV and sheep cannot get CAE it is possible for goats to get CAE from being in contact with OPPV infected sheep, and sheep, though they cannot obtain CAE, the can get OPPV from being in contact with sheep. CAE and OPPV are both lentiviruses, which is what enables them be transmissible to each other.
The Caprine Arthritis Encephalitis Virus cause several diseases including arthritis, encephalitis, pneumonia, mastitis, and wasting. Because pneumonia, mastitis, and wasting are so common, and much is known about them, I will focus more on arthritis and encephalitis.
Arthritis has an effect on adult goats, and is much like arthritis in any other species. It affects many of the main joints, and although the knees are most common (which explains the common name Big Knee), it can affect the hocks, stifles, fetlocks, and hips. Arthritis symptoms can range from slight, mild swelling to sudden severe lameness.
Encephalitis is an infection of the brain, found in growing kids, ages 1-5 months. It typically shows up as a progressive paralysis, causing nervous signs. Kids are eventually unable to stand, and their head becomes twisted to one side. When down kids may make paddling signs with their forelegs.
Although most CAE infected goats show the symptoms of CAE mentioned above, they can develop an immune response to CAE. This happens when the body produces antibodies that specifically attach to CAE. Even though an infected goat may develop an immune response to CAE, it is important to realize that they are still infected and that the virus can still be transferred to other goats.
CAE can be transferred from goat to goat in several different ways. The most common way of transfer is from the dam to her kid by means of colostrum. Of course this makes sense that this is the most common way of spread because kids are constantly drinking colostrum from the dam. There are different opinions as to whether or not CAE can be spread through regular milk. A further way of spread that is not as common as spread via colostrum, is through blood. Many times this happens when blood contaminated needles are used to give an injection to another goat. There has been evidence that CAE can be spread through direct contact to uninfected goats by be ingesting saliva and feces through contaminated feed and water, or by inhalation of aerosolized virus. Intrauterine transmission (from the infected doe to fetes) is very rare.
Because there is no cure for CAE, obviously the best thing to do is avoid it. There are many preventative measures that can be taken; for example, pasteurizing the colostrum. Because colostrum is the #1 means for spread, even most of the people who believe that they own a CAE free herd pasteurize their colostrum and milk. Avoiding the use of blood contaminated needles from one goat to another is also a good way of prevention. It is best to cull any infected goats in your herd simply for the reason that CAE can be spread through direct contact. If you choose to retain the goat it is best to isolate it from the rest of the herd, and to make an even larger effort to separate the kid from her dam immediately after birth. Try also to avoid use of the infected goats feed and water containers for uninfected goats. Testing your herd periodically for CAE is also a good preventative measure.
Testing your herd for CAE is a very necessary thing to do if you want to keep your herd CAE free. There are two different ways to test you a goat for CAE. The first is to test for the presence of antibodies in a sample of goat serum; the second is to test for the virus’s genetic material (genome) in the white blood cells.
There are two tests available to test for the presence of antibodies in the serum: the agar gel immunodiffusion (AGID) test and the ELISA test. It is suggested that a veterinarian collects and sends the sample but the labs will accept a sample collected and sent directly from the owner. The serum is separated by a veterinarian from 5 cc clotted blood that was collected. The blood is collected in red-topped blood collection tubes. The collected serum is refrigerated but not frozen, and is packaged carefully to help avoid breakage. Both tests are very similar, though the ELISA has several different techniques. They both are comparatively inexpensive, their prices ranging from $5.00-$7.50. The AGID takes 48 hours to complete while the ELISA can take any where from 48-72 hours. Both of these tests are almost always accurate.
Testing for the presence of genetic material in the white blood cells is done with the polymerase chain reaction (PCR) test. This is done by testing a sample of whole unclotted blood. The veterinarian will collect 10 cc of blood on EDTA blood collection tubes. Just like with serum the blood should be refrigerated not frozen. The cost for this test is $22.00.
It is set up once a week and can take anywhere from 3-5 days to complete.
There are questions and opinions as to which of the two forms of testing are more accurate. Based on the facts that I have learned, I would say that they both are very accurate in what the test for. For instance a goat may become infected with CAE, but not have developed the antibodies to it yet resulting in it testing negative on the AGID or ELISA tests, but positive on the PCR test. Both of these forms of testing were accurate in what they tested for. The goat can also test positive with the antibody tests and negative with the PCR test.
This happens when the cells of the lymph nodes, bone marrow, or nervous tissue become infected with the genome, not the blood which the genome must be present in order for the PCR test to work, which rouses the body to produce antibodies. Both of these forms of testing were accurate in what they tested for.
Just as there are opinions as to which test is better and more accurate, there are also opinions as to how hazardous CAE is. Some feel that there is nothing to worry about, and that CAE is hardly a threat as long as their herd is CAE free, while others take it as more serious matter and do everything within their power to prevent it. But is it necessary to prevent it to the extreme? Yes.
Exactly how prominent is CAE? That totally depends on whom and where you ask. CAE is present in North America and Europe, including the UK. In France 80%-90% of all herds are infected with CAE. In the British Isle it is much less prevalent. Why? Because of the preventive measures the people take.
CAE can be a very devastating disease, but with the correct steps taken it doesn’t have to be. Prevention is and always will be the best way to avoid it.
CAE testing Update on Caprine Arthritis Encephalitis (CAE) Virus
Questions most often asked- www.saanendoah.com
The Goat Keeper’s Veterinary Book-the Third Addition, by Peter Dunn
By: Natalie Gray
4-H Advisor: Brenda Oser
June 27, 2005
Caprine Arthritis Encephilitis Virus
(CAE or Big Knee)