Biosecurity Test Results 2020 and a Brief Overview of CAE, Johnes, and CL in Goats
If you are even a little familiar with goats, you've probably heard of those three diseases and heard something about biosecurity testing or clean or negative herds etc....
Basically, biosecurity is attempting to prevent any disease-causing agents from entering your farm. Usually, in the case of these three diseases, this means not bringing in animals that have tested positive and/or only bringing in animals from herds that can prove the entire herd has tested negative. Biosecurity protocols will vary from farm to farm. CAE is Caprine Arthritis and Encephalitis, a lentivirus that often manifests clinically as arthritis or mastitis ("hard udder") in adult goats and less commonly as encephalitis in kids. The most common route of transmission is colostrum and milk (vertical transmission) but horizontal transmission - from adult animal to adult animal - is also possible. CAE is contagious and incurable but positive animals might remain asymptomatic for years. A common practice to eradicate the disease or decrease likelihood of positive animals is to remove kids and feed CAE-negative milk or milk replacer at birth, especially if the kids are born to CAE-positive dams. Johnes, also called paratuberculosis or MAP, is a gastrointestinal disease caused by the bacterium Mycobacterium avium subspecies paratuberculosis. The most common clinical symptom is wasting despite good appetite. Profuse diarrhea can also occur. This disease can have a long incubation period and can live longer in the environment than CAE. The gold standard for Johnes testing is a fecal test, but blood serology and milk testing are also options. Johnes can transfer from ruminant to ruminant.
Caseous lymphadenitis or CL, sometimes abbreviated CLA, is caused by the bacterium Corynebacterium pseudotuberculosis. It is characterized by abscesses a major peripheral lymph nodes or within internal organs (especially the lungs) and lymph nodes. The external abscesses are more common in goats. While CL is incurable, it is is often considered more manageable than either Johnes or CAE. It usually enters the goat through an open wound or mucous membrane. It can live in the environment several months. There is vaccine for CL in the U.S. for sheep and goats now but is of limited usefulness and has had some adverse affects in goats, especially. Goat Medicine textbook has an excellent piece on this in Chapter 3. The serology test for CL is considered less reliable and culturing pus from an abscess is considered the best way to diagnose - read source 5 more on that. Goat Vet Corner also has some interesting discussions on the topic. General recommendations: Animals that have been sick or severely stressed, does within 30 days of kidding or 30 days after kidding, or any goat within 30 days of vaccinating should not be tested. Johnes tests are best on animals over a year old because of the long incubation period. CAE tests are best on animals over 6 months of age because the kids can show a false positive because of antibodies from their dam.
I do want to point out that tests are not infallible, not all labs are created equal, and biosecurity practices and goals vary from farm to farm. Because of the low specificity of the CL serology test, I choose not to test for it at this time. It was a decision made after having and reading many, many discussions with goat vets and especially folks in diagnostic labs. If a goat develops an abscess, then I will have it cultured. I have had NO history of CL in this herd. Most animals I've purchased do test and have had long-time negative results or no history of CL. I am confident the risk is very, very low. Now - on to the results! All adult animals (over 1 year old) in the herd tested negative for Johnes and CAE November 2020. I used UBRL this time (previously I used WADDL) and was very pleased!
Smith, Mary C., and David M. Sherman. Goat Medicine. Wiley-Blackwell, 2009.