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CASEOUS LYMPHADENITIS (CLA, BOILS, ABSCESSES) IN GOATS
WITH SUPPLEMENTAL COMMENTS ABOUT SHEEP
By: John S. Glenn, D.V.M, Ph.D.
What do you do after the diagnosis is confirmed?
Important characteristics -
b) once organism enters body, can be transported within cells - which protects organism from host's defense mechanisms (i.e. - antibodies); animal is infected for life and may or may not show intermittent clinical signs
c) body builds thick walls around abscesses - which protects organisms from any antibiotics administered to the animal
d) typically sets up housekeeping in lymph nodes and lymphoid tissues - especially superficial lymph nodes around head, chest, flanks; also occurs in lungs, spinal cord, liver, abdominal cavity, kidney, spleen, brain
e) animal may have external boils without having internal boils and vice versa - no way to predict
f) location of boils determines risk of transmission of organism to other animals - all external boils pose a high risk when draining, as do any boils in the lungs - boils in other tissues, while potentially harmful to the animal, probably don't pose a great risk to other animals
g) lots of argument about how long organism can persist in the environment; more important to know how long it poses a practical threat - probably a matter of days if just smeared on surfaces, probably a matter of weeks/,onths if incorporated in organic material - bottom line is that resting pastures and pens for at least a month (especially in summer) probably reduces potential exposure to a minimum; scraping the top 2" - 4" of soil from pens and replacing with new sand or dirt will reduce contamination potential miscellaneous - organsims couldtheoretically leave infected animals via the following routes:
RESPIRATORY TRACT: coughing, nasal secretions releasing stuff from lung abscesses - important! High density (crowding) foster transmission by this route
URINARY TRACT: very unlikely to be shedding in urine (would need to have an abscess in the kidney
GASTROINTESTINAL TRACT: reported to be present in the digestive tract but no one has any good data to implicate manure as a significant source of infection - plus goats are so finnicky about what they eat - certainly would be a good idea to clean up manure and keep it out of feed bunks but I wouldn't be paranoid about it - would be most concerned about animals that were thin and "wasting" - need to remember that two other causes of "wasting" are CAE and Johne's
MAMMARY GLAND: there have been reports of shedding in milk if there are abscesses in the udder - risk that offspring could be infected this way (another good reason to pasteurize milk for human consumption)
2. Initial infection of a herd
3. Perpetuation within the herd
b) environmental contamination of feed, water, and equipment (milking equipment, clipping equipment, feeders, fences) by infected animals (personally I don't think this persists as long as people say - which is to say that with good sanitation you can pretty effectively control this route)
c) human hands (touching infected material and then touching another animal or milking without thoroughly washing hands - see comments in Sanitation and Lancing Abscesses section below
4. Other causes of "abscesses"
Occasionally, goats will develop salivary cysts along the jaws. If the contents of these are aspirated, it will contain a perfectly clear, very viscous fluid.
CONTROL - identify INFECTED animals and keep completely separate (housing, feeding) from CLEAN animals - this means no contact (see exceptions below) or sharing of space. Arrange husbandry routine so you work with INFECTED group last (to lessen chances of carrying organisms back to clean group).
MILKING - milk INFECTED group last and then clean-up well. Don't bring any does with draining abscesses into the milking parlor; wear gloves and change them if you touch an abscess - don't ever treat an abscess in the milking parlor.
BREEDING - OK to use clean bucks on infected does (but never on a doe with an active abscess, severe coughing or wasting (can use AI on these cases)) - try to minimize any contact time - obviously AI would minimize the risk.
HOW TO GROUP ANIMALS
Note 1: While it is true that a wide variety of other organisms can cause the occasional boil, you can't take the chance of missing a true CLA animal - if the boil is from some other cause, you're going to be able to salvage the offspring anyway - see below.
Note 2: There is no point in spending money to test animals in the group - you have adequate evidence to assume they have been infected.
Note 3: Personally I'm not rabid about culling these animals as long as they appear healthy and are productive and you are willing to take the risk they pose to your control/eradication efforts. There is no reason the majority of them can't go ahead and lead a productive life. BUT if there is an animal in this group that you have second thoughts about for some reason, then use this as an excuse to cull them. Always cull animals with chronic weight loss - not only will you eliminate animals that may be shedding boil organisms, but will also get rid of ones with advanced CAE and Johne's.
Note 4: The most ruthless approach would be to automatically cull all visible cases, then blood test and cull all positives - retest remainder in a month - keep doing that until you got no more positives on two consecutive tests.
Note 5: Vaccines are discussed below - probably not a good idea to use and boils vaccines in this group of animals - #1, it's too late for them and #2, infected animals seem more prone to have a reaction to the vaccine.
2) Depending on number remaining in CLEAN group:
NOTE:, This is the very least effective alternative since you never get rid of animals that don't show external signs, but are still shedding the organism and infecting others - you can expect to constantly see new cases cropping up but it should slow the flow of them.
II) Blood Test
A strong response = actively INFECTED
A weak response = exposed at some point - treat as INFECTED
A negative response can mean several things: the animal could be in the incubating stages of the disease and just not have responded yet; the animal might be truly clean; the animal might have been infected and the body has the infection under control (walled off) - having said all that, I'd consider these negative at this point and just keep a close eye on them. If the CLEAN group starts popping up with abscesses, then you might want to test the group again. Test can be done by:
California Animal Health and Food Safety Laboratory System
- requires 0.5 ml of serum (red cells spun down and removed before shipping)
b) There are many different ELISA tests available and there is lots of variation in them. The ELISA tests best use is to survey a herd to determine whether the infection is present in the herd, versus using it to decide the fate of an individual animal (i.e. - it would be a good test to use on a herd from which you were considering buying replacements). In some of the ELISA tests, there has been concern that the ELISA will cross-react with Johne's Disease (Mycobacterium paratuberculosis) - although you don't want and Johne's Disease in your herd either so maybe it's a moot point.
A number of different states offer the test, as does the lab in Canada:
Mann Equitest Inc.
c) Just a few comments about laboratories - it's important to ask around and find a reliable laboratory and then stick with them - each laboratory uses slightly different procedures, uses different cut-off points and has it's own idiocycracies - it's important to develop a working relationship with the people so you can call and discuss questionable results with them (if you can't do this, then it's time to change labs) - this business of constantly changing laboratories and submitting samples to different laboratories until you get the answer you want is counterproductive - all you do is multiply the errors and confusion.
d) This discussion of tests is full of terribly gross generalizations - the reliability and interpretation of all the tests depends a lot on the level of infection in the groups of animals, so until you get some baseline data, it's pretty much conjecture as what's the best to use.
e) While it is true that all tests have some false positives, the even more disturbing aspect is that they all have some false negatives - in an eradication program it's the false negatives that really worry you. So the bottom line from an eradication standpoint is that you should feel comfortable about condemning any animal that tests positive but you should always be a little suspicious about animals that test negative (unless they came from a herd that has been thoroughly tested) - see comments above regarding possible reasons for negative tests.
f) Personally, if more than a quarter of the herd is infected and ruthless culling isn't practical, I'd skip the testing and go right to using the vaccine. If there are only a few animals infected, then the tests would be helpful in rooting out the few remaining bad actors. The MAJOR disadvantage of going directly to vaccination is that you then can't use the blood tests since you don't know whether the test is reacting to an actual infection or to the vaccination. This is a permanent downside of vaccination for this disease.
g) Regardless of what you do in terms of vaccination, it is critical to constantly observe these animals closely for any signs of abscesses. Certainly if any animals cough a lot or are very thin, it would be worth running the SHI test on them.
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