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  Discussion on Stopping pigeon fever
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Posted on Sunday, Dec 2, 2001 - 10:49 pm:

Hi...I have read the article along with many others on the web and the Merck Manual for this disease. It is quite clear that I now have a "miniepidemic" going on here at my large horse farm. My question is not about the diagnoses - although I will confirm it by culture -but rather the containment and treatment. A little history. We first moved to this property in 1986 and there were 7 horses here at the time. That late spring 2 of those horses that we boarded for a short time until they could be moved came up with pectoral abscesses that drained. My vet at the time said it was "dryland distemper" or coryne pseudotuberculosis. He was most likely correct as they followed a relatively uncomplicated course of the disease and recovery consistent with most of the literature. They went on their way and I did not think much about the reoccurrence of the disease.(although I should have!) Nor did it seem to reoccur. Even though our farm which at times has had as many as 150+ horses on it, has had it's share of what I call "daycare" diseases - including a strangles outbreak in 1988 and persistent rodococcus (now controlled by postnatal transfusions). Anyway, we are now at about 75 horses, all of which are kept completely current on all vaccines and worming etc.... In fact, the overall health care at the farm is really excellent. But there are a large number of horses in close quarters. Suddenly three weeks ago I had 4 mares in one pasture only come up with draining sores on their ventral midline and some associated edema. Thinking this might be a late season onchocerciasis (which one of the mares is prone to anyway) I rewormed them all with ivermectin again (they had been wormed one month prior), treated them heavily with fly spray for days and kept an eye on them but did nothing else as no one had fevers or was ill. The sores and edema (which I did think the edema was a little strange for onchocerciasis)subsided and the mares seemed fine within a few days. Unfortunately it is time to regroup my girls according to foaling status - so 2 of them who are pregnant were moved to a different pasture and one old lady was moved to the retirement pasture. The other 5 horses stayed put (leaving only 1 in that pasture that had the healed sores - the other 4 had been symptomless). Well, a few days ago or about two weeks after they were totally clear of all symptoms - 2 of the original 4 now have VERY large pectoral hard, hot swellings and some edema between the front legs. Their midlines are clear at this time. And yesterday the other 2 mares that had the previous sores- 1 is now draining on the midline again (but no edema)and no pectoral edema or other signs and the 4th mare also has the large pectoral swellings. Now today a 5th mare who has been symptom free until now has come up with the pectoral swelling and edema between the legs. Pigeon fever is a good name as her chest indeed looks like a pigeon. This 5th mare was one of the horses in that original pasture that the previous 4 had been sick in.

Here is my problem - oh boy....I had moved them. The 5th mare to come up with this had been moved to a pasture of other pregnant mares who were previously "unexposed" - if you go by the initial location (one pasture only that showed signs). Also the one old lady that was moved to the retirement pasture has now started draining on the midline again and has "exposed" the 2 oldies in her pasture. My other 3 I have quarantined in a paddock together for now. I am going to move all the affected horses tomorrow to the same pasture in with the old horses as this is the farthest from all my pregnant stock and not contiguous with any other pasture. I can treat them all from there. My questions - Do I attempt to disinfect any stalls in which these horses might have been temporarily placed in? (we housed some during the day temp. while we moved horses around - but no one was actively draining at that time) And with what? How did they contract this again? From the soil after 15 years??? If that is true then that pasture is contaminated and I might as well move the sick ones back to that pasture - but why now after 15 years?? (it is the same area of the farm from the infection in 1986) Plus that pasture borders a mare/foal pasture! With 2001 foals still by their dams side! Or could they have contracted this from a farrier who had trimmed that very pasture (and only that pasture) 2 weeks before anyone showed signs? Of the 8 horses he trimmed that day - 5 have now gotten sick!! From the resident goat? (who had chest edema last year that came and went in a week - we thought he had been kicked) From the deer and/or cattle next door? The deer feed frequently in the infected pasture. But why has the outbreak until this point seemed confined to that one pasture? (I am trying to decide what to do with the other horses in that pasture who are obviously exposed but not showing signs yet) Also, I am in a panic envisioning this sweeping through 75 horses and foals etc....that would be a nightmare to treat and contain. So far, no horse is showing any systemic illness and no swellings are soft enough to lance - though I will check them and have the vet also check them to make sure when they are ready. I understand how to lance/flush/etc... And know all about many antibiotics including using rifampin for walled off abscesses (as in rodococcus or an internal strep zoo.) as I am a vet tech and probably more than that a farm manager for over 20 years who has seen and treated alot. And if it stays confined to only these few horses we can manage - but with so little known about the spread of this - how do I attempt to "quarantine" these horses and keep it from the rest? One last question - if no horse is showing systemic signs - should I worry about internal abscesses? Do you only test and/or treat if they manifest clinical signs? I read you can run a serological test at UCD, but it is best for confirming internal abscesses and not external (of course external you can see) - this would be expensive for the entire herd - but to keep from losing one of them to a "silent killer" it would be worth it if needed. IF so, what timeframe would indicate infection and be best to draw the titer? Otherwise, do I just monitor the herd closely and any horse that is acting ill we suspect this as a possibility and investigate with ultrasound, blood tests and any other method?
Sorry to be so long winded but this is a tremendous management challenge for me -and my vets (I have 3 different vets for various specialties) all have very little experience with this.....other than recognizing the disease,and basic treatment plans which are basically what is recommended in your article. They do not have many answers on what to do in a large herd situation to manage and control it from spreading. They are rather at a loss as to why it has appeared again and what exactly to do besides treat the few infected now.

Any help or guidance would be GREATLY appreciated!

Becky

Posted on Monday, Dec 3, 2001 - 6:48 am:

Hello Becky,
I think you may have misunderstand what has happened in your recent outbreak Becky. The initial outbreak of Pigeon Fever was not first evidenced by the draining sores, but probably caused by them. Yes we believe these organisms are persistant in the soil for many years and possibly there forever. These sores allowed the organism, that is probably present in your soil, to get a hold on these mares.

From an epidemiological point of view, you need to try and figure what caused the sores and what more you could have done in treating them to prevent entry of the Corynebacterium pseudotuberculosis to try and prevent future cases. From your description the ventral edema and sores were most likely fly bite reactions, midline dermatitis from onchocercha does not occur in horses that have been dewormed regularly with good products. (see articles on deworming, onchocerca, and midline dermatitis).

I do not think the farrier is likely to be the source of the infection, though I cannot be sure. Perhaps if he were handling a horse with open and draining wounds before comeing to your farm.

Assuming the diagnosis is correct, these horses are not contagious while the abscesses grow, however the draining puss is likely to be a large source of contamination and needs to be confined to an area that can be disinfected. For information on disinfectants run a search on disinfectant. I highly recommend the first title that comes up from the University of Nebraska.

As to testing the whole herd for the chance of catching internal abscesses....I do not think this would be my course. Your best prevention is isolation of those with the disease, early aggressive treatment of wounds with frequent application of antibacterials and a extra eye to keeping them from becoming contaminated with dirt.
DrO

Posted on Monday, Dec 3, 2001 - 11:15 am:

Thank you for your quick response. I did consider exactly what you said - that perhaps the initial sores were the entry point. And I am very familiar with the onchocerciasis but to be sure I read your article and it concurs with the other research I have done....one of the main signs pointing to this I feel is that it will often flareup following a recent worming with ivermectin. And I have several horses that seem to be most sensitve to this.....and 2 of the 4 that intially started with this are those. We had just wormed with ivermectin when they exhibited their signs of crusty dermatitis and some edema - consistent with the reaction they often get when wormed with ivermectin. Usually, if I give them another dose or if needed a dose per week for a month - it will go away. Rarely do I have to use corticosteroids. So, that is why I treated it as their normal reaction -although suprised because these 2 mares I felt we had gotten under control with their onchocerciasis problems. And then the 2 that had never exhibited it before.... But here is the difference; in the back of my mind I did think this was more swelling than normal and one of the mares was draining quite off center of the midline and had large edema around where she was draining - something I have never seen with any onchocerciasis or even fly bite reactions. Then the 2 mares that had symptoms but had never had onchocerciasis before -- now in hindsight I realize showed some edema between the legs too.... And certainly in 15 years this is not the first open wounds to be in that pasture. Try as I might - with this many horses - wounds will occur and it may be a 1/2 day before one of my crew catches it - so I have treated many a wound through the years and scratches also in that pasture. Why now, would these wounds become contaminated with C. Pseudo?
I plan on asking the farrier if he had worked on any horses that had abscesses - he also has and works with cattle and goats daily...though it appears that may not cross species infect? I really think the initial cases just presented more with abdominal swelling than chest swelling in the initial stage - of course we will never know the answer to that - perhaps they did get contaminated through their midline wounds.

But it seems that you feel the primary contaminant then is the pus from any draining sore. That hopefully, my other pregnant mares which have been in pasture with the one mare who now has swelling but NO draining will not be exposed? So, if I quarantine all the horses with signs, symptoms to one area and treat them through this using isolation procedures I should limit the spread? Then when done I have the daunting task of figuring out how to disinfect a paddock on an organism that thrives in soil - hmmmh kind of like that rhodococcus dilemma! Near impossible. I simply cannot stall all of them right now. I only have 2 hospital stalls and my crew would spread it in 2 seconds in my show barn.

I really appreciate the response and hope indeed that these measures will curtail this! I am still mystified by the circumstances that would create this to flare again after 15 years! Such a long time through winters and unbelievably hot summers. And no real change in management practices - in fact as we learn more all the time the horses get better and better care. My farm would probably be a great lab for an epidemiolgist!

One last question. We did have a mare arrive here for breeding in 2000. She came from northern CA and was very thin, lethargic and anorexic upon arrival (the owners had missed all this). To make a long story short - she went through all the signs of an internal abscess which we did diagnose by ultrasound and palpation. We sent her home on long term antibiotics. Their vet had mentioned pigeon fever as a possible source of her abscess. I know the mare eventually was put down from a severe colic due to the abscess - they chose not to do surgery. Could this be a more recent source of the bacteria? She never did drain while at our farm - but I gather had been at a location prior to arrival where others had been sick. The unlikely problem with this is she was never in with our resident herd - but in outside mare paddocks - so she never could have contaminated the particular pasture we seem to be having problems with. But she did go into the breeding stocks etc....and so did all the other mares?

Now thinking of redoing my practices concerning outside mares in common areas?

Thank you,
Becky
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