Success in Minimizing Summer Eczema (sommerekzem) (Published in October, 2003 Eidfaxi)

By: Dr. Barbara Sollner-Webb bsw@jhmi.edu, Professor, Johns Hopkins University School of Medicine, Baltimore, MD, who has two wonderful Icelandic horses in her backyard.

As probably almost all Icelandic horse owners in the US know, SE stands for Summer Exema/Excema/Eczema (alternate spellings), also called Sweet Itch. It results from an intense allergic reaction to the bites of no-see-ums, small swarming insects technically called culicoides. It occurs primarily in horses who were not exposed to these insects early in life, and it causes extreme itching, so that the horse violently scratches and bites the afflicted area. In mild cases, sections of fur are scratched off yet the skin stays mostly intact, while in more severe cases, the horse scratches and bites until the skin on the whole afflicted area is torn open and bloody. Different varieties of no-see-ums, which live in different areas of the US, preferentially bite different parts of the horse; in Maryland we have a rather wide-spread variety that attacks mainly the belly midline, also somewhat the chest, mane and face, and less so other parts of the horse.

I would like to share with other Icelandic horse owners how we have turned the terrible SE allergy of my first Icey into a quite easily manageable condition that is not too much bother for us or him. I am anxious to find out, from owners of other SE horses, if the regime we hit on that works very well for my SE Icey and for my friend's SE horse is similarly successful on other Iceys, including ones in areas with different no-see-um varieties. Further, there is hope that treating horses prophylactically may prevent onset of the allergy.

I got my first Icelandic horse shortly after he entered the US, 2 /12 years ago, and he developed a truly bad case of SE partway through his first US summer. The entire centerline of his belly rapidly became a torn-up disaster: multitudes of fresh bloody sores were continuously developing from his violent scratching of new bites before the previous bites in an area could begin to crust over. Individual sores were also appearing on other parts of his body. This bad allergy developed despite our diligent spraying with a recognized bug spray, to try to prevent an onset of SE. (However, I later learned that this particular bug spray does almost nothing against our no-see-ums, so its use provided no deterrent to his developing the SE allergy.) My reading had turned up no simple treatment to prevent the bites, short of completely covering the horse with a Boett blanket (basically a long pajama) or arranging for someone to regularly bring the Icey into a poop-free stall, ideally with a chest-high fan, for several hours each dusk and dawn; in our backyard "farm", given our work schedules, this would have been very hard to achieve. I also had read of no way to prevent the bites' intense itching, and hence their being scratched, short of massive steroid treatments to suppress the immune system.

Being an experimental scientist by profession, I decided to test different bug sprays and liniments for their effectiveness against SE. Testing bug sprays against no-see-ums is easy, since these are the insects that cluster around fresh poop piles. I was amazed to find that many standard sprays, which work well against flies, had minimal effect on no-see-ums. But fortunately, others were successful! Try the simple "poop test" yourself: divide a fresh pile into several smaller ones and spray each with a different bug spray, except a few "control" piles that remain un-sprayed, and check a few minutes later. I found that piles sprayed with Repel-X, Gnat-Away or Skin-so-soft had nearly as many no-see-ums as unsprayed ones, but piles sprayed with FlyGone 7000 had far fewer! After repeating the experiment and confirming that Flygone 7000 kept away the vast majority of the no-see-ums, we started treating the Icey with this bug repellant morning and evening, spraying mainly the belly midline but some all over, also rubbing some by hand on the face. Impressively, my Icey's SE improved!! Rather than getting so many new bites that his whole belly midline was continually scratched bloody, the skin started to crust over, punctuated by a limited number of new bloody sores. Furthermore, the number of new sores on other parts of his body also diminished dramatically. This impressive reduction in the number of new bites was very encouraging and provides the first level in a multi-barrier approach to control my Icey's SE.

So we were part way there. I then began testing various anti-itch ointments, because of course it is the itch that causes the horse's scratching and biting, which in turn makes the bloody sores. Again, you can try the test yourself, monitoring for several days how bites progress when treated with various candidate liniments. Draw an imaginary line down the center of the belly area and one running across, dividing the horse into four quadrants, and before each bug spraying, rub a test liniment on the sores of a quadrants, while leaving one quadrant without liniment. Include also the individual bites that the horse gets further up his sides. Most informative are the developing sores that you notice when the fur is partly scratched off but before the skin becomes raw or broken. I found that SWAT and Vaseline both did minimal, while Calamine helped some. Then an Icelandic friend gave me an product called Equus Lotion from the Icelandic company SDS-Smyrsl. It worked amazingly well!! This lotion clearly makes the no-see-um bites much less itchy, since the treated belly sections began to heal with a few days of treatment. Already after one treatment, the individual developing sores elsewhere on the horse looked less irritated, in contrast to untreated ones which became more abraded, generally bloody.

After figuring out an appropriate bug spray and liniment, I stopped testing other products and started treating all the afflicted areas of the horse, and his condition improved dramatically. Throughout the remainder of his first no-see-um season, this regime sufficiently reduced the new bites and their itching so that only quite sporadically did new bloody sores develop. The old sores healed, and his belly centerline grew continuous new skin for the first time in many weeks. When it first turned hot and buggy the next summer, my Icey's second in the US, his SE started again. But this time we were ready and immediately resumed the routine of twice daily spraying with FlyGone 7000 and dabbing any starting sores with SDS lotion. He still got some bites, and scratched some, but generally none formed bloody sores, and he retained much more mane than the previous year! But on occasions when treatment got lax, sores rapidly developed, so we knew the regime was working. That fall, fur even started to grow on his belly again, which had remained bald scar tissue the previous winter.

My Icey's third US summer, 2003, was far better still. Most of the time, he needed only the Flygone to prevent any SE sores. And when a sore occasionally started to develop, a single application of the SDS lotion usually gave sufficient relief that it healed. This impressive improvement might suggest that Icey is becoming somewhat tolerant of the no-see-ums. However, I suspect it is in large part due to his having learned to minimize contact with these bugs. Specifically, each dusk and dawn, when the no-see-ums come out en masse, he leave his equine buddies in the field and walks into the barn, where there are far fewer of these insects! And after a few hours, when the no-see-ums have dissipated, he goes back outside. He certainly has learned to make good use of his free access to the barn and field.

In summary, we have hit upon a multi-barrier approach to minimizing SE: First is a bug spray that is effective at greatly reducing the number of no-see-um bites. Second is a liniment that greatly reduces the itching at each bite which gets through that first line of defense. Finally, an additional valuable line of SE defense is having the horse indoors at dawn and dusk, when no-see-ums are most active, in a poop-free breezy area. Since our schedules did not permit bringing Icey in at these times, this brilliant fellow learned to do it for himself.

Let me note a few additional points: First, while the SDS Equus Lotion seems nearly magical, it isn't sufficient alone. Without an effective bug spray to reduce the vast number of no-see-um bites the poor Icey gets, a little scratching at each bite adds up to a lot of total scratching and still a bloody belly. Second, since bug spraying is new and scary to many imported Iceys, you may have to teach its acceptance; easy is to start by spraying water (so no smell) and reinforce using lots of treats. Third, no-see-ums are smaller than the mesh on most flymasks, so you need to apply bugspray to the face (but avoid the eyes and mouth; I spray it in my hand and rub that on the face). Fourth, while Flygone 7000 and the SDS lotion work very well, there certainly will be other successful products. However my experience is that most recommended flysprays and liniments seem minimally effective for SE, so test products before relying on them.

Finally, I'd like to raise an idea for new imports. Since it is well-known that the way to prevent a bad allergic reaction (like SE) is to never get a large dose of the irritant (the no-see-um bites), I suggest that immediate regular spraying with a bug spray that is effective on no-see-ums should greatly minimize new SE cases. Indeed, when I imported a second Icey a year after the first (we all know that Iceys are like potato chips and you can't have just one!), we immediately used Flygone 7000 as her bug spray. Most encouragingly, she has not developed SE! In contrast, I know ten other Icelandic horses that arrived in our general area in this same time period, and all but one developed SE already their first US summer. While certainly not statistically significant, my Flygone-sprayed horse beating these odds is very encouraging.

If your Icey has SE, or you are importing a new Icey into a SE area, I urge you to try this regime; see if it doesn't make your horse quite comfortable. He or she will certainly be very appreciative of any relief, for SE must be something like us having a bad case of poison ivy all summer long. And please, do let me know how things go with your horse's SE; my e-mail is bsw@jhmi.edu. Good luck!
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[Purchase information: Flygone 7000 is marketed by Horseman's Dream and is available at many local tack stores ($15-$20/quart) or online from Valley Vet (http://www.valleyvet.com; $36.49/gallon plus shipping) or American Livestock (http://www.americanlivestock.com; $10.50/quart with free shipping on larger orders). I use about 2 gallons per Icey per summer. Fortuitously, SDS Equus Lotion has just started being imported into the US by BR Imports L.L.C. (http://www.sdsproductsusa.com; e-mail: info@sdsproductsusa.com); $21.95 for 500 ml (slightly over a pint); I used two bottles the first summer and two bottles since then.]
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about myself: Barbara Sollner-Webb, bsw@jhmi.edu, is a Professor at Johns Hopkins University School of Medicine, Baltimore, MD, where she and her students study basic processes of gene expression. High on her list of favorite hobbies is trail riding, and she has two wonderful Icelandic horses in her backyard. She feels that Iceys are the perfect breed of horse, at least for a middle-aged lady who loves nature and riding and having a horse who is a real compatriot. Barbara's husband and grown daughter are also confirmed riders, although of big horses. The family also includes a delightful rescue dog (an enormous St. Bernard who sleeps on the bed) and a captivating pot-belly pig (who had been thrown out on a freeway in a snowstorm).
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SE article #2:

SE is a Lesson in Immunology (Scheduled to be published spring, 2004, in Eidfaxi)

by Dr. Barbara Sollner-Webb, bsw@jhmi.edu, Professor, Johns Hopkins University School of Medicine, Baltimore, MD, who has four wonderful Icelandic horses in her backyard.

Sweet Itch (SE) is an allergic reaction to the bites of no-see-ums (technically called culicoides) and it provides a real-life lesson in basic immunology.

To better understand the affliction and to devise ways to mollify its severity and hopefully prevent its onset, lets start by reviewing a few key facts in immunology. Most fundamental, when an adult animal is exposed to a foreign protein or other biochemical ("antigen"), it generally elicits an immune response that involves developing antibodies which provide the animal with immunological protection against the invasion. However, depending on the antigen and especially on the magnitude of the initial doses, a very intense immunological response can ensue and create an allergic reaction on repeated exposure. This is the basis of SE in imported Icelandic horses.

Now, it would be disastrous if the developing immune system in a mammalian infant were to generate antibodies to molecules from its own body. So evolution has arranged that biochemicals which the baby contacts before birth and for a while after birth are recognized as "self" and do not elicit an immune response. [When this self-protection fails, it is called an "auto-immune disease".] Then for a while, until the baby's immune system is fully developed, invading antigens elicit mild immune responses but generally not the intensity for an allergic reaction.

A familiar example is chicken pox, in humans. Babies who are exposed to this virus in their first few months generally develop no obvious reaction, but when later re-exposed, they are refractory to the allergic response that we call "chicken pox". Yet without an initial exposure (or immunization, as is now available for chicken pox), later exposure almost certainly causes the allergic reaction.

With this background, SE starts to makes sense. Foals born in SE areas get bitten by no-see-ums early in life, so generally do not develop an allergic reaction. Conversely, horses imported as adults from Iceland into SE areas will have had no such early protective exposure and thus are prone to the SE allergy. It develops due to the very large number of no-see-um bites that unprotected horses can get in a single day.

Because the intensity of the exposures is important in determining whether an antigen elicits an allergic reaction, it is important to minimize the number of no-see-um bites that a horse receives. That is why bug sprays which are effective against no-see-ums can help prevent SE, even though the horse still receives some bites. It also explains the virtue of bringing SE horses inside, under fans, at dusk and dawn, when no-see-ums are the most voracious.

With this information, you may well be wondering why horses born in the US, but in an area not afflicted by SE, frequently do not develop SE when later moved into a SE area. For this, one more fact about immunology is needed, namely, that an immune response raised against a particular antigen generally provides a partial response to closely related antigens. And the US has ever-so-many more kinds of bugs than does Iceland, including various ones related to SE-causing no-see-ums. Thus, horses born in areas where they get exposed to such bugs would be much less likely to develop an allergic reaction, when brought into a SE area, than horses brought from Iceland, that did not have such an early exposure.

Now indulge me with a bit more immunology: It is known that frequent very low doses of an antigen generally do not generate an allergic reaction, but rather elicit a protective immunity. This is the principle behind desensitization shots, such as people can get for poison ivy or bee stings. Certainly this logic should extend to no-see-ums and horses. That is why my recent (October, 2003) Eidfaxi article on SE suggested that newly imported horses should religiously be treated with a bug spray that has been proven effective at markedly reducing the number of bites from no-see-ums. It will be important to spray every single day that the horse might be exposed to those bugs, for a good long period, so that the horse never receives a large number of no-see-um bites until after its immune system has been desensitized to this antigen, which fortuitously should result from the limited number of bites that the horse will receive despite the bug spray. [I suggest using FlyGone 7000 in the AM and PM throughout their whole first spring/summer/fall in the US, and in their second year at least the spring and part of the summer, and then to use this spray as their forever insect repellent.] Should the new, long-lasting bug treatments prove to be similarly effective against no-see-ums, they should simplify this treatment considerably.

By considering the immunological basis of SE, we have already found a regime that largely alleviates the allergic symptoms in my first imported Icey, who had developed a terrible case of it during his first US summer. Hopefully the above-suggested desensitization protocol can help prevent the onset of this very nasty affliction in most imported Iceys.


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Added note:

An exciting-looking product called "FLY_BAN HORSE SPOT-ON" was advertised in the spring 2004 "Country Supply" catalog that it "Kills and repels members of the Culicoidae and Simuliidae vectors that may cause Sweet Itch... especially useful on horses turned out to pasture." However, the manufacturer told me they have temporally pulled this product, to re-word their packaging and advertising, for tests have shown it is no more effective against SE than standard Permethrin-containing spot-ons.
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Another product that may help with dermatitis: M-T-G http://www.shapleys.com/