Sweet Itch. Summer Eczema. Gnat Allergy. Seasonal Equine Dermatitis.
Insect bite hypersensitivity (IBH), typically caused by Culicoides biting midges (aka gnats or no-see-ums), is an allergic skin reaction that equines have to the saliva of the little biting buggers. IBH can also be caused by black flies, horn flies, barn flies, horse flies, neck threadworms, and, of course, mosquitoes. We most commonly see Culicoides hypersensitivity in our area.
Horses who suffer from this condition scratch excessively, resulting in hair loss usually seen along their mane, tail and stomachs, and sometimes even going so far as to cause open sores. The horse will frequently be seen itching on anything they can get their neck, tails and bellies on - the ground, a tree branch, the fence. While there is currently no cure, there are some preventative steps that can be taken to try to minimize the horse's exposure to the midges.
Apply fly repellent frequently and diligently. Make sure repelling & killing gnats is on the label, as it is on Tri-Tec 14, Pro-Force, and Pyranha. For more natural options, check out Ecovet and Nature's Force. (*Note that these don't specifically list gnats on their labels but have been found to be effective)
Apply a topical ointment to affected areas. The barrier created by the ointment makes it more difficult for insects to bite and can also provide relief to skin lesions.
Use a well-fitting, breathable sweet itch blanket. These should include a belly band and may have a neck +/- head cover (Google "sweet itch blanket" for options). It is best to start using it before the itching starts, otherwise the horse may destroy the blanket while scratching on anything and everything!
Avoid putting sensitive horses near manure piles, standing water or other livestock, which can attract these biting bugs.
If the horse is stalled, use a stall fan - biting insects can be poor flyers.
Utilize Fly Predators, tiny, parasitic wasps that interrupt the life-cycle of pest flies and can help minimize pest populations.
If your horse is one of the unfortunate victims of severe insect bite hypersensitivity, and no amount of management can relieve their itchiness and discomfort, call your vet for the big guns: steroids. Once a horse hits their threshold for allergic reactions, it can be hard to get them back without the use of low doses of corticosteroids, such as dexamethasone. Topical steroids can also aid in relieving itchiness, especially on stomachs. Unfortunately, antihistamines, such as Benadryl (diphenhydramine) and Zyrtec (cetirizine) don't appear to be overly effective against IBH.
Insect bite hypersensitivity can be a challenge to deal with but, if you utilize the above management tips and work with your veterinarian, you can hopefully get your horse through the fly season with minimal stress and scratching.
**Tacoma Equine Hospital does not guarantee or endorse any of the products linked to or mentioned in this post; they are used as examples only.**