At present there is no cure for Sweet Itch. Once an animal develops the allergy it generally faces a 'life-sentence' and every spring, summer and autumn are a distressing period for horse and owner alike. The animal's comfort and well being is down to its owner's management.
There are two basic approaches:
Minimise Midge Attack
Avoid marshy, boggy fields. If possible move the horse to a more exposed, windy site, e.g. a bare hillside or a coastal site with strong onshore breezes. Chalk-based grassland will have fewer midges than heavy clay pasture.
Ensure pasture is well drained and away from rotting vegetation (e.g. muck heaps, old hay-feeding areas, rotting leaves).
Stable at dusk and dawn, when midge feeding is at its peak, and close stable doors and windows (midges can enter stables). The installation of a large ceiling-mounted fan can help to create less favourable conditions for the midge.
For slight to moderate cases of Sweet Itch this can help. However a seriously itchy, stabled horse has hours of boredom during which to think up new ways of relieving his itch - manes and tails can be demolished in a few hours of scratching against a stable wall. If stabling can be avoided it is best to do so.
Use an Insect Repellent.
Since we became involved with Sweet Itch we have always recommended and been able to supply DEET. Used at close to 100% strength this has given around six hours of excellent protection from midges. The higher the percentage of Deet contained in a product the greater the period of efficacy will be.
Unfortunately 'the powers that be' have introduced a ruling which states that fly repellent products for animals should contain no more than 20% DEET. We consider that this provides too short-lived a protection for horses suffering from Sweet Itch.
Somewhat ironically human beings can still buy and use higher percentages of DEET on themselves - presumably because we are unlikely to eat each other? We currently know of no insect repellent that repels midges for a suitably prolonged period unless it is being used for the mildest of Sweet Itch sufferers.
Use an insecticide.
Some owners achieve good results with insecticides whilst others find they have shown little benefit in controlling Sweet Itch.
Benzyl benzoate was originally used to treat itch-mites (scabies) in humans and has been used for many years to combat Sweet Itch. In its neat form it is a transparent liquid with an aromatic smell, but it is more commonly obtained from Vets or pharmacies as a diluted milky-white suspension. It is listed as an ingredient in several proprietary formulations, including Carr & Day & Martins' 'Killitch'.
Benzyl benzoate should be thoroughly worked into the skin in the susceptible areas every day. However it is a skin irritant and should not be used on the horse if hair loss and broken skin have occurred - application should therefore start before symptoms develop in the spring. If used later its irritant properties can cause areas of skin to slough-off in the form of large flakes of dandruff.
Other insecticides, including permethrin and related compounds, tend to be longer lasting but should also be used with care. Permethrin is available by veterinary prescription (e.g. Day, Son & Hewitt 'Switch' pour-on liquid). Application instructions should be followed.
Note: Gloves should be worn when applying insecticides, including benzyl benzoate. Particular care should be taken if they are used on ponies handled by children - they can cause eye irritation, for example if fingers transfer the chemical from the pony's mane to the eyes.
Oils & Greases
Coat the susceptible areas of the horse with an oil . Midges dislike contact with a film of oil and they will tend to avoid it. Commonly used preparations include Medicinal Liquid Paraffin, and 'Avon Skin-so-Soft' bath oil (diluted with water). There are several oil-based proprietary formulations, for example Day Son & Hewitt's 'Sweet Itch Lotion'.
Oils and other repellents that are effective usually work for a limited time: In summer a horse's short coat-hair does not retain the active ingredient for long and it can be easily lost through sweating or rain. Re-application two or three times every day may be necessary.
Greases (usually based on mineral oils) stay on the coat longer, but they are messy and therefore not ideal if the horse is to be ridden. They can be effective if only a small area of the horse is to be covered. However it is impractical and often expensive to cover larger areas.
Some preparations contain substances (e.g. eucalyptus oil, citronella oil, tea tree oil, mineral oil or chemical repellents) that can cause an allergic skin reaction. Always patch test first on the neck or flank of the horse - apply to an area about 3 cm across and look for any sign of swelling or heat over a 24 hour period before using more extensively.
Allow Midge Attack, but try to minimise the resultant allergic reaction by:
Depressing the immune system with cortico-steroids (e.g. by injection of 'Depo-Medrone' or 'Kenalog', or in tablet form as 'Prednisolone') may bring temporary relief, but there can be side effects, including laminitis, in some animals. With time, corticosteroids may become less effective, requiring ever larger and more frequent doses.
The use of anti-histamines may bring some relief, but high dose rates are required and they can make the horse drowsy.
Applying soothing lotions to the irritated areas. Soothing creams such as Calamine Cream or 'Sudocrem' can bring relief and reduce inflammation, but they will not deter further midge attack. Steroid creams can reduce inflammation.
It is often difficult to assess the effectiveness of a particular treatment. The incidence and severity of Sweet Itch is so highly dependent on midge numbers, apparent success may simply reflect a temporary fall in numbers due to a change in the weather, for symptoms only to return again later when weather conditions are more midge-favourable.