Sweet Itch is a problem that affects thousands of horses, ponies and donkeys in many countries of the world to a greater or lesser degree. Virtually all breeds and types of ponies and breeds can be affected, from tiny Shetland ponies to heavyweight draught horses, although the condition is rare in English Thoroughbreds. Sweet Itch is classed by vets as a reportable condition, which must be disclosed by an owner to a prospective purchaser before the sale. For the purpose of vetting, the allergy may be regarded as seriously as an unsoundness.
Diagnosis is not usually difficult – the symptoms and its seasonal nature (spring, summer and autumn) are strong indicators. However, symptoms can persist well into the winter months, with severely affected cases barely having cleared up before the onslaught starts again then the following spring.
Symptoms include severe itching, hair loss, skin thickening and flaky dandruff. Weeping sores, sometimes with a yellow crust of dried serum may occur. Without attention, sores can suffer a secondary infection. The top of the tail and the mane are most commonly affected. The neck, withers, hips, ears and forehead, and in more severe cases, the mid-line of the belly, the saddle area, the sides of the head, the sheath or udder and the legs may also suffer. The animal may roll frequently and attempt to scratch on anything within reach. It may pace endlessly to try to rid itself from the itching. There can also be a marked change in temperament – lethargy with frequent yawning and general lack of ‘sparkle’ may occur, or the horse may become agitated, impatient and when ridden, lack concentration. When flying insects are around he may become agitated, with repeated head shaking.
Horses that go on to develop Sweet itch usually show signs of the disease between the ages of one and five and it is common for the symptoms to appear first in the autumn. Hereditary predisposition may be a factor. There is anecdotal evidence that stress (e.g moving to a new home, sickness, or severe injury) can be a factor when mature animals develop Sweet Itch.
So – What is Sweet Itch?
Basically it’s an allergic skin disease. Certain horses are allergic to the saliva in the bite of a species of midge called Culicoides. This means that once a sensitive horse is bitten by a Culicoides fly, it will have an allergic reaction at the site of the bite. This will cause a localised irritation which the horse will try and rub. Self- inflicted damage will occur as the horse itches himself. Culicoides adults mainly rest among herbage and are most active in twilight, calm conditions. Breeding sites are commonly in wet soil or moist, decaying vegetation. They are tiny, with a wing length less than 2 mm and able to fly only a short distance (100 metres or so).
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. The installation of a large ceiling-mounted fan can help to create less favourable conditions for the midge. Insect-proof stables using fine-mesh screens. Try using commercially available sheets and hoods to rug the horse with when he is turned out. 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.
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.
Rugs designed to cover the horse or pony completely from the midges are also a very effective way in reducing sweet itch. Keeping turnout to night time during the warm seasons and bringing them in out of the warm sunshine helps immensly in keeping this troublesome condition at bay.
The conventional wisdom is that allergies are an over-reaction of the immune system. To this end, most veterinary treatments work by dampening the immune system. In the long term this cannot be a good thing for the horse, so prevention, as they say, is better than the cure.
For more information on Sweet Itch, please visit British Horse Society