How to Control Sweet Itch
Roger Dixon MRCVS Ashbrook Equine Hospital, Cheshire.
Sweet itch is an allergic reaction to the saliva of the Culicoides midge and the black fly (simulium). It is thought to affect over 50000 horses in the UK each year and commonly occurs after turnout in the spring. Some horses are thought to have a genetic predisposition to sweet itch e.g. Icelandics and cob type ponies are more likely to develop the condition than thoroughbreds.
Signs of Disease
When a susceptible horse is bitten by a midge, the saliva causes a hypersensitivity reaction. Histamine is released by the body’s immune system and this results in intense itching. This itching results in damage to the hair coat and the skin, particularly along the mane and the base of the tail. It can be so severe that the horse or pony can cause bite and scratch wounds in an attempt to alleviate the itching. The more often the horse is bitten by midges, the worse the reaction becomes. Indeed, signs of the disease often worsen each year and may progress from areas of dry flaky skin to rough, thickened hairless areas. Secondary bacterial infection may also develop. Affected horses can become very miserable and debilitated during the spring and summer and ridden work may not be possible.
How to Control Sweet Itch in Your Horse
It is important to remember that sweet itch is an allergy, similar to hay fever in humans. Therefore, not all horses in a population will be affected. Because it is an allergy, significant signs of disease may be caused by a small number of midges.
There are several aspects to control:
1) Midge Avoidance
The best way of reducing the signs of sweet itch is by preventing midges from biting the horse. Since midges are particularly prevalent near water, it is a good idea to remove the horse from the vicinity of ponds, mud and rivers.
Stabling the horse at dawn and dusk when the midges are most active is also extremely beneficial. Further measures which can help, include the use of fly screens across the stable door and fly paper within the stable. Maximising ventilation by opening up a side window can also help to create air movement; midges cannot fly against a wind stronger than 5 mph. If this is not possible then a fan within the stable can be helpful.
Using sweet itch rugs throughout the midge season can be very successful in preventing bites.
2) Fly Repellents
Fly repellents are crucial to the successful management of sweet itch. There are many different kinds available; however, we most commonly recommend those which contain the active ingredient permethrin. As well as being very good at repelling flies, permethrin has an excellent residual activity following application. Often we will recommend using these repellents every other day. For those looking for other repellents, Avon Skin So Soft can be used in combination on the intervening days.
3) Medications to Reduce the Itch
Some horses will continue to itch despite the use of fly repellents and midge avoidance measures described above. In these cases, your veterinary surgeon may recommend antihistamines or steroids.
Antihistamines can be effective in milder cases and have the advantage of being a very safe class of drug. However, they do not work in all cases. More severe cases may require the use of corticosteroids; prednisolone is most commonly prescribed. Prednisolone works by dampening down the immune response to the midge saliva and preventing the excessive allergic response. Steroids are extremely effective at reducing the itch, discomfort and signs of sweet itch, although may have the potential side effect of laminitis in susceptible horses. For this reason, we are likely to use prednisolone at the lowest effective dose, particularly if it is required for long-term therapy.
4) Fidavet Cavalesse – Start before the midge season for the best results
Cavalesse is a natural food supplement which contains the active ingredient Nicotinamide, a type of Vitamin B3. It works in two ways:
1) It reduces the production of histamine (which is the substance which produces the itch).
2) It increases the amount of natural fats in the skin’s surface, therefore improving the ‘barrier protection’ against midge bites.
Cavalesse works best if started in the Spring, about a month before the signs of sweet itch develop. It is therefore a very useful therapy if you know your horse suffers from sweet itch annually.
Allergen Specific Immunotherapy (ASIT)
This is known as densensitisation vaccine therapy and is formulated after confirmation of the diagnosis with a dermatologist. Although this can be very successful for other causes of allergic skin disease such as atopy, unfortunately ASIT is though to be less successful for desensitisation of the sweet itch reaction.
Summary
The signs of sweet itch can range from a mild scurfy mane to an extremely debilitating disease. It is important to bear in mind that there is no ‘quick fix’ cure and the signs will recur and possibly worsen in subsequent years. Successful control usually depends on a combination of management changes to avoid contact with midges, regular use of proven fly repellents, and medical therapy where appropriate. Your vet will be able to advise you on the most suitable approach for your horse.
