Equine Matters - Summer 2018

21 Equine Matters Summer 2018 Sweet Itch Q&A Figure 3: A horse with sweet itch Figure 4: Horses need to be carefully managed during the summer months What causes sweet itch? Sweet itch is an allergic reaction to the bite of the culicoides midge. It is not the midge that causes the damage, but the effect of the horse constantly rubbing to alleviate the irritation. When does it happen? Sweet itch is seasonal and only affects horses and ponies when the midges are around and the weather is warmer; so it starts in late spring and continues through to the autumn. What does it look like? Affected horses and ponies rub their manes, tails and faces on anything they can find in an attempt to relieve the itching brought about by the midge bites. Mild cases may just lose some mane and tail, bad cases will break the skin causing open sores. In chronic cases the skin on the crest may become ridged and thickened (Figure 3). Is there a cure? No. The disease can be managed but not cured. Often it gets worse as the pony gets older. Are there any breeds more susceptible to sweet itch? Sweet itch is seen more in ponies than horses. It is seen in all our native pony breeds and Arabs. It is also common in the Icelandic pony. Can I breed from a pony with sweet itch? There is some evidence that it is inherited so it is best not to breed from affected animals. Is it catching? No. Should I consider buying a pony with sweet itch? Think carefully before buying an affected pony. They will need careful managing over the summer months and are also harder to sell. How do I treat it? You need to prevent the midge coming in contact with the horse’s skin and then reduce the horse’s response to any bites they do get. Stabling the horse for the part of the day when midges are most active helps. So turn out at night and stable from early morning until dark if possible. Using a fly rug means the affected horse can be turned out for longer periods of time (Figure 4). Fly repellents, of which those containing DEET or permethrins appear most effective. Paraffin oil and bath oils, such as ‘Avon Skin So Soft’ act as a barrier to stop the midges getting at the horse’s skin. Corticosteroids given orally in tablet form or as an injection by your vet are useful in severe cases where the horse is damaging itself with the constant rubbing. In very rare cases, corticosteroids can cause laminitis in horses and ponies, and so their use should be decided on a case by case basis and with a degree of caution. Although not licensed for use in horses in the UK, some antihistamines are effective in some horses. Always seek veterinary advice before using human or unlicensed medicines on your horse. Numerous lotions and salves, many containing benzyl benzoate, aloe vera or tea tree can soothe itchy skin. Some improvement has been seen in some horses given small doses of an imported ringworm vaccine, although this is unlicensed in this country and can only be used under the advice and guidance of your veterinary surgeon. Feed supplements containing high levels of vitamin B3 or nicotinic acid. This vitamin is also found in brewers yeast. It has anti-inflammatory actions and reduces the immune response to the midge bites. The range of advice and treatments available shows that no one single treatment is effective, and affected horses can live a life of misery through the summer months if they are not carefully managed. With thanks to Avacta for the reproduction of Horace the Horse and the Allergic Threshold. The most common allergic condition we encounter in the summer is sweet itch. ‘The range of advice and treatments available shows that no one single treatment is effective and affected horses can live a life of misery through the summer months if they are not carefully managed.’