Sweet Itch – an Introduction
Sweet itch , also known as Culicoides Hypersensitivity, is a skin disease caused by an allergic reaction to midge bites. Affected horses and ponies are sensitive to the irritants in midge saliva, which cause a localised irritation within the skin. So it is not just the bites themselves, like general insect bite hypersensitivity (IBH), which can also cause itchiness.
Pruritus is the technical term for itchiness. This describes the unpleasant sensation that leads horses to bite, scratch or rub at their skin. Sometimes the sensation is so strong that horses will cause severe damage to themselves or their environment, while in extreme cases, horses cannot tolerate tack on their skin, let alone a rider.
Although poorly understood, pruritus is known to result from the stimulation of special nerve endings and receptors in the skin. In the horse, the main factors inducing itchy skin are ectoparasites (such as biting insects), allergies and some infections. Biting insects including lice, midges, black flies and horse flies can trigger cases of pruritus, but milder cases can occur simply as a horse sheds its coat.
Incidence of sweet itch
Ponies are generally more frequently affected by sweet itch. There is evidence that susceptibility to sweet itch is genetic, with evidence that the disease may be passed from one generation to the next with foals from an affected stallion or mare being more likely to develop the condition.
The fact that it is passed on may not be immediately obvious as the disease rarely shows in horses Certain breeds seem more likely to be affected by sweet itch, including Icelandic ponies, Welsh and Shetland ponies, Connemaras, Friesians, Arabians, some Shires, Warmbloods and Quarter horses amongst others.
Signs and diagnosis
Signs of Sweet Itch
- Mild to severe itching and rubbing, usually along the mane, back and tail
- Loss of tail and mane hair
- Bald patches, which can look ugly and grey due to permanent hair loss and skin damage
- Areas of sore, open, broken skin, which tend to bleed
- In some cases, itching along the legs and under the belly
- Some affected horses or ponies can become very irritated by the constant itchiness.
Different types of midges will attack different parts of the body, resulting in different areas of skin being affected, but typically sweet itch mostly affects the mane and base of the tail, which is a clue to the identity of the problem.
This can be usually confirmed based on the clinical signs. Also in the British climate the condition typically appears in spring after settling down to virtually disappear during the winter, provided it is cold enough for the midges not to be flying, which is usually when the temperature is less than about 4 °C. For this reason, purchasers need to be aware of the potential risk of buying a horse or more likely a pony with no signs during the winter which, by mid-summer, could develop sweet itch.
The signs of itchiness due to sweet itch are often worse in hot humid weather, especially around dawn and dusk and/or whenever there are more midges about.
Management & treatments
Management of Sweet Itch in Horses
Preventing horse to midge contact is key:
- Good insect control is essential to prevent the midges biting. Regular application of insect repellents, use of fly sheets or rugs and stabling during times of high midge activity (dawn and dusk). Some people have success with the longer lasting pour on insect repellents like Deosect®. DEET is effective but can cause soreness.
- Barrier treatments such as Avon skin-so-soft or benzyl benzoate are also useful.
- It is a good idea to move affected horses to open, more exposed fields with a good breeze (midges are weak fliers and get blown away with a wind more than 4mph!) and keep affected horses and ponies well away from woodland and water – especially standing water, such as ponds.
- Small areas of water can be midge breeding areas, such as water troughs, so they need to be cleaned often.
- Stable affected horses and ponies from about 4pm to 8am (i.e. dusk to dawn) when midges are at their worst. Using insect-proof mesh on the windows and door of stables may help.
- Keep your horse’s skin covered using an ear to tail rug and a hood designed to help prevent the condition, making sure the mesh holes are sufficiently small to prevent midges getting through the gaps.
- Use strong electric fans in stables, where safe to do so, as midges cannot fly against a strong air current.
- Carry out medicated treatments regularly, often required on a daily basis, otherwise the midges will start to bite which triggers the itch/scratch cycle. Many horses or ponies with this condition will also need treatment to control the itch and sometimes to resolve secondary skin infections. Often topical treatment is effective, such as the right soothing shampoo (and has fewer potential side effects) but sometimes tablets and/or injections are needed.
- There is limited research available and also anecdotal evidence from owners of horses suffering from sweet itch suggests feed supplements designed to support skin health can help. This included things like Cavelesse, Brewer’s Yeast or vitamin B supplements
- It is hoped that in the relatively near future, vaccines may become available to make affected horses and ponies tolerant to the irritation. Currently a European Ringworm vaccine INSOL is being use off license and seems to help some cases.
RECOMMENDATIONS for Management of Sweet Itch:
Consult your vet early on and make sure it is sweet itch and not other causes of itchiness, such as pinworm, lice or another allergy. It is really important to start treatment early Spring before the midges take hold – so all sweet itch suffers should be wearing a rug from February.
Medication for Sweet Itch in Horses:
Steroids can be used to combat the irritation, but unless they are accompanied by treatment for the underlying cause of the pruritus, a relapse is likely. They may be beneficial to give short-term relief, although they are not always as effective as one might expect. Side-effects also need to be considered, especially with long term usage.
Steroids are not the only option available to make the horse more comfortable while further investigations into the cause of the problem are carried out. Soothing emollient shampoos, solutions and sprays can help some cases. Cold water hosing and ice packs applied to the irritated areas can also lead to an improvement. Shampoos containing colloidal oatmeal and oils such as borage, tea tree, evening primrose and aloe vera can also have palliative effects.
Both humectant and emollient sprays are available as therapy in pruritic horses. A humectant is an oil-free product, which increases the water-absorbency of the top layer of the skin, producing subsequent soothing effects. An emollient is an oil-based solution, which coats the skin and prevents water loss. Oil sprays applied via a simple plant sprayer can also prevent the skin drying out.
Antihistamines can cause drowsiness and are sometimes used with caution. There are currently no antihistamines specifically licensed for use in the horse. PLEASE be aware that a horse on antihistamines may test positive as a prohibited substance during or around the time of competition. It is best to check with your vet beforehand to ensure it is safe to give any treatment.
Call BELL EQUINE on 01622 813700 if you have any questions or would like to discuss your horse.