Most owners will be familiar with the condition Sweet Itch, characterised by extreme itching leading bald and sore areas, including the ‘toilet brush’ tail. In the 2018 National Equine Health Survey skin conditions made up 33% of all reported problems, and Sweet Itch is certainly a very common condition, and it can be quite challenging to manage.
The disease is caused by a hypersensitivity or allergic skin reaction to the saliva of biting insects as they feed on the horse; namely the black fly and the midge (Culicoides). After allergic horses are exposed to the allergen they develop a Type 1 hypersensitivity with histamine being produced by the body. Horses who have Sweet Itch are ‘hypersensitive’, and the immune reaction to the bite and saliva is effectively ‘over the top’ which is why not all horses suffer from the condition.
These insects are active from March to November, and some remission is generally noted during the Winter, although this does depend on seasonal factors such as temperature. All breeds of horses can be affected, and there is evidence of breed susceptibility with a hereditary component noted for Welsh, Shire and Icelandic breeds.
Sweet Itch, or summer eczema is characterised by hair loss, crusted or bleeding wounds, and self trauma as the horse continues to itch.
The classic signs of Sweet Itch are itching of the mane, base of the tail, and itching under the belly is also common. Itching of the legs may be noted as well. Often the area is rubbed bald, the skin may break, weep and bleed. You might notice ripped and torn rugs, or the horse rubbing against fence posts or stable walls.
The skin acts as a very effective barrier, it provides protection from the outside world, it is the largest organ the horse possesses and plays an important role in thermoregulation. However once this barrier is compromised environmental irritants can cause inflammation and the ‘itch scratch cycle’ becomes activated. The more the horse itches and scratches the more the skin is damaged, and the irritants or allergens have a greater effect. As a result horse itches and scratches more, and it is literally a vicious circle.
Symptoms can develop from 4 or 5 years of age, and generally worsen throughout the horse’s lifetime.
It is essential to rule out other skin conditions such as fungal, bacterial or parasitic conditions, so if you are concerned that your horse has Sweet Itch do discuss the case with your vet and don’t be tempted to ‘self-diagnose’.
A horse with Sweet Itch is extremely uncomfortable, and one of the biggest challenges is managing the self inflicted trauma, including hair loss, bleeding and thickening of the skin, as well as halting the ‘itch-scratch cycle’.
The best option for a horse suffering from Sweet Itch is protection from a purpose made sweet itch rug, which covers the neck, belly and dock with a very fine mesh. It is ideal to use this rug before the horse starts reacting to the insect bites, not once symptoms have been noted . The horse will most likely need to use the rug all the time, and it is worth noting that a specialised Sweet Itch rug can be covered by some insurance policies, so do have a check if this is covered by your insurance policy.
The use of topical oils are well reported to assist with the management of Sweet Itch, as this will prevent the flies and midges from landing and biting. Likewise insect repellents can offer some prevention, with preparations containing DEET being more effective.
Midges are attracted to water, and like damp sheltered conditions, so ensuring that the horse is turned out in a field away from any water sources, such as a pond. An open windy field on higher ground is ideal. Windy conditions will prevent the insects from landing, and this can be replicated in the stable with the use of a fan.
Keeping your horse stabled at dawn and from 3pm until dusk will help, as this is when the midges are most active, although in warmer humid weather the midges may be present all day. The use of net curtains, or a mostique net, around the stable can help prevent midges entering.
Some cases of Sweet Itch will need close veterinary management to control the discomfort and itching, as well as any secondary skin infections. It may also be necessary to use medication, such as a short term acting corticosteroid treatment, for a short period to stop the ‘itch scratch’ cycle and allow environmental changes to have an effect. Owners are often concerned about the use of steroid treatments but do have a chat with your vet about treatment options as providing an interlude for other treatments to work would help your horse.
The oral supplement Cavalesse is often recommended as this contains Nicotinamide (a type of Vitamin B3), which is known to have a specific effect on the immune system within the skin. It is useful for all types of allergic skin disease in the horse, in particular sweet itch as it reduces the production of histamine, and can help the skin barrier by improving the skin lipid.
As with so many conditions a proactive approach is required, and preventing the horse from initial bites is the best method of managing sweet itch. Do ensure that your horse is suffering from sweet itch and not another skin condition causing similar symptoms such as lice. Management changes can make a big difference and do consider what methods you can employ to make your horse as comfortable as possible.
Fettelschoss-Gabriel, A.; Fettelschoss, V.; Thoms, F.; et al. Treating insect bite hypersensitivity in horses with active vaccination against IL-5. J Allergy Clin Immunol. Oct 2018, vol. 142, no. 4; pp. 1194-1205].