Sweet itch is an allergic reaction to the saliva of a number of species of the Culicoides biting midge.
It is characterised by intense itching which usually results in hair loss through rubbing – which can be furious – thickening of the skin and the development of sore, raw bleeding areas, especially at the mane and tail.
If left untreated, these areas can become infected, causing further discomfort.
Although sweet itch can occur in any breed and affects around 5% of the UK equine population, it is most commonly seen in Icelandic horses and native breeds.
What are Culicoides midges?
There are several species of Culicoides midge in the UK and their numbers vary throughout the year – highest in the summer and lowest in the winter.
Sweet itch signs fluctuate with Culicoides activity and can start as early as March and continue through to October. Most species only fly when the temperature is above 10 degrees.
The female midge requires a blood meal to mature her eggs and they usually get this from horses by biting the head, mane, tailhead or along the belly.
Midges are tiny and poor flyers with wings less than 2mm long, so they struggle to hang around in strong wind and heavy rain, and most dislike bright sunshine – this is why they are most active around dusk.
They like warm and damp conditions to breed, meaning muck heaps are a dream location!
To prevent and control sweet itch we approach the problem from four different angles:
Environmental fly control
Fly avoidance for the individual horse
Medical prevention
Medical treatment
Environmental fly control
Removing all sources of flies from your premises isn’t feasible but you can reduce their populations by minimising breeding sites on the farm.
Standing water that collects in old tins, tyres or buckets can provide popular breeding grounds and should be removed.
Also make sure there is good drainage in stables and paddocks with no moist areas created by leaking taps or water systems.
Any wet organic material such as manure, old bedding and wasted hay should be regularly removed from the stable and turn-out areas.
The muck heap should ideally be as far away as possible from the stables and turnout areas.
It is a good idea to keep your muck heap covered in black plastic – this helps keep the flies off, preventing breeding, and the heat generated beneath the plastic will kill any fly eggs and larvae that are developing there.
With midges being most active in warm, overcast or dusky conditions, contact can be minimised by stabling horses during these hours, instead turning them out overnight.
Midges can venture into the stables but the numbers will be limited.
Further reductions in the midges can be made by using fly netting to cover doors and windows. Fans can also be positioned in the stables to create an air current pushing the midges out.
Fly avoidance for the individual horse
A sweet itch rug that covers the whole body, including the belly, and made of a fine fabric that does not let midges through is a minimum requirement for any horse affected by sweet itch.
It should be worn from before the start of the sweet itch season right through to the season’s end, to avoid your horse rubbing through the rug.
Repellents and insecticides can be used with variable effect. We frequently recommend Deosect which can be sprayed or sponged onto horses and only requires an application every 10 to 14 days.
Medical prevention
Although many attempts have been made to produce a dedicated vaccine for sweet itch, as yet there has been little success.
Several years ago, however, a vaccine was developed to prevent and treat ringworm in horses.
When this vaccine was given to horses with sweet itch, some owners reported that their animal’s sweet itch was less severe than before. Although it may not work for every horse, it can be worthwhile trying.
Even in the event of a vaccine being used, it is important to note that it should not be a replacement for fly control and protecting a horse or pony from being bitten by flies.
Medical treatment
Antibacterial washes are recommended if your horse has a concurrent skin infection, a common problem secondary to rubbing.
Shampoos that soothe the skin are an option to try and alleviate the signs, for example washes that contain oatmeal have been proven to have some beneficial effect in allergic skin disease.
Dietary supplements containing high levels of Omega 6/3 fatty acids such as linseed and evening primrose oil can help to reduce the inflammation in the skin.
Steroids are the main treatment option to calm down any allergic reaction in horses since antihistamines have been found to have very little effect.
We can use short-acting drugs to settle down an acute flare-up of sweet itch and allow the use of a protective rug. Topical steroid creams and sprays may also help to alleviate the issue short-term.
In very severe cases where all of the above is insufficient to allow your horse a normal life through the fly season, we can use long-acting steroid injections.
However, these must not be used in horses and ponies with a history of laminitis or equine metabolic syndrome.