Sweet itch

Sweet Itch can be the bane of many horse’s lives throughout the spring and summer months.  If you have a horse or pony that suffers from sweet itch, there’s actually quite a lot you can do to help.   

What is sweet itch?
Basically it’s an allergic skin disease.  Certain horses are allergic to the saliva in the bite of a species of midge called Culicoides.  This means that once a sensitive horse is bitten by a Culicoides fly, it will have an allergic reaction at the site of the bite.  This will cause a localised irritation which the horse will try and rub.  Self- inflicted damage will occur as the horse itches himself.

Flies
Due to the life cycle of the flies in question, this is a seasonal disease, occurring only between April and October.  It is characterised by itchiness, which can be severe.  The horse may be restless, keep rubbing himself against trees or fences, and keep swishing his tail in an effort to keep the flies away.

There are many different species of Culicoides midge, and each one prefers to bite a different part of the horse.  The horse will then itch the area around where the fly has bitten.  Most common are the “dorsal feeders” who bite, and cause damage around the horses ears, poll, mane, withers, rump, and tail head.  The “ventral feeders” are less common, and tend to cause the itching around the horse’s face, chest, and belly.

Signs of disease
Constant rubbing will cause hair loss over the affected area, often the mane and rump.  Early on in the disease, the skin will be bald, red, inflamed, crusting and sore.  As the disease progresses, the skin becomes chronically thickened, blackened, and wrinkled and the hair becomes sparse and coarse.  The tail takes on a characteristic rat-tailed appearance.  Over the winter, a horse may totally heal, only for the disease to come back in the spring at the first contact with flies.

Treatment
There are three separate approaches here.  Firstly, and most importantly, you need to decrease your horse’s exposure to the Culicoides flies.  Secondly, we need to kill the flies that do attack your horse, and thirdly we need to stop the horse itching.

Fly control
■ Best begun before the start of the fly season.
■ Insect-proof stables using fine-mesh screens.
■ Use ceiling or wall mounted fans in stables to create a breeze – flies will find it harder to land on the horse.
■ Stable horses one hour each side of sunrise and sunset, as this is when flies are most active.
■ Stabling at night may also help.
■ Try using commercially available sheets and hoods to rug the horse with when he is turned out.
■ Culicoides flies breed around ponds and marshes, but do not fly more than a few hundred metres from their breeding areas. 
■ Moving horses farther than half a mile from such areas should dramatically reduce fly exposure.
■ Improve pasture drainage to prevent fly breeding.
■ Similarly, clean the  water trough regularly to prevent flies breeding here.

Insecticides
Insecticides containing pyrethrins or pyrethroids are best.  Treatment may have to be applied weekly or fortnightly in worst affected cases.
We recommend (and supply) the pour-on preparation ‘Switch’.
Insect repellents, such as benzyl benzoate, will keep flies away, but need to be constantly reapplied.

Anti-allergy treatment  

Corticosteroids remain the most useful product for treating the skin allergy.  As steroids do have side-effects in horses, they must only be prescribed by a vet.  A potent anti-inflammatory is advised as it will stop the itching and allow the skin to heal quicker.

Anti-histamines are not as useful in the horse as they are in man.  They tend to be very expensive, and often not particularly effective.