Sweet Itch

Sweet Itch, or Summer Seasonal Recurrent  Dermatitis (SSRD), is 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 midge, it will have an allergic reaction at the site of the bite.  This will cause a localised irritation which the horse will try to scratch and rub.  Self- inflicted damage will occur as the horse itches himself.

Due to the life cycle of the midges in question, this is a seasonal disease, occurring between April and October. 

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 midge 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.

Clinical signs
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.

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 midges.

Treatment and management

There are three separate approaches: 

• Most importantly, decrease the horse’s exposure to the Culicoides midges 
• Kill the midges that do attack the horse
• Stop the horse itching and scratching to prevent self-trauma

• Best to instigate 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, especially as sunrise and sunset during the summer months are relative unsociable hours!
• 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 wetlands areas should dramatically reduce fly exposure
• Improve pasture drainage to prevent fly breeding
• 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.  They are very potent anti-inflammatories which will stop the itching and allow the skin to heal.

Anti-histamines are not as useful in the horse as they are in man as they are often not particularly effective. However, they are very safe so may be used as part of the treatment regime.

The National Sweet Itch helpline has a web site for further information - www.sweet-itch.com