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What is sweet itch? And what are the symptoms to look out for

Sweet itch is a skin condition affecting horses and ponies which is caused by an allergic reaction to the saliva of the biting midge and also mosquitoes.  Sweet itch can affect any equid but it does seem to be more prevalent in ponies particularly the native breeds. 

What are the symptoms of sweet itch?

The clue is in the name of the condition.  The allergic reaction to the midge or mosquito bite causes intense itching which, even with scratching, the horse or pony cannot relieve.  Some horses suffer a mild response and will occasionally scratch against a fence or tree whereas are others are driven almost mad with the itching to the point of constantly rubbing skin that is open and raw.

Most commonly sweet itch appears at the top of the tail or on the mane.  It is not really a winter condition which is why some people will always try and sell a sweet itch horse or pony over the winter months when they are not obviously rubbing.

The main season for sweet itch is March through to November depending on how warm and wet the spring and autumn are.

What should you look out for if you have never seen sweet itch before?

You should always keep an eye on any horse or pony which is scratching as there could be other causes creating an allergic response.  It is also quite easy for them to break the skin and cause a secondary infection.  However, there are some real telltale signs and symptoms which might indicate that this is sweet itch and these include:-

  • Itching on the mane and tail rather than elsewhere on the body. In severe cases of sweet itch, the horse can start biting and scratching at other areas on his body but in the initial reactive stages, it is usually the mane and tail
  • Repeated rubbing will cause the itchy areas to become lumpy and/or scaly and they will feel hot and inflamed when you touch them. Persistent sweet itch sufferers can be left with a permanently ridged or corrugated skin which can be spotted even during the winter months.  These areas will be absent hair which does grow back to a degree in the colder months but the skin underneath is a bit of giveaway
  • There can be bleeding as the horse rubs the skin raw to relieve the itch
  • The horse may seem restless and agitated

Your vet can confirm a diagnosis of sweet itch, it is usually pretty unmistakeable but in the early stages, can be confused with other things.

Managing sweet itch

It is really important to both relieve the itch and stop any further bites from occurring; the more the horse itches, the more he wants to itch, it is a vicious circle. 

  • Treat the itchy area and any soreness topically – what doesn’t itch won’t get rubbed – and break the cycle. De-itch cooling and soothing creams can be applied to calm the irritation
  • Depending on how bad the sweet itch is, the vet may recommend antibiotics and/or anti-histamines
  • Once you have stopped the itch, the only way to prevent recurrence is to stop the horse from getting bitten again. Turn out at night and bring in at daybreak
  • Keep the horse in the stable during the day and put midge screens over the stable door and windows otherwise, you may need to leave the horse in his sweet itch rug even whilst he is stabled
  • Fans can keep a good airflow going as midges prefer static or stagnant air
  • If you can’t avoid turning out during daytime then use a fly rug or better still, a sweet itch rug which encases the horse completely in a rug with a tight mesh that simply cannot be penetrated. These rugs can make the horse very warm which is why it is preferable to turn out at night
  • Whenever you turn out, dusk and dawn are the most popular biting times so try and avoid these if possible and keep the horses stabled
  • Avoid low-lying or marshy grazing and any locations where there are ponds. Open windy grazing with few trees will have a far lower density of midges and mosquitoes.  If it is not practical to change your grazing and you have a pond then fence this area of the field off

Is there a vaccine for sweet itch?

Swiss scientists have been working on a vaccine to reduce the horse’s sensitivity to the bite of the midge and mosquito.  The vaccine targets something called Interleukin 5 or IL-5 a substance produced by the horse’s own immune system.  IL-5 is the lead regulator of white blood cells called eosinophils and which play a key role in allergic reactions.

When a horse with a propensity for sweet itch is bitten, the saliva from that insect triggers an immune response which causes eosinophils to infiltrate the skin.  The eosinophils release their contents which is what causes the damage to the skin, the sore areas and the lesions.

The vaccine works by tricking the horse’s body into thinking that IL-5 is a foreign invader.  IL-5 is attached to a protein and injected and the horse activates its immune system as the protein is foreign to it.  The immune system effectively produces antibodies against itself.  In the science of immunology, the process is called the hapten-carrier complex.

The aim is not to obliterate eosinophils as they perform other important functions within the horse’s body such as the regulation of parasites but just to control the response so the horse does not develop unpleasant symptoms.  In most horses trialled so far, symptoms were reduced considerably easing the horse’s comfort.

Sweet itch is not curable and any veterinary interventions are only designed to relieve symptoms.  The management of the conditions stands and falls almost entirely on the preventative actions taken by the horse owner.  It is thought that the vaccine may be available as early as 2021 and this will help to control the uncomfortable and distressing symptoms of sweet itch.

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