An overview of Sweet Itch 

By Vet Charlotte Pennington

It may seem a strange topic to talk about this early in the year, however a vaccine is available to assist in the prevention of sweet itch and is recommended to be administered ahead of the midge season to provide optimal protection. So, if you are interested in this you need to think ahead and act soon! 

Sweet itch (Culicoides Hypersensitivity) is a skin disease caused by an allergic reaction to midge bites. 

Affected horses and ponies are sensitive to the irritants in midge saliva, which cause a localised irritation within the skin as well as the reaction to the actual bite itself.  This heightened sensitivity reaction causes intense itching leading affected horses to bite, scratch or rub at their skin causing further trauma. Sometimes the sensation is so strong that horses will cause severe damage to themselves or their environment.

Usually, the affected areas are where the midges like to bite such as the mane, back and tail or occasionally the belly and legs. Itching causes rubbing, hair loss and skin damage. 

The broken skin can ooze and bleed and potentially become infected. Horses then end up in a bit of a vicious cycle where they can become very irritated by the constant itching, causing more damage and so on.

Symptoms of sweet itch often worsen in hot humid weather, especially around dawn and dusk when there are more midges about. In the British climate the midges usually start flying and become a problem in spring (February onwards) and settle down and virtually disappear over winter when temperature is less than 4 degrees.

There is some evidence that susceptibility to sweet itch is genetic, with foals from an affected stallion or mare being more likely to develop the condition. Certain breeds seem more likely to be affected by sweet itch, including Icelandic ponies, Welsh and Shetland ponies.

Sweet itch is usually fairly easy to diagnose based on the history and clinical signs. It is important where needed to use medication to treat the damaged skin and calm the inflammatory reaction down and reduce itching and further trauma. What is used depends on the individual horse but a mixture of steroids, antihistamines, soothing shampoos, barrier creams and medicated creams are used.

Another essential part of treatment is preventing the midges from contacting the skin and biting (i.e. trying to break the cycle).

There are a number of general recommendations for prevention. 

Insect control is important  - regular application of insect repellents, use of fly sheets or sweet itch specific rugs, and stabling during times of high midge activity (dawn and dusk 4pm-8am). 

Barrier treatments coating the skin are useful.

Where possible affected horses should be kept on more exposed fields with a good breeze (as midges are not strong fliers) and keep affected horses and ponies well away from woodland and water, especially standing water, such as ponds.

Water troughs should be cleaned regularly as they can act as breeding grounds for midges.  Using insect-proof mesh on the windows and door of stables may help.

Anecdotal evidence from owners suggests feed supplements designed to support skin health can help. This includes Cavelesse, Brewer’s Yeast or vitamin B supplements.

There is also the option of vaccination. The vaccine was originally developed against ringworm however it has been found to be helpful at combating sweet itch. It is used off licence and imported into the UK.

The initial vaccination is split over two doses, with 14 days between the first and second. Subsequently the vaccine should be repeated after 9 months for optimal ongoing protection. 

The vaccine will be effective from 5 weeks which is why it is recommended to start vaccination early February / March. Vaccinating before the midge season begins will offer optimal protection and give the best results.