Sweet Itch

As summer approaches and the weather starts to warm up, it heralds the return of those pesky midges and flies that can drive our equine friends mad. A bite from one of these winged fiends can be irritating enough at the best of times, but 5% of horses and ponies in the UK will suffer from an abnormal overreaction to these bites, leading to the condition known as sweet itch.

Also known as summer seasonal recurrent dermatitis, this condition can affect any breed of horse, pony and donkey, though a hereditary predisposition has been shown to exist and thoroughbreds seem to be less susceptible. Affected individuals suffer a delayed hypersensitivity reaction to insect bites in which there is an overly dramatic response to proteins in the insect saliva. The immune system mounts an attack on the skin cells involved and the ensuing damage results in sweet itch.

putland_June13_1Symptoms include a severe itchiness, with the tail head and mane being the two most typically affected areas. The scratching that occurs to try and alleviate this itchiness will then lead to hair loss, thickening of the skin and flaky dandruff. Other areas that may be involved are the neck, withers, hips, ears, forehead and the area around the eyes with even the stomach, saddle area, sheath or udder and legs becoming affected in the most severe cases. The skin may be disrupted enough for sores to form which will consequently become infected if they are not addressed promptly.

 

A horse suffering from sweet itch will frequently swish their tail, roll and vigorously scratch themselves against any available surface. If no surface is available, as with horses confined by electric fencing, they may scratch at themselves with their hind feet and bite at their flanks instead. The discomfort caused by the midges will lead to restlessness and seeking out companion horses for excessive mutual grooming. Changes in temperament may be observed: this can be increased lethargy for some, agitation and an inability to concentrate when being asked to work for others.

For most individuals the first signs of sweet itch will manifest themselves between the ages of 1 and 5 years; however stressful situations (e.g. castration, moving yard) may trigger its’ development in more mature animals. The first time that symptoms are seen they often develop in the autumn months, but will then occur during spring, summer and autumn in following years, reflecting the breeding season of the midges. This seasonal incidence, as well as the often classic symptoms presented, makes diagnosis of sweet itch relatively straightforward.

putland_June13_3In the UK, various culicoides midge species are the main offenders responsible for this problem, but blackfly can also contribute. The midges are at their most active during periods of low light and when the air conditions are calmer, which is typically at dawn and dusk. They are very small and so are poor fliers, declining to venture forth in strong winds or heavy rain. Bright sunshine and hot, dry conditions are also a deterrent. Their preferred breeding environments are areas where there is wet soil and decaying vegetation and the breeding season may potentially extend from March to November if conditions remain suitable.

Sweet itch is a condition that is best controlled with careful management. Avoiding wet, boggy pastures or fields that include a water source will help reduce the prevalence of midges by removing their preferred type of environment. Drainage must be good and sources of rotting vegetation such as muck heaps, uneaten hay and rotting leaves should be removed. If possible susceptible individuals are better off grazing more exposed and windy sites. Stabling at dusk and dawn, when the midges are at their most active, will reduce exposure, whilst mounting a fan in the stable to take advantage of the midges’ poor flying skills in turbulent air will also be helpful. These environmental control measures may be sufficient to manage the problem for less severely affected horses, but more sensitive animals will probably require further treatment.

Insecticides will help to keep the midges at bay. Benzyl benzoate is one that is commonly used; available in liquid form, it should be worked into the skin daily before the sweet itch signs first develop in spring as it is irritant and not safe for use on damaged skin. Permethrin based insecticides are obtainable by veterinary prescription in a number of different formulas that are often slightly longer lasting.

Applying oils or greases to the coat can act as a barrier to the midges as they dislike the contact. Liquid paraffin is a basic example, but again there are many products with specific formulations designed to act in the same way. The main problem with these is that they do not last particularly long, requiring several applications a day, and they can also be quite messy to use. Such products should always be tested on a small patch of skin first in case they generate an allergic response. Blankets, hoods and masks are a different sort of barrier that can be used to great effect starting with a simple fly sheet going right up to the specially designed Boett blankets offering full body protection.

There are medicinal treatments available. These include giving immunosuppressive doses of steroids, but unfortunately there is always the risk of laminitis as a side effect to consider and it is also often the case that the dose will become less effective over time. Antihistamines are an option, though high dose rates are usually required and again there is the risk of side effects such as drowsiness.

putland_June13_2More recent developments include immunotherapy, which involves giving injections of tiny amounts of the product causing the allergic response in sweet itch in order to desensitise the horse to it over time. Varying results have been achieved, with some individuals responding very well and others not, but improvements continue to be made to this relatively new treatment option.

Another recent development, Cavalesse, is a vitamin B based dietary supplement that has beneficial effects on the skin including reducing histamine production (what causes the itch) and increasing the natural oil barrier within the skin. There is also a topical form available that can be applied directly to the skin.

Sweet itch can be an intensely uncomfortable and distressing condition for any horse, but fortunately, as seen above, there are many strategies for managing this problem. The main point to remember is to take those steps towards dealing with it as early as possible, before it has a chance to escalate.

If you have any questions about any aspects of your horses’s health, or indeed your pet, farm or smallholding animals, please do not hesitate to contact us on 01892 835456. Putlands Veterinary Surgery is based in Paddock Wood in Kent, and offers a friendly, proffessional and personal service for all species of animal. We have four dedicated large animal vets with a wealth of equine experience between us, and are always happy to help

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