There’s nothing sweet

…ABOUT SWEET ITCH

Summer seasonal recurrent dermatitis, generally referred to as sweet itch, is a common and debilitating skin disease. It is caused by an allergic reaction to the bite of the Culicoides midge, which is the midge that carries African Horse Sickness (AHS). All horses are bitten by this midge over the course of the year, but just like with AHS, only some horses develop sweet itch.

PATHOLOGY

The Culicoides midge mostly feeds at dusk and dawn in warmer weather and breeds in wet conditions. This allows them to thrive in southern Africa's spring, summer and autumn months, which is why the condition is most prevalent at these times. Symptoms of the disease most commonly start to appear at the end of spring and continue into autumn. However, in a few cases, the condition can be present almost all year round, with last year's symptoms barely disappearing before the condition flares again the following spring.

When the Culicoides midge bites a susceptible horse, a local allergic reaction occurs to a protein in the saliva of the midge. The protein is essentially harmless, but in horses with the allergy, it causes the immune system to overreact and attack its own skin cells. It is the damage caused by this attack on the skin that leads to the symptoms of sweet itch. Sweet itch is, therefore, fundamentally a problem of the immune system and, as such, is very difficult to treat successfully.

The most affected areas in cases of sweet itch are under the mane, at the root of the tail, on the ears, along the neck, on the forehead, around the withers and across the hindquarter. However, in severe cases, the condition also appears along the midline of the belly, the saddle area, the sides of the head, the sheath or udder and the legs. In fact, the condition can really affect just about any part of the horse's body when severe!

Animals who are predisposed to sweet itch will start to show signs between one and four years of age in most cases. Older animals who show the disease for the first time are thought to do so because of some outside stressor which impacts the immune system, such as moving to a new home or experiencing an illness or serious injury. However, in both younger and older horses, the major contributing factor to developing sweet itch is obviously the prevalence of the midge in the area.

While immensely distressing for the affected horse, sweet itch is not contagious. One or more animals in the same stable yard may have the condition, but this is simply due to environmental factors (the high burden of Culicoides midges) and the fact the condition is common in the equid population!

DIAGNOSIS

If you suspect your horse or pony has sweet itch, you must get a proper clinical diagnosis from your vet. Diagnosis should not be difficult, especially with the disease being seasonal. Still, a formal diagnosis does eliminate other causes of similar symptoms, which are more easily treatable, like lice and ringworm.

CHARACTERISTICS

Sweet itch is characterised by intense itching, causing the horse or pony to vigorously rub or scratch the affected parts of the body on anything they can get access to. If there is nothing convenient to rub on, they may even pull themselves along the ground to scratch their belly or sit like a dog and wriggle around on the floor to scratch their tail. Alternatively, they may bite their flanks and the base of the tail and scratch their manes and ears with a hindfoot. Sufferers frequently pester their paddock mates for extra mutual grooming or may pace up and down continuously until they get access to something to scratch on. Vigorous tail swishing or excessive rolling is also seen.

Constant scratching and rubbing over time causes the skin to thicken and the hair to become broken and fall out. It is not uncommon for the condition to worsen each year until, eventually, the skin is so damaged that the hair no longer grows back. Constant damage to the hair may also result in the hair growing back white, so if you are buying a horse over the winter months when you are less likely to

see active disease, check for white hairs in the mane or tail as this may suggest a case of chronic sweet itch that is just less obvious in the cooler months.

Other symptoms of sweet itch include flaky skin and weeping sores, sometimes with a yellow crust. Secondary infection with bacteria, viruses or fungi can affect these sores if they are not kept clean. If you suspect a secondary infection, you must contact your vet to get the area treated.

IMPACT ON PSYCHOLOGY AND PERFORMANCE

Aside from the physical signs of the condition, the psychological impact on the horse can be huge. Suffering from sweet itch is a pretty miserable predicament, and horses with sweet itch need help to minimise their symptoms and lots of TLC!

Symptoms of sweet itch can cause some horses to lose their ability to concentrate. These horses typically become lethargic and yawn a lot or become fidgety and restless. They often lose interest in their work, and their performance deteriorates. Tack can become unbearable for them, and insects buzzing around can set off a bout of head shaking. With all of this extra stress, it is not unusual for these horses to drop weight and lose condition.

NOTE

Avoid spraying fly sprays or applying ointments on broken or damaged skin. This can be painful for the horse and also result in other issues, including chronic scarring. Check with your vet how to manage the damaged areas of skin and follow their advice.

TREATMENT

The key to managing sweet itch is prevention and persistence. Preventative environmental measures to reduce exposure to the midge are certainly the most effective. However, you will still need to be diligent in applying treatments and fly sprays regularly to get the condition under control.

ENVIRONMENTAL MANAGEMENT There are several measures you can take to reduce the midges' access to the horse, which is ultimately the most important arm to treatment. Firstly, horses must be removed from areas near woods, ponds, lakes, rivers, standing water, wet ground or rotting vegetation, as these are the main breeding grounds for the midge. These areas should also be avoided when riding. An ideal location for the horse is, in fact, an exposed windy area, as the midges cannot fly in windy conditions.

It is for this reason that fans in the stable can really help these horses by keeping the midges at bay. The fan should be directed towards the door or window to prevent the midges from flying in and accessing the horse. It is important to note that fans must be securely fastened and well out of the horse's way to avoid injury.

Rugging the horse with a lightweight rug that has a hood and covers the belly is also helpful. Many tack shops stock specific blankets for this purpose.

Finally, fly repellants with midge repelling action should be applied all over the body, usually twice a day.

PHARMACOLOGICAL TREATMENT If the allergic reaction is severe, vets can prescribe systemic corticosteroids to minimise the issue. However, these drugs only bring temporary relief and carry the risk of nasty side effects, including laminitis. Similarly, some vets will prescribe antihistamines (specifically hydroxyzine), which have been shown to be of benefit in some cases of sweet itch. Steroid and antihistamine creams can also be used, and some people have experienced good results with these.

Antibiotics may be required in cases where the skin has been broken and become infected. cold hosing and ice packs on the affected areas. Finally, many alternative therapies are purported to help, and it's worth discussing these with a specialist.

You must not expect any of the above treatments to be effective immediately. Horses who have suffered from sweet itch have often become habitual scratchers; therefore, it will take a while to break the itch-scratch cycle.

OTHER OPTIONS Certain creams and oils can reduce the itch but need regular application. Some horses experience relief from

SUMMARY

With sweet itch, there are no cures and no quick fixes, and even a short exposure to a few biting Culicoides midges can result in weeks of itchiness. Throughout the main 'biting' season, preventative measures must not be relaxed if the programme is to successfully control the condition and minimise discomfort. This is time-consuming but must be done to achieve the best outcome for your horse.