Itchy scratchy

THERE’S NOTHING SWEET ABOUT SWEET ITCH

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

PATHOLOGY

The Culicoides midge mostly feed at dusk and dawn in warmer weather and breed in wet conditions. This allows them to thrive in the spring, summer and autumn months, which is why the condition is most prevalent at these times. Symptoms of the disease start to appear at the end of spring and continue into autumn. However, in a few rare cases, the condition can be present almost all year round with last year’s symptoms having barely cleared up 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 over-react 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, with the condition being worse in the summer months. Older animals who show the disease for the first time are thought to do so because of some outside stressor, such as moving to a new home, disease 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.

Sweet itch, while immensely distressing for the affected horse, is not contagious. One or more animals in the same stable yard may have the condition, but this is simply due to the environmental factors (the high burden of Culicoides midges) or pure coincidence.

DIAGNOSIS

If you suspect that your horse or pony has sweet itch, it is important to get a proper clinical diagnosis from your vet. Diagnosis should not be difficult, especially with the disease being seasonal, but 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 down continuously until they get access to something to scratch on. Vigorous tail swishing or excessive rolling is also seen.

Constant scratching and rubbing 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, 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 secondary infection you must contact your vet immediately 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, as well as lots of TLC!

Symptoms of sweet itch commonly cause 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.

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, but if the midges are still biting you need to be diligent in applying treatments and fly sprays regularly to get the condition under control.

ENVIRONMENTAL MANAGEMENT There are a number of measures you can take to reduce the midges’ access to the horse, which is the most important arm to treatment. Firstly, horses must be removed from areas near to 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 the 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 flying in and getting access to the horse. It is important to note that fans must be securely fastened and well out of the way of the horse 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 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. Antibiotics may be required in cases where the skin has been broken and become infected. Steroid and antihistamine creams can also be used, and some people have experienced good results with these.

OTHER OPTIONS Certain creams and oils can reduce the itch but need regular application. Some horses experience relief from 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 the treatments to be effective immediately. Horses who have suffered from sweet itch have often become habitual scratchers, and therefore it will take a while to break the itchscratch cycle.

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.