Longer days and warmer nights mean that summer is getting nearer. For many horses and ponies, it brings with it the misery of sweet itch. The condition, which is found throughout the temperate regions of the world, is also known as kasen, Queensland itch, summer itch or summer seasonal recurrent dermatitis.
Affected animals are very itchy and will rub on anything they can find. They often have bald patches in their mane and at the base of the tail. In some cases the skin may be sore and weeping. The signs tend to get worse over the grazing season.
Up to 5% of horse and ponies in Britain suffer from sweet itch. Many breeds are affected. Although it is often thought of as a disease of ponies, horses of any size can be affected. Even Shires are not immune.
Sweet itch is an allergic disease in which the horse or pony over-reacts to bites from certain species of midge. Normally, when exposed to foreign proteins, an animal produces antibodies that help to inactivate the foreign material. Horses affected with sweet itch have an abnormal immune response. Instead of producing the normal antibodies, they produce allergic antibodies which cause the allergic reaction in the skin. It is not that the midges only bite certain horses. They probably bite all horses, but only affected horses react.
Only the female midges feed on blood. They cut the skin with their mouthparts and secret saliva, which contains active substances to dilate the blood vessels, and stop the blood clotting. The midges then drink the resulting pool of fluid. The midges tend to feed along the top of the horse, from the ears to the tail and under the belly. So those are the areas most commonly affected. When you consider that several hundred midges can be found on a single pony in an hour, it is not surprising that some ponies will have such a marked reaction.
At present there is no cure for the disease. Once an animal is affected the signs are likely to recur annually, usually getting worse each year. But there are several things you can do to reduce the irritation and make the horses more comfortable.
Ideally, the aim should be to prevent the midges biting in the first place. This may require several different lines of attack.
As the midges are active between dawn and dusk, bringing ponies into a stable overnight can reduce their exposure to the midges. You can put fine mesh netting over the windows to try to keep the midges out, and hang sticky fly strips in the stable to catch those that do get inside.
Try to avoid pasture in damp boggy areas, shaded by hedges and tress, which is an ideal breeding ground for the midges.
Insecticidal fly repellents may help, but need to be applied frequently. Various oil-based preparations are available, which may act as a barrier and help repel the midges. Again they need to be applied frequently.
Protective blankets such as the Boett blanket that cover the horse's body and prevent the midges reaching their favorite feeding sites are usually very effective.
There are various things that can be done to reduce the horse's reaction to the midge bites.
Short-acting corticosteroids such as prednisolone tablets are usually safe and effective. Longer acting corticosteroid injections may increase the risk of the pony developing laminitis. As a result, many vets are related to treat sweet itch with corticosteroids.
Anti-histamines generally have little effect once the allergic reaction has started. They are more likely to cause sedation than reduce the itching.
A vaccine can be prepared to try to stimulate the pony to produce good antibodies rather that the allergic ones that cause the problem. Regular doses are injected (initially every other day) in the hope of inducing a normal immune response to replace the allergic one. Opinions among veterinarians and dermatologists are divided on whether this treatment is effective. So it is obviously something you would need to discuss with your veterinarian first.
But there is a glimmer of light at the end of the tunnel. Research at University College London suggests that regular treatment with a preparation containing certain killed bacteria may modify the immune response in affected horses. A trial is currently underway and the initial results look promising.