Sweet Itch
(AKA 'Summer Eczema', 'Queensland Itch', 'Summer Seasonal Recurrent Dermatitis')

This is one of the seasonal problems that besets some unfortunate horse owners at this time of the year. It affects all types of horses but is more likely to be found in the pony and cob breeds, Icelandic horses too seem particularly prone. It is also thought to be hereditary and for this reason it is unadvisable to breed from an animal with this complaint.

The cause of Sweet itch is a midge called Culicoides pulicaris.
These minute flies breed in wet, muddy areas in marshes, along the esturies of rivers and around lakes or in wet, decaying vegetable material, e.g woodlands. These midges are active, usually in swarms, principally in the early morning and late afternoon, although if it is cool and humid with no wind they may remain active throughout the day. A small proportion of horses, usually but not always, those that are outdoors all the time develop a hypersensitive reaction to a protein in the saliva of the female midge. These midges are active between the months of April to late October, but tend to be more prevelent during the months of May, June and September.

The midges that cause sweet itch usually feed along the dorsal surface of the horse (forehead, base of mane, withers, back, rump, base of tail) and it is in these areas that symptoms are first seen. These can vary from occasional rubbing of the mane and tail to complete loss of the mane and upper tail hairs. The itching can become so severe that the horse may rub itself for prolonged periods against trees and posts, often developing open sores on the head, neck, withers and dock. The skin often becomes scurfy and itchy along the whole length of their back. In time the repeated rubbing causes the characteristic thickening and ridging of the skin at the base of the mane and tail. Sometimes secondary bacterial infections can develop.
Treatment
This is very much the case of 'prevention is better than cure'. So if you know your animal is prone to this then you should aim to prevent the symptoms by careful management rather than waiting for them to develop.