Sweet itch

Sweet itch is a medical condition in equines caused by an allergic response to the bites of Culicoides midges.

[2] A hypersensitivity reaction to specific allergens (protein molecules causing an extreme immune response in sensitised individuals) in the saliva of Culicoides midges.

There are multiple allergens involved,[3] although some works claim that the larger proteins (of molecular weight 65kDa) are the most important.

[5] The hypersensitivity response is mediated by IgE, an antibody produced by the horse's immune system which binds the allergens, causing a cascade production of histamine and cytokines which make the horse's skin inflamed and itchy.

Of these, histamine appears the most important in the initial phase of reaction.

Sweet itch sores on a Tunisian pony
Fly mask