Changes

==Signalment==

==Signalment==

Although sweet itch may occur in horses of all breeds and ages, the disease has a peak age of onset of between 2 and 4 years. Most breeds are affected although sweet itch is rare in Thoroughbreds.

Although sweet itch may occur in horses of all breeds and ages, the disease has a peak age of onset of between 2 and 4 years. Most breeds are affected although sweet itch is rare in Thoroughbreds. It has suggested that genetic factors may have a role in the pathogenesis of the disease as the prevalence of sweet itch in some breeds is higher, such as Icelandic ponies and German Shire horses. ''Culicoides'' require marshy areas or still water and horses kept in fields near streams or water may be at higher risk of developing sweet itch.

==Pathogenesis==

==Pathogenesis==

The condition is thought to occur due to both immediate (Type 1) and delayed (Type 4) hypersensitivity reactions to Culicoides salivary proteins. The female ''Culicoides'' midge lands on the host and crawls down the hairs to the skin surface, using its mouthparts to pierce the skin. Saliva is injected into the site containing vasodilators, anticoagulants and pro-inflammatory mediators. IgE antibodies are produced in repsonse by susceptible animals.

The condition is thought to occur due to both immediate (Type 1) and delayed (Type 4) hypersensitivity reactions to Culicoides salivary proteins. The female ''Culicoides'' midge lands on the host and crawls down the hairs to the skin surface, using its mouthparts to pierce the skin. Saliva is injected into the site containing vasodilators, anticoagulants and pro-inflammatory mediators. Allergen-specific IgE antibodies are produced in repsonse by susceptible animals, leading to mast cell degranulation and the release of histamine and many other inflammatory mediators.

==Clinical signs==

==Clinical signs==