CAUSES OF SWEET ITCH.
Sweet Itch is caused by the bite of the Culicoides midge and to a lesser extent by the black fly Simulium equinum.
Please refer also to the section entitled Culicoides midge - The Culprit.
GENETIC PREDISPOSITION TO DISEASE.
Young horses which develop Sweet Itch may have a genetic predisposition to the disease whereas older, more mature animals are thought to develop the disease as the result of adverse environmental conditions, especially stress
The exact interplay between hereditary factors and environmental ones is not known.
As Dr Tim Watson observes in an article in Scottish Horse entitled Sweet Itch in the Scottish Horse "IBH - Insect Bite Hypersensitivity - is a genetic trait inherited from generation to generation"..and.. "is more common in certain breeds, especially Icelandic horses".. "scientists have identified several genes that make a horse susceptible to Sweet Itch and these work in a highly complex manner When the DNA of Icelandic horses was examined they were found to have similar numbers of these susceptibility genes as other types of horse that are more resistant to Sweet Itch"
NO SWEET ITCH IN ICELAND
In Iceland there are no culicoides biting midges. Consequently, there is no Sweet Itch in horses. But when brought to Europe over one in four Icelandic horses may develop Sweet Itch, according to Dr Doug Wilson, a Bristol vet who researches Sweet Itch immunotherapy.
Genetically Icelandic horses are no more likely to get Sweet Itch than other horses,apparently. Although there are genes in some horses that make them more likely to get Sweet Itch these are no more common in Icelandic horses than other breeds.
Icelandic horses born in Britain don't get Sweet Itch any more often than other breeds.
A British based foal's immune system is programmed to ignore midge bites. An Icelandic foal in Iceland is not progammed this way as there are no midges.
MIDGE BITES MISTAKEN FOR PARASITES IN SWEET ITCH HORSES.
Horses affected by Sweet Itch mistake a midge bite as an invading parasite, and therein lies the problem. How do scientists reprogramme the immune sytems of Sweet Itch horses to react like normal, healthy horses?
Immunotherapy is a treatment, or treatments, designed to reprogramme the immune sytems of humans and animals with allergies.
A STRESSED HORSE IS A SUSCEPTIBLE HORSE
The most likely trigger of Sweet Itch in adult horses is thought to be an adverse environment, especially stress.
Like humans, horses ability to cope with stress varies from animal to animal. What affects one horse won't affect another
A horse can find numerous life-style things stressful: environmental pollution, irregular feeding, loss of regular companions, change of environment, movement by lorry, competitive situations, change of diet or wrong diet, enclosure in a stable for long periods, insufficient regular exercise, injuries, insensitive handling by its owner.
For more on HORSE STRESS please read veterinary herbalist Stephen Ashdown's article