Insect Bite Hypersensitivity (IBH), also known commonly as “Sweet Itch”, is currently diagnosed by ruling out other causes of itching (lice, skin diseases, etc.). IBH is caused by an immunoglobulin E (IgE)-mediated hypersensitivity response to salivary antigens (proteins in the saliva of the midges) from Culicoides spp. (biting midges). Researchers undertook a project whose aim was to evaluate the IgE levels in the plasma of 343 Warmblood horses that were classified as either IBH-affected (167 horses) or IBH-unaffected (176 horses) according to the owners’ description. The IBH-affected horses were then further subdivided by the severity of their symptoms and how “classic” the history of their symptoms was considered to be. Blood was collected from all of these horses and their IgE levels were measured using an ELISA test. It was noted that the accuracy of this blood test measuring the horse’s “allergic response” to the proteins in the midge saliva, determined by the IgE level, was increased when the clinical signs of IBH were the most pronounced. Midge saliva contains many different proteins and the researchers also discovered that the accuracy of the test was improved if the IgE levels from 4 different proteins were combined.
Relevance? This test may be valuable to help confirm a suspected case of IBH, but the researchers hope to see an even more sensitive test that “could help to diagnose horses under circumstances in which IBH symptoms do not occur (during winter, when stabled a lot, or in environments with few midges or when the owner uses preventive measures such as blankets to reduce clinical syptoms).”(from theHorse.com) Being that the Friesian horse breed does suffer from ‘Sweet Itch”, it would be wonderful for owners and veterinarians alike to be able to definitively diagnose IBH and move forward with a treatment plan to manage the symptoms.
Scientific Article: Peeters, LM et. al. “Evaluation of an IgE ELISA with Culicoides spp. extracts and recombinant salivary antigens for diagnosis of insect bite hypersensitivity in Warmblood horses”. Vet J 2013, oct. 198 (1).
Companion Article: Lest’e-Lasserre, MA “Researchers Developing Equine Sweet Itch Test”, theHorse.com, Dec 2013, Article #33062.