Also known as Queensland Itch, Summer Itch or more technically, Culicoides Hypersensitivity.

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

Ceratopogonidae

Ceratopogonidae, or biting midges , are a family of small flies in the order Diptera...

 midge

Midge

A midge is a very small, two-winged flying insect. "Midge" may also refer to:-Real:* Midge Costanza , American politician* Mildred Gillars , aka "Midge", American broadcaster of Nazi propaganda during World War II...

s. It may be found in any horses and ponies, especially in the warmer regions. It may also occur, too, in other equines. It is also found in Canada, Australia, the US and many other parts of the world.

Causes

A hypersensitivity

Hypersensitivity

Hypersensitivity refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. These reactions may be damaging, uncomfortable, or occasionally fatal. Hypersensitivity reactions require a pre-sensitized state of the host. The four-group classification...

 reaction to specific allergen

Allergen

An allergen is any substance that can cause an allergy. In technical terms, an allergen is a non-parasitic antigen capable of stimulating a type-I hypersensitivity reaction in atopic individuals....

s (protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 molecules causing an extreme immune response in sensitised individuals) in the saliva

Saliva

Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,...

 of Culicoides midges. There are multiple allergens involved, although some workers claim that the larger proteins (of molecular weight 65kDa

KDA

KDA may refer to:* Karachi Development Authority* Kongsberg Defence & Aerospace* Kotelawala Defence Academy* Kramer Design Associates* Lithium diisopropylamide, KDA is the potassium analogue of lithium diisopropylamideOr kDa may refer to:...

) are the most important. These allergens appear to be cross-reactive across many species of Culicoides - i.e. many different varieties of midges produce similar allergens, giving the same effects upon horses.

The hypersensitivity response is mediated by IgE

IGE

IGE was one of the largest services company buying and selling virtual currencies and accounts for MMORPG. During its peak time, it had offices in Los Angeles, China , and headquarters & customer service centre in Hong Kong. IGE was one of the main monopoly in virtual economy services, also known...

, an antibody

Antibody

An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...

 produced by the horse's immune system

Immune system

An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...

 which binds the allergens, causing a cascade production of histamine

Histamine

Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by...

 and cytokines which make the horse's skin inflamed and itchy. Of these, histamine appears the most important in the initial phase of reaction.

Symptoms

• The allergic reaction develops at the site where the insects feed
• The majority of affected horses show skin lesions affecting the mane
  Mane (horse)
  The mane is the hair that grows from the top of the neck of a horse or other equine, reaching from the poll to the withers, and includes the forelock or foretop. It is thicker and coarser than the rest of the horse's coat, and naturally grows to roughly cover the neck...
  
   and tail and dorsal midline.
• Ventral midline symptoms may also occur.
• Lesions around the ears and head are also common.
• These lesions are characterised by intense pruritus (itching), which results in rubbing and considerable self-trauma. This damage is cause by the horse violently rubbing itself against objects, and causes:
  • broken hairs
  • broken and sometimes bleeding skin
  • bald patches.
• Secondary infections
  Infection
  An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
  
   may result

Treatment and prevention

Few treatments are fully efficacious once lesions have appeared. The only effective form of treatment is preventitive - i.e. prevent further insect bites - so these techniques will also be discussed here. Treatments generally fall into one of the following categories:

1) Insecticides and Repellents: These may be applied to the horse or its environment. The most commonly used and effective are permethrin

Permethrin

Permethrin is a common synthetic chemical, widely used as an insecticide, acaricide, and insect repellent. It belongs to the family of synthetic chemicals called pyrethroids and functions as a neurotoxin, affecting neuron membranes by prolonging sodium channel activation. It is not known to...

s. and benzyl benzoate

Benzyl benzoate

Benzyl benzoate is the ester of benzyl alcohol and benzoic acid, with the formula C6H5CH2O2CC6H5. This easily prepared compound has a variety of uses.-Synthesis:This colorless liquid is formally the condensation product of benzoic acid and benzyl alcohol...

 Citronella

Citronella

Citronella is a word used for several things, including:* Citronella , a genus of trees and shrubs in the Cardiopteridaceae* Citronella oil, an insect-repelling essential oil derived from Cymbopogon...

 has been used, with variable effect. Some sources advocate draining of any stagnant water or pools, to reduce the local breeding potential of the insects. Midge numbers are often larger near water sources, for example ponds, bogs, and slow moving water. Moving the horse away from these areas may help to prevent further problems.

2) Barrier Techniques: Rugs etc., that prevent flies and midges settling on the animal's skin to bite. These include "Boett Rugs" and fly masks. In addition, thin screens may be placed over stable doors and windows to exclude biting insects. Stabling the horse at times of day when the midges are most prevalent is also quite effective.

3) Immunotherapy: A wide variety immunotherapy

Immunotherapy

Immunotherapy is a medical term defined as the "treatment of disease by inducing, enhancing, or suppressing an immune response". Immunotherapies designed to elicit or amplify an immune response are classified as activation immunotherapies. While immunotherapies that reduce or suppress are...

 and desensitisation

Desensitization (medicine)

For medical purposes, desensitization is a method to reduce or eliminate an organism's negative reaction to a substance or stimulus.For example, if a person with diabetes mellitus has a bad allergic reaction to taking a full dose of beef insulin, the doctor gives the person a very small amount of...

 protocols have been trialled in attempts to reduce or modify the immune response, with variable success rates. So far, there appear to be none that show a benefit in more than a very small, statistically insignificant, number of cases. The most recent trial results have not yet been published, however, BioEos is confident that the results will be positive and has said that the 2007 series will be the "final" trials for the product. The BioEos vaccination protocol is designed to shift the immune system from a Th2 (theoretically allergy-producing) to Th1 (non-allergy producing) mode.

4) Nutritional supplements: Various supplements may be effective in individuals, including fatty acid

Fatty acid

In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...

 supplemantation and linseed oil

Linseed oil

Linseed oil, also known as flaxseed oil, is a clear to yellowish oil obtained from the dried ripe seeds of the flax plant . The oil is obtained by cold pressing, sometimes followed by solvent extraction...

. However, although owners perceived an improvement, this was not bourne out by objective statistical analysis.

5) Symptomatic Control: Control of symptoms to some degree can be achieved with antihistamines (especially hydroxyzine

Hydroxyzine

Hydroxyzine is a first-generation antihistamine of the diphenylmethane and piperazine classes. It was first synthesized by Union Chimique Belge in 1956 and was marketed by Pfizer in the United States later the same year, and is still in widespread use today....

, and with corticosteroids, although the potential side effects (e.g. laminitis

Laminitis

Laminitis is a disease that affects the feet of ungulates. It is best known in horses and cattle. Symptoms include lameness, and increased temperature in the hooves...

, immune suppression) make this a less preferred option. In addition, antibiotics may be required to manage any secondary infection.

6) Alternative Medicines: A wide variety of herbal

Herbal

AThe use of a or an depends on whether or not herbal is pronounced with a silent h. herbal is "a collection of descriptions of plants put together for medicinal purposes." Expressed more elaborately — it is a book containing the names and descriptions of plants, usually with information on their...

, homeopathic and other alternative remedies have been suggested. Among the natural remedies suggested are sulfur

Sulfur

Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

, wild geranium (as the base for a shampoo), Lavender oil

Lavender oil

Lavender oil is an essential oil obtained by distillation from the flower spikes of certain species of lavender. Two forms are distinguished, lavender flower oil, a colorless oil, insoluble in water, having a density of 0.885 g/mL; and lavender spike oil, a distillate from the herb Lavandula...

, Aloe vera

Aloe vera

Aloe vera, pronounced , also known as the true aloe or medicinal aloe, is a species of succulent plant in the genus Aloe that is believed to have originated in the Sudan. Aloe vera grows in arid climates and is widely distributed in Africa, India, Nepal and other arid areas.The species is...

 (to reduce the itching).

Overall, the wide variety of treatments proposed leads to the conclusion that no one method is universally effective.

See also

Ceratopogonidae

Ceratopogonidae

Ceratopogonidae, or biting midges , are a family of small flies in the order Diptera...

 (The family of which Culicoides is a member)

Culicoides imicola

Culicoides imicola

Culicoides imicola is a midge which transmits the bluetongue virus. Other suspected BTV vectors areCulicoides pulicaris and species in the Culicoides obsoletus complex....

 (species of midge)

Culicoides Impunctatus (species of midge)

Veterinary parasitology

Veterinary parasitology

Veterinary parasitology is the study of animal parasites, especially relationships between parasites and animal hosts. Parasites of domestic animals, , as well as wildlife animals are considered...

External links

• British Horse Society Sweet Itch Datasheet