Sugariness Itch

Sweetness itch or insect-seize with teeth hypersensitivity (q.v.) is a seasonally recurrent hypersensitivity skin reaction to antigens in the saliva of Culicoides species characterized by widely distributed pruritic crusting dermatitis.

From: The Equine Manual (Second Edition) , 2006

Ectoparasites of Horses

Joy Fifty. Barbet , in Equine Infectious Diseases, 2007

Clinical Findings and Diagnosis

Biting midges are the most common cause of equine insect hypersensitivity, besides known as "sweet itch," "kasen," "Queensland itch," "muck itch," "dhobie itch," and "Sommerekzem." Types I and Iv hypersensitivity reactions are implicated in the pathogenesis, and a genetic predisposition is suspected because certain major histocompatibility types are highly represented in afflicted horses of susceptible breeds. 27 It is not unusual to see the condition in related horses. Affected animals should be removed from convenance programs.

Clinical signs ascend between 1 and iv years of age or 1 to four years after beginning exposure to the insects. In temperate climates a seasonal onset is characteristic, occurring in the summer and early fall. Horses in tropical and subtropical locations may be exposed for 9 or 10 months of the year, possibly from successive species emerging throughout the season. 27 During the beginning season the condition tends to be mild, worsening each year every bit long every bit exposure to the insects continues. Pruritus is the major symptom, resulting in cocky-inflicted lesions. Classically, the head, ears (Fig. 64-three), mane, withers (Fig. 64-4), rump, and tail (Fig. 64-5) are affected. All the same, some species of Culicoides feed in other areas on the animate being, resulting in lesions with a different distribution. A ventrally distributed grade, described in the southeastern United States, involves the head and ears, the intermandibular space, chest (Fig. 64-6), upper forelegs, ventral abdomen, inguinal region, and usually the tail. 28 Rubbing and self-trauma result in alopecia, lichenification, crusting, erosions, ulcerations, and eventual wrinkling or corrugation of the skin. Secondary infections of the traumatized pare often follow.

Tentative diagnosis should be possible based on history and clinical signs. Response to appropriate insect command measures is diagnostic. Intradermal skin testing can exist a useful method for confirming the clinical diagnosis. Biopsy findings of perivascular cuffs of mononuclear cells and eosinophils advise allergic dermatitis but are non diagnostic for an etiologic agent because similar results can exist seen with many ectoparasitic conditions. xviii The parasitic manges, louse infestation, other causes of allergies, and cutaneous onchocerciasis should be ruled out.

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Ectoparasites of Horses

Joy L. Barbet , in Equine Infectious Diseases (Second Edition), 2014

Clinical Findings and Diagnosis

Biting midges are the nearly common cause of equine insect hypersensitivity, also known every bit "sugariness itch," "kasen," "Queens­land crawling," "muck itch," "dhobie itch," and "Sommerekzem." Types I and IV hypersensitivity reactions to multiple salivary antigens are implicated in the pathogenesis, and a genetic predisposition has been shown in several breeds. 38-forty It is not unusual to come across the condition in related horses. Affected animals should be removed from breeding programs. In vitro immunologic studies have shown the presence of circulating immunoglobulin East (IgE) antibodies reacting to salivary antigens and that peripheral blood mononuclear cells from afflicted Icelandic horses have reduced T regulatory FOXP3 expression when exposed to Culicoides allergen as compared to cells from unaffected horses. 41,42

Clinical signs arise betwixt 1 and 4 years of age or 1 to 4 years afterwards first exposure to the insects. In temperate climates, a seasonal onset is characteristic, occurring in the summer and early on autumn. Horses in tropical and subtropical locations may be exposed for 9 or 10 months of the year, possibly from successive species emerging throughout the season. 43 During the get-go flavor, the status tends to be mild, worsening each year as long every bit exposure to the insects continues. Pruritus is the major symptom, resulting in cocky-inflicted lesions. Classically, the head, ears (Fig. 59-3), mane, withers (Fig. 59-4), rump, and tail (Fig. 59-5) are afflicted. Notwithstanding, some species of Culicoides feed in other areas on the animal, resulting in lesions with a different distribution. A ventrally distributed grade, described in the southeastern United States, involves the head and ears, the intermandibular infinite, chest (Fig. 59-6), upper forelegs, ventral abdomen, inguinal region, and usually the tail. 44 Rubbing and cocky-trauma result in baldness, lichenification, crusting, erosions, ulcerations, and eventual wrinkling or corrugation of the skin. Secondary infections of the traumatized skin often follow.

Tentative diagnosis should exist possible based on history and clinical signs. Response to appropriate insect command measures is diagnostic. Intradermal pare testing can exist a useful method for confirming the clinical diagnosis. Biopsy findings of perivascular cuffs of mononuclear cells and eosinophils suggest allergic dermatitis merely are non diagnostic for an etiologic amanuensis because similar results tin can exist seen with many ectoparasitic conditions. 24 The parasitic manges, louse infestation, other causes of allergies, and cutaneous onchocerciasis should be ruled out.

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Index of Drugs Used in Equine Medicine

Derek C. Knottenbelt OBE, BVM&S, DVM&S, DipECEIM, MRCVS , Fernando Malalana DVM, DipECEIM, FHEA, MRCVS , in Saunders Equine Formulary (2nd Edition), 2015

(yard) Ectoparasiticides

Benzyl benzoate

NFA-VPS

Indications: Acaricide for control of mange mites and Culicoides spp. irritation and allergy (sweet itch).

Presentations: 25% w/5 with emulsifying wax in water pulverisation in shaker; 500   mL and 1.8   kg.

Dose: Applied daily to mane and base of tail as repellent/insecticide.

Notes:
●

For topical treatment only. Care should be taken with handling.

●

Non very effective in many cases, but others are significantly improved.

Coumaphos

NFA-VPS

Indication: Ectoparasiticide for control of lice.

Presentation: 3% pulverization in shaker with propoxur 2% and sulphanilamide 5%.

Dose: Repeat at xiv-24-hour interval interval (NOT LESS).

Note:
●

For topical handling but. Intendance should be taken with handling.

Cypermethrin/permethrin

NFA-VPS

Indications: Ectoparasiticide for control of nuisance flies such as H. irritans, H. bovis, G. intestinalis, etc. Cattle ear tags repellent for flies.

Presentation: five% emulsifiable concentrate; 250 and 1000   mL.

Dose: Diluted ane:fifty with water used as TOPICAL Wash. Applied to mane, neck, etc., at sites of predilection for flies. Repeat 14–28 days.

Equus caballus needs half dozen   + cattle tags (halter/mane/forelock/tail plaited in).

Notation:
●

For topical treatment but. Intendance should be taken with handling.

Doramectin

POM VPS

Indication: Treatment of chorioptic mange.

Presentation: ten   mg/mL injectable solution.

Dose: 0.iii   mg/kg, subcutaneous, 2 weeks apart.

Notation:
●

Not licensed for equine use.

Fipronil

POM V

Indications: Control of mange (chorioptic, sarcoptic, psoroptic), trombiculidiasis and lice.

Presentation: Fipronil 0.25%; 100 and 250   mL solution in hand-held sprayer.

Dose: Clip affected hair if necessary, clean scabs abroad and so apply directly to afflicted areas. If lesions generalised, care for half fauna then treat other half 1–ii weeks later.

Note:
●

Not licensed for equine use.

Piperonyl butoxide

NFA-VPS

Indications: Treatment of Culicoides sensitivity, sweetness crawling and lice.

Presentation: Solution containing piperonyl butoxide 0.5%   +   pyrethrum extract 0.four%; 500   +   5000   mL.

Dose: Use to mane, neck, etc., at sites of predilection for flies. Repeat 14–28 days.

Note:
●

For topical treatment merely. Care should exist taken with handling.

Ivermectin

See sections nether endoparasiticides (p. 185).

Moxidectin

See sections under endoparasiticides (p. 187).

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Disorders of the Skin

Christine A. Rees , in Equine Internal Medicine (Second Edition), 2004

INSECT HYPERSENSITIVITY

Insect hypersensitivity is a common crusade of skin disease in the horse. Mosquitoes and species of Culicoides (biting midges, "sweet crawling"), Simulium (black flies), Tabanus (equus caballus flies), Chrysops (deer flies), Stomoxys calcitrans (stable flies), Haematobia (horn flies), Musca (business firm flies), bees, and wasps cause skin lesions in horses. 7

Insect hypersensitivity reactions are seasonal in colder climates, can be nonseasonal in warmer climates, and may bear on any age, sex, or brood of horse. This dermatologic status may have an inherited component, but specifics of these claims have not been verified. The distribution of skin lesions varies and may depend on the type of insect involved. Certain insects have preferred feeding sites. 7,xxx The blackness fly tends to feed on the caput, ears, and ventral abdomen. Stable flies adopt feeding on the lower legs but likewise have been known to feed on the ventral abdomen, chest, and back. The location for Culicoides spp. feeding is species dependent. Classically, Culicoides spp. feed on the dorsal surface of the horse (specially the mane and tail areas), face, and ears (Figure 11-7). In Florida, some Culicoides spp. prefer feeding on the lower legs, ventral body and neck. Horn flies feed on the ventrum around the omphalos (Figure 11-eight). Mosquitoes prefer feeding on the lateral aspects of the trunk.

A few insects seize with teeth anywhere on the body and do not prefer a specific location. Examples include deer flies, horse flies, house flies, bees, and wasps.

Some insects require a specific environment to propagate. Knowledge of these requirements may be helpful in establishing insect control programs. Culicoides spp. and mosquitoes adopt free-continuing brackish water for propagation. In contrast, black flies prefer moving water such every bit a stream, brook, or river. Horn flies are obligate parasites of cattle that crave fresh cattle feces for reproduction. Several species of insects, including stable flies and house flies, adopt decaying vegetation or manure for reproduction. They tend to be a bigger trouble when sanitation practices at the stabling facility are problematic.

The fourth dimension of day that an insect prefers to feed also differs between species. Horseflies, stable flies, black flies, and horn flies are commonly active during the daylight hours. Mosquitoes and most Culicoides spp. are active at night. Mosquitoes are most agile at dusk and the first 2 hours subsequently sunset. If the time of feeding is known for the potential offending insect, the horse may be stalled during peak feeding hours to limit exposure.

Types of dermatologic lesions seen with equine insect hypersensitivity include pruritus, alopecia, excoriations, and lichenification. A generalized papular-crusted eruption likewise may occur.

Diagnosis of insect hypersensitivity is based on a compatible history, concrete findings, and elimination of other causes of pruritus in the horse. Pare scrapings show no abnormalities. Skin biopsies may reveal the presence of a superficial or deep perivascular eosinophilic dermatitis with epidermal spongiosis (intercellular edema of the epidermis), necrosis, and collagen degeneration. Intradermal skin testing is useful for diagnosing insect hypersensitivity. 31 Some insect allergens are inconsistently available (eastward.g., Culicoides spp.), and purchase of insect allergens for the nonspecialist veterinary may be cost-prohibitive. Fortunately, therapy and ecology control measures are similar for most biting and flying insects, and therefore confirming the diagnosis by intradermal skin testing may non exist crucial.

Treatment of insect hypersensitivity involves insect control and judicious use of glucocorticoids. 31 Boxes 11-1 and 11-2 and Table 11-one summarize recommendations. Ideally, one should stable horses during the target peak feeding period for insects and should screen windows with a small-meshed screen and spray with a residue parasiticide. If possible, i should eliminate bedding areas for flies (e.one thousand., continuing water and manure). Spraying horses with residual insecticides (due east.chiliad., pyrethrins or pyrethroids) is useful, and sprays containing permethrin and pyrproxifen (Knock-Out Spray, Vibrac, Fort Worth, Texas) are effective for treating horses with Culicoides spp. hypersensitivity. Anecdotal reports suggest that weekly application of fipronil (Frontline, Merial, Iselin, New Jersey) may be useful for treating horses with Culicoides spp. hypersensitivity. Avon Skin So Soft bath oil (Avon Products, Inc., New York, New York) mixed in equal volumes with water has been used to repel insects in horses. Nevertheless, one should employ this production with care considering contact dermatitis has been reported. I should follow characterization recommendations with changes depending on the response of the individual horse. Cattle tags impregnated with insecticide may be helpful if attached to manes, tails, or halters.

Anecdotal reports suggest the importance of applying repellents and insecticide sprays to the horse when the skin is cool and dry out. This may minimize development of sensitivity reactions to products by limiting percutaneous assimilation. Many horses are sensitive to petroleum-based products and develop erythematous pare and pilus loss in areas where the insecticide, fly wipe, or bath oil has been applied to the pare. If a horse has a history of this type of reaction, performing an open patch test with any new production before applying the spray over the unabridged trunk is advisable. One applies a small amount of the test substance to an area of skin and observes the site for 72 hours for signs of erythema, swelling, and hair loss. Fly masks or wing sheets are useful adjunct therapy for control of insects.

In many cases, insect control alone is insufficient to alleviate discomfort and clinical signs. Hydroxyzine hydrochloride may be beneficial in some horses with insect hypersensitivity when administered orally at a dose of 200 to 400 mg every 8 to 12 hours. 32 This drug besides has been useful in managing insect-induced urticaria. Side effects associated with hydroxyzine in horses include sedation or hyperactivity. If the equus caballus does non respond after hydroxyzine administration, ane may try systemic corticosteroids. The recommended dose for prednisone or prednisolone is i mg/kg orally administered daily until the pruritus is relieved (usually ane to ii weeks); one and so tapers the dose to the lowest constructive every-other-day dose.

Anecdotal reports suggest that a DMSO dervivative, methylsulfonyl methane, may be constructive as an aid to save pruritus associated with equine insect hypersensitivity. This medication is bachelor equally a powder to exist sprinkled on food and should be used according to label directions.

Fatty acids have been recommended for control of pruritus associated with insect hypersensitivity. 33,34 The effectiveness of this therapy may depend on dose and fatty acid source. Ane written report in Florida used flaxseed oil in horses with Culicoides spp. hypersensitivity and institute no benefit in decreasing pruritus. 33 A study in Canada demonstrated that flaxseed meal was beneficial in treating pruritus in horses with Culicoides spp. hypersensitivity. 34 These apparently disparate results may be explained by geographic factors or the source of flaxseed.

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Herbal Medicine in Equine Practice

Joyce C. Harman , in Veterinary Herbal Medicine, 2007

Research

2 studies investigated the use of evening primrose oil (EPO) in the horse. 1 explored the allergic dermatologic problem, "sweet itch" ( Craig, 1997). EFA absorption and metabolism are species specific and have not been well researched in the equus caballus. An interesting ascertainment was fabricated that no gamma-linoleic acid (GLA) was found in the plasma of any of the horses supplemented with EPO capsules, merely rapid elevations in dihomogammalinoleic acid (DGLA) levels were observed later on EPO was taken. The decision was that horses very rapidly and efficiently catechumen GLA to DGLA. Clinical signs were non significantly improved in the study; withal, in practice, EPO and other EFA supplements are very effective in improving the condition of the skin in many of these cases.

The other controlled and blinded written report documented the effects of EPO on the characteristics of the hoof wall. A total of 12 horses were fed 30 mL per day of an EPO solution for 12 weeks. A statistical departure was noted in perioplic lipid assay, along with a significant reduction in free cholesterol in the periople of the horse'due south feet during weeks 4 to eight, but no changes were observed to occur in the stratum medium (Reilly, 1998).

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The Equine Allowed System

Stephen M. Reed DVM, Dipl ACVIM , ... David Due west. Horohov , in Equine Internal Medicine (2d Edition), 2004

HYPOSENSITIZATION

Because horses endure from a number of hyposensitivity diseases, attempts take been made to perform antigen-specific immunosuppression; for example, for sweet crawling and recurrent airway obstacle. The principle of this type of therapy is that the allowed response to an allergen can be redirected to reduce hypersensitivity disease. For instance, type 1 hypersensivity illness may depend on a type 2 T helper cell immune response, and treatments that tin can modify this to a type one T helper cell immune response may eliminate or control the hypersensitivity disease by changing the immune response from one dominated by IgE to one dominated by IgG. 46 Typically, hyposensitization treatments use injections of the allergen itself, starting with small doses and gradually increasing the dose over fourth dimension. This form of handling depends on correct identification of the allergen confronting which the hypersensitivity illness is directed. The difficulty in identifying these allergens using bachelor intradermal testing methodologies 47,48 may provide an explanation for the mixed success of hyposensitization treatment in horses. 49 Prospects for hyposensitization therapy may be improved by new techniques to produce large numbers of recombinant allergens. 50,51 These allergens are defined far better than conventionally prepared allergen extracts. In initial experimental studies of recurrent airway obstruction, these allergens were institute to be far superior in terms of specificity and sensitivity for detection of allergen-specific IgE. Such developments, together with the evolution of DNA vaccination strategies incorporating CpG immunomodulation for hyposensitization, 52–54 mean that a practiced run a risk exists that new and constructive therapies will be adult in the future.

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The skin

J.D. Littlewood , ... P. Heidmann , in The Equine Transmission (Second Edition), 2006

Etiology

Type I and type Four hypersensitivity reactions to the bites of Culicoides spp. (midges, "no-see-ums") are the cause of the syndrome likewise known as "sweetness itch", "kasen", "Queensland itch", "muck crawling", "dhobie itch" or "Sommerekzem" ( q.v.). In most geographic locations these insects feed primarily at dusk and dawn, less so during the night, and not during the day. Windless conditions with temperatures above 10°C are ideal for their action. Culicoides spp. breed in areas of moist, muddy ground around ponds, marshes, ditches and tidal flats.

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Veterinary Entomology

Bradley A. Mullens , in Encyclopedia of Insects (2nd Edition), 2009

Allergic Responses to Saliva

Blood-feeding arthropods possess a potent arsenal of chemicals in their saliva to maintain claret flow (vasodilators, anticoagulants) and sometimes take anesthetics to reduce host defensive response. Similar humans, animals tin develop allergies to these compounds. Horses commonly react to biting midge (Culicoides ) feeding with an allergic reaction called Queensland crawling or sweet itch, resulting in peel inflammation and hair loss. Mass emergences of the blackflies Simulium arcticum in Canada and Cnephia pecuarum in the valley of the southern Mississippi River have resulted in the deaths of livestock, probably from allergic responses likewise every bit blood loss. Larvae of sheep blowfly (Lucilia) feed near the skin surface, especially where the wool is wet, and tin can contribute to a toxic shock-type syndrome fatal to infested sheep. Pets may develop serious allergies to fleas, with resulting hair loss and other symptoms.

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Bitter Midges (Ceratopogonidae)

Gary R. Mullen , C. Steven Murphree , in Medical and Veterinary Entomology (Third Edition), 2019

Equine Allergic Dermatitis

Horses exposed to bites of certain Culicoides species commonly exhibit an allergic skin reaction. This typically occurs as a seasonal dermatitis affecting the withers, mane, tail, and ears. The back, ventral midline, and other body regions as well can exist affected, presumably reflecting the feeding sites of different bitter midges involved. Equine allergic dermatitis was first attributed to Culicoides bites in Australia in the early on 1950s, where it was known equally Queensland itch. It is now known to occur widely throughout the world by various names such equally sugariness crawling , summer dermatitis, summer recurrent dermatitis, summertime eczema, equine Culicoides sensitivity, Dhobie crawling (Philippines), and Kasen illness (Nippon). A similar seasonal dermatitis in response to Culicoides bites as well occurs in sheep.

The dermal response plainly is a sensitivity reaction to components of salivary fluids introduced to the seize with teeth wound while the flies are feeding (Fig. 13.twenty). Normal, nonsensitized horses normally react to these bites by developing small welts with relatively trivial associated discomfort. Sensitized horses, however, react more severely past developing intense local inflammation and pruritus; this can result in irritability, rubbing and scratching of involved areas, open wounds and secondary infections. Ponies are specially sensitive. Affected animals oftentimes are unsuitable for riding and, in the instance of show horses, may have a substantial decrease in commercial value considering of their irritable behavior, pilus loss, and skin blemishes.

Figure xiii.20. Allergic dermatitis in neck region of equus caballus in response to injections of Culicoides extracts.

 Courtesy of Yehuda Braverman, Kimron Veterinary Institute, Israel.

In one case sensitized, horses experience either an immediate hypersensitivity response that peaks within 4   h or a delayed hypersensitivity response in which large welts develop after 24   h, with inflammation persisting up to three   weeks or more than. In that location is good show to bear witness that Culicoides-induced hypersensitivity is a polygenic hereditary trait that predisposes certain animals to this response. This sensitivity occurs primarily in older horses, ordinarily after 4–v   years of historic period.

A number of Culicoides species take been implicated equally the cause of equine allergic dermatitis. Almost are based on correlations between seasonal occurrences of the midges and clinical signs, bitter sites on horses, and positive reactions to intradermal injections of horses with extracts of the respective biting midges. The following species are suspected of being involved: C. insignis, C. obsoletus, C. spinosus, C. stellifer and C. venustus in the United states; C. pulicaris in England; C. nubeculosus and C. punctatus in Republic of ireland; C. chiopterus, C. impunctatus, and C. obsoletus in Norway; C. imicola in Israel; and C. brevitarsis in Australia.

Treatments for equine allergic dermatitis in the form of antihistamines and corticosteroids ordinarily provide only temporary relief of symptoms. Desensitization of animals with injections of Culicoides extracts has not proved to be effective. Equus caballus owners in areas where this status is recognized every bit a problem should avoid convenance their animals with lineages of known sensitivity. Insecticides applied directly to horses to repel or impale biting midges affords some protection and tin can substantially reduce the severity if administered on a regular ground throughout the wing season. Ivermectin is ineffective, however. Stabling horses at night or pasturing them abroad from the attack of biting midges can also convalesce the problem.

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Skin diseases

In Diagnostic Techniques in Equine Medicine (2d Edition), 2009

Pruritus

Broadly, pruritus is nigh commonly associated with ectoparasitic infestations, infections or allergic skin affliction. It may also be a characteristic of contact irritants, urticaria, early on photosensitization and pemphigus foliaceous during the crusting phase of the illness.

Appropriate tests for investigating pruritus

•

Skin scrapings and acetate tape preparations to rule out parasites.

•

A therapeutic trial with a parasiticide may be indicated under some circumstances to rule out parasitosis.

•

Skin surface cytology to identify infections.

•

If the history and presentation are consequent with allergic peel disease and then intradermal testing and/or dietary restriction are indicated.

•

Pare biopsies are more often than not not helpful in the pruritic equus caballus as a similar reaction pattern tin can exist seen with multiple diseases.

Ectoparasites

Lice

are a late wintertime/early bound trouble associated with crowded housing conditions. In a skillful light they may be seen with the naked eye (or aided by a magnifying glass) at the base of operations of the mane and tail. Biting lice (Damalinia equi) are fawn in color and may exist distributed in the dorsolateral trunk area. Sucking lice (Haematopinus asini) are a darker blueish-black every bit a result of blood intake. The presence of copious scaling is probable, every bit are signs of rubbing. Shiny eggs ('nits') are seen fastened to the hair.

Biting flies

are probably the commonest ectoparasite causing pruritus. They are a summertime cause of annoyance and local skin eruption in the course of papules or weals. Lesions are exacerbated by private animal hypersensitivities (allergies) to the bite. Horse flies (Tabanidae) inflict painful bites that tin can result in big wheals and focal crusting and ulceration. Stable flies (Stomoxys calcitrans) inflict severe bites to feed on blood/tissue fluids and tin can cause multiple wheals that develop into crusts along the cervix, trunk and legs. Blackness flies (Simulium) attack the more sparsely haired areas such every bit the axillae, ventral midline and inguinal areas, producing a papular response. Horn flies (Haematobia irritans) are associated with a ventral midline dermatitis characterized by foci of hair loss, inflammation and scaling under the belly.

It is difficult to differentiate between these causes and a diagnosis of 'fly bite' may exist achieved by the response to daytime stabling in a wing-proofed box. Biopsy of an early on (primary) lesion will reveal a variety of tissue changes characteristic of an arthropod bite merely it will not distinguish between them. In theory, hypersensitivity tests should place specific allergies (come across later).

Culicoides

species are associated with the development of a common skin hypersensitivity known as 'sweetness itch'. Predilection sites are the mane, croup and tail base. Horses rub the affected areas, resulting in baldness, which is followed chronically by lichenification, hyperpigmentation, excoriations and crusts. A presumptive diagnosis is suggested by the history and clinical appearance. Culicoides hypersensitivity tin can be confirmed by intradermal testing if the allergen is available.

Bees and wasps

may attack every bit swarms producing multiple papules and plaques, which are painful rather than pruritic.

Acarid mites

uncommonly produce infestations in horses, but should always be considered in the differential diagnosis of pruritus.

Chorioptic mange is caused by non-burrowing Chorioptes equi (Fig. 17.1). The condition is uncommon and tends to be seen in the winter months. Lesions are usually bars to the lower limbs and pruritus induces foot stamping. It may be more common in the 'feathered' draught horses. The mites are usually numerous and may be identified in a superficial skin scraping.

Psoroptic mange does not presently occur in the UK horse population. Psoroptic mites are occasionally establish in the aural canal, but the absence of associated lesions makes their significance doubtful.

Sarcoptic mange (Sarcoptes scabei var. equi) is extremely rare in the UK horse population. Lesions are associated with pruritus, alopecia, lichenification and crusting over the head, neck and ears, progressing caudally.

Harvest mites (Trombicula autumnalis and other species; 'chiggers') are an opportunist infection acquired in the tardily summer and fall. They attach to areas of the horse in contact with herbage and weeds, so that the head and limbs are most ordinarily affected. The engorged red/orange mite is visible to the naked middle, assisted past a magnifying lens. There are no marked skin lesions, but oft intense pruritus.

Endoparasites

Oxyuris equi is an uncommon gut parasite. The developed female person causes intense perianal irritation by depositing eggs on the perineum. Large numbers of eggs may be seen at the anal sphincter ('anal rust'). Smaller numbers may be detected microscopically using an agglutinative acetate tape sampling technique (meet below).

Contact irritant dermatitis and contact hypersensitivity

Nigh contact dermatitis is caused by irritants dissentious the skin as a result of persistent exposure to chemicals contained in tack treatments, drugs, sure plants, or torso fluids such as urine. The distribution relates to the points of contact with the irritant, typically the head, limb extremities, ventral body surfaces and tack-associated areas. Lesions progress from erythema to crusting pruritus, lichenification and patchy alopecia. In some cases the initial contact response is urticaria. Contact dermatitis of the lower limbs may progress to the 'greasy heel' or 'mud fever' syndrome (see beneath).

Much less commonly, contact dermatitis has an immunological basis. In this situation the sensitizing agents human action equally haptens, forming allergens with pare proteins. A response may ascend to an agent that has been nowadays in the horse's environs, without harm, for years. One time sensitivity has developed, contact with the inciting agent produces a pruritic dermatitis within i–3 days. The lesions produced are similar to those seen in contact dermatitis due to irritants (encounter in a higher place). Diagnosis is by maintaining the horse in an 'allergen-gratis' area (see below under 'Elimination tests for irritants and allergens'). Biopsy of the affected area may aid diagnosis, but an accurate history and elimination of potential agents is almost useful.

Atopic dermatitis and nutrient allergy

Atopic dermatitis classically refers to an hereditary tendency to develop IgE-mediated hypersensitivity reactions to environmental allergens. The status is not well characterized in the horse although a number of individuals develop seasonal or non-seasonal pruritus and positive reactions to environmental allergens can be demonstrated on intradermal testing. It is of import to dominion out other causes of pruritus, as this is substantially a diagnosis of exclusion. Most horses will nowadays with pruritus, which variably affects the flanks, face, limbs, cervix and tail base. Some volition nowadays with recurrent urticaria (see after). Concurrent recurrent airway obstruction is occasionally seen. A role for food allergens should be ruled out by performing an elimination diet. Intradermal testing is useful to formulate treatment with allergen specific immunotherapy.

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