Equine Allergy Consensus statement Flashcards by Treasa Clifford

Most common allergic trigger in horses

Insect bites

*Culicoides > Black fly (Simulium)

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“Sweet itch” cause

Culicoides

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IgE has been detected in horse serum after WHICH insect bites

*Simulium (black fly)
*Tabanidae (horse fly)
*Culicoides (midges)

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Body distribution of culicoides

Varies by species, geography

*C. pulicaris on dorsum
*C. punctatus on ventral abdomen

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Clinical signs of IBH

Tail swishing
Head shaking
Stamping
Skin twitching

**They DO remove most tabanids (horse fly)

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How do horses fight off tabinids (horse fly)

Scratching behaviors, go to dark areas (horse flies like sun)

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When time of day do tabanids (horse flies) prefer

Bright sunlight

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During which seasons are culicoides less active

Winter: cold, dry

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During which time of day are culicoides most active

Dust/dawn

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T or F: anaphylaxis has occurred 2’ culicoides bite

FALSE. Has not been reported

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T or F: anaphylaxis has occurred 2’ Simulium (black fly) bite

True. Developed shock from histamine in Simulium saliva

Anaphylaxis shock in sensitized animals

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Which sex of Culicoides bites

Females– need blood to support egg production

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Culicoides are “pool feeders”. What does that mean? Factors to help with ingestion

*Form a pool of unclotted blood to ingest efficiently

*Factor X: hydrolyzes prothrombin to thrombin
*Apyrase: enzyme that converts ATP (needed for platelet aggregation) to AMP (vasodilation)
*Digestive enzymes (hyaluronidaze, trypsin, chymotrypsin) to disrupt skin and connective tissue when biting; digestion of blood meal

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Major allergens for Culicoides

*Cul n 1
*Cul n 2 (hyaluronidase)
*Cul n 4
*Cul n 5

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T or F: Duration of IBH significantly affects the degree of sensitization

FALSE

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Horse breed with high rate of Culicoides hypersensitivity

Icelandic born horses

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Types of hypersensitivity reaction for IBH

Type I and Type IV (24-48hr later)

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Which cell type is abundant in IBH skin, follicular epithelium, and intradermal sweat ducts

Langerhans cells
(MHC cl II, Birbeck granules)

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Which type of T cell is higher in skin from IBH horses

CD4 > CD8

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Where in the IBH horse do IL-13 and IL-4 have their effect

IL-13 drives inflammation in the peripheral tissue

IL-4 has a central inflammatory effect

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Which transcription factor is downregulated in skin of IBH horses (lesional and nonlesional skin)

FoxP3 (TF for TRegs)

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Which T-cell response is increased, decreased in IBH horse

Th2 is increased. Th1 is decreased. Treg is decreased

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During summer, is IL-4 or IFNg increased in IBH horses?

During winter, is IL-4 or IFNg increased?

Summer: IL-4 is higher (Th2)

Winter: IFNg is higher (Th1)

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T or F: microarray IgE serological tests with pure r-Culicoides allergens has high specificity and sensitivity for IBH diagnosis

True

Just not commercially available yet

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An increased in _______ antibodies PRECEDES clinical signs in IBH horses

IgG5, IgG1 IgE levels increase CONCURRENTLY with clinical signs. Not a great predictor of a flare

While basophils play a role in IBH, these 2 cells characterize the skin infiltration in IBH

Mast cells, eosinophils

T or F: Blood eosinophil numbers correlate with IBH severity

TRUE

Which TYPE of Type IV hypersensitivity are eosinophils a part of

Type IV b

T or F: IL-5 plays a key role in IBH

TRUE Eosinophils are a major skin infiltrate in IBH leisons

Which sensory nerves mediate pruritus in IBH horses

Unmyelinated polymodal C fibers

Which histamine receptors are expressed on sensory nerve endings to cause immediate itch responses

H1, H4

Which histamine receptor regulates sleep, cognitive functions

Which histamine receptor is on the enterochrommaffin cells of the stomach

Which histamine receptor is on lymphocytes, DCs, mast cells, eos, keratinocytes

H4 --> immune and inflammatory response mediator

Which enzyme converts amino acid histidine into histamine

Histidine decarboxylase

Other than mast cells, which 2 cells types also produce histamine in inflamed settings

Macrophages Keratinocytes

What protein is present in mosquito saliva as an antiinflammatory? (As opposed to Simulium, which has histamine in its saliva for vasodilation)

**D7 proteins** bind: -Histamine -5-hydroxytryptamine -Thromboxane -Cysteinyl leukotrienes

Function of 5-hydroxytryptamine (5-HT) at high and low doses

Low dose: itch High dose: pain

Which vasoactive amine is responsible for pain from bee stings

5-HT

T or F: Antihistamines work well for IBH

FALSE. Same efficacy as placebo

How does PAR-2 contribute to the itch sensation

Binds MRGPR on sensory nerves --> itch

Which major itch receptors are on nociceptor nerves

TSLP, IL-33, IL-31

Risk factors for IBH

EXPOSURE LATER IN LIFE *Grazing outside *Sunlight *Climate *Rainfall *Vegetation *Stabling *Type of bedding *Deworming frequency

Which body regions are affected by Culicoides spp (geographics matter)

Pruritic papules on the: *Ears *Face *Chest *Legs *Withers *Rump *Tail base *Inguinal region *Ventral midline

"River blindness"

Onchocerciasis

What is the vector for Onchocerca cervicalis (microfilaria)

Culicoides

Clinical lesions of Onchocerca cervicalis, body region

Microfilaria: scale, crusts, ulceration, alopecia, and depigmentation on the VENTRAL MIDLINE Adults live in the nuchal ligament

Treatment Onchocerca cervicalis

Macrocyclic lactones for microfilaria No adulticides for adults

What is the most common cause of equine eosinophilic granulomas

Insect bites

T or F: Horses can develop hyperreactive airways 2' IBH

True

T or F: Horses with IBH also have concurrent environmental allergies

True

Which is better: IDST vs Serum for IBH

Good agreement

Most effective treatment for IBH

Insect avoidance -move away from standing water -stable horses at night -use fans (if needed, use systemic GCs)

Fly sprays that are effective

Permethrin DEET (Citronella, cypermethrin were NOT)

What topical product can help with IBH skin lesions (but not pruritus)

*Cream with OFA3, humectants, emollients

T or F: high dose N-3 fatty acids can help with IBH pruritus and skin lesions

FALSE. No significant effect (but possible flaw with the study. OFA was from flax-seed. Can try algae/fish)

What is the mast cell INHIBITORY receptor

FCgRIIb ASIT shifts Th2-> Th1, IgG blocks binding of IgE to allergens, prevents mast cell degranulation by binding to FcgRIIb

Combining Culicoides crude extract with _____ may make ASIT more effective

Mycobacterial cell wall fraction (immunostimulant)

Is ASIT with current commercial extracts recommended for IBH treatment?

Evidence is lacking. Hoping for improvement with recombinant vaccines

2 vaccine targets for IBH horses

IL-5 IL-31

Horse breeds predisposed to Atopic Dermatitis

*Arabians *Finn horses *Thoroughbreds

Skin barrier defects in horses with Atopic Dermatitis

*Alterations in lipid lamellae -Retained lamellar bodies *Altered phospholipid profiles -lower levels of phosphatidylcholine and spingomyelin

Atopic Dermatitis in horses: top 3 clinical signs

1) Urticaria 2) Pruritus 3) Urticaria + Pruritus

Location of pruritus for Atopic Dermatitis in horses

Face, trunk, flexural surfaces +/- urticaria

Most common triggers for urticaria in horses

Food Bug Drug environmental allergens Oral supplements Vaccines

Age of onset for Atopic Dermatitis in horses

Any age Consider geographical moves

Most common positives on IDT in horses

Culicoides Dermatophagoides farinae

Withdrawal time for oral glucocorticoids and antihistamines before IDT in horses

Antihistamine: 1 week Glucocorticoids: 14 days

Is IDT or serum testing better for Atopic Dermatitis in horses

Both are good-- good correlation

Reasons why prednisolone > prednisone in horses

*Poor absorption *Rapid excretion *Failure of hepatic conversion of prednisone to prednisolone via 11-B hydroxysteroid dehydrogenase

Which steroid is most likely to trigger laminitis in horses

Triamcinolone (also steroid hepatopathy)

Reason glucocorticoids may trigger laminitis

*Vasoconstriction *Increased circulating insulin or glucose *Decreased collagen production in lamellae *Diminished keratin production in hoof wall *Diminished growth of coronary band

Which horses are most likely to develop laminitis 2' steroid administration

Those with predisposing factors (breed, weight, endocrinopathy)

What is the most common adverse effect of hydroxyzine in horses

Sedation

MOA of pentoxifylline

*Synthetic xanthine derivative *Inhibits phosphodiesterase ALLERGY: inhibits T and B cell activation, increase IL-10, PGE2, decrease leukocyte adhesion, decrease neutrophil superoxide, degranulation, IFNg, NK cell activity *Rheological effects *Improves wound healing (Increased fibroblast collagenases, decrease TNFa)

What diseases is pentoxifylline used for in horses

Endotoxemia Laminitis Airway disease

Which topical glucocorticoid is not absorbed systemically in horses

Hydrocortisone aceponate (Cortavance) Use for mane/tail pruritus short term

Which eicosinoid was decreased after using fish oil supplementation in a horse

Prostaglandin E2 n-3 OFAs can decrease IDST!

Effect of Apoquel on horses with atopic dermatitis

Decreased pruritus, no change on skin lesions Unlicensed in horses SID dosing

Time to improvement with ASIT in horses

As early as 2 months!

Efficacy of ASIT in horses

70% improve 2/3 stay in remission after ASIT d/c

Impact of ASIT on level of Tregs, TGFb, IL-10, IFNg in horses

No change after 1 year!

Impact of ASIT on IgE levels in horses

Decreased at 6 months, but increased at end of study

Which cases of atopic dermatitis in horses could receive autoserum

Autoserum separation, so abnormal aggregate complexes of lipids are dissolved --> allows normalization of cell signaling. 70% of horses respond per owners

Environmental changes that can minimize horse Atopic Dermatitis flares

*Change bedding from straw to low-dust cardboard *Change feed (avoid hay) to pelleted diet. OR immerse hay in water to minimize dust *Ventilation in stables *Move hourse from indoor to pasture (minimize dust, mites, mold) *Wash bedding-- HDM on blankets *Storage mites on mouldy bedding, hay

CAFR triggers in horses

Oats Pasture Pasture plants But consider everything

Which food should be avoided if suspicious of CAFR horse

High protein grasses (alfalfa, peanut hay)

Which foods have triggered urticaria

Peanut hay Garlic supplements Concentrated foods

How long until improvement is noted for CAFR in hroses

*Usually within a few days *Recommend 4+ weeks

T or F: serologic tests for food are great in horses

False

T or F: positive IDST to hays is highly suspicious of a CAFR in horses

False. Could be epicutaneous exposure

T or F: urticaria is always a type I hypersensitivity

False. Reports of Type II and III hypersensitivities. IgG against IgE (rather than an allergen)

Non-hypersensitivity triggers for urticaria in horses

*Exercise *Physical stimuli (dermatographism) *Thermal stimuli *Psychogenic stress Cholinergic "Sweat-induced" Urticaria

Which cytokines are upregulated in urticarial skin in horses

IL-4 IL-13 TSLP IL-4ra

Where on the body do urticaria typically occur

Neck, sides, face

T or F: Urticaria are always pruritic

Not always pruritic

Differential for urticaria in horses

Erythema multiforme

T or F: Horses with urticaria have more positive IDST reactions

True

Treatments for urticaria in horses

Glucocorticoids, antihistamines Consider pentoxifylline and OFA for chronic cases

T or F: diphenhydramine is readily available in the horse

False. Poor bioavailability. Need injectables.