Equine Allergy Consensus statement Flashcards
Most common allergic trigger in horses
Insect bites
*Culicoides > Black fly (Simulium)
“Sweet itch” cause
Culicoides
IgE has been detected in horse serum after WHICH insect bites
*Simulium (black fly)
*Tabanidae (horse fly)
*Culicoides (midges)
Body distribution of culicoides
Varies by species, geography
*C. pulicaris on dorsum
*C. punctatus on ventral abdomen
Clinical signs of IBH
Tail swishing
Head shaking
Stamping
Skin twitching
**They DO remove most tabanids (horse fly)
How do horses fight off tabinids (horse fly)
Scratching behaviors, go to dark areas (horse flies like sun)
When time of day do tabanids (horse flies) prefer
Bright sunlight
During which seasons are culicoides less active
Winter: cold, dry
During which time of day are culicoides most active
Dust/dawn
T or F: anaphylaxis has occurred 2’ culicoides bite
FALSE. Has not been reported
T or F: anaphylaxis has occurred 2’ Simulium (black fly) bite
True. Developed shock from histamine in Simulium saliva
Anaphylaxis shock in sensitized animals
Which sex of Culicoides bites
Females– need blood to support egg production
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
Major allergens for Culicoides
*Cul n 1
*Cul n 2 (hyaluronidase)
*Cul n 4
*Cul n 5
T or F: Duration of IBH significantly affects the degree of sensitization
FALSE
Horse breed with high rate of Culicoides hypersensitivity
Icelandic born horses
Types of hypersensitivity reaction for IBH
Type I and Type IV (24-48hr later)
Which cell type is abundant in IBH skin, follicular epithelium, and intradermal sweat ducts
Langerhans cells
(MHC cl II, Birbeck granules)
Which type of T cell is higher in skin from IBH horses
CD4 > CD8
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
Which transcription factor is downregulated in skin of IBH horses (lesional and nonlesional skin)
FoxP3 (TF for TRegs)
Which T-cell response is increased, decreased in IBH horse
Th2 is increased. Th1 is decreased. Treg is decreased
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)
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
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
H3
Which histamine receptor is on the enterochrommaffin cells of the stomach
H2
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.
