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What are the potential insect allergens that cause insect hypersensitivity? (4)
salivary proteins, venoms, excrement, proteinaceous body parts
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What type of hypersensitivity is caused by insects? (2)
- IgE-induced immediate HS
- cell-mediated delayed HS later on
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Common historical findings with insect hypersensitivity? (3)
- clinical signs after puberty
- recurrent seasonal pruritus in cool climates
- nonseasonal continuous pruritus in warmer climates
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Describe Culicoides characteristics. (2)
dusk and dawn feeders, manure lagoons perfect habitat for larvae development
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What is the distribution of lesions with culicoides?
- species dependent, BUT grouped into dorsal feeders vs ventral feeders
- mostly face and ears
- Ventral feeding pattern: chest, axillae, ventral midline
- Dorsal feeding pattern: mane and tail base
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What lesions are usually present with culicoides HS? (7)
excoriations, alopecia, ulceration, depigmentation, crusts, lichenification, scale
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Describe Simulium characteristics. (3)
day feeders, sunny warm weather, require running water for egg laying and larvae development
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What lesions are present with simulium HS? (5)
papules and wheals, vesicles, hemorrhagic, necrotic center in wheal
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What is the distribution of lesions with simulium HS? (7)
[thin-haired areas] legs, face, ears, intermandibular space, neck, ventrum, pinnal papillary acanthosis (aural plaques)
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How do black flies (simulium) take their blood meal?
creates subdermal hematoma and imbibes from the hematoma (danger to horses b/c they deposit anticoagulant and cause vasodilation)
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Why to black fly (simulium) bites cause aural papillary acanthosis?
the fly carries a papilloma virus
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Describe characteristics of Haemotobia irritans (horn flies). (4)
associated with cattle, spend entire life on host, day feeders, female fly begins ovipositing before the cow has completed defecation
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What lesions are present with Haemotobia HS? (4)
crusted papules, alopecia, scaling, lichenification
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Describe the distribution of lesions with Haemotobia HS.
focal ventral midline dermatitis that may progress to involving the entire ventrum
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Describe characteristics of Tabanus (horse fly). (4)
day feeders, sunny warm days with no wind, located host by movement and polarized light, hibernate in unfavorable conditions
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What is the location of lesions with Tabanus (horse fly) HS? (4)
ventral midline dermatitis, legs, neck, withers
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What lesions are present with Tabans (horsefly) HS? (3)
- wheals and nodules that become pruritic
- also have anticoagulant activity in saliva but does not cause death like black fly
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What are characteristics of chorioptes? (5)
- surface mite in stratum corneum
- transmitted directly or from environment (can live off host for months)
- may have asymptomatic carriers
- distal limb feeder, may become generalized rarely
- draft horses with heavy feathers
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Lesions associated with chorioptes. (6)
papular eruptions, alopecia, scaling, crusting, lichenification, severe self-trauma
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How is chorioptic mange treated in horses? (5)
- TREAT ALL ANIMALS and environment
- clip feathers
- sulture-based shampoos (anti-parsitic, break sup crusts)
- lime sulfur dips
- fipronil spray
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Describe characteristics of psoroptes. (4)
- non-burrowing, superficial mite
- head shaking, tail rubbing, scaling and exudate along ear margins
- don't confuse with pinworms
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When are lice infestations most severe?
winter
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How do you diagnose lice infestations?
- see them with naked eye
- horses have patchy alopecia and scale, pruritic
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Where do sucking versus biting lice localize?
- sucking: neck, tail, limbs
- biting: dorsum, back, sides of neck
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What are infectious differentials for dermatitis in horses? (3)
- superficial bacterial pyoderma: pruritic, folliculitis, crusts, tufted fur, secondary to trauma
- dermatophilosis: pain but no pruritus
- dermatophytosis: no pruritus
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How do you diagnose hypersensitivity? (4)
- 1. history suggestive
- 2. distribution of lesions
- 3. rule out pruritic differentials (infectious, lice)
- 4. substantiate dx with intradermal tests, response to strict insect control
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When are intradermal tests used on horses?
used for confirmation of allergen-specific HS to the offending insects
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Describe the prognosis for insect hypersensitvity. (3)
treatment is lifelong, severity progresses as horse ages, controllable but not curable
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How is insect hypersensitivity managed? (3)
- late stages w/ secondary infection: trimethorpim-sulfa antibiotics
- topicals: shampoos, ointments, sprays
- systemic and topical anti-pruritics
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What are potential side effects of using sulfa drugs in horses? (4)
idiosyncratic reactions: uritcaria, vasculitis, SLE, pemphigus
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What systemic glucocorticoid do you use in horses? When?
prednisolone (can't metabolism prednisone) given in the morning (correlates with diurnal spike in endogenous steroids- safer)
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How are antihistamines used?
- give antihistamine for 10-14 days and if they aren't effective in that time, move on to another group b/c they won't ever work
- [hydroxyzine pamonate, cetirizine, tripelennamine, chlopheniramine]
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What topical insecticides do we have for horses?
- pyrethrin- quick knock down
- piperonyl butoxide
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What should you do for pyrethrin toxicity?
dawn dish soap bath, vit E
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What fly gear do we recommend?
fly masks, fly sheets- SHOULD BE WHITE, may be embedded with permethrin
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What premise modifications can you make for management of insect hypersensitivity? (4)
fans in front of stalls, double screen stalls, spray-mist insecticide systems, CO2 octenol traps
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Describe planned avoidance for horses with insect HS.
stable horse during peak feeding hours (this is why we need to figure out which flies are feeding)
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What is pruritus is persistent after management of insect HS?
consider concurrent atopic or food HS
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