What are the potential insect allergens that cause insect hypersensitivity? (4)
salivary proteins, venoms, excrement, proteinaceous body parts
What type of hypersensitivity is caused by insects? (2)
- IgE-induced immediate HS
- cell-mediated delayed HS later on
Common historical findings with insect hypersensitivity? (3)
- clinical signs after puberty
- recurrent seasonal pruritus in cool climates
- nonseasonal continuous pruritus in warmer climates
Describe Culicoides characteristics. (2)
dusk and dawn feeders, manure lagoons perfect habitat for larvae development
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
What lesions are usually present with culicoides HS? (7)
excoriations, alopecia, ulceration, depigmentation, crusts, lichenification, scale
Describe Simulium characteristics. (3)
day feeders, sunny warm weather, require running water for egg laying and larvae development
What lesions are present with simulium HS? (5)
papules and wheals, vesicles, hemorrhagic, necrotic center in wheal
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)
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)
Why to black fly (simulium) bites cause aural papillary acanthosis?
the fly carries a papilloma virus
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
What lesions are present with Haemotobia HS? (4)
crusted papules, alopecia, scaling, lichenification
Describe the distribution of lesions with Haemotobia HS.
focal ventral midline dermatitis that may progress to involving the entire ventrum
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
What is the location of lesions with Tabanus (horse fly) HS? (4)
ventral midline dermatitis, legs, neck, withers
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
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
Lesions associated with chorioptes. (6)
papular eruptions, alopecia, scaling, crusting, lichenification, severe self-trauma
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
Describe characteristics of psoroptes. (4)
- non-burrowing, superficial mite
- head shaking, tail rubbing, scaling and exudate along ear margins
- don't confuse with pinworms
When are lice infestations most severe?
How do you diagnose lice infestations?
- see them with naked eye
- horses have patchy alopecia and scale, pruritic
Where do sucking versus biting lice localize?
- sucking: neck, tail, limbs
- biting: dorsum, back, sides of neck
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
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
When are intradermal tests used on horses?
used for confirmation of allergen-specific HS to the offending insects
Describe the prognosis for insect hypersensitvity. (3)
treatment is lifelong, severity progresses as horse ages, controllable but not curable
How is insect hypersensitivity managed? (3)
- late stages w/ secondary infection: trimethorpim-sulfa antibiotics
- topicals: shampoos, ointments, sprays
- systemic and topical anti-pruritics
What are potential side effects of using sulfa drugs in horses? (4)
idiosyncratic reactions: uritcaria, vasculitis, SLE, pemphigus
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)
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]
What topical insecticides do we have for horses?
- pyrethrin- quick knock down
- piperonyl butoxide
What should you do for pyrethrin toxicity?
dawn dish soap bath, vit E
What fly gear do we recommend?
fly masks, fly sheets- SHOULD BE WHITE, may be embedded with permethrin
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
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)
What is pruritus is persistent after management of insect HS?
consider concurrent atopic or food HS