Lecture 20 4/14/25 Flashcards by Danika Boltz

What are the characteristics of culicoides hypersensitivity?

-“flea allergy of horses”
-types 1 and 4 hypersensitivity
-culicoides are night-time feeders; feeding location equals distribution of clinical signs
-culicoides vector Onchocerca cervicalis; hereditary predisposition can lead to hypersensitivity

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What are the clinical signs of culicoides hypersensitivity?

-seasonal pruritus in spring and summer
-sporadic signs
-recurrent signs that get progressively worse

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What are the three clinical features of culicoides hypersensitivity?

-“classic” dorsal surface distribution
-diffuse ventral dermatitis
-generalized disease

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How is culicoides hypersensitivity diagnosed?

-history and clinical findings
-skin scrapings and cytology
-intradermal allergy testing
-response to treatment

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How can exposure to culicoides be decreased?

-stable horses from dusk until dawn
-fine mesh screens
-drapery sheers
-ceiling/paddock fans
-horse blankets or bodysuits
-eliminate standing water
-insect repellents

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How can the pruritus associated with culicoides hypersensitivity be treated?

-antihistamines
-corticosteroids
-identifying and treating infections
hyposensitization is NOT effective

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Which other insects can cause hypersensitivities?

-black fly
-mosquito
-horsefly

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How are hypersensitivities to other insects diagnosed?

-clinical signs
-IDAT

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Which insects have promising results in hyposensitization research?

-mosquito
-black fly

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What are the characteristics of pollen allergies in horses?

-not well documented
-some have positive skin test reactions
-some respond to hyposensitization

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What are the characteristics of food allergies in horses?

-can be seasonal or non-seasonal
-often a reaction to protein
-can occur with grains, supplements, concentrates, or alfalfa
-no documented age predilection
-pruritus can be multifocal to generalized; tail rubbing urticaria is common

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How are food allergies diagnosed?

-thorough history
-restrict grains and feed supplements
-change hay source
-4 week duration for all “diet trials”

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What are the characteristics of pediculosis/louse infestation?

-common
-host-specific obligate parasites
-life cycle of 20 to 40 days
-nits “glue” to host’s hair
-transmission via direct and indirect contact
-most severe in winter months; longer coat, closer contact with other horses

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What are the clinical signs of pediculosis?

-pruritus along dorsum, neck, tail, and limbs
-patchy alopecia from rubbing
-scaling and crusts
-lichenification
-exacerbation with malnutrition, overcrowding, and/or stress

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How is pediculosis diagnosed?

-close inspection
-tape cytology

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What are the treatment options/steps for pediculosis?

-good nutrition
-ivermectin
-fipronil spray
-permethrins
-selenium sulfide shampoo
-treat environment with flea products
-treat in-contact horses
-decontaminate tack, fomites, and premises with flea products

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What are the characteristics of mange?

-3 genera; Chorioptes, Sarcoptes, and Psoroptes
-transmission via direct contact, environment, or fomites
-causes pruritus in winter
-diagnosed with superficial skin scrapings

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What are the characteristics of chorioptic mange?

-pruritus of lower limbs
-common
-lives in surface debris
-may be difficult to eradicate
-must treat contact animals

What are the characteristics of the Psoroptes body mange form?

-rare and reportable
-lesions begin as papules and alopecia on the head, base of mane, and tail base
-becomes generalized

What are the characteristics of the Psoroptes ear mites form?

-causes ear irritation and head shaking
-thick, greasy crusts build up in ear canal
-occasionally spread to face and neck

What is the treatment for Psoroptes?

-ivermectin (both forms)
-treat any in-contact animals

What are the differential diagnoses for mane and tail pruritus?

-culicoides hypersensitivity
-lice
-pyoderma
-mange
-pinworms (tail only)
-vice (tail only)

What are the differential diagnoses for ventral midline pruritus/dermatitis?

-culicoides hypersensitivity
-horn fly
-pyoderma
-dermatophilosis
-dermatophytosis
-contact irritant

what are the characteristics of horn fly hypersensitivity?

-causes focal ventral midline dermatitis
-mechanical and hypersensitivity mechanisms

What are the clinical features of horn fly hypersensitivity?

-focal ventral midline alopecia -leukoderma -ulceration -crust -mild to moderate pruritus

What is the treatment for horn fly hypersensitivity?

-clean -antibiotic/corticosteroid treatment -fly repellant -petroleum jelly

What are the common causes of crusting and scaling in horses?

-dermatophilosis (most common, it is this until proven otherwise) -dermatophytosis -folliculitis -contact dermatitis

What are the characteristics of dermatophilosis/rain scald?

-most common cause of crusting in the horse -caused by Dermatophilus congolensis, a gram+ facultative anaerobic actinomycete -clinical infection occurs with moisture and skin damage -more severe with immune suppression

What are the characteristics of dermatophilosis presentation?

-dorsal surface infection occurs in fall and winter with rainy weather and winter hair coat -infection on legs and muzzle occurs after contact with wet pasture -infection under fly masks and blankets can occur when horses sweat

What is the typical presentation of dermatophilosis?

-classic crusts in a paintbrush-stroke style lesion -erythematous papules -photosensitization

What are the chronic lesions that occur with dermatophilosis?

-patchy alopecia -scale -easy epilation of hairs with crusts binding them

What are the differentials for dermatophilosis?

-dermatophytosis -folliculitis -pemphigus -photosensitivity

How is dermatophilosis diagnosed?

-cytology of crust showing "railroad tracks" -PCR -biopsy and culture possible but not always necessary or helpful

What is the treatment for dermatophilosis?

-chlorhexidine bath/spray -systemic antibiotics -improve overall health of animal to decrease susceptibility

What are the characteristics of dermatophytosis?

-fungal infection of superficial keratinized layers -disease of younger animals -more common in winter -zoonotic, but rare to see spread

Which species of dermatophytes are important in horses?

-Trichophyton equinum -T. mentagrophytes -T. verrucosum -Microsporum gypseum -M. canis

What are the clinical signs of dermatophytosis?

-multifocal lesions -scaling and crusting -circular alopecia -pruritus -peripheral spread -located where tack contacts body -early lesions may resemble urticaria

What are the atypical forms of dermatophytosis?

-kerion -crusts without alopecia -limited to pastern region -limited to coronary band

How is dermatophytosis diagnosed?

-clinical appearance -microscopic exam of hairs -fungal culture on vitamin-enriched media

What is the treatment for dermatophytosis?

-can resolve spontaneously if removed from infested environment -good nutrition and adequate sunlight -topical fungicides -treatment of in-contact animals -decontaminate environment

What are the characteristics of topical fungicide treatment?

-want to apply daily for 1 week and then twice weekly until clinical resolution -spot treatment NOT recommended -can use lime sulfur or chlorhexidine/miconazole shampoos or sprays

Which products should NOT be used for dermatophytosis treatment?

-chlorhexidine alone -bleach -captan -products containing steroids

What are the characteristics of dermatophytosis vaccination?

-vaccine against T. equinum found to be 91% effective -lesions are fewer and less severe with vaccination

How is a dermatophytosis outbreak prevented?

-isolate and treat affected horses -handle affected animals last -good health care practices