19.4.2: Equine dermatology Flashcards
Examples of Type I hypersensitivity
Type I hypersensitivity
* IgE mediated involving release of histamine by mast cell
* Aggravated after serial exposure
* e.g. Insect-bite hypersensitivity a.k.a. Sweet itch
Examples of Type II hypersensitivity
Type II hypersensitivity
* IgG mediated cytotoxic response associated with complement binding
* e.g. Pemphigus complex
Examples of Type III hypersensitivity
Type III hypersensitivity
* Immunocomplex deposition on endothelial beds
* Neutrophil activation leads to vasculitis
* e.g. Pastern leucocytoclastic vasculitis, Purpura haemorrhagica, Lupus
Examples of Type IV hypersensitivity
Type IV hypersensitivity
* T cell mediated
* Insect bite
* Drug eruptions
Sweet itch
(Insect bite hypersensitivity)
Pemphigus foliaceus
Vasculitis/ purpura haemorrhagica
Lesion distribution around the mane, tail and ventral line may be suggestive of…
Insect-bite hypersensitivity
Lesion distribution around the base of the tail may be suggestive of…
- Oxyuris equi
- Insect-bite hypersensitivity
- Lice infestation (this is normally more truncal)
Lesion distribution around the neck and sometimes face may be suggestive of…
Fungal infections
Lesion distribution around the back, chest, rump and sometimes face may be suggestive of…
Rain scald
Lesion distribution around the pastern and canon bone area may be suggestive of…
- Mud fever: bacterial ± fungal
- Mite infestation: Trombiculidiasis, chorioptic mange
Lesion distribution around the truncal area, neck and occasionaly head may be suggestive of…
- Urticarias
- Atopia
- Lice infestation
Lesion distribution around the back and girth area may be suggestive of…
- Contact dermatitis
- Fungal infections
What might you use coat brushingsto detect?
Ideal for ectoparasites
Remember to use sealed containers if delayed examination under microscope/ magnifying lens!
What should a hair pluck show you? What might you detect?
- Should show a similar number of hairs in anagen and telogen
- Fractured shafts -> suggests self-inflicted trauma e.g. pruritus, pain
- Swollen frayed shaft with fungal spores -> dermatophytosis
- Exclamation mark shaped hair bulbs -> Alopecia aureata
Feather mite
Biting louse
Sucking louse
What might you detect on skin scrape? Which direction do you move the scalpel blade?
- Move in the direction of hair growth (with the grain)
- Ideal for mites and dermatophytes
- Mites - add 2 drops of mineral oil to microscope slides
- Dermatophytes - blue staining on slide, qPCR collected in sterile containers
What can you use skin biopsies to detect?
- Can be excisional or punch skin biopsies
- Ideal for nodules and deep pyodermas
- You can perform culture and histology
Oxyuris equi
Causative agent of rain scald
Dermatophilosis congolensis
What forms of allergy testing are available in horses and which are most reliable?
- Serum allergy testing (SAT) - not reliable, poor specificity and sensitivity. Interpret alongside clinical exposure and always test during flares.
- Intradermal (IDT) - better diagnostic yield but poor repeatibility. Most reactions are to mites, dust, insects, plants. Useful to establish immunotherapy treatments.
What hormones drive hair coat shedding in horses?
- Hair coat is shed dependent on daylight hours
- This process is melatonin and prolactin driven
- Short days -> increasing melatonin and declining prolactin -> winter coat growth
