Skin Lecture 4

Pathology of the
Integumentary System
Lecture 4
Parasitic / Immune
(web)
Paul Hanna Fall 2012

PARASITIC SKIN DISEASES
• cause disease directly by: inflammation
blood sucking
toxin injection
results: annoyance
reduced production
unthrifty / blemished hides
• cause disease indirectly by:
important vectors eg WNV, RMSF, Lyme, Leishmaniasis, dirofilariasis
predispose to pyoderma, myiasis or local viral infections
Diagnosis
• history & clinical signs (esp. pruritus) / lesions
• parasite ID
• skin biopsy

MITES
Demodectic Mange
• normal microfauna, neonates acquire from dam.
• see mainly in dogs with genetic predisposition &/or immunodeficiency
Localized form
young dogs (3-10 months), usually self-limiting.
1 to 5 patchy areas of alopecia; variable erythema, scaling & hyperpigmentation
Generalized form
in juveniles following localized form (~10%)
in older dogs internal disease &/or immunosuppression
massive proliferation of mites folliculitis/furunculosis, 2 o pyoderma

Localized Demodecosis
With localized demodecosis can see focal
areas of alopecia, erythema and/or
hyperpigmentation, and comedones.

Generalized Demodecosis
Generalized demodecosis with secondary pyoderma, note widespread alopecia with scaling / crusting

note: perifolliculitis with
demodex mites in
follicular lumina.
Demodex mites
from scrapings

Sarcoptic Mange (Scabies)
• pigs > dogs > ruminants, horses
• highly contagious, host-adapted varieties (eg. S. scabiei var. suis)
• zoonotic; humans readily parasitized, but usually limited reaction to animal varieties
• lesions due to: mechanical damage from burrowing
irritation from mite saliva and excreta
hypersensitivity to mite products

note: alopecia & excoriations
note: marked crusting within ear canal of pig
note: alopecia, lichenification,
hyperpigmentation

Pruritic papules on human arm (above) which
is a typical skin reaction to animal mites
note: mite tunneling
within cellular crust
Note severe excoriations / crusting on a human hand due
to hypersensitivity reaction to an animal variety of mite.

Notoedric Mange
Cheyletiellosis
Otodectic Mange
Psoroptic Mange
Chorioptic Mange
Psorergatic Mange
Trombiculidiasis
note: marked crusting and excoriation on face
of cat with Notedric mange.

TICKS
• divided into 2 families, ie hard ticks (Ixodidae) and soft ticks (Argasidae)
• vectors for many viral, bacterial & protozoal diseases of domestic animals
• can also cause local skin damage, anemia or paralysis

FLEAS
• most important cause of skin disease in small animals (C. felis & C. canis)
• can cause pruritus / irritation skin, anemia, infectious disease vectors, HS reactions
• clinically, can see: asymptomatic carriers
flea-bite dermatitis
flea allergy dermatitis
Flea dirt (ie flea feces composed of dried digested blood), may be more readily found than the fleas themselves

LICE (PEDICULOSIS)
Sucking lice - feed on blood and tissue fluids
Biting lice - feed on exfoliated epithelium and debris
Note many lice with
numerous eggs (nits)
attached to hairs.

FLIES
vetgrad.co.uk
• cause : annoyance (“fly-worry”)
localized skin damage / pruritus, (fly bite dermatitis)
+/- hypersensitivity (eg Culicoides HS)
direct toxicity (eg black fly toxin)
anemia
vectors for infectious agents
myiasis
Feline Mosquito-bite dermatitis / hypersensitivity.
See characteristic crusted papules on the bridge of
the nose, pinnae and perauricular regions.
FIGURE 5-92 (Sm An Derm) Fly Bite Dermatitis. Alopecia
& crusting (hemorrhagic) on the ear tip of a dog. Note
the similarity to scabies and autoimmune skin disease.

FLIES
Black fly bite on glabrous skin of a dog’s abdomen. Some
animals show these characteristic annular lesion of a central
pale zone of edema, with peripheral erythematous rim

FLIES
Myiasis - infestation of living animals tissues with fly larvae (maggots / grubs)
Warbles (Hypoderma)
• primarily cattle, occasionally horses & others
• eggs laid on hair (esp legs) larva burrow into skin migrate & overwinter in
epidural fat or esophagus in spring migrate to subQ along back and form nodules
mature larvae emerge & pupate on soil
eg damaged hide due to warble fly larvae in subQ nodules along the back of cattle

FLIES
Myiasis - infestation of living animals tissues with fly larvae (maggots / grubs)
Cuterebriasis
• typically small wild mammals, but occasionally infest cats and others
FIGURE 5-84 (Sm An Derm Atlas) Cuterebra. Erythema and
fibrosis surround the breathing hole of the Cuterebra on the
neck of an adult cat. A purulent exudate is common.
FIGURE 5-85 (Sm An Derm Atlas) Cuterebra. The
Cuterebra has been removed with hemostats. The lesion
consists of a fibrosed tunnel with a purulent exudate.

HELMINTH DISEASE
Cutaneous larval migration
• adults live in non-cutaneous sites while larval stages migrate through skin
Cutaneous Habronemiasis (“summer sores”)
• due to aberrant deposition and migration of Habronemia & Draschia spp larvae
• normally larvae deposited near mouth swallowed develop in stomach wall
• when larvae deposited on moist skin / wounds by flies ulcerative dermatitis
note: ulcerated / nodular lesions on lip and periocular regions (r/o sarcoid, squamous cell carcinoma)

Ulcerated lesion on fetlock (above) and multiple ulcerated
papules and nodules involving the prepucial orifice and
urethral process (below - from Eq Derm 2 nd ed)
On histologic examination there is typically eosinophilic
granulomatous inflammation, which often contain
segments of Habronema larva within areas of necrosis.

HELMINTH DISEASE
Filarial Dermatitis
adults or microfilaria spend some time in the skin
Onchocerciasis
Stephanofilariasis
Dirofilarial (heartworm) dermatitis
Equine cutaneous ochocerciasis.
Adults O. cervicalis live in nuchal
ligament and microfilaria in dermis.
The prevalence of infection is high in
North America, but most horses don’t
have lesions. There is strong evidence
that those horses that develop skin
lesions have individual (sporadic)
hypersensitivity to microfilarial
antigens. The characteristic lesions
are areas of alopecia, scaling / crusting
and leukoderma.

PROTOZOAL DISEASES
Sarcocystosis
Leishmaniasis
Besnoitiosis
Fig 6-25 Leishmaniasis. (Atlas Sm An Derm) Alopecia and crusting on the
nose and periocular skin of a Labrador. Note the mild nature of the lesions.

IMMUNE-MEDIATED SKIN DISEASE
HYPERSENSITIVITY REACTIONS
Definition
in response to normally harmless foreign compounds (Ag’s)
most cutaneous HS's are mediated by types I or IV HS reactions
pruritus is a feature common to most HS's

HYPERSENSITIVITY REACTIONS
Diagnosis
• history and clinical signs / lesions (esp pruritus)
• skin biopsy (mostly non-diagnostic)
• intradermal skin testing, elimination of Ag’s, response to therapy

1. ATOPIC DERMATITIS
• common in dogs (genetic/familial); less in cats and horses
• variety of predominately transepidermally absorbed allergens (+/- seasonal)
• complex type I (+/- IV) HS to normally innocuous exogenous Ag's.
• possible dysfunction of Th2 cells with overproduction of specific IgE
• mast cell degranulation pruritus self-trauma

Gross
• pruritus self-trauma erythema, excoriation, alopecia (esp face / feet / abdomen)
hyperpigmentation & lichenification

Histology
• early perivascular / interstitial dermatitis
• later hyperplastic P/I dermatitis; often 2 o pyoderma / Malasseziasis
Differential Diagnosis
• histology non-diagnostic, R/O other allergies and ectoparasitism
note: edema of
superfical dermis
and mild
perivascular /
interstitial infiltrate
of inflammatory cells

2. FLEA ALLERGY DERMATITIS (Flea-bite Hypersensitivity)
most common hypersensitivity of cats and dogs, in flea endemic areas
combination of types I & IV HS to antigens in flea saliva
once sensitized, few fleas are needed for severe reaction.
intense pruritus self trauma / secondary infections
Gross
primary lesion is an erythematous papule or wheal
self-trauma alopecia, excoriation & crusts
chronicity hyperpigmentation & lichenification

note: excoriation / crusts / early
lichenification of lateral thorax &
lumbosacral area

note: alopecia / excoriations (above) and mostly just
alopecia due to excessive “grooming” (below)
Crusted papules of “miliary dermatitis”
(note millet seeds on bread in top pic)

Histology
• P/I dermatitis with eosinophils & mast cells early and later mononuclear cells
• may see spongiosis &/or eosinophilic microabscesses ("nibbles")

3. SOME OTHER HYPERSENSITIVITY REACTIONS
Urticaria (hives or wheals) / Angioedema (edematous swellings)
Allergic Contact Dermatitis [Contact HS]
Food Hypersensitivity (Food Allergy)
Equine Insect (Culicoides) Hypersensitivity
Etc.

SOME OTHER HYPERSENSITIVITY REACTIONS
Allergic Contact Dermatitis [Contact HS]
Occurs following prolonged contact (sensitization) with the offending
allergen (eg plants, cleaners, synthetic carpets plastic dishes, rubber
chew toys, etc. Early lesions of erythema, papules / plaques and
vesicles are seen in the areas of contact (esp sparsely haired regions).

AUTOIMMUNE REACTIONS
when autoAb’s or T cells react against self Ag’s
most have hereditary predisposition; rare in domestic animals (dogs > horses, cats)
Pemphigus
• autoAb’s to desmosomal Ag's (desmogleins) loss of cohesion & inflammatory
mediators acantholysis intraepidermal pustules with acantholytic cells
Acantholysis = loss of cohesion between keratinocytes

Pemphigus foliaceous
Note: immune staining of deposits of
intracellular autoimmune IgG in
the upper epidermal region.
Note: subcorneal pustule with
numerous acantholytic cells
admixed with neutrophils

Pemphigus foliaceus
The primary lesion is superficial pustules, but they are often obscured by hair
coat or have ruptured because they are fragile.

Pemphigus foliaceous
Pemphigus foliaceous, dog.
Note, widespread alopecia, scaling, crusting
Note thick crusts on footpads of dog
with pemphigus folicaceous. Crusts
result from adherence of the content of
ruptured pustules to the skin surface.

Pemphigus foliaceous
note: numerous pustules
and epidermal collarettes

Bullous pemphigoid
• autoantibodies against BPAg2 in hemidesmosome subepidermal vesicles/pustules
Note subepidermal vesicle, with complete
separation of the intact epidermis (including
basal layer) from the dermis.

Bullous pemphigoid
grossly see vesicles / bullae which often
rupture to leave ulcers;
Fig 8-45 (Atlas Sm An Derm) Bullous Pemphigoid.
Severe ulcerative dermatitis on the abdomen. The punctate
lesions coalesced to form large ulcerative lesions. Note the
similarity to erythema multiforme, cutaneous drug reactions,
and vasculitis.

Discoid (cutaneous) lupus erythematosus
• UV light alters keratinocyte Ag’s autoimmune reaction interface dermatitis
See interface dermatitis, with dense lichenoid band of lymphocytes &
plasma cells, apoptotic basal keratinocytes and pigmentary incontinence
Fig 9-39 (Eq Derm, 2 nd ed) Note apoptotic keratinocyte
(upper black arrow) and melanophage (lower black arrow).

Discoid (cutaneous) lupus erythematosus
Note, alopecia, erythema, erosion / ulceration,
crusting, & depigmentation of nasal planum region.
Same dog following treatment; note resolution
of inflammation but depigmentation remains.

AUTOIMMUNE REACTIONS
Diagnosis
history and clinical signs / lesions
skin biopsy of fresh lesions
immunologic tests – esp IHC

SOME OTHER IMMUNE-MEDIATED DISORDERS
Immune-mediated Vasculitis
Erythema Multiforme
Toxic Epidermal Necrolysis
Vogt-Koyanagi-Harada-like syndrome
Plasma Cell Pododermatitis
Cutaneous Amyloidosis
Infarction of facial skin following
immune-mediated vasculitis