Pathology of the

Integumentary System

Lecture 4 Parasitic / Immune-mediated

(web)

Paul Hanna Fall 2017

PARASITIC SKIN DISEASES

• cause disease directly: inflammation

blood sucking

toxin injection

results: annoyance

reduced production

unthrifty / blemished hides

• cause disease indirectly:

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

• proliferation of mites folliculitis / furunculosis, 2o 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

Demodecosis

Demodex mites from scrapings

Histopathology showing perifolliculitis with

demodex mites in follicular lumina.

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

Alopecia & excoriations

Marked crusting within ear canal of pig Alopecia, lichenification, hyperpigmentation

Pruritic papules on human arm (above) which

is a typical skin reaction to animal mites Mite tunneling within cellular crust

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 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, rickettsial, bacterial & protozoal diseases

• can also cause local skin damage, anemia or paralysis

• 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

FLEAS

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

Many lice with numerous eggs (nits) attached to hairs.

FLIES • cause : annoyance (“fly-worry”)

localized skin damage / pruritus (fly bite dermatitis)

+/- hypersensitivity (eg Culicoides HS)

anemia

direct toxicity (eg black fly toxin)

vectors for infectious agents

myiasis

vetgrad.co.uk

Feline Mosquito-bite dermatitis / hypersensitivity.

See characteristic crusted papules on the bridge of

the nose, pinnae and perauricular regions.

Fig 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.

Black fly bite on glabrous skin of a dog’s abdomen. Some

animals show this characteristic annular lesion of a central

pale zone of edema, with peripheral erythematous rim.

Don’t confuse this with the human skin lesion associated

with Lyme disease, called erythema migrans, at the site of

the tick bite – because a) skin lesions are often not seen in

dogs at the site of tick bites and b) when rare lesions have

been observed they have been poorly delineated areas of

erythema (rash), urticaria or moist dermatitis

FLIES

Myiasis - infestation of living animals tissues with fly larvae (maggots / grubs)

Warbles (Hypoderma)

• primarily cattle, occasionally horses & others

• eggs laid on hair larva burrow into skin migrate & overwinter in epidural fat or esophagus

in spring migrate to subQ on back & 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.

FLIES

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

• 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)

Involvement of the prepuce &/or penis is common

On histologic

examination there

is typically

eosinophilic

granulomatous

inflammation,

which often

contain segments

of Habronema

larva within areas

of necrosis.

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Ulcerative dermatitis

on fetlock due

Habronemiasis

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.

HELMINTH DISEASE

PROTOZOAL DISEASES

Leishmaniasis

Sarcocystosis

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.

HYPERSENSITIVITY REACTIONS

IMMUNE-MEDIATED SKIN DISEASE

Definition

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

Diagnosis

• history and clinical signs (esp pruritus) / lesions

• skin biopsy (mostly non-diagnostic)

• intradermal skin testing, elimination of Ag’s, response to therapy

HYPERSENSITIVITY REACTIONS

1. ATOPIC DERMATITIS

• common in dogs (genetic / familial); less in cats and horses

• complex type I (+/- IV) HS to normally innocuous exogenous Ag's

• epidermal barrier dysfunction transepidermally absorbed allergens (eg dust mites, pollen)

• switching of TH1 to TH2 proinflammatory cytokines + overproduction of specific IgE

mast cell degranulation + inflammatory mediator synthesis pruritus self-trauma

Gross

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

chronicity hyperpigmentation & lichenification

Histology • early perivascular / interstitial dermatitis

• later hyperplastic perivascular / interstitial dermatitis; often 2o pyoderma / Malasseziasis

Differential Diagnosis • histology non-diagnostic, R/O other allergies and ectoparasitism

Skin biopsy showing 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

Excoriation / crusts / early lichenification

of lateral thorax & lumbosacral area

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

• early perivascular / interstitial dermatitis with eosinophils & mast cells 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]

Allergic contact dermatitis

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

Acantholysis = loss of cohesion between keratinocytes

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 loss of cohesion (acantholysis) & inflammatory mediators

intraepidermal pustules with acantholytic cells

Fig17-55 (Zachary)

Immune staining of deposits of intracellular

autoimmune IgG in the upper epidermal region.

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 very superficial and fragile.

Pemphigus foliaceous

Pemphigus foliaceous, dog. Widespread alopecia, scaling, crusting

Thick crusts on footpads of dog with pemphigus folicaceous.

Crusts result from adherence of the content of ruptured pustules

to the skin surface

Hnilica, Small Animal Dermatology, 3rd ed

Pemphigus often begins on the bridge of the nose, around the

eyes, and on the ear pinnae, before it becomes generalized

Pemphigus foliaceous

Numerous pustules & epidermal collarettes

Discoid (cutaneous) lupus erythematosus

• UV light alters keratinocyte Ag’s autoimmune reaction interface dermatitis

Interface dermatitis, with

dense lichenoid band of

lymphocytes & plasma

cells, apoptotic basal

keratinocytes (arrow) &

pigmentary incontinence

Discoid (cutaneous) lupus erythematosus

Same dog following treatment; note resolution

of inflammation but depigmentation remains. Note, alopecia, erythema, erosion / ulceration,

crusting, & depigmentation of nasal planum region.

Autoimmune subepidermal blistering diseases (AISBDs)

• a group of diseases with autoAb’s against components of the basement membrane

Bullous pemphigoid collagen XVII (BPAg-2)

Epidermolysis bullosa

acquisita collagen VII

Mucous membrane

pemphigoid

variety: collagen XVII

laminin-5 (332)

BPAg-1

[For information only]

Grossly see vesicles / bullae which often rupture to leave ulcers

(Hnilica) Bullous Pemphigoid. Severe ulcerative dermatitis on the abdomen

Subepidermal vesicle - complete separation of the entire

epidermis from the dermis at the dermo-epidermal junction.

[For information only]

Diagnosis

history and clinical signs / lesions

skin biopsy of fresh lesions

immunologic tests – esp IHC

AUTOIMMUNE REACTIONS

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

[For information only]