Dermatology Flashcards
What are the key clinical impacts of ectoparasites?
Direct impact on host welfare
- esp. parasites causing pruritus & cutaneous myiasis
Predisposition to secondary infections
Vectors of disease
Clinical signs mimic other disease
- e.g. allergic skin disease
Act as pointers to other disease
- E.g. lice may indicate underlying immunocompromise
Zoonotic importance
Economic importance
Give examples of ectoparasites that act as vectors of disease
Ticks can transmit:
- babesiosis (cattle/dogs)
- louping ill (sheep/grouse)
- Echinococcus (hydatidosis) (sheep)
Fleas can transmit:
- Dipylidium caninum (dog)
- myxomatosis (rabbit)
Sandflies can transmit:
- leishmaniasis
Give examples of zoonotic ectoparasites
Sarcoptes, Cheyletiella, fleas
Give an example of an ectoparasite with significant economic importance
Psoroptes ovis (sheep scab)
What are the common clinical signs of ectoparasites on skin surface?
Pruritus –> alopecia +- erosions, crust, scale, secondary bacterial infections, chronic changes
Why may fleas not always be found on an animal?
Most of their life cycle occurs in the environment
What are common ectoparasites on the skin surface?
Fleas
Lice
Surface mites
Which animals are commonly affected by lice?
Farm animals, horses, guinea pigs, birds
Incidence greater when animals housed together – seen esp farm animals/horses in winter
How do lice appear on an animal?
Approx. 3mm long, visible to naked eye, eggs (‘nits’) attached to hairs
Name surface mites in cattle
Chorioptes bovis (common) - tailhead, lower legs, scrotum, udder
Psoroptes (rare)
Name surface mites in sheep
Psoroptes ovis - sheep scab
Chorioptes bovis - scrotal mange
Name surface mites in horses
Chorioptes equi (common) – leg/tail mange, esp horses with ‘feathers’
Psoroptes spp – body + ear mange
Neotrombicula sp (harvest mite) – head/legs – late summer/autumn
Name surface mites in dogs/cats
Otodectes (ear mite) – otitis – dark dry otic exudate
Cheyletiella (fur mite) – truncal scale - zoonotic!
Neotrombicula (harvest mite) – esp head/limbs, late summer/autumn
Name surface mites in rabbits
Cheyletiella (fur mite) – (common) truncal scale - zoonotic!
Leporacus gibbus (fur mite) –often asymptomatic, occ –> lesions – brown mite just visible
Psoroptes cuniculi (ear mite) – painful flakey adherent otic crust
Give examples of ectoparasites below the skin surface
Burrowing (round) mites
Demodex
What clinical signs do burrowing mites cause?
Pruritus, alopecia +- papules, hyperkeratosis, crust
Name a burrowing mite that affects dogs and describe the signs of infestation
Sarcoptes scabiei (zoonotic) causes sarcoptic mange, leading to intense pruritus, crusting on pinnal margins, hocks & elbows, along with a positive pinnal-pedal reflex
What burrowing mite affects guinea pigs and is zoonotic?
Trixacarus – causes extreme pruritus & can lead to seizures/death
What is a common burrowing mite in birds?
Cnemidocoptes (Knemidocoptes) – ‘scaley beak’, ‘scaley leg’
What is Demodex and what clinical signs does it cause?
Follicular mite (lives in hair follicles) causing folliculitis, pustules, comedones, alopecia & furunculosis (deep pyoderma)
Which species are most commonly affected by demodicosis?
Dogs, hamsters & occasionally cats
Associated with underlying immunocompromise – most common in young/elderly animals
What are the clinical impacts of tick infestations?
Can act as disease vectors, cause anaemia with heavy infestations & lead to tick granulomas (if mouthparts retained)
What is cutaneous myiasis, and which animals are most susceptible?
Also known as blowfly strike
Infestation with fly larvae (maggots) that feed on host tissue
Sheep & rabbits particularly susceptible, especially in areas with faecal soiling or wounds
How do flea infestations differ in cats and dogs?
Dogs: Lesions mainly on caudal/dorsal part of body
Cats: Present with 4 cutaneous reaction patterns (head/neck pruritus, symmetrical alopecia, eosinophilic granuloma complex, or miliary dermatitis)
Which flea species commonly infest rabbits, and where are they found?
Ctenocephalides felis/canis – found on dorsum/rump
Spilopsyllus cuniculi – found on pinnae (ears)
Which ectoparasite is responsible for ‘sweet itch’ in horses?
Culicoides spp. (midges), causing hypersensitivity reactions
Transmit diseases (e.g. bluetongue virus of cattle/sheep)
How do Nuisance flies (biting & non-biting) affect animals?
–> irritation –> behavioural changes —> injury & production loss
Transmit diseases (e.g. infectious bovine keratoconjunctivitis (pink eye) or summer mastitis)
–> skin disease (e.g. ventral dermatitis or eosinophilic granulomas (horse))
What is Dermanyssus gallinae and why is it important?
Poultry red mite
Lives in environment & only feeds at night
Causes irritation, feather loss & debilitation
Zoonotic
How do you diagnose ectoparasitic disease?
Consider species, age, husbandry, lesion distribution
Determine if parasite is likely on animal or in environment
Use appropriate sampling techniques
Recognise limitations of diagnostic tests
Consider trial treatment in uncertain cases
Where do bacterial organisms causing skin disease come from?
Present on normal skin (endogenous infection)
- e.g. Coagulase +ve Staphylococci
From environment
- e.g. Mycobacteria from soil
From other animals
- e.g. Treponema cuniculi (rabbits)
Why does microbial skin disease occur?
Skin’s normal protective mechanisms are compromised
- Mechanical damage to skin (e.g trauma or ectoparasite)
- Immunocompromise
- Defects in skin barrier function (e.g. Canine atopic dermatitis or inherent weakness (dogs))
- Changes to skin microclimate (e.g. moisture)
Why are dogs predisposed to bacterial skin disease?
Dogs have inherent weaknesses in skin barrier function, including:
- Thin stratum corneum
- Lack of lipid seal at hair follicle openings
- Relatively high skin pH, which favours bacterial growth
Which bacterial skin diseases are influenced by changes to skin microclimate?
Dermatophilosis – ‘rain scald’, ‘mud fever’, ‘lumpy wool’ - predisposed by wet skin
Pseudomonas infections – thrive in wet environments
Intertrigo (skin fold pyoderma) – occurs in dogs due to warm, moist skin folds
What is dysbiosis, and how does it relate to bacterial skin disease?
Imbalance in skin microbiome, where normal bacterial diversity is reduced, leading to overgrowth of certain species like Staphylococci & Malassezia
Label the portals of entry of microbes
a. Via follicles (bacterial folliculitis)
b. Direct entry through damaged skin
c. Haematogenous spread (rare)
What factors determine the manifestation of bacterial skin disease?
Organism & its virulence factors
Predisposing or coexisting conditions
The host immune response
What are the three main types of inflammatory responses in bacterial skin disease?
Pyogenic – Pus-producing, mainly neutrophils (pyoderma)
Granulomatous – Mainly macrophages
Necrotising – Involves vascular damage –> ischaemia
What is surface pyoderma?
Bacteria multiply on skin surface only
Give examples of surface pyodermas in dogs
Canine intertrigo (‘skin fold pyoderma’)
- mixed microbial overgrowth +/- neutrophilic inflammation
Acute moist dermatitis (pyotraumatic dermatitis, ‘hotspots’)
- acute lesion caused by skin self-trauma
Bacterial overgrowth syndrome
- bacterial multiplication with no/minimal inflammation
- often highly pruritic
What is superficial pyoderma and what are the clinical signs?
Infection within epidermis or hair follicles
–> papules/pustules –> crust, epidermal collarettes/scale, follicular plugs, alopecia
Primarily neutrophilic inflammation
Give examples of superficial pyodermas in small animals
Bacterial folliculitis - infection within hair follicle
Impetigo - interfollicular (between hair follicles) infection of epidermis
Exfoliative superficial pyoderma - infection between layers of stratum corneum (exfoliative toxins –> intraepidermal splitting –> scale)
Give examples of superficial pyodermas in large animals
Dermatophilosis – esp horse, cattle, sheep
Fleece rot – Pseudomonas - sheep
Greasy pig disease (exudative epidermitis) - Staph hyicus
What is deep pyoderma and what are the clinical signs?
Infection outside epidermis or hair follicle epithelium due to
- rupture of hair follicle wall (furunculosis)
- penetrating wounds
- haematogenous spread (sepsis)
Usually associated with thickening of skin/subcutaneous tissue, nodules, draining sinuses
What are examples of deep pyoderma?
Furunculosis (ruptured hair follicles releasing bacteria/keratin into dermis)
Abscesses (especially in large animals, cats)
Cellulitis (poorly delineated deep infection, may cause tissue necrosis)
What is furunculosis, how does it develop, and what are its key features?
Deep pyoderma caused by rupture of hair follicle (extension of folliculitis), releasing keratin & bacteria into dermis —> pyogranulomatous inflammation (neutrophils + macrophages)
Results in thickened skin, nodules, draining sinuses & severe inflammation
What is an abscess (deep pyoderma), how does it form, and which animals are commonly affected?
Well-defined accumulation of pus in dermal or subcutaneous tissue, surrounded by fibrous connective tissue
Commonly forms due to wounds, foreign bodies, or infections & frequently ruptures & drains spontaneously
Common in large animals & cats
Wide range of organisms involved, dependent on species & cause of abscessation
What is cellulitis (deep pyoderma)?
Poorly-delineated suppurative inflammation of deep subcutaneous connective tissue
May lead to skin devitalisation, sloughing & necrosis
Various bacteria, including Clostridia, which can produce gas & malodorous infections
What causes bacterial granulomatous dermatitis?
Traumatic implantation of saprophytic organisms
What are the key examples of bacterial granulomatous dermatitis, and what causes them?
Mycobacterial Granulomas/Pyogranulomas
Non-Filamentous Bacterial Granulomas (Botryomycosis)
- e.g. Staphylococci, Streptococci, Actinobacillus
- Lesions: Small yellow ‘sulphur’ granules
Filamentous Bacterial Granulomas
- e.g. Nocardia, Actinomyces
- Lesions: Nodular masses, may involve bone
How can systemic bacterial infections cause skin lesions?
Systemic bacterial infections –> vascular damage in skin –> necrosis
e.g. erysipelas in pigs
What is a toxin-producing bacterial infection, and how does it affect the skin?
Rare
Toxin-producing bacteria trigger severe systemic reaction (similar to toxic shock syndrome) –> fever, shock, organ dysfunction & widespread skin lesions
What are the key diagnostic methods for bacterial skin infections?
Cytology
- From lesion surface, exudate, FNA
- Visualise inflammatory cell type & microorganism
- May use special stains (e.g. Ziehl-Neelsen for mycobacteria)
Culture
- From pustules, exudate, deep tissue biopsy
Histopathology
- Skin biopsy
- +/- special stains (e.g. ZN for mycobacteria)
What are the broad principles of bacterial skin disease treatment?
Kill organism
- Avoid antibiotics – use topical antibacterials for superficial infections
- Use systemic antibiotics for deep infections (based on culture/sensitivity) & abscesses with cellulitis/pyrexia
Drainage of abscesses (except in rabbits, where surgical excision is required)
Address underlying causes
Enhance body’s defences
What are the three main roles of fungi on the skin?
Commensals (e.g. Malassezia) – normally present, may overgrow
Transient contaminants (e.g. saprophytic fungi, some dermatophytes)
Active pathogens (e.g. dermatophytes causing ringworm)
What are the types of fungal skin disease?
Superficial mycoses – affects outer skin layers
Subcutaneous mycoses – deeper skin involvement
Deep/systemic mycoses – may spread beyond the skin
Hypersensitivity reactions – rare but seen in atopic dogs
What are the classifications of dermatophytes?
Geophilic – live in soil, occasional infections
Zoophilic – adapted to animals, most common cause of disease
Anthropophilic – adapted to humans
What is the pathogenesis of dermatophytosis?
Frequent skin contaminants but usually skin defence mechanisms prevent infection. However –> clinical disease if immune system or skin barriers compromised:
- Skin microtrauma & moisture → inoculation of fungal arthrospores
- Spores germinate, penetrate stratum corneum & form hyphae
- Lesions develop within 5-7 days
How are dermatophytes transmitted?
They are contagious & transmitted via direct/indirect (fomites) contact
Zoonotic
What are the common causes of dermatophytosis?
Microsporum spp., Trichophyton spp
What are the common clinical features of dermatophytosis?
Common in cows, horses & cats
Infection of hair/surface keratin leading to:
- folliculitis –> alopecia
- adherent scale
- erythema, crust, comedones
- occasional pustules
- variable pruritus
Lesions are well-demarcated & often asymmetric
What are some uncommon presentations of dermatophytosis?
Furunculosis
- Looks similar to deep pyoderma - nodular swelling +/- draining sinus
Fungal kerion
- Nodular inflammatory mass due to inoculation of fungus into dermis
- Esp. hunting/working dogs
Pseudomycetoma
- Esp in Persian cats, Yorkshire Terriers
- Subcutaneous/deep mycosis –> nodular granulomas
- ulceration & draining tracts with grains
Onychomycosis (claw disease)
What are the main diagnostic tests for dermatophytosis?
Microscopy (Direct exam of hair/scales) – look for arthrospores & hyphae
Wood’s lamp – detects apple-green fluorescence in Microsporum canis
Fungal culture
- McKenzie toothbrush technique
- Use dermatophyte test medium or Sabouraud’s agar
- Daily monitoring required; positive cultures turn red
Fungal PCR – highly sensitive & fast, but can’t differentiate infection from carriage
Skin biopsy – for deep infections
What can be visualised using microscopy when diagnosing dermatophytosis?
x4-10 objective - infected hairs look distorted, paler/wider than normal hairs
x40 objective - arthrospores around hair +/or hyphae within hair shaft
What is the pathogenesis of Malassezia?
- Commensal yeast normally found in skin & ears
- Overgrowth due to host factors (e.g. skin folds, other skin diseases, systemic illness)
- Results in dysbiosis (imbalance in microbiome)
- Causes clinical disease
(not contagious & potentially zoonotic)
What is the common presentation of Malassezia in the skin of dogs?
Pruritus
Erythema, grease, scale, crust –> chronic changes (lichenification, hyperpigmentation)
Often malodourous
Focal/multifocal/generalised
Diffuse/well-demarcated
Commonly affected areas ears, lips, muzzle, interdigital skin, flexor surfaces/medial aspects of limbs, ventral neck/body, axillae, perineum
Also paronychia (claw fold infection)
What is the common presentation of Malassezia in the ears of dogs?
Pruritus
Usually erythro-ceruminous otitis, rarely purulent
How does Malassezia infection differ in cats?
Less common than in dogs
Pruritus more variable
See otitis, chin acne, paronychia or systemic disease
How is Malassezia diagnosed?
- Identify appropriate lesions
- Identify Malassezia at these sites with cytology
- Stained acetate tape strip or stained impression smear
- See peanuts using x40-x100 objective - If present, assess response to antifungal therapy
What are some examples of notifiable viral skin diseases in large animals?
Foot and Mouth Disease
Vesicular Stomatitis
Swine Vesicular Disease
Bluetongue Virus
Rinderpest
Lumpy skin disease
Scrapie
Classical Swine Fever, African Swine fever
Sheep Pox
Goat Pox
What happens if a viral notifiable skin disease is diagnosed on a farm?
Usually no treatment
Slaughter & disposal of infected & in-contact animals
Quarantine/Protection zone
Movement restrictions
Disinfection
+/- Vaccination
Eradication programmes
Surveillance programmes – monitor spread
What are the clinical signs of vesicular (viral) diseases?
Vesicles, erosions, ulcers & crusts
Affect muzzle, oral mucosa, tongue, udder, teats, coronary band
Can lead to shedding of hooves & horns in severe cases
Affect wide range of species, esp. cloven-hooved species
Name some notifiable vesicular diseases
Foot and Mouth Disease*
Vesicular Stomatitis*
Swine Vesicular Disease*
Bluetongue Virus*
Rinderpest*
What is the importance of vesicular diseases?
Many notifiable
- often difficult to differentiate from non-notifiable
Cause wide economic loss
Some zoonotic
What are the general characteristics of Papilloma virus skin infections?
Proliferative epitheliotropic lesions (warts)
Usually host-specific
Enter via microabrasions
Usually young animals, regress spontaneously
Can undergo malignant transformation to squamous cell carcinomas (rare)
Describe Bovine Papilloma Virus (BPV)
Very common in cows (50%)
Transmitted by fence posts, halters, contaminated tagging equipment etc.
BPVI & II can induce sarcomas/fibrosarcomas
Can also cause equine sarcoids
Describe the clinical signs of equine papilloma virus
Warts (‘grass warts’) - young horses, self limiting
Aural plaques – horses >1yr, persist
Describe the clinical signs of canine papilloma virus
Warts
- Young dogs, self limiting
Pigmented viral plaques
- Esp French bulldogs, pugs
- Lesions may persist
What are the general clinical signs of pox viruses?
Macules, papules, vesicles, pustules, crusts
What are some important poxvirus diseases?
Cowpox – Rare in cattle but causes disease in cats (zoonotic, transmitted by rodents)
Horse pox, swine pox
Sheep pox, goat pox, lumpy skin disease (cattle)
- notifiable
Myxomatosis (rabbits)
What are the clinical signs of Myxomatosis (rabbit pox virus)?
Transmitted by fleas
–> oedematous thickened eyelids, lips, genitalia, perineum –> death
Occasionally cutaneous form ‘lumpy bunny disease’
What are some important parapox viruses?
Contagious pustular dermatitis (Orf) – Oral lesions lambs, teat lesions (mastitis) ewes
Pseudocowpox (affects teats)
Bovine papular stomatitis (oral/muzzle lesions)
All zoonotic!
What causes Porcine Dermatitis Nephropathy Syndrome (PDNS), and how does it present?
Caused by circovirus (ubiquitous in pig populations)
Results in vasculitis, leading to blotchy (purpuric) skin lesions
Can cause subcutaneous microhaemorrhages
Must be differentiated from Classical/African Swine Fever (similar skin lesions but more severe systemic effects & notifiable)
What virus causes Psittacine Beak and Feather Disease (PBFD)?
Circovirus
What is Border Disease, and how does it affect lambs?
Caused by pestivirus
Congenital infection results in:
- Small, weak, hairy lambs with skeletal muscle tremors (‘Hairy Shakers’)
- Can cause abortion & stillbirth
How are viral diseases diagnosed?
Often diagnosed clinically
Many tests available to verify/identify virus
- Detection of virus, viral antigens or nucleic acid
- Diagnostic serology - detection of antibodies to virus
Diagnostic lab/DEFRA will advice test/sample required
What is leishmaniasis (protozoa), and how is it transmitted?
Vector-borne disease caused by Leishmania spp., transmitted by sandflies
Causes wide range of skin & systemic signs
- Long incubation (years), slowly progressive
Can control but no cure
What animals are commonly affected by leishmaniasis?
Dogs»_space; Cats
Zoonotic, seen in dogs imported from endemic areas (e.g. Mediterranean, Portugal)
How is leishmaniasis diagnosed?
Aspirates (lymph node, bone marrow)
Serology/PCR
Skin biopsy (detects organisms inside macrophages)
What are the most common causes of dermatological disease?
Metabolic
Neoplastic
Inflammatory
Immune mediated
Infectious
Traumatic
In order to treat a dermatological disease effectively what needs to be established first?
What is happening to the skin?
Why is this occurring?
- Often secondary to underlying cause
What do we need to investigate in the history of the dermatology patient?
Give examples of how sex can influence dermatological disease
Entire male dogs – endocrine skin changes from testicular neoplasia
Post-whelping bitches – may develop temporary generalised alopecia
Give examples of how breed can influence dermatological disease
Welsh ponies – Culicoides hypersensitivity
Feathered horses – Chorioptes mange
Persian cats, Yorkshire Terriers – Dermatophytosis
Shar Pei, Bulldogs, Labradors – Atopic dermatitis
Staffordshire Bull Terriers, Bulldogs – Demodicosis
Give examples of how lifestyle can influence dermatological disease
Housed/stabled animals – more lice, dermatophytosis, Chorioptes mange
Outdoor grazing (dawn/dusk) – more Culicoides hypersensitivity
Overcrowding – increases facial dermatitis in sheep
Hunting terriers/cats – higher risk of Trichophyton dermatophytes, cowpox
Give examples of how general health can influence dermatological disease
Underlying relevant systemic disease
- e.g. In hyperadrenocorticism (cause of alopecia) owners will usually report marked polydipsia & polyphagia
Underlying comorbidity
- e.g. concurrent cardiac failure –> sedation is riskier & some treatments not appropriate
Drug history
- cutaneous drug reaction?
- iatrogenic effects?
What do we need to investigate in the clinical examination of the dermatology patient?
What are the key history questions in dermatology?
Age of onset?
Pruritus – Is it primary (itch that rashes) or secondary (rash that itches)?
Lesion type & distribution – symmetrical, localised, generalised?
Progression? – acute vs. chronic
Contagion – risk to other animals/humans
Response to previous treatment – owner recall bias can be issue
How does the age of onset influence the diagnosis of dermatological disease?
Young/Immature Animals
- Diseases linked to immunological immaturity: Demodicosis, dermatophytosis, viral papillomas
- Congenital defects
Young Adults
- Prone to environmental atopy (dogs, cats, horses)
- Immune-mediated diseases
Older Adults
- Endocrinopathies (e.g. hypothyroidism, hyperadrenocorticism in dogs)
- Systemic disease & neoplasia
Why is it important to do a general clinical examination?
Signs of systemic disease may
- Underlie dermatological disease
- Affect diagnostic approach
- Affect treatment of skin
What are the key steps in performing a dermatological examination?
Ensure adequate restraint & good lighting (e.g. pen torch)
Be systematic – don’t just examine areas noticed by owners
Check hard-to-access areas:
- Under the tail, inguinal region
- Mucocutaneous junctions
- All feet, including undersides
- Ears
Feel & smell the coat
Look beneath hair for hidden lesions
Record findings accurately
- area affected, lesion (descriptors, size, distribution), use diagrams
Why are first lesions crucial in dermatological diagnosis?
Primary lesions provide key diagnostic clues before secondary changes occur
E.g. Demodicosis may present initially with non-pruritic alopecia & comedones
Misdiagnosis or inappropriate treatment (e.g. steroids for pruritus) can worsen condition
Identifying first lesions helps avoid progression & inappropriate treatment choices
What are the 5 major presenting signs of dermatological disease and why are they important to identify?
Pruritus
Alopecia
Crusting
Scale
Nodules /ulceration
Allows standardised approach to be used as basis for case. Overlapping signs can be confusing – always ask what happened 1st
What are the key in-house tests used in dermatology?
Coat brushing – for ectoparasites, scale
Skin scrapes – deep (Demodex), superficial (Sarcoptes, Cheyletiella)
Skin cytology – bacteria, yeast (Malassezia)
Dermatophyte culture
Trichogram (hair pluck)
Wood’s lamp
What laboratory tests may be needed for dermatology cases?
Haematology & biochemistry
Endocrine testing
Bacterial culture & sensitivity
Fungal PCR
Biopsy & histopathology
What test procedures might be done in dermatology?
Parasite treatment trials
Food elimination trials
Changes in housing or activities
How do secondary bacterial and yeast infections impact dermatological disease?
Common
Increase disease severity & pruritus
Alter lesion appearance, making diagnosis harder
Change nature of pruritus
Require treatment (cytology-guided) to resolve primary disease effectively
What is the importance of accurate diagnosis in dermatology?
Ensures a good outcome
Avoids unnecessary use of drugs
Entirely possible in house for most dermatological problems
Symptomatic treatment (esp. pruritus) often –> owner frustration, cost & adverse effects of chronic therapy
3yo FN Labrador presents to you with lesions on ventrum, as pictured.
Dog has developed these lesions over past week, but they haven’t been seen before. However she has suffered from low-grade pruritus of ventrum, face & feet for past 12 months, & ventral pruritus has increased in past 1-2 weeks.
In-contact dogs/people are fine & her general health is good
All dogs are treated every 4w with sarolaner/milbemycin tablets
There is no contact with other animals or change of environment
What is your ranked differential diagnosis list?
What initial investigations would you propose to progress your diagnosis?
2yo Scottish Blackface ewe in December, farmer is concerned about skin problem he has just noticed.
Ewe is one of group of 30 that are currently housed.
Similar lesions found today on few others in group.
Believed to be pruritic, though farmer is bit unsure.
Farmer recently developed red patch of skin on her hand.
The sheep are well otherwise.
What is your ranked differential diagnosis list?
What initial investigations would you propose to progress your diagnosis?
