1. Infectious & parasitic skin diseases in dogs & cats. Otitis externa

What are infectious and parasitic causes of skin diseases in dogs and cats?

1. Bacterial

   1. Primary

   2. Secondary

2. Viral

   1. Canine distemper

   2. Canine papillomavirus

   3. Pseudorabies

   4. Feline cowpox

3. Fungal

   1. Dermatophytosis

   2. Malassezia pachydermatis

4. Parasitic

   1. Mites

   2. Lice

   3. Ticks

   4. Fleas

What are the causes for bacterial skin infections?

1. Secondary infection - must treat the underlying cause!

2. Pyoderma/break of skin - Superficial, surface or deep bacterial infection.

3. Immunosuppression - by disease or glucocorticoids

4. Young animals

5. Breed predisposition: Skin folds

What is the primary pathogen associated with bacterial skin infections in dogs?

Staphylococcus pseudintermedius (MRSP)

What are some secondary bacteria that can cause skin infections in dogs?

Staphylococcus aureus (MRSA), Streptococci, Micrococcus, Bacillus, Corynebacterium, E.coli, Proteus, Pseudomonas

How is bacterial pyoderma typically triggered?

By an overgrowth/overcolonization of normal resident or transient flora

Which areas of the skin are more prone to bacterial infections due to higher bacterial counts?

Warm, moist areas like lip folds, facial folds, neck folds, axillary areas, dorsal/plantar interdigital areas, vulvar folds, and tail folds

Why are pressure points like elbows and hocks prone to infection?

Possibly due to follicular irritation and rupture

What are some methods used to diagnose bacterial skin infections?

1. Physical examination - look for alopecia, pruritus, type of lesion.

2. Cytologic examination - swab, sticky tape impression smear - Diff Quick

3. Skin scrapings (after sticky tape), cultivation, histopathology (last option)

What are some topical treatment options for bacterial skin infections?

1. Chlorhexidine wash (shampoos, gels, sprays)

2. Keep lesions dry

When is systemic treatment indicated for bacterial skin infections?

When topical treatment is insufficient, and based on culture results

What are some viral causes of skin diseases?

1. Canine distemper

2. Canine papillomavirus

3. Pseudorabies

4. Feline cowpox

What is the causative agent of canine distemper?

Canine morbillivirus

What are the dermatological effects of canine distemper in its skin form?

Pustular dermatitis, lesions on the ventral abdomen, hyperkeratosis of nasal planum and foot pads (hardpad)

How is canine distemper diagnosed?

PCR, clinical signs, history

What are some differential diagnoses for canine distemper?

Kennel cough, leptospirosis, infectious canine hepatitis, intoxications

What is the treatment for canine distemper?

No specific treatment. Symptomatic, supportive. (interferon injections?)

What is the causative agent of canine papillomatosis?

Canine papillomavirus-1 (DNA virus)

What are the dermatological effects of canine papillomavirus?

Papillomas (cauliflower-like, pale colour) in the oral cavity, tonsils, epiglottis, around the eyes, head, and legs

How are canine papillomaviruses treated?

1. Spontaneous regression

2. Crushing (stimulates immune response to heal other growths)

3. Surgical removal (cauterisation, cryotherapy)

What is the causative agent of pseudorabies ("mad itch disease")?

Suid herpesvirus-1

What are the dermatological effects of pseudorabies?

Intense pruritus, especially on the head, with neurological signs like self-mutilation

How is pseudorabies diagnosed?

Clinical signs (pruritus) and history (boar contact)

What are some differential diagnoses for pseudorabies?

Rabies, lead poisoning, salt poisoning

What is the treatment for pseudorabies?

None - euthanasia

What causes feline cowpox?

Orthopoxvirus

How is feline cowpox transmitted?

Direct contact (bites)

What are the dermatological effects of feline cowpox?

Papules and vesicles on the head and forelimbs

What are the two main categories of mites that affect dogs and cats?

Burrowing and non-burrowing mites

What are some examples of burrowing mites?

Sarcoptes, Demodex, Notoedres

What are some examples of non-burrowing mites?

Otodectes, Cheyletiella, Chiggers/harvest mites

What are the dermatological effects of mite infestations?

Itching, intense pruritus, erythematous papules, crusted papules, skin damage from scratching and rubbing, alopecia, secondary infections

How are mite infestations diagnosed?

Mite detection in skin scrapings (deep or superficial)

What types of treatments are used for burrowing vs. non-burrowing mites?

Burrowing: systemic

Non-burrowing: topical

What are some systemic treatments for burrowing mites?

Ivermectin, Milbemycin

What are some topical treatments for non-burrowing mites?

Selamectin, Moxidectin

What are the two types of lice that affect dogs and cats?

Sucking lice (Anoplura) and biting lice (Mallophaga)

What are some examples of sucking lice?

Linognathus setosus

What are some examples of biting lice?

Trichodectes canis, Heterodoxus spiniger

What are the dermatological effects of lice infestations?

Self-trauma, hair loss, abrasions, itching, scratching, matted fur, stressed animals

How are lice infestations diagnosed?

Lice detection in fur

How are lice infestations treated?

Shampoo: lime sulphur, fipronil, ivermectin/permethrin also possible.

What are some examples of hard ticks?

Ixodes ricinus, Rhipicephalus sanguineus, Dermacentor marginatus/reticulatus, Hyalomma marginatum

What is an example of a soft tick?

Otobius megnini

What are the dermatological effects of tick infestations?

Local skin irritation, dermatitis, inflammation, swelling, ulceration, itching. Vectors of other diseases

What are the most common fleas affecting dogs and cats?

Ctenocephalides felis, Ctenocephalides canis

What is the most common dermatological disease of dogs?

Flea allergy dermatitis or flea bite hypersensitivity

What is the pathogenesis of FAD?

When feeding, fleas inject saliva that contains a variety of histamine-like compounds & enzymes that induce immune hypersensitivity & cause itching, erythema & papules

What are the clinical signs of flea allergy dermatitis?

Intense pruritus, papulocrustous lesions on the lower back, tail head, posterior and inner thighs, restlessness, scratching, licking, rubbing, chewing, nibbling

Common secondary lesions include areas of alopecia, erythema, hyperpigmented skin, scaling, papules & broken papules covered w/ reddish brown crusts

How is flea allergy dermatitis diagnosed?

Clinical signs, presence of fleas

What are some treatment options for flea infestations?

Insecticides (fipronil, ivermectin, selamectin, pyrethroids, imidacloprid)

What are the two main types of fungal infections affecting dogs and cats?

Dermatophytes (ringworm) and Malassezia pachydermatis

What are some examples of dermatophytes?

Microsporum, Trichophyton

What are the clinical signs of dermatophyte infections?

Dry/wet flaky lesions with crusting and alopecia

How are dermatophyte infections diagnosed?

Wood's lamp fluorescence (for Microsporum), fungal culture

What are some treatment options for dermatophyte infections?

Lime sulphur or miconazole shampoo

What are the clinical signs of Malassezia pachydermatis infection?

Erythema, greasy skin, crusts, smelly, pruritus, alopecia, hyperpigmentation

How is Malassezia pachydermatis diagnosed?

Skin scrapings and staining with Diff-Quick

What are some treatment options for Malassezia pachydermatis infection?

Topical antifungal drugs (miconazole, ketoconazole)

What is otitis externa?

Inflammation of the external ear canal +/- ear pinna

What are some primary causes of otitis externa?

1. Hypersensitivity

2. Immune-mediated

3. Cornification defects

4. Endocrine disorders

5. Foreign body, polyp, tumour.

6. Parasites

What are some secondary causes of otitis externa?

1. Bacterial infection (Staphylococcus, Pseudomonas, Proteus, Pasteurella)

2. Fungal/yeast overgrowth (Malassezia)

What are some examples of hypersensitivity reactions that can cause otitis externa?

Atopy, food allergy, contact allergy

What are some immune-mediated diseases that can cause otitis externa?

Pemphigus, discoid or systemic lupus erythematosus, drug reactions

What are some cornification defects that can cause otitis externa?

Seborrhoeic diseases → increased epidermal turnover rates → changes in otic glandular secretions → ceruminous otitis externa

What are some endocrine disorders that can cause otitis externa?

Hypothyroidism

What are some parasites that can cause otitis externa?

1. Otodectes cynotis (ear mite)

2. Sarcoptes scabiei

3. Notoedres cati

4. Demodex canis/cati

5. Otobius megnini (ear tick)

What is the pathogenesis of Otodectes cynotis?

Local allergic reaction. Purulent inflammation & discharge of external ear, may perforate tympanic membrane

What are the clinical signs of Otodectes cynotis infestation in cats?

Massive, coffee-ground excretions in the ear canal without itching (sometimes severe pruritus).

What are the clinical signs of Otodectes cynotis infestation in dogs?

Small excretions with vigorous ear itching

How is Otodectes cynotis diagnosed?

Detection with otoscope, ear smear, microscope

What are some treatment options for Otodectes cynotis?

Selamectin, moxidectin, amitraz (spot-on), thiabendazole/acaricide ear drops

How long should Otodectes cynotis infestations be treated?

Multiple times over 3-4 weeks to cover the whole life cycle (treatment does not affect eggs)

What are some clinical signs of otitis externa?

Headshaking, odour, pain on ear manipulation, exudate, erythema, head tilt

How is otitis externa diagnosed?

Otoscopy, dermatologic examination (cytology of exudate or crusts, skin scrape), x-ray

What should be checked before treating otitis externa?

If the tympanic membrane is intact

What are some treatment options for otitis externa?

1. Clean ears: ceruminolytic agents (cerumaural, dioctyl sodium succinate, carbamine peroxide). Irrigate ear with cleansing agent (warm water & isotonic/hypertonic saline)

2. Topical anti-inflammatory agent: corticosteroids (betamethasone, hydrocortisone)

3. Topical antibacterial agents: gentamicin, neomycin, enrofloxacin

4. Topical antifungal agents: imidazoles

5. Anti-parasitics: pyrethrin, ivermectin

What are some ototoxic drugs to avoid in otitis externa with a ruptured eardrum?

Aminoglycoside antibiotics (neomycin, streptomycin), Macrolide antibiotics (erythromycin)

What is the difference between the clinical manifestations of sarcoptic mange and demodicosis?

Scabies is pruritic, demodicosis is not.

Does juvenile demodicosis need to be treated?

No. Self limiting as the immune system develops.

What is it called when Staphylococcus is resistant to ATB?

Methicillin-resistant

Why can corticosteroids be used in treatment of otitis externa?

To decrease irritation

What are the two skin manifestations of distemper?

1. Hard pad disease (nasal planum, paw pads)

2. Vesicles

Which skin manifestation of distemper can be associated with CNS disease?

Hard pad due to abnormal gait

What are examples of skin manifestations involved in FIV?

Some cats with FIV develop nonpruritic, generalised, papulocrustous lesions with concurrent alopecia and scaling, which are most severe on the head and limbs.

Abscesses, skin and ear bacterial infections, and mycotic infections.