Veterinary Medicine Notes Endocrinology and Integument 2 Notes
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DERMATOPHILOSIS
Dermatophilosis is characterised by an exudative dermatitis with scab formation. It is caused by Actinomycetes, and is often caused by Dermatophilus congolensis.
In horses it is commonly referred to as mud fever and rain scald.
Clinical signs
Exudative dermatitis
Scale
Crust formation
Common sites include feet, lower limbs and the dorsum.
Pathogenesis
The initial infection requires superficial skin damage.
The motile zoospore stage is activated to form a mycelium.
The infection is confined to the epidermis, and the zoospore can remain dormant in skin debris and scabs for months in dry conditions.
Penetration of the hyphae into the epidermis cause an acute inflammatory reaction.
D. congolensis is gram positive, non-acid fast and a facultative anaerobe.
Diagnosis
Impression smears of lesions stained in Giemsa or Diff Quick for cytology
Histology.
Culture and identification.
Treatment
Often heals rapidly and spontaneously.
The primary problem should be managed, e.g. rain or flies.
A short course of antibiotics may be used
Erythromycin
Penicillin G
Ampicillin
Amoxicillin
Tetracyclines
Topical antibacterials may be used
Chlorhexidine
Benzoyl peroxide
Prognosis
Good.
CASEOUS LYMPHADENITIS (SHEEP AND GOATS)
Caseous lymphadenitis is caused by Corynebacterium pseudotuberuclosis, which is a commensal of sheep skin.
Clinical signs
Raised lymph nodes
Ill thrift
Depression
Abscesses that are green in colour
Pneuomia
Pathogenesis
Infection is chronic and follows tissue trauma such as shearing wounds.
The bacteria proliferate within macrophages.
Transmission is due to eruption of bacteria from lymph nodes of infected animals, which then causes contamination of dipping fluids and equipment.
Diagnosis
Clinical signs
Sandwich ELISA tests to detect circulating antibodies to phospholipase toxin.
Treatment
Antibiotic treatment
Topical iodophore shampoo
Screening and culling of infected animals.
Strict hygiene.
Inactivated vaccine available.
Prognosis
Good.
EXUDATIVE EPIDERMITIS (GREASY PIG DISEASE)
Greasy pig disease is caused by Staphylococcus hyicus and is characterised by an exudative dermatitis.
Clinical signs
Affects pigs <3 months of age.
Dark, localised areas of grease and scale
Excess sebum
If severe, the skin turns black due to necrosis.
Systemic illness due to toxin release possible.
Pathogenesis
Greasy pig disease is often a secondary condition. Primary causes include
Abrasions
Faulty procedures for iron injections, removing tails or teeth in piglets.
Fighting and skin trauma at weaning.
Mange
Abnormal behaviour such as tail or ear biting.
Highly contagious and persists in the environment for long periods of time.
S. hyicus produces an exfoliative toxin that causes separation of cells in stratum spinosum.
Diagnosis
Clinical signs.
Bacterial culture and susceptibility testing.
Treatment
Individuals can be treated with antibiotic injection
Sensitive to most antibiotics including penicillins.
Topical antibacterial washes may be used.
Prognosis
If severe, disease can be fatal.
DERMATOPHYTOSIS (RINGWORM)
Dermatophytes are closely-related fungi that use keratin for growth. Dermatophytosis tends to be confined to superficial layers of the skin, nails, claws and hair.
Clinical signs
Circular or irregular lesions
Scaling
Crusting
Alopecia
Erythema
Follicular papules and pustules
Varying pruritus.
Pathogenesis
Ringworm in horses and cattle is usually caused Trichopyton verrucosum, and occasionally Trichopyton mentogrophytes.
Young animals are particularly affected.
Dermatophytes only invade the keratin of growing (anagen) hairs.
Transmission is by direct contact with the infected animal, or indirect via contaminated environment.
Diagnosis
Woods Lamp examination
Uses UV light
Green fluorescence will be seen in 50% of cases
Trichogram examination
Hairs from lesion suspending in 10% KOH
Look for hypae or arthrospores
Technically difficult.
Fungal culture
Using plucked hairs from edge of lesion or skin scrape.
Sabouraudβs medium that contains cyclohexaimide to inhibit growth of other fungi and gentamicin and chloreotetracycline to inhibit bacterial growth.
Red colour change is suggestive of dermatophytosis.
Skin biopsies for histopathology and/or culture.
Treatment
Griseofulvin treatment.
Topical enilconazole treatment (Imaverol)
Treatment of in-contact animals and the environment
Prognosis
Good.
EQUINE ATOPY
Equine atopy is a hypersensitivity disorder in which the horse becomes sensitised to inhaled or percutaneously absorbed allergens.
Clinical signs
Pruritus
Urticaria and angio-oedema
Excoriations
Alopecia
Lichenification
Secondary infection
Nodules
Eosinophilic granulomata
Tufted papules that may coalesce or crust
Eosinophilic mural folliculitis
Pathogenesis
Common allergens implicated in equine atopy include dust mites and forage mites.
Diagnosis
Serology
Intradermal skin testing.
Treatment
Allergen avoidance
Immunotherapy
Corticosteroids
Antihistamines
Fatty acids
Prognosis
Good.
EQUINE CULICOIDES HYPERSENSITIVITY (SWEET ITCH)
Sweet itch is caused by a hypersensitivity reaction to the saliva of biting insects.
Clinical signs
Peak onset between 2-4 years.
Intense pruritus
Commonly affected areas include head, mane, tail, withers and ventral abdomen.
Papules
Self-excoriation may lead to
Alopecia
Broken hairs
Erosions
Ulcers
Pathogenesis
Due to both type I and type IV hypersensitivity reactions.
Allergen-specific IgE to Culicoides saliva is produced, resulting in mast cell degranulation and histamine release.
Often seasonal β seen from spring to late autumn.
Diagnosis
History and clinical signs.
Allergy testing may be used.
Sensitivity and specificity is low.
Treatment
Control of pruritus
Corticosteroids may be necessary
Treatment of secondary bacterial infections.
Reduction of Culicoides contact
Anti-midge rugs
Insect repellants...
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