Fungal skin disease Flashcards
What are the diagnostic techniques in dermatology for fungal infection?
- Wood’s lamp examination
- Fungal culture
- McKenzie toothbrush culture
How are Mycotic infections classified?
‘Superficial’
Skin hair and claws.
Limited to surface epidermis and outer layers of hair and claws.
‘Intermediate’
Infections of the dermis and subcutaneous tissues.
‘Deep’
Involve body organs.
Name organisms of veterinary interest?
Dermatophytes:
- Microsporum and Trichopyton species
- Use keratin to grow.
Yeast and Yeast like organisms:
- Candida: mostly seen in immune compromised hosts
- Malassezia: most commonly SA
- Trichosporon: RARE
Discuss dermatophytosis?
- Dermatophytes are closely-related fungi which use keratin for growth
- Tend to be confined to superficial layers of the skin, nails, claws and hair
- Only invade the keratin of growing (anagen) hairs. Reason for ring worm lesion looks like it does in people as it spreads out as it exhaust the keratin.
- Usually M.canis (cat is natural host will carry it with no clinical signs), occ T.mentogrophytes (mice/voles) May see that in animals like terriers that stick heads down rabbit holes and maybe damage skin and get a secondary infection with T. mentogrophytes more severe in non-host species.
Name the ringworms of cattle and horses?
Cattle – Trichopyton verrucosum
Less common T. mentagrophytes
Horses most common - T. equinum (horses with active ringworm are not allowed to race)
Common in young stock but adults also affected.
Not debilitating but has an effect on animal and hide value.
What are the reservoirs for dermatophytosis?
- Infected by direct contact with infected animal/contaminated environment
- Ringworm spores can survive for many months
- Contaminated environment.
- Exposure to infected host.
- Fomites
What are the 2 groups of asymptomatic canine and feline carriers that can occur?
Two groups:
Culture positive (dogs or) cats with subtle active infections.
Culture positive (dogs or cats) no active infection - CARRIERS
What is the pathology of ringworm?
- Incubation period is approx 1 week.
- Spores of the fungus invades anagen hairs – hence circular lesions
- Germinate – produce hyphae - invasion by digestion of keratin
- New arthrospores produced
- Hair breaks off due to weakening leading to partial alopecia
- Inflammatory reaction leads to folliculitis or furunculosis.
- Variable degree of pruritus
Dermatophytosis - Clinical signs?
- Lesions VERY variable
- Circular, patchy alopecia (broken hairs)
- Variable erythema (peripheral?) and pruritus
- Scale, crusts
- Local/patchy/generalised
- Trichophyton in dogs – more generalised? Terriers
- Nails may be affected, lost and grow back deformed – onychomycosis (not common)
- Horses – tack contact
- Can develop into Mass lesions – called kerions – lumps and bumps
- Always a differential diagnosis?
Skin Diseases of Exotic Pets – RABBITS?
- T. mentagrophtes & M. canis most common
- Zoonosis
- Young animals most susceptible
- Lesions often confined to the pinna and feet
- Topical miconazole or clotrimazole, oral itraconazole or griseofulvin usually effective
Skin Diseases of Exotic Pets – GUINEA PIG?
- Dermatophytosis
- Severe mange
- Trichofolliculoma
How do you do a fungal culture?
- Pluck fluorescing hairs from edge of lesion or skin scrape edge of lesion - viable material most likely here.
- Comb coat with sterile toothbrush especially if no obvious lesions, “Mackenzie technique” e.g. screening in contacts/suspected sources
- Lab/in house – Sabouraud’s medium
- DTM (dermatophyte media) (differentiates between pathogen (produce colour change vs non-pathogen no colour change )
- 1 - 3 weeks
- Identify type of dermatophyte
How does dermatophyte media/sabouraud’s media work?
Contains additional:
- phenol red (pH indicator)
- Cyclohexaimide inhibits growth of other fungi.
- Gentamicin and chlorotetracycline (inhibits bacterial growth).
- DTM useful for rapid growth of dermatophytes and inhibits saprophytic fungi. pH turns red with pH increase from growth. This colour changes and presence of white or buff cotton like colonies is highly suggestive of dermatophytes.
- DTM does not enhance sporulation of dermatophytes which is needed for speciation.
- RSB is a rapid sporulation media) similar to DTM but with different ingredients. Bromothymol blue (pH) and chloramphenicol instead of gentamicin.
Dermatophytosis – treatment?
LICENSED antifungal agents
Systemic
- Griseofulvin – in feed for horses (not available for treatment anymore)
- Azole – itraconazole – cats (“Itrafungol”)
- Topical
- Azoles
- enilconazole – cattle, horse, dog
- Miconazole – cats (maleseb contains chlorhexidine and miconazole so effective against bacterial and fungal agents)
- Lime sulphur dip – cheap, smelly
Describe malassezia?
Malassezia (Yeasts)
- Principally isolated from skin and mucous membranes of a variety of mammals and birds.
- M. pachydermatis is a normal inhabitant of healthy canine skin and mucosa.
- It is an opportunistic pathogen of cats and dogs.
- Infected animals have 100-10000 fold increase in numbers of yeast on their skin.
- Skin levels in breeds predisposed (such as Basset hounds) are higher than other breeds.
- Often get concurrent infection with Staphylococcus pseudintermedius.
- Humans connection with increased dandruff
How does a malassezia infection manifest in dogs and cats?
Dog primarily
- Seborrhoeic dermatitis (seborrheic means flow of sebum)
Cat
- NORMAL COMMENSAL ORGANISM
Secondary condition
- Complicates many conditions esp allergy and endocrinopathy
- Usually generalised
- Scale – “dry” seborrhoea (dandruff)
- seborrhoea sicca
- Greasy coat (typically see)
- Seborrhoea oleosa
Most common deep mycoses?
- In cats Cryptococcus neoformans.
- Cats with FIV at increased risk and may have more severe disease.
