DERMATOLOGY - Fungal skin diseases 1 + 2 Flashcards Preview

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Flashcards in DERMATOLOGY - Fungal skin diseases 1 + 2 Deck (80):

What are the 3 morphological groups of fungi?

- yeast (unicellular, budding)
- filamentous
- dimorphic (exist as yeast or filament depending on circumstances)


How do fungi reproduce?

vegetative growth and spores (not like bacterial endospores which are resistant. fungal spores are stable and viable in the dry state but are killed by disinfectants and boiling)


What are arthrospores?

= vegetative spores. formed by disarticulation of a septate hypha into separate cells. Frequently produced by dermatophytes (ringworm).


What are conidiospores and when are they found?

- formed externally by abstriction of teh conidiophore (simple or specialised) which arises directly from the mycelium or may be produced within a specialised fructification
- unicellular or multicellular
- some fungi species produce 2 types of conidia (different size and numbers of cells, micro and macro)


Outline dermatophyte production of micro and macroconidia

- microconidia and macroconidia only in culture
- dermatophytes exist only as hyphae or arthroconidia in hairy skin


How is the class of fungus determined?

sexual spores they produce and morphology


What are the 3 main ways fungi can cause disease?

- mycoses
- mycotoxicoses
- allergy


Define mycoses

fungi cause disease by invading and growing in tissue
- primary or opportunistic pathogens


Define mycotoxicosis

a fungi causes disease by producing toxigenic substances in themselves or in their growth substrates which when ingested cause disease


Define fungal allergy

a fungus that causes disease by producing sensitising substances that lead to hypersensitivity to fungal allergens


What do Histoplasma, Coccidioides and Dermatophytes have in common?

They are primary pathogens (capable of causing disease in healthy hosts)


What do Candida, Aspergillus and Zygomycetes have in common?

they are all opportunistic pathogens


How can mycoses be classified? 3

- superficial or cutaneous
- subcutaneous
- systemic
- endogenous versus exogenous


Define superficial/ cutaneous mycoses

- where skin and/or hair are involved
- ringworm
- resembles most bacterial and viral diseases (short incubation, sudden onset, CS decrease in severity over time, spontaneous healing)


Define subcutaneous mycoses

- SC tissues involved
- cutaneous manifestations may also occur (Sporotrichosis)
- Can spread through lymphatics


Define systemic mycoses

- internal organs affected (aspergillosis)
- SC and systemic mucoses tend to resemble aberaant bacterial diseases such as TB and leprosy (protracted incubation period, insidious onset, increasingly severe, death results)


Define endogenous mycoses

a few species of fungi which are normally harmless commensals of the body can cause illness when the host metabolism is in some way abnormal. Malassezia.


Define exogenous mycoses

caused by fungi from an external source. fungus must enter host, germinate and grow.


T/F: the parasitic state of fungi is of little or no significance in the LC of the fungus



What is the most important source of fungal infection?

airbone spores (e.g. conidiospores)


How can fungi cause damage to tissues?

- PENETRATION (tissues, nn, BV walls)
- THROMBI (zygomycetes have a predilection for BVs and penetrate the lumen)
- induce intense inflammatory and immunological reaction --> necrosis, sinus and fistula formation, dissolve bone (--> osteitis and osteomyelitis)


T/F: toxins are important to fungal pathology

False - although many fungi are known to produce exotoxins and enzymes but there is no conclusive evidence of toxin production within the body.


What are the 3 main mycoses caused by yeasts?

- Cryptococcosis
- Candidosis
- Malassezia pachydermatitis


What are the features of Cryptococcus neoformans

- spherical yeast
- polysaccharide capsule (only encapsulated yeast)
- bud on narrow base
- primary pulmonary infection, occasionally skin infection
- may spread by RES to CNS
- tip of nose (cats)
- worldwide distribution
- main source of infection = pigeon droppings. Also fruit, milk, soil.


How can Cryptococcosis be defined?

- exogenous mycosis
- acute, sub-acute or chronic
- no clearly defined clinical ppatern


Which systems does Cryptococcosis affect and how does this differ between species?

- SYSTEM: respiratory, CNS or systemic. Also possibly: cutaneous, skeletal, visceral and ocular.
CATTLE - Mastitis most important in cattle.
HORSE causes myxoma-like lesions of lung and lip.
DOGS/CATS show oral, pulmonary or cutaneous lesions and CNS. CATS - respiratory often accompanied by proliferative lesions of nasal cavity - tip of nose commonly too.


Which 3 species of Candida are responsible for candidosis?

C. albicans


What type of infection is candidosis usuallt?

C.albicans is normally an endogenous mycosis but occasionally exogenous infections may arise by ingestion or deposition. Mycoses caused by other Candida species are usually exogenous in origin.


How does C.albicans reproduce?



What type of fungus is Malassezia pachydermatis?

- lipophilic
- normal inhabitant of skin and mucosa of dogs, cats, carnuivores
- frequent opportunistic pathogen of dogs (otitis externa and dermatitis)


Name 4 mycoses caused by filamentous fungi

- Saprolegniosis
- Mucormycosis
- Aspergillosis
- Dermatophytosis


What are the 4 different presentations of aspergillosis?

- Avian types (moudly plaques)
- Canine nasal aspergillosis
- Mycotic abortion (late stage, necrotic skin and skin sloughing from back)
- Equine GP mycosis (acute epistaxis or nerve damage leading to dysphagia and head shaking)


What is the colloquial name for Dermatophytosis?



What causes Ringowrm?

Infection of the hair, nail or stratum corneum by a fungus of the general Microsporum, Trichophyton or Epidermophyton. They digest keratinous debris and tend not to invade living tissue.


Why is dermatophytosis really important to treat?

zoonotic. often incorrectly diagnosed (especially in dogs with bacterial skin disease)


What is the first test that should be done if Dermatophytosis is suspected?

Wood's lamp (WL) examination:
no fluorescing hair observed - unlikely infection
- hairs fluorescing bright apple green - probable M.canis infection
BUT sensitivity = 50%


After wood's lamb exam, what is the next test for investigating dermatophytosis?

microscopial examination of scales and plucked hairs for hyphae and arthroconidia (spores in or around the hair). Spores or hyphae confirmed in the hair confirms dermatophytosis (species unknown at this stage)


Where does Trichophyton erinacei originate from?



How are dermatophyte infections acquired?

contact with infected animals, soil or fomites (care: hair clippers)


What is the commonest source of M.canis?

infected cats


What is a common source of Trichophyton species?

often carried by wild rodents


Where is T.gypseum found?

soil organism


How long can M.canis spores remain viable?

over 1 year


Outline Dermatophytosis infection

- skin invasion initiated by adherence of arthrospores to stratum corneum cells
- spores germinate and hyphae invade stratum corneum , aided by production of keratinases
- most dermatophytes then penetrate hair shafts (only anagen) but don't invade mitotically active hair matrix
- invasion of keratinised tissues and the production of fungal enzymes and metabolites induces an inflammatory response in the host.
- normally the host response --> disease resolution in 1-3 months
- chronic disease may result when the organism either fails to induce or has the ability to suppress these response or when host immunity is compromised


Outline a typical history for dermatophytosis

- progressive skin disease
- may spread from a point focus (dog)
- contact with wild rodents, cats, infected animal
- stable or farm history
- owner lesions
- pruritis variable
- commonest in dogs/cats <1 year
- long-haired cats
- JRTs predisposed to Trichophyton spp. infections
- YTs predisposed to M.canis infections


CS - dermatophytosis

- highly variable (dogs and cats)


CS - canine dermatophytosis - 5

- localised disease commonest
1.) typical lesion = focal alopecia + scaling, exapnds peripherally, heals centrally. focal or multifocal
2.) localised or generalised folliculitis and furunculosis (well-defined). Severe facial lesions resemble autoimmune disease
3.) localised or generalised scaling +/- erythematous margin. Healed areas become smooth and shiny (especially Trichophyton)
4.) Onchomycosis, +/- paronchyia
5.) kerion (nodular form of dermatophytosis with deep, suppurant, inflammatory lesions)


.Define onchomycosis

fungal infection of the nail


Define paronchyia

nail fold infection


CS - feline dermatophytosis - 6

* Most commonly irregular patchy alopecia +/- scaling*
- ulcerating nodules + granulomatous perifolliculitis (persians)
- papulocrustuous eruption (miliary dermatitis)
- recurrent chin acne
- clinically normal carriers.


CS - equine dermatophytosis

- patches of scale and hairloss (especially areas of tack)


CS - bovine dermatophytosis

focal patches of thick grewy scales or crust with alopecia, especially head. well-defined regions. scales/hairs shed from these regions infect environment. AIAO only way to eradicate.


What is the main principle of dermatophytosis diagnosis

Demonstration of invasion of host tissue by a dermatophyte


What are the methods for diagnosis dermatophytosis

- Wood's Lamp (WL) examination
- Direct microscopy
- Fluorescence microscopy
- Culture
- Biopsy


Outline Wood's lamp examination

- commonest method to diagnose dermatophytosis
- hairs infected by M.canis fluoresce apple-green when illuminated but 50% sensitivity (good quality, warmed lamp, dark room)
- diagnosis cannot be dismissed it WL exam is negative
- Trichophyton spp of veterinary importance never fluoresce


Outline direct microscopy for dermatophytosis diagnsosis

- look for fungal spores or hyphae
- use hair plucks and skin scrapes
- mont samples in KOH or liquid paraffin
- failure to observe doesn't exclude diagnosis due to low sensitivity


Outline fluorescen microscopy for dermatophytosis diagnosis

- fluorescent dye (calcafluor white) binds to dermatophyte cell walls --> fluoresce when illuminated by UV light. Greatly enhances sensitivity of direct microscopy but UV microscpe severely limits its use


Outline culture for diagnosing dermatophytosis

- skin scrapes and hair plucks
- Sabouraud's dextrose agar
- aerobic incubation, 26 degrees, 2-4 weeks
- flat white colonies
- microscope exam of hyphae and spores needed for ID-
- T.verrucosum best grown at 37 degrees


Why shouldn't steroids be used for dermatophytosis?

the adaptive immune response may cure the infection and you don't want to hinder this by giving steroids


Tx - dogs and cats - dermatophytosis - 5

- clip hair around lesion
- consider total body clips (severe/generalised)
- systemic antifungal therapy (griseofulvin - NL nor available, OR an azole e.g. itraconazole)
- apply topical therapy (e.g. enilconazole) assists removal or organisms and reduces environmental contamination but doesn't cure alone)
- monitor tx (repeat cultures)


Outline itraconazole in the treatment of dermatophytosis

- UK license (cats)
- 3 cycles of therapy (one week on, one week off etc) because it is lipophilic and persists in stratum corneum
- comparable efficacy to griseofulvin (NL, nor available)


Outline griseofulvin in the treatment of dermatophytosis

- NL for small animals
- dose is 25-50mg/kg for 2 weeks after clinical and mycological cure
- teratogenic (CI in pregnancy)
- haematological side effects (neutropenia in FIV positive)
- wear gloves to handle tablets
- comparable efficacy to itraconazole but latter is preferred


Outline enilconazole in the treatment of dermatophytosis

- topical treatment
- licensed in doggs
- apply every 3 days in conjunctin with systemic therapy
- fatal idiosyncratic reactions (cats)


What topical treatment can be used in cats for dermatophytosis

- NOT enilconazole (idiosyncratic reactions)
- miconazole + chlorehexidine shampoo preferred
- combine with griseofulvin systemically


Differentiate dermatophytosis and pemphigus folliaceus

- DERMATOPHYTOSIS - doesn't affect nasal planum, steroids are contraindicated
- PEMPHIGUS FOLLIACEUS - does affect nasal planum, requires steroids.


Outline dermatophytosis treatment in large animls - 4

- Topical therapy (enilconazole OR miconazole + chlorhexidine shampoo)
- Griseofulvin in past but efficacy uncertain
- disinfect tack
- effective vaccine = Bovilis Ringvac for prevention in cattle in affected herds


Describe Malasseizia pachydermatis

- causes Malassezia dermatitis (common in dogs, rare in cats)
- monopolar/unicellular budding yeast
- skin and MM of healthy dogs (and to a lesser extent on cats)
- normally balance between yeast virulence and host defence so no disease. Sometimes hyperproliferation + skin disease. In such cases, populations of pathogenic Staph are increased.


Describe the taxonomy of M.pachydermatis

- NON-LIPID DEPENDENT = M.pachydermatis


Outline the pathogenesis of M.pachydermatis

- liberates enzymes and metabolites --> cutaneous inflammation (esp. high population densities).
- Sometimes (especially AD dogs), hypersensitivity to M.pachydermatis may be important
- Concurrent skin diseases (AD and primary defects of keratinisation) in 66% referred cases
- Basset hounds, cocker spaniels, westies predisposed


CS - Malassezia dermatitis

- complicate or mimic allergic skin disease AND scaling/crusting skin disorders
- highly pruritic
- refractory to previous symptomatic tx (steroids, ABs, parasiticidals)
- erythema (variable alopecia and scaling)
- greasy exudate/ brown gunge in lower part of hair (especially folded areas)
- hyperpigmentation and lichenification (chronic)
- ventral neck, interdigitial skin, axillae, groin
- concurrent erythematous otitis externa, variable ceruminous discharge
- frenzied facial pruritus (uncommon, don;t mistake for neuro)


Diagnostic criteria - Malassezia dermatitis

- elevated M.pachydermatitis populations on lesional skin
- good clinical response to appropriate antifungals
- good mycological response to appropriate antifungals


How can M.pachydermatis yeast populations be assessed?

- tape strips (applied to lesion, removes superficial skin layers, stained, examined using oil-immersion objective)
- direct smears
- cultures (skin biopsy) - sabouraud's dextrose agar (SDA), 32-37 degrees, 3-7 days. OR modified Dixon's agar which supports growth of more lipid-dependent strains and species.
- cytology (useful because of superficial location and characteristic morphology = peanut shaped), inexpensive and rapid


What is the basis of M.dermatis treatment?

reduction of yeast (and bacterial) counts and ID and correction of any underlying factors


Outline tx protocol for M.dermatis

- 2% miconazole / 2% chlorhexidine shampoo (Malaseb), every 3 days, for 3 weeks or until controlled, then reduce intervals. Has anti-yeast and anti-bacterial effects and is a good degreaser
- others (less effective) = selenium sulphide, ketoconazole, chlorhexidine shampoos. Enilconazole can be used as a rinse after selenium baths or as sole tx to localised areas.
- SYSTEMIC - ketoconazole or itraconazole, very effective, expensive, NL for UK dogs, hepatotoxic and CI in pregnancy
- COnsider concurrent diseases if response to tx is not complete but yeast has been removed


What layer of skin do dermatophytosis and Malassezia dermatitis affect?

superficial layers of the skin (candida too in humns, dogs but rare)


Define systemic mycoses

infections of internal organs which may spread secondarily to the skin


Outline Cryptococcus neoformans infection

- granulomatous,nodular skin disease
- especially cats
- sometimes in association with URT infections


Where are histoplasmosis, blastomycosis and coccidiomycosis found?

systemic mycoses, not UK, not uncommon in certain regions of URA


What is sporotrichosis?

- nodular skin disease (dogs, cats, horses)
- zoonotic
- v rare in UK


Define mycetoma

localised nodular lesions with draining sinuses and granules of implanted fungus which develop after traumatic implantation (e.g. porcupine spine dog???)

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