Chapter 5 - Fungal Flashcards
Which fungal cell membrane element does nystatin bind to?
Ergosterol (leads to altered permeability and cell death)
What effect do azoles have on ergosterol?
They inhibit its synthesis
Which azole can penetrate CNS and ocular tissues?
Fluconazole
Name the reservior hosts of: M. canis T. mentagrophytes T. erinacei M. persicolor
M. canis = cats
T. mentragrophytes = rodents
T. erinacei = hedgehogs
M. persicolor = mice/voles
Which dermatophyte does not cause follicular signs?
M. persicolor - causes scaling
Name Malassezia species found in cats.
Pachydermatis, furfur, globosa, slooffiae, sympodalis and nana
What % of dogs with blastomycosis have pulmonary lesions?
5%, 28%, 53%, 85%?
85%
What is the most common systemic mycosis in cats?
Cryptococcus
Which toll-like receptors are over expressed by feline polymorphonuclear cells in response to M. canis PAMPs?
TLR-2 and TLR-4
Which lipid dependent species of Malassezia is most common in cats and where is it typically isolated from?
M. nana
Ear canals
Which lipid dependent species of Malassezia is most commonly isolated from the claw folds of cats?
M. slooffiae
In which breed of cat has the highest abundance of Malassezia been reported?
Devon Rex
M. pachydermatis is most commonly found on canine atopic skin using NGS and qPCR, but which species were more common in healthy skin?
M. globosa (both NGS and qPCR)
M. restricta (NGS)
Malassezia pachydermatis is most commonly found at which anatomical sites in healthy dogs?
Perioral and interdigital skin
Elevated IgE levels to Malassezia yeasts or Staphylococcus bacteria in human atopic dermatitis are related to the skin severity index, has the same finding been reported in dogs?
Khantavee et al. (2019) reported that specific IgE and total IgG against yeasts and bacteria were significantly increased in atopic dogs of all ages but were not significantly related to clinical score.
Which breeds of dog have been identified as being at increased risk of Malassezia dermatitis?
West Highland white terriers (WHWT), English setters, shih tzus, basset hounds, American cocker spaniels, boxers, dachshunds, poodles, and Australian silky terriers
Which breed of cat, other than Devon Rex, are prone to high carriage rates of Malassezia dermatitis?
Sphynx
Which diseases are associated with Malassezia dermatitis in older cats?
Pancreatic paraneoplastic alopecia and thymoma-associated exfoliative dermatitis
Mutations in which gene (amino acid substitutions) have been associated with azole resistance in M. pachydermatis?
ERG11 gene
It encodes lanosterol 14 –alpha-demethylase, the target site for antifungal azoles
Which C-type lectin, expressed by Langerhans cells, recognises mannose and beta-glucans and has a strong affinity for Malassezia and Candida spp?
Langerin
Which C-type lectin, expressed by activated phagocytes, that binds glucosyl and mannosyl-glycolipids can selectively recognise Malassezia but not other fungi?
Mincle
What is is the preferred medium for the isolation and quantification for M. pachydermatis from canine and feline skin?
Modified Dixon’s agar (will pick up lipid-dependent Malassezia too - good for cats)
Sabouraud’s dextrose agar is a good alternative for M. pachydermatis only!
Which special histopathology stains can be used to identify fungi?
PAS
GMS (Grocott’s-Gomori methenamine silver)
Which dermatophytes are associated with kerion development?
M. canis > M. gypseum and T. mentagrophytes
TLR-2 recongises which toxin that is produced by several fungal organisms?
Zymosan
What % of dogs with coccidiodomycosis will have skin lesions?
50%
How do you diagnose coccidiodomycosis in dogs?
Cytology, histopathology and culture (zoonotic - specialist lab to culture!)
Agar gel immunodiffusion assay can detect IgG in serum and urine
What is the sensitivity of cytology in the diagnosis of sporotrichosis in cats?
78-87%
Cats typically show a large number of yeasts on sampling
Why does Pythium not stain well with PAS?
It does not produce chitin (oomycete, cell wall contains cellulose and beta-glucan)
Use GMS
Which organ system is more commonly affected than the skin in dogs with pythiosis?
GI tract
Do the saprophytic fungi that cause phaeohyphomycosis form tissues grains?
No
What is the pigment made of in phaeohyphomycosis and which special stain can be used to better visualise it?
Melanin
Masson-Fontana
Name a fungus that causes phaeohyphomycosis
Alternaria spp. Xylohypha bantianum Phialophora spp. Bipolaris spiciferum Exophilia spp. Scedosporium spp. Cladophialophora (Cladosporium) spp. Phialemonium spp. Wangiella spp.
Define phaeohyphomycosis, hyalohyphomycosis and eumycotic mycetoma
Phaeohyphomycosis = pigmented hyphal or yeast forms
Hyalohyphomycosis = non-pigmented hyphal forms
Eumycotic mycetoma = formation of fungal colonies in tissue that can be visualized grossly as black or white tissue grains
What is the reported incidence of opportunistic fungal infection in dogs being treated for immune-mediated disease?
6.5%
Which endocrinopathy has been associated with opportunistic fungal infections?
Diabetes mellitus
- phaeohyphomycosis in cats
- Candida spp. urinary tract infection in diabetic dogs and cats
What is a potent virulence factor of phaeohyphomycosis?
Melanin
Surgical resection with wide margins is the treatment of choice for focal lesions
Name a fungus that causes hyalohyphomycosis
Acremonium Chrysosporium Fusarium Geosmithia Oxyporus Paecilomyces Purpureocillium Pseudallescheria and its asexual form (anamorph) Scedosporium Sagenomella Geomyces Schizophyllum Scopulariopsis Lecythophora Westerdykella
Do eumycotic mycetomas have tissue grains?
Yes - can be pigmented (black) or non-pigmented (white)
Why are Malassezia lipid dependent?
They lack a fatty acid synthase gene
Is M. pachydermatis now considered lipid-dependant?
Yes - it lacks the fatty acid synthase gene
Which breed of dog has been shown to have significantly increased frequencies and population sizes of M. pachydermatis in the nose, mouth, vulva and axilla?
Basset hound
Are Malassezia the predominant fungal species on the skin of dogs and cats (mycobiome studies)?
No - filamentous contaminants from the environment (Alternaria, Cladosporium and Epicoccum spp.) were predominant
The activity of which enzyme was significantly higher amongst M. pachydermatis isolates derived from the dogs with otitis externa or skin lesions compared to healthy dogs?
Phospholipase
Once activated by Malassezia, keratinocytes can alter their cytokine expression, with up-regulation of cytokines ____ and_____ and down-regulation of the inflammatory cytokine IL-1alpha.
IL-10 and TGF-beta
Dendritic cells have been shown to be activated by interaction between Malassezia antigens and various members of the C type lectin class of receptors such as ______, _________ and _______
Mincle, Dectins 1 & 2, and Langerin.
True or false; In dogs, concentrations of IgE antibodies to M. pachydermatis are significantly higher in atopic dogs than in healthy dogs or non-atopic dogs with Malassezia over-growth
True
True or false; dogs with recurrent Malassezia otitis had similar concentrations of allergen-specific IgE to those with healthy ears, suggesting that hypersensitivity is not always involved in such infections
True
In response to Malassezia antigen presentation by Langerhans/dermal dendritic cells, Th1 cells would promote IgG production by secreting IL-2 and IFN-gamma, whereas Th2 cells would promote Ig__ by producing ____ and ____
IgE
IL-4 and IL-13
In cats without skin disease, retroviral infection was associated with ________ density of Malassezia spp. isolation from the hair coat as compared to non-infected cats
Increased
The presence of __________ is a common risk-factor for localised disease due to Malassezia
Skin folds - reduced air movement, increased skin temperature and humidity, retained secretions, and surface frictional trauma
The __________ technique was shown to be a convenient, rapid and inexpensive method for the quantitative culture of M. pachydermatis from canine and feline skin
Contact plate
What is considered the ‘gold standard’ method for quantitative culture of Malassezia?
Detergent (cup) scrub technique - rapid sample processing required!
Malassezia spp. yeasts and extracellular cocci were recovered in higher numbers from the dorsal claw fold (following skin eversion) with which technique?
Gentle scraping with the sharp point of a tooth pick
Which method is most effective at recovering Malassezia from the skin, tape stripping, swabbing or direct impressions?
Tape stripping (or dry scrapes)
Which strain of M. pachydermatis isolated from canine atopic dermatitis skin produced higher amounts of phospholipase A2 than strains of other genotypes?
Subtype 3D
Genotypic typing of Malassezia involves which sequences?
- D1/D2 domain of the 26S rRNA
- Internal transcribed spacer (ITS) region
- Chitin synthase 2 (CHS2)
- beta-tubulin
Can histopathology be used to diagnose Malassezia dermatitis?
Not reliable - surface scale and yeasts are readily lost during histological processing
What are the criteria for histopath findings in Malassezia dermatitis?
- Pronounced irregular epidermal and infundibular hyperplasia
- Prominent epidermal and infundibular parakeratotic hyperkeratosis
- Diffuse epidermal and infundibular intercellular oedema (spongiosis)
- Diffuse epidermal and infundibular lymphocytic exo-cytosis
- Superficial perivascular to interstitial dermatitis wherein lymphocytes are a prominent inflammatory cell
- Presence of unipolar budding yeast in the surface and/or infundibular keratin
Similar histopath findings to Malassezia dermatitis can be seen with which common disease? How can they be differentiated?
cAD
Features more supportive of Malassezia dermatitis include scalloping of epidermal and follicular margins, eosinophilic pustules and diffuse lymphocytic exocytosis, but none of these are pathognomonic!
Which species of Malassezia are most susceptible to terbinafine?
M. sympodialis and M. pachydermatis
Which azole is Malassezia least susceptible to?
Fluconazole
Topical therapy for canine OE contains antifungals at how many times above the MIC for Malassezia?
At least 650 times the MIC of the wild-type
A pruritic facial __________ is occasionally seen in association with Malassezia cheilitis
Hyperaesthesia
Feline immunodeficiency virus-positive cats have been shown to carry more Malassezia organisms compared with normal cats, was this associated with clinical signs?
No
Malassezia can complicate idiopathic facial dermatitis; this is seen in which breeds of cat?
Persians and Himalayans
Malassezia organisms have been identified with cytology methods and/or histopathology in what % of feline acne cases?
16-18%
What dose of ketoconazole should be used for dogs with Malassezia dermatitis?
5–10 mg/kg/day
What dose of itraconazole should be used for dogs with Malassezia dermatitis?
5 mg/kg either daily or for two consecutive days per week
According to WAVD, strong evidence (SoR A) is available only for the use of a _____________ shampoo, used twice weekly to treat Malassezia dermatitis in dogs.
2% miconazole and 2% chlorhexidine
According to WAVD, moderate evidence (SoR B) is available for a _________ shampoo to treat Malassezia dermatitis
3% chlorhexidine
True or false; bathing dogs in 2% chlorhexidine/2%miconazole shampoo every three days can reduce oral carriage of Malassezia organisms
True
Twice weekly topical ____________ shows promise in the prevention of Malassezia otitis externa associated with allergic skin diseases
Hydrocortisone aceponate
Which Malassezia spp. was associated with a facial granuloma in a dog owner?
M. pachydermatis
Malassezia may be associated with what % of cases of canine OE?
Up to 70%
Did once daily application of a leave-on spray formulation containing zinc, ethyl lauroyl arginate, laureth-9, urea, panthenol, glycerine and butylene glycol (AptusR©) improve cytological and clinical scores of Malassezia pododermatitis in dogs?
Yes
Name a geophilic dermatophyte (associated primarily with the decomposition of keratin of hair, feathers and horn pre-sent in the soil)
M. gypseum
What type of dermatophyte is Arthroderma?
Teleomorph (sexual stage)
E.g. Arthroderma benhamiaeis the teleomorph obtained by mating strains of T. mentagrophytes isolated from rodents
How common is dermatophytosis in dogs and cats presented for signs of skin disease (WAVD guidelines)?
Cats 1.3-3.6%
Dogs <1%
What are the risk factors for dermatophytosis (WAVD)?
Young age (puppies/kittens and < 2 years)
Lifestyle
Free roaming
Warm climate
Which breeds of dog may be prediposed to M. persicolor and M. gypseum?
Hunting and working breed dogs (German short-haired pointers, fox terrier, Labrador retriever, Belgian Groenendael, beagle, pointer, Jack Russell terrier, German shepherd dog and Jagdterrier)
Which breed of dog is predisposed to M. canis?
Yorkshire terriers - predisposed to superficial dermatophytosis and subcutaneous dermatophytic infection