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
Does seropositive FIV and/or FeLV status in cats increase the risk of dermatophytosis?
No
What is the infective form of dermatophytes?
Arthrospore - formed by fragmentation of fungal hyphae into very small infective spores
__________ to the skin is an important factor in development of clinical infection with dermatophytes
Microtrauma
How significant is environmental transmission of M. canis?
Transmission from contaminated environments is not an efficient route of transmission
What are the stages, and time frames, in dermatophyte infection?
- Adherence of arthroconidia to corneocytes, which is thought to occur within 2–6 h of exposure
- Fungal conidial germination in which germ tubes emerge from the arthroconidia and then penetrate the stratum corneum. This infection step was shown to occur within 4–6 h or up to 24 hours
- Dermatophyte invasion of keratinized structures, which occurs as dermatophyte hyphae invade the stratum corneum and grow in multiple directions
How long does it take for dermatophytes to complete their life cycle on the host?
Within 7 days
How long does it take for clinical lesions to appear with dermatophytosis?
2-3 weeks
Dermatophytes secrete both endoproteases, such as _________ and __________, and exoproteases that digest keratin into usable peptides and amino acids
Subtilisins
Fungalysins
What does the dermatophyte sulphite efflux pump, encoded by the SSU1 gene, do?
Reduces/cleaves keratin cysteine disulphide bonds
What do dermatophyte cell wall mannans do?
Inhibit lymphocytes
Which type of immunity is important for resolution of dermatophytosis?
Cell-mediated immunity
How do kerion differ clinically from pseudomycetoma?
Kerions: single or multiple erythematous, alopecic, dome-shaped, exudative nodules - good prognosis
Pseudomycetomas and mycetomas: nodules that fistulate, ulcerate and drain serous to purulent debris with tissue grains - guarded prognosis
The characteristic green fluorescence observed on M. canis-infected hair shafts is due to a water-soluble chemical metabolite called ______, located within the cortex or medulla of the hair
Pteridine
Give examples of false positive Wood’s lamp fluoresence
Lint, topical medicaments, seborrhoeic material and soap residue
True or false; Wood’s lamp fluorescence will remain long after the hair shafts are dermatophyte culture negative
True
What can be seen on dermoscopy in cases of dermatophytosis?
Opaque, slightly curved or broken hairs with a homogenous thickness (“comma hairs”) - different to other causes of hair loss!
____________ binds specifically to the fungal cell wall and fluoresces strongly when viewed under a fluorescence microscope; it has been found to be significantly superior to routine microscopy (76% versus 39%)
Calcofluor white
How often is direct microscopy +ve in cases of dermatophytosis?
~60%
What are the three types of sample collection for dermatophyte fungal culture?
- Mackenzie” brush (preferred by WAVD - no difference between toothbrush and carpet techniques)
- Plucking hair/scale/crust
- Tape (press directly onto agar plate)
What is the colour change seen with DTM and why is it seen?
Yellow to red
Change in pH associated with fungal growth
Other than a positive or negative result, how can culture be used to monitor response to therapy for dermatophytosis?
Counting colony forming units
What is the aim of topical therapy for dermatophytosis?
To decrease the infectious, contagious and zoonotic risks associated with this disease by disinfecting the hair coat and minimizing contamination of the environment
What are the adverse effects of lime sulfur?
Drying of the footpads, loss of hair on the ears, drying of the hair coat and, with repeated application, yellow discolouration of the hair coat of white cats
Which adverse effects have been reported with enilconazole rinses?
- Slight discolouration to the hair coat.
- Drooling for several minutes to 1 h post-treatment - drying of the hair coat post-application avoids this
- Mild elevations of serum ALP
True or false; 2% miconazole and 2% chlorhexidine shampoo shows additive or synergistic efficacy to treat dermatophytosis compared to either agent used alone
True
What are the WAVD recommended topical treatments for dermatophytosis?
Twice weekly application of lime sulfur, enilconazole or a miconazole/chlorhexidine shampoo (prevents environmental contamination too)
Accelerated hydrogen peroxide products as well as climbazole and terbinafine shampoos show promise
How effective is chlorhexidine, used alone, for treatment of dermatophytosis
Poorly effective
Itraconazole can caused vasculitis in dogs at what dose?
10 mg/kg or more (seen with treatment for subcutaneous, opportunistic or deep mycoses)
Which azole are dermatophytes least susceptible to?
Fluconazole
Which systemic treatments are most effective for dermatophytosis (WAVD)?
Itraconazole and terbinafine
Ketoconazole and fluconazole are less effective treatment options and ketoconazole has more potential for adverse effects
Can vaccines for dermatophytosis prevent infection in dogs and cats?
No - may be a useful adjunct therapy
Why should you perform environmental disinfection in cases of dermatophytosis?
- To minimise the risk of disease transmission to people and other animals
- To minimise fomite carriage on the hair coat of animals that can complicate monitoring of disease
True or false; contact with a dermatophyte contaminated environment alone, in the absence of concurrent micro-trauma, is an exceedingly rare source of infection in both people and animals
True
How should you disinfect non-porous surfaces?
- Vacuum/sweep to remove debris
- Wash with a detergent to lift debris from surfaces then rinse (these two steps may be sufficient)
- Application of a disinfectant to kill any residual spores e.g. 1:100 concentration household bleach or accelerated hydrogen peroxide
How should bedding etc. be washed to remove dermatophyte spores?
Two washes on the longest wash cycle
Long et al. (2020); which breeds of dog and cat were most likely to yield positive dermatophyte cultures in the UK?
JRT, Yorkshire terrier, Persian and Chinchilla
Stuntebeck and Moriello (2019); first negative fungal culture was indicative of mycological cure in what % of cats?
90 %
In cats where there has been high compliance with environmental cleaning, as well as topical and systemic treatment recommendations, two consecutive negative fungal cultures may not be necessary to determine mycological cure
Does cold atmospheric microwave plasma have anti-Malassezia efficacy?
Yes - potential as a new anti-fungal option for M. pachydermatis and has synergistic antifungal effects with CHX in vitro
In dogs with chronic Malassezia otitis, what % could be resolved with one ear flush?
87%
In dogs with chronic Malassezia otitis, which factors did not influence outcome?
- Duration of otitis
- Presence of neutrophils in aural discharge
- Administration of oral itraconazole
In dogs with chronic Malassezia otitis, what % had concurrent Malassezia OM?
17%
In the study by Esumi et al. (2021), was an emollient shampoo as effective at reducing Malassezia overgrowth in atopic dogs as 2% miconazole/2% chlorhex?
Yes
What is lactoferricin and does it have anti-Malassezia activity?
It is an antimicrobial peptide (from milk) and is effective at 20% concentrations in vitro
Niae et al. (2021); which Malassezia species was most frequently isolated from healthy cats and from where?
M. pachydermatis from the ear canal
Niae et al. (2021); which factors were reportedly associated with M. pachydermatis isolation from healthy cats?
Long hair coat
Cleaning ears no more than every 2 weeks or never
Which is more sensitive for detecting Malassezia from the skin, slurry preps or tape stripping?
Tape stripping
Andreano et al. (2021); M. pachydermatis was the most common yeast from OE samples from dogs. Which other Malassezia species were identified using long-amplicon PCR?
M. sympodalis and M. globosa
Ishimaru et al. (2020); were IgE levels to Malassezia different between food induced and non-food induced atopic dogs?
Yes - IgE to Malassezia was higher in non-food induced atopic dogs (IDT reactions were also more frequent)
Bradley et al. (2020); what effect did OE in dogs have on the microbial diversity of the ear canal?
Ears cytologically positive for cocci had decreased diversity (bacterial and fungal), and all types of OE were associated with decreased fungal diversity compared to controls
Staphylococcus was the most common genus identified by next-generation sequencing in all groups, even in those cytologically positive for rods and culture-negative for Staphylococcus
Tang et al. (2020); how did microbial populations compare between healthy ears and OE in dogs?
78.3% of the OE samples had microbial overgrowth; 69.8% bacterial overgrowth, 16.3% fungal overgrowth, and 7.0% had both.
The most important microbial taxa enriched in clinically affected ears were Malassezia pachydermatis, Staphylococcus pseudintermedius, Staphylococcus schleiferi, and a few anaerobic bacteria
Next generation sequencing of fungi typically uses which region?
ITS (Internal Transcribed Spacer) region
How does melanin act as a virulence factor?
Its negative charge and hydrophobicity transform the charge of the fungal cell surface and inhibit phagocytosis. In addition, melanin decreases nitric oxide production, which consequently decreases the host oxidative capability.
Malassezia is recognized by the host either directly through interaction of fungal cell wall components with membrane bound ________________ or indirectly through soluble metabolites that are released by Malassezia spp.
Pattern recognition receptors (PRRs) / C-type lectin receptors
In addition to C-type lectin receptors, Toll-like receptors (TLRs), and in particular ____, also contribute to fungal recognition by the host.
TLR2
How do Malassezia-derived lipases and phospholipases, which are required to assimilate host-derived lipids, initiate an inflammatory response in the skin?
- By releasing unsaturated free fatty acids from the sebum lipids
- Oleic acid has irritant and desquamative effects
- Arachidonic acid produces proinflammatory eicosanoids and leads to inflammation and damage to the stratum corneum
Which dermatophyte has white, cotton-like colonies?
M. canis
Which dermatophyte has white to buff, powdery colonies?
M. gypseum
Which dermatophyte has white, powdery colonies with a granular texture?
T. mentagrophytes
How do you sample dermatophyte colonies from an agar plate for microscopic identification?
- Use tape to lift away sample
- Stain with methylene blue or Diff Quik (blue stain)
- Need macroconidia not hyphae
What is the difference between M. canis and M. gypseum macroconidia?
M. canis has numerous large spindle‐shaped, thick‐walled spores with a terminal knob and six or more internal cells
M. gypseum produces numerous large spindle‐shaped spores with thin walls, no terminal knob, and six or
less internal cells
What do macroconidia look like with T. mentagrophytes?
T. mentagrophytes produces long cigar‐shaped macroconidia with thin walls; spores may be few in number
Spiral‐shaped hyphae are also characteristic of Trichophyton
What is DTM made of?
Sabouraud’s dextrose agar with cycloheximide, gentamycin, and chlortetracycline as antifungal and antibacterial agents to retard growth of contaminant organisms and the pH indicator phenol red.
How should DTM plates be processed once inoculated?
Fungal cultures should be incubated at room temperature (25–30°C) with 30% humidity.
Most organisms will appear within 7–10 days, however plates should be kept for 14-21 days. Plates should be checked daily after 48 hours.
How does storage of samples affect dermatophyte growth?
24 h of storage led to increased isolation rates of non-dermatophytic contaminant moulds and decreased isolation rates of M. canis.
Samples processed after 48 and 72 h presented more than half of the plates with a high degree of fungal contamination.
Does fungal dysbiosis play a role in dermatophytosis in Persian cats?
Persian cats with dermatophytosis do not exhibit decreased fungal diversity
What are the suspected reasons that Persian cats are predisposed to dermatphytosis?
- Ineffective grooming associated with brachycephaly, or health disorders such as respiratory disease or osteoarthritis
- A primary immunodeficiency
- Unique characteristics of Persian hair
Long et al. (2020); what % of isolates were M. canis and T. mentagrophytes?
M. canis: 78% cats, 42% dogs
T. mentagrophytes: 14% cats 38% dogs
Does room lighting affect the growth of dermatophytes?
No
Which medium do dermatophytes grow best on?
Dermatophytes grew more rapidly on SAB than DTM agar
What were the previously used names for:
Nannizia gypsea
Trichophyton benhamiae
Nannizia gypsea was previously Microsporum gypseum
Trichophyton was previously Arthroderma benhamiae - T. mentagrophytes complex
What is the natural host for Trichophyton (Arthroderma) benhamiae?
Guinea pigs
Are dermatophyte cultures more often positive in long haired or short haired cats?
Long haired cats
What are the three main genera of dermatophyte that are associated with skin disease?
Micropsorum, Trichophyton, and Epidermophyton
Gordon et al. (2020); In a shelter environment, contaminant fungal growth with no dermatophyte growth was present in what % of DTM plates?
28%
Moriello (2020); which whole body topical treatments for dermatophytosis have residual action for up to 72h?
Whole body products:
- lime sulfur and enilconazole showed residual activity, 2%miconazole nitrate/ 2% chlorhexidine shampoo did not.
Moriello (2020); which focal topical treatments for dermatophytosis have residual action for up to 72h?
Focal therapy products:
- clotrimazole 1%
- terbinafine 1%
- miconazole at 0.2, 1 or 2% (with or without chlorhexidine)
- climbazole 0.5% with chlorhexidine gluconate
- ketoconazole 1% with chlorhexidine gluconate
What are considered to be important virulence factors in dermatophytosis?
Proteases (including keratinases), especially during the invasive stage of infection e.g. subtilisins and fungalysins
Has M. gypseum been reported in cats?
Yes - uncommon
In DeTar et al. (2019); how long did DTM positive cultures take in infected and asymptomatic cats?
Infected - within 7 days (median 4)
Asymptomatic - within 12 days (median 5)
Should see growth within 14 days!
What is the optimum inoculation technique for toothbrush samples when investigating dermatophytosis?
Press toothbrush bristles onto agar plates (not removing hair/scale from bristles)
- maximizes growth of M. canis and minimize introduction of contaminants
How should pet food bowls be cleaned to remove dermatophytes?
Mechanical washing alone can decontaminate pet food bowls exposed to naturally infective material (hot soapy water)
Does staining of hairs with methylene blue increase correct identification of dermatophyte infection?
No - illustrated guides increased accuracy.
Sensitivity and specificity of direct examination were 70.5% and 56%
Is this M. canis or M. gypseum?
M. gypseum
M. canis looks like:
Do zoophilic dermatophytes typically produce ecto- or endohtrix spores?
Ectothrix (on outside of hair shaft, disrupt cuticle)
What is piedra?
Asymptomatic fungal infection in dogs - white piedra = Trichosporon beigelii
- white to grey concretions encircling hair shafts
- see hyphae on microscopy
- tx: clip hair or topical antifungal
From an alopecic, draining module in a cat’s nose. What is the diagnosis?
Sporothrix organisms = sporotrichosis
Poorly staining hyphae with 90° branching is characteristic of which fungus?
Lagenidium spp.
Oomycete
What is this thick walled, broad based budding fungus from a draining tract?
Blastomyces
What is this fungus from a cat? Think capsule and narrow based budding.
Cryptococcus
Which fungus is pictured? Numerous, small and within macrophages.
Histoplasma
Which dogs are most often affected by blastomycosis and how many have skin lesions?
Young, large breeds and hunting dogs
20-50%
Is blastomycosis more common in dogs or cats?
Dogs
Blastomyces dermatitidis
Mainly seen in North America
What are the common cutaneous signs and location of lesions with blastomycosis?
Firm papules, nodules and plaques that may ulcerate and drain fluid
Nasal planum and claw bed most common
How do you treat blastomycosis?
Itra- (1st choice) or fluconazole or amphotericin B
Prognosis fair but poor if severe respiratory or neuro involvement
How do you diagnose blastomycosis?
Cytology or histopathology (GMS, PAS) - culture is a health risk!
Detecting Ag of B. dermatitidis in the urine (more sensitive than serum)
What % of cats develop skin lesions with Cryptococcus neoformans infection?
40%
Rare in dogs - 20% develop skin lesions
Which special stains can be used for cyptococcosis on histopath?
GMS, PAS and Mayer’s mucicarmine
Usually organisms are abundant in pyogranulomatous inflammation with a ‘soap bubble’ appearance. Atypical lesions reported were capsule-deficient strains of Cryptococcus spp. with a severe inflammatory response with rare intralesional organisms that may not be readily identified without special stains/PCR
What are the typical clinical signs of cyptococcosis?
Nodules that may ulcerate/drain on the face, pinnae and paws. Especially at/near nasal planum (extension of sinonasal pathology)
How do you treat cryptococcosis?
Itra/fluconazole
Which groups of dogs are predisposed to histoplasmosis (Histoplasma capsulatum)?
Young
Large breed
Working/herding often have disseminated disease
Toy breeds often have GI form
How do you diagnose histoplasmosis?
Numerous, small, oval yeasts usually within macrophages
PAS, GMS
Culture not recommended due to health risk!
What is the drug of choice for histoplasmosis in dogs and cats?
Itraconazole
What are likely prognostic indicators for histoplasmosis in cats?
More severe respiratory, hepatic, hematologic or neurologic disease
Cutaneous disease as the only manifestation has been reported!
How do you diagnose coccidiodomycosis?
Histopath - pyogranulomatous, oragnisms may be low in number and difficult to find - PAS/GMS
Culture is a health risk!
Serology
How do you treat coccidiodomycosis?
Azoles systemically for 3-6 months past resolution of clinical signs; serology can help monitoring.
What are the clinical signs of coccidiodomycosis?
- Subcutaneous nodules most common lesions in both dogs and cats.
- Widely distributed and not often found over sites of bone infection.
- In 75% of dogs and 54.5% of cats with cutaneous lesions there were clinical signs of systemic illness, (cutaneous disseminated disease).
- Can see localized lesions with no systemic illness, (primary cutaneous infection?)
Many opportunistic fungal infections are acquired via inhalation and haematogenous spread, is the same true for sporotrichosis?
No, inoculation of wounds is more common
Do dogs and cats present with disseminated sporotrichosis?
Cats - disseminated disease common
Dogs - usually localised to the skin, can track along lymphatics
How do you diagnose sporotrichosis?
Cytology/histopath - numerous organisms in cats, rare in dogs and may need PAS/GMS or IHC
Culture
What is the treatment of choice for sporotrichosis?
Itraconaozle
What are the clinical signs of pythiosis?
Non-healing wounds, invasive masses that ulcerate and have draining tracts
Cutaneous and GI signs are rarely encountered together!
How do you diagnose Pythium insidiosum infection?
- Pyogranulomatous inflammation with numerous eosinophils and scatted hyphae (GMS stain) on cytology or histopath
- Culture (growth is inhibited by low temperatures)
- PCR
- IHC
How do you treat pythiosis?
Radical surgery followed by combination systemic antifungals for 2-3 months (e.g. itraconazole and terbinafine). Can use serology for monitoring response.
How does lagenidiosis differ from pythiosis? Both are oomycetes.
- Lagenidiosis is not reported in cats
- Lagenidiosis does not cause GI disease
- Cutaneous signs in lagenidiosis are often accompanied by lesions in distant blood vessels/lymph nodes and the lungs
- Lagenidium hyphae can be found in MNGCs on histopath as well as extracellularly cf Pythium which is found at the center of necrosis/granulomas
What causes zygomycosis?
Fungi in the class Zygomycetes, including the genera Basidiobolus (trunk, GI) and Conidiobolus (mucocutaneous and oral) = chronic localized infections in subcutaneous tissue or nasal submucosa of immunocompetent patients)
Rhizopus, Absidia, Mucor, Saksenaea (Mucorales) = rapidly progressive disease in debilitated or immunocompromised individuals)
Are fungal organisms numerous or sparse in zygomycosis?
Sparse - GMS helpful
Fungal culture to help identify species (through molecular methods)
What type of fungus is Prototheca?
Algae - causes opportunistic infection in immunocompromised animals
How do you diagnose protothecosis?
Find numerous spherules with a wheel/cut-pie appearance within cells - culture for definitive diagnosis
Which opportunistic fungal infections occur in immunocompetent animals?
- Basidiobolus and Conidiobolus
- Pythiosis and lagendiosis
- Sporotrichosis
- Coccidiodomycosis
- Histoplasmosis
- Cryptococcosis
- Blastomycosis
Name changes of epidermal surface microclimate that predispose to Malassezia overgrowth
- Increased moisture
- Altered surface lipids and/or disruption of stratum corneum barrier function
- Aberrant immune responses
Apart from hypersensitivity disorders name other diseases that favour Malassezia overgrowth in dogs
Endocrinopathies (hypothyroidism, hyperadrenocorticism) Primary seborrhea Zn-responsive dermatitis SND Ichthyosis
Apart from hypersensitivity disorders name other diseases that favour Malassezia overgrowth in cats
Paraneoplastic alopecia
Thymoma-non-thymoma associated exfoliative disease
Feline facial acne
Feline idiopathic facial dermatitis
Cigar shaped yeasts on histopathology are characteristic of which fungal infection?
Sporotrichosis
Name oomycetes
Pythium
Lagenidium
(aquatic dimorphic water moulds)
