Malassezia, Dermatophyte, Candida (NAVDF, Consensus x2) Flashcards
Cell wall component of fungi
*Chitin (also arthropod exoskeleton)
*Chitosan
*Glucan
*Mannan
NO CELLULOSE
Name of asexual reproduction spores
Conidia
Nonmotile
Fungi that are present on NORMAL dog and cat skin
*Alternaria
*Cladosporium
*Aspergillus
*Penicillium
*Rhizopus
*Trichoderma
Do cats with FIV/FeLV have MORE or LESS fungal diversity on their skin
MORE
Preferred temperature for fungi relative to body temperature
Fungi prefer LOWER temp than body temp
(physiologic barrier to fungal growth, along with oxidation-reduction potential)
Chemical barrier by keratinocytes against fungi
*Fungistatic fatty acids and sphingosines
T or F: Clinically healthy pets cats can have Microsporum canis on skin
It is NOT a commensal
BUT it has been isolated on 2% of clinically healthy cats
Climate with more M canis
Tropical (17.5%) > temperate (4%)
At what temperature, seasona is Microsporum gypseum most common?
Humid, (sub)tropic
Summer, autumn
Are Dermatophytes sexual or asexual fungal organisms
Asexual (anamorphs)
Zoophilic dermatophytes (adapted to animals)
M canis
M equinum
T equinum
Sylvatic dermatophytes (adapted to rodents/hedgehogs)
T mentagrophytes
M persicolor
Anthropophilic dermatophytes (adapted to humans)
Epidermophyton
T tonsurans
T rubrum
Geophilic dermatophytes (adapted to soil, saprophytes)
M gypseum
Infective portion of dermatophyte? How does it form?
Arthrospore
Forms by segmentation and fragmentation of fungal hyphae
Predisposition (environment) for dermatophyte
*Young animals
*Overcrowded
*Dirty
*Damp
*Inadequate nutrition
*Immunosuppression
Predisposed breeds for M canis
*Yorkshire terrier
*Pekingese
*Persian
*Himalayan
Predisposed breeds for T mentagrophytes
Parson Russel Terrier
T or F: Daily baths with nonmedicated shampoo will help treat dermatophtysosis
FALSE
Excessive bathing/grooming can REMOVE fungistatic sebum and serum
T or F: Fleas can transmit dermatophytes
True, potentially
T or F: If protected from UV light, dermatophyte- infected hair fragments can remain infectious for >18 months
True
3 main stages of dermatophyte infection
1) Arthrospores adhere strongly to keratin
-Mediated by adhesins on arthroconidia, proteases like subtilisins
-Within 2-6 hours of exposure
2) Conidial germination (germ tube emerges from arthroconidia, penetrates SC)
3) Invasion of cornified tissues by producing proteolytic enzymes (keratinase, elastase, collagenase)
Mechanical injury and humidity facilitate penetration
*Hyphae form arthroconidia within 7 days –> complete lifecycle
Where does dermatophyte infection STOP in the hair shaft
Adamson’s fringe/ keratogenous zone
In what phase of the hair cycle does dermatophyte growth cease?
Telogen, as no new keratin production
-Hairs are weak and easily broken
Time of dermatophyte incubation (until lesions appear)
1-3 weeks
Is humoral or cell mediated immunity more critical for dermatophyte clearance
Cell mediated (IFNg!, mac, neut)
(strong delayed-reactions on IDST in humans who can clear dermatophytosis)
T or F: cats who have received antifungal meds do not develop a robust cell-mediated immune response to dermatophytes, and are at risk of reinfection
True :(
What is the dermatophyte antigen that is MOST immunologically active?
What type of hypersensitivity reaction does it produce?
Glycopeptide (cell wall)
-Carb portion: immediate-type hypersensitivity
-Peptide portion: delayed-type hypersensitivity
Animal most likely to develop a fungal kerion
Dirty digging dogs
On face, forelimbs
Animal most likely to develop a Pseudomycetoma
Persian cat
Possible tissue grains
Clinical signs of Dermatophyte in cats that are easily confused as other diseases
*Uni or bilateral pinnal pruritus
*Recurrent chin folliculitis
*Recurrent stud tail
What is #unique about Microsporum persicolor
Scaling, but no alopecia
Infects surface keratin, does NOT invade hair
Which dermatophyte species is least likely to cause alopecia
Microsporum persicolor
Infects surface keratin, does NOT invade hair
Scaling w/no alopecia
What is the name of the M canis metabolite that fluoresces with Woods Lamp
Pteridine
Woods lamp wavelength
320-400nm
T or F: If a hair is still fluorescing, you have not successfully treated the M canis infection
False. Hairs continue to fluoresce for a long time after negative culture
Are M canis spores endo- or ectothrix
Ectothrix
T or F: you may find dermatophyte macroconidia on a direct impression of an M canis lesion
FALSE. Macroconidia are never formed in tissue.
May seen ectothrix spores.
What type of hair will you see on Dermoscopy with dermatophytosis
Comma hairs
Slightly curved or broken hairs with homogenous thickness
What dermascopy findings would you expect with dermatophytosis vs alopecia areata
Dermatophyte: comma hair
Alopecia areata: Exclamation point hair
What are the contents of Dermatophyte Test Medium (DTM)
*Nutrient medium
*Bacterial and saprophytic fungal inhibitors (gentamicin, tetracycline, cycloheximide)
*Phenol red - pH indicator
What temperature is ideal for DTM plates
Above room temperature has increased sporulation
Is light or dark environments better for DTM plates
Doesn’t matter!
How long should you let a DTM sit before calling it negative overall
21 days
How often do you need to check your DTM plate
Daily. Need to determine if color changes prior to pathogen growth.
Dermatophytes will show color change WITH growth of pathogen. Use proteins (keratin) before carbs!
Nonpathogens will induce color change AFTER colony has grown. Use carbs before proteins.
Color of Microsporum mycelium on DTM
White-to-buff colored, powdery to cottony mycelium
Underside is yellow/orange
Flat with a depressed center
T mentagrophytes macroconidia, microconidia shapes
Macroconidia = Cigar (rare to see)
Microconidia = branched (common to see)
Hyphae are spiral
M gypseum macroconidia shape
Ellipsoidal
Thin wall
<6 cells
Rounded distal end
M gypseum colony on DTM
Cinnamon brown top
Powdery consistency
Yellow/tan underside
Flat
M canis macroconidia shape
Spindle/canoe shape
Thick walls, outer spines
>6 cells
Terminal knob
Trichophyton colony on DTM
White to cream top
Tan/brown/red bottom
Who is this
Saprophyte
Colonies that are grey, black, brown, green are NOT dermatophytes
What should you do if there are no macroconidia on your cellophane tape sample from your DTM?
Repeat in 4-7 days. Some colonies produce spores as they mature
What color are dermatophytes on GMS stain
Black/brown on a pale green background
What color are dermatophytes on PAS stain
Dark red on a lighter pink background
When is histopath most useful for diagnosis of dermatophytosis
Nodular forms
Otherwise, culture is more sensitive
T or F: M canis will resolve in many cats without treatment
True. In about 3 months.
But rec tx in order to avoid shedding infection
T or F: Trichophyton and M persicolor will always resolve without treatment in healthy dogs
False. Chronic dermatophytosis can last up to 5 years in immunocompetent animals
Definition of Mycological cure
2 negative cultures taken at least 2 week apart
Topical tx for dermatophytosis
2x/week
Lime sulfur, enilconazole, miconazole/chlorhexidine (NOT micon alone)
Most effective, safe systemic treatments for Dermatophytosis
*Itraconazole (noncompound)
*Terbinafine
Do NOT use griseofulvin. It works but has AEs
T or F: Lufenuron may work for dermatophyte
FALSE
Antifungal disinfectants to use in the environment
*Sodium hypochlorite
*Enilconazole
*Accelerated H2O2
*Potassium peroxymonosulfate
Use AFTER removing organic debris
Laundry protocol for dermatophyte household
AGITATION is what removes dermatophytes
Wash TWICE on LONGEST cycle
*Any temperature
*Does NOT need bleach
How to clean wood floors in dermatophyte household
Swiffer sheet (electrostatic)
then wood oil soap
At risk human populations for Dermatophytosis
*Children
*Transplant/cancer patients
*Immunocompromised
*Elderly
*Vet professionals
Dermatophyte virulence factors
*Keratinolytic enzymes (keratinase)
*Endoproteases
*Exoproteases
Elastase, collagenase
Hydrolyze keratin
Allow invasion into hair shaft
T or F: It is easy for normal skin be infected by a dermatophyte
False. Normal skin has too low humidity, antifungal substances on surface, normal resident flora
*Sebum = fungistatic fatty acids
*Continuous shedding of stratum corneum removes organisms as keratin is sloughed
T or F: Malassezia pachydermatis can grown on a media without lipids
FALSE. Lacks fatty acid synthase gene (like all Malassezia)
Uses lipid fractions from within peptones of Sabouraud’s dextrose agar.
But technically called “non-lipid-dependent”, because it is the only Malssezia that can grow on Sabouraud’s dextrose agar
Is Malassezia pachydermatis a pathogen or commensal
Commensal
Can become pathogenic if altered host microenvironment, immune system
How to Malassezia pachydermatis reproduce
Budding
Broad base, monopolar
Thick cell wall
Predisposed breeds to Malassezia in dogs
*Basset hounds
*WHWT
*Cocker Spaniels
*Toy/Mini poodles
*Dachshunds
*Boxers
*CKCS
*Shih tzu
*Australian, silky terriers
*GSD
*Bull terriers with Lethal Acrodermatitis
Which genetic disease from MKLN1 can result in Malassezia infections
Lethal acrodermatitis in bull terriers
If a dog has a Malassezia hypersensitivity based on IDST, we would expect their IgG and IgE to be ______
High titers
Predisposing factors for Malassezia in cats
*Allergies
*Metabolic dz
*FIV/FeLV
*Paraneoplastic dz (pancreatic, thymoma)
*Breeds (Devon rex, Sphynx)
Cat breeds with more Malassezia infections
Devon Rex, Sphynx
What general temperature does Malassezia like
Increased heat and humidity
What type of immune response is developed against Malassezia
Innate, antibody and cell mediated responses
Hypersensitivity reactions
How do keratinocytes respond to Malassezia
*Identify Malassezia with TLRs
*Upregulate IL-10, TGFb (immunosuppressive)
*Downregulate IL-1a
T or F: cell mediated responses to Malassezia can lead to a Type IV hypersenstivity in cAD patients
True
What do claws infected with Malassezia look like
Pedal pruritus
Red/brown discoloration of claw
Ungual exudate
Can Malassezia be reliably diagnosed on histopathology?
No. Surface scale + Malassezia is lost in tissue processing
Use cytology
BUT PAS, GMS is your best option.
What culture media can you grow Malassezia pachydermatis on
Sabaroud’s dextrose agar
All other Malassezia require additional lipids!
What culture media do you use for most Malassezia species
modified Dixons agar (lipid enriched)
1) contact plates = convenient
2) Detergent scrub sampling = gold standard but research only
What do Malassezia colonies look like on culture
Cream to yellow
Smooth to lightly wrinkled
Glistening or dull
Margins are entire or lobate
Where is Malassezia within the skin?
Stratum corneum
Topicals work great! Shampoos, gels, lotions
Which topical therapies work for Malassezia dermatitis
Strong evidence for Miconazole 2% /Chlorhexidine 2% shampoo 2x/w
Moderate evidence for 3% chlorhexidine shampoo
Best systemic antifungal therapies for Malassezia in dogs
Ketoconazole
Itraconazole
Terbinafine and fluconazole need additional studies.
Fun fact: paper in Vet Derm Jan 2024 shows Fluconazole is noninferior to Itra for Malassezia!
Best systemic antifungal therapies for Malassezia in cats
Itraconazole
How well does ASIT work for Malassezia hypersensitivity
Improvement noted in studies
Needs more data
T or F: Malassezia is zoonotic
RARE. Very low risk. But hand hygiene for immunocompromised people
PAMPs identify _____ on Malassezia
*Mannan
*Zymosan
PRRs for Malassezia
C-type lectins! Need Ca2+ to bind carbohydrates
*Langerin
-Recognizes mannose, beta-glucans
-on Langerhan cells
Many fungi recognized
*Mincle
-Recognizes glucosyl and mannosyl-glycolipids
-on Phagocytes
Malassezia specific
*Mincle + Dectin 2 stimulate proinflam cytokines (TNFa, MIP2, TNFa)
Malassezia virulence factors
*Hydrolases (lipase, phospholipase, aspartyl protease, acid sphingomyelinase)
*Biofilm
Antimicrobial resistance in Malassezia (2)
1) Increased expression of ERG11 gene
Encodes lanosterol 14-alpha-demethylase (Azole target)
2) Increased expression of Drug efflux pumps (CDR1, CDR2; MDR1)
T or F: Candida are commensals of MC junctions, GI tract, Genital tract
True
RARE to cause infections in animals
Most common species of Candida isolated from animals
Candida albicans
Immune response against Candida
Neutrophils
T cell mediated immunity
Culture media, colony color, organism shape for Candida
Blood Agar
Sabouraud’s Dextrose agar
Cream-white colonies
Rounded yeasts, pseudohyphae, septate hyphae
Where do Candida yeast versus hyphase live in the skin
Yeast are on the surface
Hyphae, pseudohyphae extend into epidermis
Are Candida zoonotic
No
Virulence factors for Candida
*Ligands for adherence
-Afflutinin-like (AL) family
-Hyphal wall protein (Hwp) family
*Adhesins: Mannose, mannoproteins
Bind to receptors on epithelial cells: E cadherin, fibrinogen, fibronectin, thrombin, collagen, laminin, vitronectin-binding proteins
*Invasin proteins (affect mucosal skin)
*Aspartyl proteinases are hydrolytic, injure mucosa
Most common Malassezia sp in cat ears
Malassezia nana
Most common Malassezia species in cat clawfolds
Malassezia sloofiae
Most common Malassezia species on the cat overall
Malassezia pachydermatis
What stimulates phospholipase activity in Malassezia pachydermatis?
Endogenous opiod peptides
Beta-endorphins in skin of dogs with dermatitis
Higher phospholipase activity in OE/dermatitis dogs
What cell surface markers are expressed by Langerhans cells when activated by Malassezia
CD83 initially
Then increase in CD80, CD86
Malassezia antigens are resistant to lysis by WHICH cell type
NK cells
What immune response type is present against Malassezia
Th2
Increased IL-4, IL-5, IL-10, IL-13
Which immunoglobulins are elevated in Basset hounds with Malassezia dermatitis
IgG, IgA
IgG4 induces Th2 response; correlated with IgE concentration in cAD
T or F: IgE against Malassezia is higher in atopic dogs than healthy dogs
True
But IgE not higher in OE ears than healthy. Infection is not dependent on hypersensitivity
What type of immune responses can occur against Malassezia
Type 1 (IgE sensitized mast cells)
Type 4 (contact hypersensitivity, Delayed type T cell hypersensitivity)
T or F: IgG against Malassezia may offer some protective immunity
OR
IgG may activate the complement system, to cause epidermal damage/inflammation
True
T or F: The Consensus Guidelines recommend IgG testing for Malassezia dermatitis
False. Do NOT recommend
T or F: More Malassezia pachydermatitis correlates with higher CADESI-3
True
High levels of phospholipase A2 is associated with _____ (increased vs decreased) pathogenicity of Malassezia pachydermatis
Increased!
Subtype 3D has higher PLA2, more pathogenic in dogs
Pulse antifungal therapy for Malassezia
Itraconazole 5 mg/kg 2d/week consecutively
May work bc accumulation of lipophilic itraconazole in SC
MOA terbinafine
Synthetic allylamine derivative
Inhibits fungal ergosterol biosynthesis at SQUALENE EPOXIDATION step
MOA Nystatin
Polyene cyclic macrolide
Altered cell membrane permeability; preferential binding to ergosterol
T or F: aminoglycosides may work against Malassezia pachydermatis
TRUE! need more studies though
Combination of multiple antifungal drugs may have ________ effects (ie caspofungin and flu/itraconazole)
Synergistic
2 causes for high MIC needed against Malassezia pachydermatis
ERG11 mutation
Biofilm
BUT topical products do get high MICs!
T or F: we have excellent CSLI and EUCAST breakpoints for M pachydermatis
FALSE. But regardless, M pachydermatis seems susceptible to most azoles.
What ear treatment may be effective at preventing Malassezia otitis externa
Hydrocortisone aceponate 2x/w
T or F: Cats with FIV/FeLV are at increased risk for dermatophytosis
FALSE. They are NOT at increased risk
Major dermatophyte of hedgehogs
Trichophyton erinacei
Major dermatophyte of guinea pigs
Arthroderma benhamiae
Major dermatophyte of cats, dogs, rabbits, rodents (mice, chinchillas)
Arthroderma vanbreuseghemii
Major dermatophyte of horses
Trichophyton equinum
(also Microsporum equinum, but more rare)
Major dermatophyte of monkeys, poultry, dogs
Trichophyton simii
(India only)
Major dermatophyte of chickens
Trichophyton gallinae
Major dermatophyte of rodents, voles
Microsporum persicolor
Major dermatophyte of pigs
Microsporum nanum
Major dermatophyte of horses, donkeys
Trichophyton bullosum
Major dermatophyte of mice (favus)
Trichophyton quinckeanum
Major dermatophyte of the soil (geophilic)
Microsporum gypseum
T or F: many dermatophyte infections come from contact with a contaminated environmental
FALSE. Uncommon. Usually need contact with cat, rodent
(except geophilic)
Endoproteases secreted by dermatophytes
*Substilisins
*Fungalysins
Digest keratin into usable peptides and amino acids
Function of SSU1 gene (dermatophyte)
Encodes for Dermatophyte Sulphite Efflux Pump
-Degrades disulfide bonds between keratin cysteines
cdo1 function (dermatophyte)
*Cysteine dioxygenase
Regulates sulfite formation from cysteines in keratins
Helps with keratin degradation
2 genes important for keratin degradation (dermatophytes)
SSU1: dermatophyte sulphite efflux pump
Cdo1: cysteine dioxygenase
T or F: Microsporum gypseum and Microsporum persicolor will fluoresce on Woods Lamp
FALSE
If a dermatophyte grows on DTM, what color change occurs
Before: Yellow
W/Dermatophyte: Red
Change in pH. Dermatophytes release alkaline metabolites
Is Lime Sulfur fungicidal or fungistatic?
Keratolytic or keratoplastic?
Fungicidal
Formation of Hydrogen sulphide
Keratolytic
AE of Lime Sulfur
Oral ulcerations (don’t let cats lick!)
MOA of chlorhexidine
Biguanide compound
Affects cell membranes at low concentrations
Congeals cytoplasm at high concentrations
MOA of essential oils against dermatophytes
Fungal cell wall damage
-Slows growth
-Destroys intracellular organelles
Is Itraconazole fungistatic or fungicidal
Low doses: Fungistatic
High doses: Fungicidal
MOA of itraconazole
Inhibits fungal cytochrome P450 enzyme (140alpha demethylase)
Prevents conversion of lanosterol to ergosterol
Ergosterol needed for cell wall integrity, activity
Can you use itraconazole in pregnant animals?
No. Embryotoxic, tertogenic at high doses
Which antifungal medication is associated with vasculitis at doses >10mg/kg
Itraconazole
Which medications can you NOT combine with itraconazole, ketoconazole (lipophilic, concentrate in sebaceous glands).
Gastroprotectants/ antacids. Will decrease bioavailability
Need low GI pH to be absorbed.
T or F: Ketoconazole’s interference with endogenous steroid synthesis is irreversible
False. Steroid synthesis issues do occur with ketoconazole, but it is reversible
What happens if you combine ketoconazole with ivermectin, midazolam in dogs
or
Cyclosporine in dogs, cats
INCREASED plasma concentrations
(azoles = fungal Cytochrome p450 inhibitors)
What is different about fluconazole compared to the other azoles
*Water soluble, minimally protein bound
-Others are lipophilic
*NOT affected by concurrent antacids, do not need food for absorption
*Poor efficacy against dermatophytes
T or F: Terbinafine affects the Cytochrome P450. Caution with other medications
FALSE. Terbinafine does NOT affect Cyp450 (keto and itra do!)
Which antifungal medication has the LOWEST MIC for Microsporum and Trichophyton
Terbinafine!
Compared to itraconazole, fluconazole, ketoconazole and griseofulvin: terbinafine has the lowest MIC for Microsporum sp. and Trichophyton spp
Does terbinafine persist in SC or sebum at higher concentration than serum (like itrafungol)
No
However, terbinafine is highly concentrated in cat hair
MOA of griseofulvin
Binds fungal tubulin –> causes mitotic arrest in METAPHASE
Inhibits nucleic acid synthesis, cell mitosis
Fungistatic
AEs of griseofulvin
Lethargy, pyrexia, anorexia, depression, ataxia, upper respiratory signs, leukopenia, pancytopenia
Potent inducer of P450 enzymes
Need CBC q2w.
MOA of Amphotericin: “polyene class”
Irreversibly binds/alters fungal membrane sterols (ergoserol) –> creates pores in cell membrane
NEPHROTOXIC
Activates macrophages
(Nystatin is also a polyene)
Which antifungal causes toxic epidermal necrolysis in dogs
Flucytosine
Which antifungals are a POOR choice for aspergillosis
Fluconazole (intrinsic resistance), ketoconazole (ineffective)
MOA capsofungin
Inhibits 1,3-beta-glucan synthase
(important for beta glucan synthesis of fungal and oomycete cell wall)
What disease does Candida cause in veterinary medicine ains living fungi ONLY
Thrush (white tongue) on pigs
Which 2 dermatophytes are in the stratum corneum ONLY (not in hair follicles)
1) Trichophyton mentagraphytes
2) Microsporum persicolor
