Dermatophytes Flashcards
List zoophilic dermatophytes
M.canis (cat, dog)
M.equinum (horse)
M.persicolor (voles)
M. nanum (pig)
T. equinum (horse)
T. verrucosum (cattle)
Several species of T.mentagrophytes complex (rodents, rabbits, hedgehogs)
Name geophilic dermatophytes
M. gypseum complex (teleomorph species Arthroderma fulvum, A. gypseum, A. incurvatum)
What are anamorphs and teleomorphs?
Anamorphs are asexual forms (genus Microsporum or Trichophyton) on macroscopic and microscopic characteristics of the organism grown in the culture
Teleomorphs are sexual or perfect states which classifies dermatophytes in genus Arthroderma, phylum Ascomycota
Name factors that showed increased prevalence of positive dermatophytes cultures?
Dermatophytes were more commonly isolated from animals with consistent clinical signs (vs. asymptomatic), animals housed in groups, free-roaming cats and from warm climate locations (Brazil, Chile, India, Italy, SE USA), age (puppies and kittens), lifestyle, free-roaming animals
Is M. canis part of the normal fungal flora in cats and dogs?
No
Name 4 most common normal fungal flora of pet cats (13 saprophytes and 2 dermatophytes)
Aspergillus, Alternaria, Penicillium, Cladosporium spp.
Name 2 most common normal fungal flora found in dogs?
Cladosporium and Alternaria spp.
Do FIV or FeLV seropositive cats have greater or lesser diversity of saprophytic fungi ?
Greater + increased carriage of Malassezia, dermatophyte carriage was rare and there was no difference between seropositive and seronegative cats (but systemically ill cats)
Are cats receiving immunosuppressive treatment in risk of developing dermatophytosis?
NO (only one case in pseudopelade)
Name concurrent illnesses that are described with dermatophytosis in dogs
Dermatophytosis + HAC, leishmaniosis, leishmaniosis and ehrlichiosis, DM, demodicosis
Name breed predispositions for dermatophytosis?
Persian cats, Yorkshire terrier
+ hunting and working breed dogs (German short-haired pointers, fox terriers, LR, Belgian Groenendael, beagle, pointer, JRT, GSD, Jagdterrier)➙ specially for M. persicolor and M. gypseum
Name breed predispositions for subcutaneous dermatophytic infections?
Yorkshire terrier and Persian cats
What is the infective form of dermatophytes and how is it formed?
Arthrospore
-formed by fragmentation of fungal hyphae into very small infective spores
How are dermatophytes transmitted ?
Direct contact and fomite transmission (grooming appliances, bedding, collars, ectoparasites and exposure to contaminated environment)
Name factors that contribute to conditions optimal for dermatophyte infection?
Increased microtrauma (pruritus/self trauma), humidity, ectoparasites
Name 3 stages of development of dermatophyte infection?
- stage- adherence of arthroconidia to corneocytes
-2-6 h of exposure
-mediated by carbohydrate-specific ADHESINS expressed on surface of arthroconidia, dermatophyte-secreted PROTEASES like SUBTILISINS - Stage –involves fungal conidial germination
In which germ tubes emerge from arthroconidia and then penetrate the SC
Within 4- 6 h in corneocyte model and 24 h a human full-thickness epidermis model - stage-involves dermatophyte invasion of keratinized structures (including follicular unit)
How many days is needed to complete the fungal life cycle (when hyphae begin to form arthroconidia)?
Within 7 days of incubation
When do the clinical lesions typically occur after exposure?
One to three weeks after exposure
What do the dermatophytes secrete to digest keratin?
ENDOPROTEASES ( subtilisins, fungalysins) and EXOPROTEASES
+ reduction and cleavage of keratin cysteine disulphide bonds (via dermatophyte sulphite efflux pump encoded by SSU1 gene)
+ regulation of sulfite formation from cysteine (important pathogenic mechanism, enzyme cysteine dioxygenase Cdo1)
What are the mechanism in which dermatophytes can counter host immune response ?
-lymphocyte inhibition by cell wall mannans
-macrophage function alteration by catalase
-altered/ slowed keratinocyte turnover: mannan
-produce keratinolytic enzymes, endoproteases and exoproteases, which hydrolyze keratin: penetrate and invade the hair shaft.
Clinical cure and protection against re-infection is mediated by which type of immunity?
Cell-mediated immune response (involving effector cells : macrophages, neutrophils and IFN-𝜸)
Describe immune processes/changes in natural infections and in cats currently of previously infected with M. canis?
Natural infection: positive immediate and delayed IDT reactions to fungal proteins, elevated antibody titres and alterations in lymphocyte blastogenesis response to fungal antigens
Currently or previously infected: significantly higher lymphocyte reactivity to dermatophyte antigens (when compared to uninfected ones), and lymphocyte reactivity was similar in culture-positive and infected/recovered cats, but antibody titres were significantly higher in the culture-positive group (suggest that high ly reactivity is due to cell-mediated Th1 response and that Ab are more reflective of exposure, but NOT PROTECTIVE!)
Name clinical signs found in dermatophyte infections?
Alopecia, papules, scales, crusts, erythema, follicular plugging, hyperpigmentation, changes in the nail growth/appearance, asymmetrical lesions, variable pruritus (in general minimal to absent)
Name most common places where lesions occur in cats and dogs?
Cats: face, ears, muzzle, then progress to paws and other body areas
Hunting dogs: muzzle, paws
What are the 2 factors that complicate confirmation of infection?
1 st- difficulty of detection of lesions within the hair coat (infected hairs can be small or obscured by inflammatory crusts) +prior treatment that may change appearance of lesions or inability to restrain the animal
2nd- fomite carriage from contact within an infected animal or exposure to contaminated object can lead to FALSE POSITVE FUNGAL CULTURES (arthrospore trapped within hair coat)
What are the factors that influence diagnostic testing ?
-stage of the infection
-presence or absence of treatment
-sampling technique
-site selection
-clinician training
-quality of the tool (e.g. Woods lamp)
-ability to examine the animal
How does the Wood’s lamp work and what actually fluorescents ?
Fluorescence occurs when light of shorter wavelengths initially emitted by the lamp, is absorbed and radiation of longer wavelength is emitted
-UV band between 320 to 400 nm
-green fluorescence is due to chemical metabolite PTERIDINE located in the cortex or medulla
-it is due to chemical interaction that results from INFECTION and not associated with spores
Name diagnostic test used to diagnose dermatophytosis?
Wood’s lamp
Dermoscopy
Direct examination of hairs and/or scale
Fungal culture
PCR
Biopsy
Which dermatophytes fluorescence ?
M. canis
T. schoenleinii
M. Distortum
M. Audouinii
Does the usage of shampoos, enilconazole or lime sulfur destroys the fluorescence and can it be used for monitoring th?
No x2
What is the percentage of isolates of M. canis that fluorescence?
30-54%
Do all strains of M. canis fluorescence?
Yes
Are all fluorescent hairs culture positive and explain why yes/not?
Not all fluorescent hairs are culture positive
It depends when hairs are examined in the course of the infection. Fluorescence develops 5-7 days p.i., usually 10-14 d p.i. (then the whole hair shaft is involved). As hair grows intrafollicular portion of the HS stops to glow while the distal HS glows. Often have “glowing tips”- infection has been eliminated and cultures are negative ( max glow of tips is 18 years!)
What are the findings in cats with dermatophytosis using dermoscopy?
Comma hairs= opaque, slightly curved or broken hairs with a homogenous thickness (easier to see in lightly coloured cats, in black cats appear as white or pale)
Affected areas had variable amounts of brown to yellow crust
Microscopic examination of comma hairs reveals hyphae and spores + positive Wood’s lamps
Hairs with a corkscrew or coiled appearance
Name mediums which can be used for direct examination of hairs or scales and which is recommended ?
Mineral oil – recommended
KOH
Compounded chlorphenolac
Name sampling techniques for dermatophytes?
Hair coat brushing (superior to hair plucking)-Mackenzie toothbrush technique and carpet squares
Hair plucking
Sticky tape sampling (more sensitive than brush technique)
In DTM a change in colour from yellow to red is a consequence of what and alone is it diagnostic of dermatophytes?
Due to pH change triggered by fungal growth.
No, wide range of contaminants can cause colour change in medium
Does the volume of the medium and incubation in the dark, light or 12h dark/12 h light, or room lighting influences the growth and sporulation?
Small volume of the medium was inferior (when compared to large)
No differences in any of mentioned environmental factors
What are the causes of positive PCR, false positive and false negatives?
Positive PCR: result of active infection
False positive: fomite carriage or nonviable fungal organism
False negative PCR: sampling techniques are not optimized or if the global dermatophyte marker is not used
What is the golden standard for diagnosing dermatophytes ?
No test
What is recommended to do as part of monitoring a response to therapy?
Monitoring clinical response, use of Wood’s lamps if possible and fungal culture + monitoring of colony forming units is helpful
Name the most effective systemic treatment for dermatophytosis in dogs, cats and ferrets, based on available evidence?
Cats and dogs: Itraconazole and Terbinafine
Ferrets: fluconazole
The organism have the ability to self cure during a dermatophyte infection. Can you mention some mechanism that favor self-healing?
1) Stop downwards migration at keratogenous zone (Adamson’s fringe),
2) Enter telogen
3) Sebum (fungistatic FA, transferin), serum & sweat (transferin),
4) Self grooming (C),
5) Immune response: delayed type-hypersensitivity, CMI > innate immunity (C, neutrophils, transferin);
→ feline neutrophils IL-1b, IL-8, TNF-α after exposure to MC, ↑TLR-2 and TLR-4a)
