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