Microsporum canis
Microsporum canis | |
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Spindle-shaped, warted macroconidia of Microsporum canis
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Fungi |
Division: | Ascomycota |
Class: | Eurotiomycetes |
Order: | Onygenales |
Family: | Arthrodermataceae |
Genus: | Microsporum |
Species: | M. canis
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Binomial name | |
Microsporum canis (E.Bodin) E.Bodin (1902)
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Synonyms | |
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Microsporum canis is a
Taxonomy and evolution
Microsporum canis reproduces by means of two conidial forms, large, spindle-shaped, multicelled
Morphology
Colony morphology
Microsporum canis forms a white, coarsely fluffy spreading colony with a distinctive "hairy" or "feathery" texture.[4][5] On the underside of the growth medium, a characteristic deep yellow pigment develops due to the metabolites secreted by the fungus.[4][5] The intensity of this yellow pigmentation peak on the 6th day of colony growth and fades gradually making the identification of older colonies difficult.[4] Some strains of M. canis fail to produce yellow pigment altogether, exhibit abnormally slow colony growth and form undeveloped macroconidia.[4] Cultivation on polished rice tends to reestablish the typical growth morphology and is helpful for identification.[4]
Microscopic morphology
Microsporum canis reproduces asexually by forming macroconidia that are asymmetrical, spindle-shaped and have cell walls that are thick and coarsely roughened.[4][5] The interior portion of each macroconidium is typically divided into six or more compartments separated by broad cross-walls.[4][5] Microsporum canis also produces microconidia that resemble those of many other dermatophytes and thus are not a useful diagnostic feature.[3][4]
Identification
Microsporum canis produces infections of scalp and body sites, creating highly inflammatory lesions associated with hair loss.
Most M. canis infections are caused by the "-" mating strain of its sexual progenitor, Arthroderma otae.[3]
Microsporum canis has no specific growth factor or nutrition requirements, hence it grows well on most commercially available media.[5] In addition, M. canis exhibits rapid colony growth at 25 °C.[5] Two growth media that help distinguish M. canis from other Microsporum spp. (notably the morphologically similar species, M. audouinii) - specifically polished rice and potato dextrose agar.[4] On potato dextrose agar, M. canis produces a lemon-yellow pigment that is easily visualized, due to the presence of aerial hyphae, while on the polished rice, most isolates (even atypical strains) produce yellow pigment.[4][5]
Pathophysiology
It is considered a zoophilic dermatophyte, given that it typically colonizes the outer surface of animal's body.
Microsporum canis is among the most common dermatophytes associated with tinea capitis and tinea corporis.[3][5] Unlike some dermatophyte species, M. canis typically does not cause large epidemics. Humans become infected as a result of direct or indirect contact with infected pets.[1][2][3] Microsporum canis generally invades hair and skin; however, some nail infections have been reported.[3] When hair shafts are infected, M. canis causes an ectothrix-type infection where the fungus envelopes the exterior of the hair shaft without the formation of internal spores.[4] This colonization of the hair shaft causes it to become unsheathed, resulting in characteristic round or oval non-inflammatory lesions the develop on the scalp.[4][9] Infection triggers an acute leukocytic reaction in subcutaneous tissues, which gradually becomes highly inflammatory and leads to hair loss, in the case of tinea capitis.[3]
Diagnosis
Typically, infections caused by M. canis are associated with
Treatment
Microsporum canis infections can be easily managed by topical antifungal agents; however severe cases may necessitate systemic therapy with griseofulvin, itraconazole or terbinafine.[1][9] Treatment of human cases also requires the identification and elimination of the infectious reservoir, which typically involves the investigation and treatment of colonized animals and the elimination of infected bedding and other environmental reservoirs.[10]
Habitat
Despite its species name ("canis" implies dogs), the natural host of M. canis is the domestic cat. However this species can colonize dogs and horses as well. In all cases, it resides on the skin and fur.[10][13] Microsporum canis may also persist as dormant spores in the environment for prolonged periods.[10]
Geographic distribution
Microsporum canis species have a worldwide distribution.[1][3] Extremely high occurrence has been reported in Iran, while lower incidence is associated with England and Scandinavian countries, as well as South American countries.[3] Microsporum canis is uncommon in some parts of US and Europe, and is completely absent from equatorial Africa.[4]
References
- ^ PMID 24635009.
- ^ ISBN 978-0-89863-157-9.)
{{cite book}}
: CS1 maint: multiple names: authors list (link - ^ ISBN 978-0-7216-2444-0.
- ^ a b c d e f g h i j k l m n o p q Rebell, Gerbert; Taplin, David; Blank, Harvey (1964). Dermatophytes: recognition and identification. Miami, Florida: self published.
- ^ a b c d e f g h i j k l Bodin E. (1902). Les champignons parasites de l'homme (in French). Paris, France: Masson et Cie. p. 137.
- ^ PMID 15450196.
- ^ Summerbell, Richard C. "What is the evolutionary and taxonomic status of asexual lineages in the dermatophytes?". Studies in Mycology. 47: 97–101.
- PMID 16702098.
- ^ PMID 7070401.
- ^ .
- .
- ^ Caddell, Jeremy R (2002). "Differentiating the dermatophytes". CLINICAL PRACTICE: MICROBIOLOGY. Clinical Laboratory Science. pp. 15(1):13. Retrieved 2 January 2010.
- ^ PMID 17893177.
- PMID 19457268.
- PMID 15283801.