Microsporum canis

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Microsporum canis
Mcanis036.JPG
Spindle-shaped, warted macroconidia of Microsporum canis
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Fungi
Division: Ascomycota
Class: Eurotiomycetes
Order: Onygenales
Family: Arthrodermataceae
Genus: Microsporum
Species:
M. canis
Binomial name
Microsporum canis
(E.Bodin) E.Bodin (1902)
Synonyms
  • Microsporum audouinii var. canisE.Bodin (1900)
  • Sabouraudites canis(E.Bodin) Langeron (1945)

Microsporum canis is a pathogenic, asexual fungus in the phylum Ascomycota that infects the upper, dead layers of skin on domesticated cats, and occasionally dogs and humans. [1] [2] The species has a worldwide distribution. [3]

Contents

Taxonomy and evolution

Microsporum canis reproduces by means of two conidial forms, large, spindle-shaped, multicelled macroconidia and small, single-celled microconidia. [4] [5] First records of M. canis date to 1902. [5] Evolutionary studies have established that M. canis, like the very closely related sibling species M. distortum and M. equinum, is a genetic clone derived from the sexually reproducing species, Arthroderma otae. [6] Members of Ascomycota often possess conspicuous asexual and sexual forms that can coexist in time and space. Microsporum canis exemplifies a common situation in ascomycetous fungi in which, over time, one mating type strain has undergone habitat divergence from the other and established a self-sustaining reproductive population that consists only of the asexual form. [3] It is hypothesized that asexual lineage of Microsporum canis evolved as a result of host-specific interactions, changes in ecological niche, as well as, geographic isolation of + and – mating types of Arthroderma otae, hence making it difficult to sustain sexual reproduction. [6] Early domestication of animals, such as cats and dogs, in Africa led to a later evolution of host-specific fungus, Microsporum canis, which is commonly associated with loose fur animals. [6] Nearly all reported isolates of Microsporum canis represent the "–" mating strain of A. otae. [6] [7] Together with two closely related taxa, M. ferrugineum and M. audouinii, the clade is thought to have an African center of origin. [8]

Morphology

Characteristic yellow, feathery colony of Microsporum canis photographed on a slope of Modified Leonian's agar after 7 days growth. Mcanis3220.jpg
Characteristic yellow, feathery colony of Microsporum canis photographed on a slope of Modified Leonian's agar after 7 days growth.

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. [3] Infection by this species can often be detected clinically using Wood's lamp, which causes infected tissues to fluoresce bright green [4] [9] Fluorescence is attributed to metabolite pteridine, which is produced by the fungus in actively growing hairs. [3] Infected hairs remain fluorescent for prolonged periods of time (over the years), even after the death of the fungus. [3] Despite the frequent use of Wood's lamp in the clinical evaluation of ringworm infections, diagnosis of M. canis requires the performance of additional tests given the potential for false positives. [10] Culture of the fungus is most commonly used to evaluate morphological and physiological parameters of growth, and confirm the identity of the agent. Growth of the fungus on Sabouraud's agar (4% glucose), Mycosel or rice medium characteristically yields the bright yellow pigment. Microscopic examination of the growth can show the presence of the typical, warted and spindle-shaped macroconidia, confirming the identity of the isolate as M. canis. [11] The In vitro hair perforation test, commonly used to differentiate many dermatophytes, is not particularly useful for this species as it reveals the formation of "pegs" that penetrate into hair shafts - a characteristic shared widely among many zoophilic species. [5] [12] Genetic analyses can be useful to establish the identity of atypical strains of M. canis; however the highly characteristic appearance of this species generally obviates the need for this more sophisticated method. [1] [13]

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. [4] Hence, animals, cats and dogs are believed to be the population hosts of this fungus, while humans are occasional hosts, in which the fungus can induce secondary infections. [4] Microsporum canis has been identified as a causal agent of a ringworm infection in pets, tinea capitis and tinea corporis in humans, children in particular. [2] [3] [5] [14] [15]

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 alopecia in the case of tinea capitis, while ringworm infections in pets produce characteristic inflammatory lesions, which may or may not result in hair loss. [3] This species has a propensity to cause subclinical infections in some animal species, particularly long-haired cats are frequent reservoirs of infection. [10] Isolation of the fungus from brushed pet hair can aid in detection of either an actively growing fungus or a passive carriage of fungal hyphae or arthroconidia. [10] In asymptomatic cases it is highly recommended to perform both Wood's lamp examination and microscopic analyses of suspected areas. [10] In the case of transient carriers, lack of clinical manifestations is accompanied with low number of M. canis colonies, number of which declines upon re-testing. [10]

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]

Related Research Articles

Dermatophyte is a common label for a group of fungus of Arthrodermataceae that commonly causes skin disease in animals and humans. Traditionally, these anamorphic mold genera are: Microsporum, Epidermophyton and Trichophyton. There are about 40 species in these three genera. Species capable of reproducing sexually belong in the teleomorphic genus Arthroderma, of the Ascomycota. As of 2019 a total of nine genera are identified and new phylogenetic taxonomy has been proposed.

<span class="mw-page-title-main">Tinea capitis</span> Cutaneous fungal infection of the scalp

Tinea capitis is a cutaneous fungal infection (dermatophytosis) of the scalp. The disease is primarily caused by dermatophytes in the genera Trichophyton and Microsporum that invade the hair shaft. The clinical presentation is typically single or multiple patches of hair loss, sometimes with a 'black dot' pattern, that may be accompanied by inflammation, scaling, pustules, and itching. Uncommon in adults, tinea capitis is predominantly seen in pre-pubertal children, more often boys than girls.

<span class="mw-page-title-main">Dermatophytosis</span> Fungal infection of the skin

Dermatophytosis, also known as tinea and ringworm, is a fungal infection of the skin, that may affect skin, hair, and nails. Typically it results in a red, itchy, scaly, circular rash. Hair loss may occur in the area affected. Symptoms begin four to fourteen days after exposure. The types of dermatophytosis are typically named for area of the body that they affect. Multiple areas can be affected at a given time.

<span class="mw-page-title-main">Kerion</span> Medical condition

Kerion or kerion celsi is an acute inflammatory process which is the result of the host's response to a fungal ringworm infection of the hair follicles of the scalp that can be accompanied by secondary bacterial infection(s). It usually appears as raised, spongy lesions, and typically occurs in children. This honeycomb is a painful inflammatory reaction with deep suppurative lesions on the scalp. Follicles may be seen discharging pus. There may be sinus formation and rarely mycetoma-like grains are produced. It is usually caused by dermatophytes such as Trichophyton verrucosum, T. mentagrophytes, and Microsporum canis. Treatment with oral griseofulvin common.

<span class="mw-page-title-main">KOH test</span> Test to differentiate between skin fungi

The KOH Test for Candida albicans, also known as a potassium hydroxide preparation or KOH prep, is a quick, inexpensive fungal test to differentiate dermatophytes and Candida albicans symptoms from other skin disorders like psoriasis and eczema.

<i>Trichophyton rubrum</i> Species of fungus

Trichophyton rubrum is a dermatophytic fungus in the phylum Ascomycota. It is an exclusively clonal, anthropophilic saprotroph that colonizes the upper layers of dead skin, and is the most common cause of athlete's foot, fungal infection of nail, jock itch, and ringworm worldwide. Trichophyton rubrum was first described by Malmsten in 1845 and is currently considered to be a complex of species that comprises multiple, geographically patterned morphotypes, several of which have been formally described as distinct taxa, including T. raubitschekii, T. gourvilii, T. megninii and T. soudanense.

<i>Trichophyton</i> Genus of Fungi

Trichophyton is a genus of fungi, which includes the parasitic varieties that cause tinea, including athlete's foot, ringworm, jock itch, and similar infections of the nail, beard, skin and scalp. Trichophyton fungi are molds characterized by the development of both smooth-walled macro- and microconidia. Macroconidia are mostly borne laterally directly on the hyphae or on short pedicels, and are thin- or thick-walled, clavate to fusiform, and range from 4 to 8 by 8 to 50 μm in size. Macroconidia are few or absent in many species. Microconidia are spherical, pyriform to clavate or of irregular shape, and range from 2 to 3 by 2 to 4 μm in size.

<i>Microsporum</i> Genus of fungi

Microsporum is a genus of fungi that causes tinea capitis, tinea corporis, ringworm, and other dermatophytoses. Microsporum forms both macroconidia and microconidia on short conidiophores. Macroconidia are hyaline, multiseptate, variable in form, fusiform, spindle-shaped to obovate, 7–20 by 30–160 um in size, with thin or thick echinulate to verrucose cell walls. Their shape, size and cell wall features are important characteristics for species identification. Microconidia are hyaline, single-celled, pyriform to clavate, smooth-walled, 2.5–3.5 by 4–7 um in size and are not diagnostic for any one species.

<i>Microsporum audouinii</i> Species of fungus

Microsporum audouinii is an anthropophilic fungus in the genus Microsporum. It is a type of dermatophyte that colonizes keratinized tissues causing infection. The fungus is characterized by its spindle-shaped macroconidia, clavate microconidia as well as its pitted or spiny external walls.

<i>Trichophyton tonsurans</i> Species of fungus

Trichophyton tonsurans is a fungus in the family Arthrodermataceae that causes ringworm infection of the scalp. It was first recognized by David Gruby in 1844. Isolates are characterized as the "–" or negative mating type of the Arthroderma vanbreuseghemii complex. This species is thought to be conspecific with T. equinum, although the latter represents the "+" mating strain of the same biological species Despite their biological conspecificity, clones of the two mating types appear to have undergone evolutionary divergence with isolates of the T. tonsurans-type consistently associated with Tinea capitis whereas the T. equinum-type, as its name implies, is associated with horses as a regular host. Phylogenetic relationships were established in isolates from Northern Brazil, through fingerprinting polymorphic RAPD and M13 markers. There seems to be lower genomic variability in the T. tonsurans species due to allopatric divergence. Any phenotypic density is likely due to environmental factors, not genetic characteristics of the fungus.

<i>Microsporum gypseum</i> Species of fungus

Microsporum gypseum is a soil-associated dermatophyte that occasionally is known to colonise and infect the upper dead layers of the skin of mammals. The name refers to an asexual "form-taxon" that has been associated with four related biological species of fungi: the pathogenic taxa Arthroderma incurvatum, A. gypsea, A. fulva and the non-pathogenic saprotroph A. corniculata. More recent studies have restricted M. gypseum to two teleomorphic species A. gypseum and A. incurvatum. The conidial states of A. fulva and A. corniculata have been assigned to M. fulvum and M. boullardii. Because the anamorphic states of these fungi are so similar, they can be identified reliably only by mating. Two mating strains have been discovered, "+" and "–". The classification of this species has been based on the characteristically rough-walled, blunt, club-shaped, multicelled macroconidia. Synonyms include Achorion gypseum, Microsporum flavescens, M. scorteum, and M. xanthodes. There has been past nomenclatural confusion in the usage of the generic names Microsporum and Microsporon.

Trichophyton concentricum is an anthropophilic dermatophyte believed to be an etiological agent of a type of skin mycosis in humans, evidenced by scaly cutaneous patches on the body known as tinea imbricata. This fungus has been found mainly in the Pacific Islands and South America.

Microsporum nanum is a pathogenic fungus in the family Arthrodermataceae. It is a type of dermatophyte that causes infection in dead keratinized tissues such as skin, hair, and nails. Microsporum nanum is found worldwide and is both zoophilic and geophilic. Animals such as pigs and sheep are the natural hosts for the fungus; however, infection of humans is also possible. Majority of the human cases reported are associated with pig farming. The fungus can invade the skin of the host; if it is scratched off by the infected animal, the fungus is still capable of reproducing in soil.

<i>Aphanoascus fulvescens</i> Species of fungus

Aphanoascus fulvescens is a mould fungus that behaves as a keratinophilic saprotroph and belongs to the Ascomycota. It is readily isolated from soil and dung containing keratin-rich tissues that have been separated from their animal hosts. This organism, distributed worldwide, is most commonly found in areas of temperate climate, in keeping with its optimal growth temperature of 28 °C (82 °F). While A. fulvescens is recognized as a geophilic fungal species, it is also a facultative opportunistic pathogen. Although it is not a dermatophyte, A. fulvescens has occasionally been shown to cause onychomycosis infections in humans. Its recognition in the laboratory is clinically important for correct diagnosis and treatment of human dermal infections.

<i>Microsporum gallinae</i> Species of fungus

Microsporum gallinae is a fungus of the genus Microsporum that causes dermatophytosis, commonly known as ringworm. Chickens represent the host population of Microsporum gallinae but its opportunistic nature allows it to enter other populations of fowl, mice, squirrels, cats, dogs and monkeys. Human cases of M. gallinae are rare, and usually mild, non-life-threatening superficial infections.

<span class="mw-page-title-main">Favus</span> Medical condition

Favus or tinea favosa is the severe form of tinea capitis, a skin infectious disease caused by the dermatophyte fungus Trichophyton schoenleinii. Typically the species affects the scalp, but occasionally occurs as onychomycosis, tinea barbae, or tinea corporis.

<i>Trichophyton verrucosum</i> Species of fungus

Trichophyton verrucosum, commonly known as the cattle ringworm fungus, is a dermatophyte largely responsible for fungal skin disease in cattle, but is also a common cause of ringworm in donkeys, dogs, goat, sheep, and horses. It has a worldwide distribution, however human infection is more common in rural areas where contact with animals is more frequent, and can cause severe inflammation of the afflicted region. Trichophyton verrucosum was first described by Emile Bodin in 1902.

<i>Epidermophyton floccosum</i> Species of fungus

Epidermophyton floccosum is a filamentous fungus that causes skin and nail infections in humans. This anthropophilic dermatophyte can lead to diseases such as tinea pedis, tinea cruris, tinea corporis and onychomycosis. Diagnostic approaches of the fungal infection include physical examination, culture testing, and molecular detection. Topical antifungal treatment, such as the use of terbinafine, itraconazole, voriconazole, and ketoconazole, is often effective.

Microsporum fulvum is a wildly-distributed dermatophyte species in the Fungi Kingdom. It is known to be a close relative to other dermatophytes such as Trichophyton andEpidermophyton. The fungus is common within soil environments and grows well on keratinized material, such as hair, nails and dead skin. It is recognized as an opportunistic fungal pathogen capable of causing cutaneous mycoses in humans and animals. Originally, the fungus was thought to be Microsporum gypseum until enhanced genetic examination separated the two as distinct species in 1963.

References

  1. 1 2 3 4 5 Shafiee, Shabnam; Khosravi, Ali Reza; Tamai, Iradj Ashrafi (2014). "Comparative study of Microsporum canis isolated by DNA fingerprinting". Mycoses. 57 (8): 507–512. doi:10.1111/myc.12189. PMID   24635009.
  2. 1 2 3 Kane, Julius; Summerbell, Richard; Sigler, Lynne; Krajden, Sigmund.; Land, Geoffrey (1997). Laboratory handbook of dermatophytes: a clinical guide and laboratory handbook of dermatophytes and other filamentous fungi from skin, hair, and nails. Belmont, CA: Star Pub. ISBN   978-0-89863-157-9.{{cite book}}: CS1 maint: multiple names: authors list (link)
  3. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Rippon, John Willard (1988). Medical mycology : the pathogenic fungi and the pathogenic actinomycetes (3rd ed.). Philadelphia, PA: Saunders. ISBN   978-0-7216-2444-0.
  4. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Rebell, Gerbert; Taplin, David; Blank, Harvey (1964). Dermatophytes: recognition and identification. Miami, Florida: self published.
  5. 1 2 3 4 5 6 7 8 9 10 11 12 Bodin E. (1902). Les champignons parasites de l'homme (in French). Paris, France: Masson et Cie. p. 137.
  6. 1 2 3 4 Kaszubiak, A; Klein, S; de Hoog, G.S; Graser, Y (2004). "Population structure and evolutionary origins of Microsporum canis, M. ferrugineum and M.audoinii". Infection, Genetics and Evolution. 4 (3): 179–186. doi:10.1016/j.meegid.2003.12.004. PMID   15450196.
  7. ↑ Summerbell, Richard C. "What is the evolutionary and taxonomic status of asexual lineages in the dermatophytes?". Studies in Mycology. 47: 97–101.
  8. ↑ Gräser, Y; De Hoog, S; Summerbell, RC (2006). "Dermatophytes: recognizing species of clonal fungi". Medical Mycology. 44 (3): 199–209. doi: 10.1080/13693780600606810 . PMID   16702098.
  9. 1 2 3 Ibolya, Torok; Simon, Gy; Pap, Maria (1982). "Microsporum canis infections in Hungary". Mykosen. 25 (1): 42–46. doi:10.1111/j.1439-0507.1982.tb02715.x. PMID   7070401.
  10. 1 2 3 4 5 6 7 8 Mignon, B.R; Losson, B.J (1997). "Prevalence and characterization of Microsporum canis carriage in cats". Journal of Medical and Veterinary Mycology. 35 (4): 249–256. doi: 10.1080/02681219780001231 .
  11. ↑ Abu-Samra, Muk.T; Imbabi, S.E; Mahgoub, El Sheikh (1975). "Microsporum canis infections in Calves". Sabouraudia. 13 (2): 154–156. doi:10.1080/00362177585190281.
  12. ↑ Caddell, Jeremy R (2002). "Differentiating the dermatophytes". CLINICAL PRACTICE: MICROBIOLOGY. Clinical Laboratory Science. pp. 15(1):13. Retrieved 2 January 2010.
  13. 1 2 Sharma, Rahul; Hoog, S.de; Presber, Wolfgang; Graser, Yvonne (2007). "A virulent genotype of Microsporum canis is responsible for the majority of human infections". Journal of Medical Microbiology. 56 (10): 1377–1385. doi:10.1099/jmm.0.47136-0. PMID   17893177.
  14. ↑ Wu Y, Yang J, Yang F, et al. (2009). "Recent dermatophyte divergence revealed by comparative and phylogenetic analysis of mitochondrial genomes". BMC Genomics. 10: 238. doi: 10.1186/1471-2164-10-238 . PMC   2693141 . PMID   19457268.
  15. ↑ Ginter-Hanselmayer G, Smolle J, Gupta A (2004). "Itraconazole in the treatment of tinea capitis caused by Microsporum canis: experience in a large cohort". Pediatr Dermatol. 21 (4): 499–502. doi:10.1111/j.0736-8046.2004.21419.x. PMID   15283801.
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