View source for Biology:Trichophyton tonsurans

{{Short description|Species of fungus}}
{{Taxobox
| image = File:Ttonsurans011.jpg
| regnum = [[Biology:Fungus|Fungi]]
| divisio = [[Biology:Ascomycota|Ascomycota]]
| classis = [[Biology:Eurotiomycetes|Eurotiomycetes]]
| ordo = [[Biology:Onygenales|Onygenales]]
| familia = [[Biology:Arthrodermataceae|Arthrodermataceae]]
| genus = ''[[Biology:Trichophyton|Trichophyton]]''
| species = '''''T. tonsurans'''''
| binomial = ''Trichophyton tonsurans''
| binomial_authority = Malmsten (1848)
}}

'''''Trichophyton tonsurans''''' is a [[Biology:Fungus|fungus]] in the family [[Biology:Arthrodermataceae|Arthrodermataceae]] that causes ringworm infection of the scalp. It was first recognized by David Gruby in 1844.<ref name=price1952/> 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 (particularly in children) whereas the ''T. equinum''-type, as its name implies, is associated with horses as a regular host.<ref name=graser/> Phylogenetic relationships were established in isolates from Northern {{wipe|Brazil}}, through fingerprinting [[Biology:Polymorphism#Genetics|polymorphic]] RAPD and M13 markers. There seems to be lower genomic variability in the ''T. tonsurans'' species due to allopatric divergence.<ref name=sidrim/> Any phenotypic density is likely due to environmental factors, not genetic characteristics of the fungus.<ref name=sidrim/>

==Colony morphology==
[[File:T_tonsurans_colony_800.jpg|thumb|alt=Powdery, sulfur-coloured fungal colony with mahogany brown underlying mycelium.|Colony of ''Trichophyton tonsurans'' from scalp scraping cultured on Sabouraud's dextrose agar with cycloheximide, chloramphenicol and gentamicin (7 d)]]''Trichophyton tonsurans'' may be identified through analysis of its fast-growing colonies.<ref name=kane1997/> Colonies tend to be flat, powdery, and yellow with a reddish undercolour. It develops into a folded colony, and may vary in colour from off-white to grey, with dark pigments that may diffuse into the medium.<ref name=rebell1964/> The younger colonies fluoresce green on Sabouraud's agar,<ref name=rebell1964/> and are also flat, but are mahogany red or lemon-yellow coloured.<ref name=kane1997/> On this agar the fungus grows peripherally and develops into a flatter, creamy disk with raised edges.<ref name=price1952/> ''Trichophyton tonsurans'' also produces many inflated, pear-shaped microconidia, borne on matchstick-like stalks. It also forms fewer macroconidia that are 4-6 cells long, with thick cell walls.<ref name=kane1997/>

A different simple method for identification at early stages is through the detection of [[Biology:Chlamydospore|chlamydospore]]-like structures (CLS), which are found on the reverse side of the culture under light microscopy. Chlamydospores are asexual spores that are created through hyphal modification, often with thick cell walls arising from the deposition of [[Chemistry:Hydrophobic|hydrophobic]] materials along the original cell wall.<ref name=mochi/> After inoculation on culture media (such as commonly used Mycosel agar), mycelia extend into the media and create the CLS. Normally, strains will produce CLS regardless of the media it is grown on.<ref name=mochi/> CLS growth is essentially unaffected by [[Chemistry:Antibiotic|antibiotic]] treatment with [[Chemistry:Chloramphenicol|chloramphenicol]], as well as by [[Chemistry:Cycloheximide|cycloheximide]].<ref name=mochi/> After 5 days of incubation, CLS production will be evident, suggesting the fungus is highly likely to be ''T. tonsurans''.<ref name=mochi/>

Responses of ''T. tonsurans'' to different growth conditions and nutrient media is useful in aiding identification. For example, growth is enhanced in the presence of [[Physics:Thiamine|thiamine]],<ref name=rebell1964/> and this exogenous requirement for thiamine distinguishes ''T. tonsurans'' from similar species.<ref name=kane1997/> Since thiamine stimulates growth, ''T. tonsurans'' also displays this behaviour on [[Chemistry:Vitamin|vitamin]]-free, thiamine-supplemented [[Chemistry:Casamino acid|casamino acid]]s agar but the growth is more sparse, and subsurface growth is absent.<ref name=kane1997/> BCP-milk solids glucose agar can also be used as an indicator of this fungus. This medium turns from pale blue to purple in colour in 7–14 days of growth at {{convert|25|C|F}}. The colour change is due to an [[Chemistry:Alkaline|alkaline]] shift arising from the release of [[Chemistry:Ammonium|ammonium]] during protein hydrolysis.<ref name=kane1997/>

==Epidemiology==
''Trichophyton tonsurans'' causes [[Medicine:Tinea capitis|tinea capitis]] infection globally, but it is especially endemic in Latin America (especially northern {{wipe|Brazil}}),<ref name=sidrim/> Mexico, and [[Earth:Africa|Africa]].<ref name=kane1997/> Infections due to this species have become increasingly common in the United States and Canada since the 1980s as a consequence of changing patterns in global travel and immigration, and it is responsible for a majority of pediatric tinea capitis infections in the US.<ref name=sidrim/><ref name=rebell1964/>

The modes of dispersal are unclear, though it is associated with homes, schools and other institutions, and barbershops.<ref name=ilkit2007/> Transmission can occur through direct transfer, or through the use of shared resources and facilities such as pillows, couches, rugs, and pets, which should be thoroughly examined because they can be carriers of ''T. tonsurans''.<ref name=ilkit2007/> Children are most susceptible to Tinea capitis whereas adult infections more often manifest as [[Medicine:Tinea corporis|tinea corporis]].<ref name=kane1997/> This species is a major cause of family and institutional outbreaks because of its persistent nature in indoor environments, and its ability to be transmitted through asymptomatic carriers.<ref name=kane1997/>

==Pathophysiology==
Once the fungal infection has been contracted, it invades hairs and sporulates in the hair shaft, causing it to burst and curl, creating a black dot on the scalp.<ref name=rebell1964/> [[Medicine:Tinea capitis|Tinea capitis]] is the clinical disease, but it may also cause [[Medicine:Tinea corporis|Tinea corporis]], [[Medicine:Onychomycosis|onychomycosis]], and [[Medicine:Tinea pedis|Tinea pedis]].<ref name=rebell1964/> Cutaneous lesions due to ''T. tonsurans'' do not fluoresce under Wood's Lamp.<ref name=asawanonda/> Although some people may not show the symptoms of carrying ''T. tonsurans'', it has a distinctive manifestation. During pathogenesis, the fungus undergoes [[Biology:Protease|protease]] elaboration to hydrolyze structural proteins (such as the [[Biology:Keratin|keratin]] found in hair), and isolates show peak values between days 18–22 during the sporulation phase.<ref name=gokulshankar/>

There are potentially 23 genes that may have mechanistic roles of this skin infection, and 21 show significant differences in infection rates, especially among children. The genes are typically involved in leukocyte activation and migration, and formation and integrity of the [[Biology:Extracellular matrix|extracellular matrix]].<ref name=nenoff/> In molecular studies of its virulence, common target genes include CarbM14, CER, and Sub2, which encode the proteases [[Biology:Carboxypeptidase|carboxypeptidase]], ceraminidase, and [[Biology:Subtilisin|subtilisin]], respectively. Among other virulence-related [[Biology:Enzyme|enzyme]]s, ''T. tonsurans'' also produces [[Biology:Urease|urease]].<ref name=sidrim/>

This fungus has also been found to produce [[Chemistry:Melanin|melanin]], which may be phenotypically demonstrated through ''in vitro'' induction in [[Chemistry:Caffeic acid|caffeic acid]] media. Melanin acts as an [[Biology:Antioxidant|antioxidant]] molecule, providing protective properties to the fungus from damaging UV rays. Since it is endemic in sunny regions, the melanin production is perhaps crucial for survival.<ref name=sidrim/>

In early stages of infection, the lesion has a clear and raised border, although there is not much hair loss yet.<ref name=price1952/> However, as it progresses, infected hairs break off at the scalp surface and the scalp is eventually coated in a scaly layer, with short hair stubs remaining. Twisted hairs may be found in keratotic follicular papules that will be formed.<ref name=price1952/> The infection is often called "black dot ringworm" due to the small dark hair stubs that are found on the scalp.<ref name=gupta2000/> Inflammatory reactions are also quite common and can manifest as [[Medicine:Edema|edema]], [[Medicine:Abscess|abscess]],<ref name=price1952/> or highly inflammatory [[Medicine:Kerion|kerion]].<ref name=gupta2000/> Hair regrowth does occur, although some scarring may remain.<ref name=price1952/> Males have a tendency to show greater improvement in non-inflammatory presentation as well.<ref name=gupta2000/> Although there are several treatments available, tinea capitis often has no subjective symptoms, so people at risk for infection should still receive fungal examinations regularly.<ref name=sugita/>

==Treatment==

Treatment options include antifungal shampoo,<ref name=pomeranz/> systemic antifungals, or both. Oral therapy is indicated for complicated infections of those that fail to respond to topical treatment. Still, the use of selenium sulphide or [[Chemistry:Povidone-iodine|povidone-iodine]] shampoos greatly reduce fungal viability and may be helpful in person-to-person transmission.<ref name=ilkit2007/> Advancements have been made in detection of ''T. tonsurans'' in patients with Tinea capitis, using TaqMan [[Biology:Polymerase chain reaction|PCR]] assay and primers and probes designed to detect this fungus rapidly and specifically, excluding contaminating skin microorganisms.<ref name=sugita/>

==References==
{{Reflist|30em|refs=

<ref name=rebell1964>{{cite book|last1=Rebell|first1=Gerbert|last2=Taplin|first2=David|last3=Blank|first3=Harvey|title=Dermatophytes Their Recognition and Identification|date=1964|publisher=Dermatology Foundation of Miami|location=Miami, FL}}</ref>

<ref name=kane1997>{{cite book|last1=al.]|first1=Julius Kane ... [et|title=Laboratory handbook of dermatophytes : a clinical guide and laboratory handbook of dermatophytes and other filamentous fungi from skin, hair, and nails|date=1997|publisher=Star Pub.|location=Belmont, CA|isbn=978-0898631579}}</ref>

<ref name=price1952>{{cite journal|last1=Price|first1=Harold|last2=Taylor|first2=David R.|title=Trichophyton tonsurans (crateriforme) infection of the scalp|journal=California Medicine|date=1952|volume=76|issue=4|pmid=14925831}}</ref>

<ref name=ilkit2007>{{cite journal|last1=Ilkit|first1=Macit|last2=Demirhindi|first2=Hakan|title=Asymptomatic dermatophyte scalp carriage: laboratory diagnosis, epidemiology and management|journal=Mycopathologia|date=23 November 2007|volume=165|issue=2|pages=61–71|doi=10.1007/s11046-007-9081-0|pmid=18034369}}</ref>

<ref name=mochi>{{cite journal|last1=Mochizuki|first1=Takashi|last2=Anzawa|first2=Kazushi|last3=Sakata|first3=Yuichi|last4=Fujihiro|first4=Machiko|title=Simple identification of by chlamydospore-like structures produced in culture media|journal=The Journal of Dermatology|volume=40|issue=12|pages=1027–1032|doi=10.1111/1346-8138.12354|pmid=24304336|year=2013}}</ref>

<ref name=gokulshankar>{{cite journal|last1=Gokulshankar|first1=S|last2=Ranjitsingh|first2=AJA|last3=Venkatesan|first3=G|last4=Ranjith|first4=MS|last5=Vijayalakshmi|first5=GS|last6=Prabhamanju|first6=M|last7=Subashini|first7=S|title=Is moderation of protease production an adaptation of well-defined anthropization in dermatophytes?|journal=Indian Journal of Pathology and Microbiology|volume=53|issue=1|pages=87–92|doi=10.4103/0377-4929.59191|pmid=20090230|year=2010|doi-access=free}}</ref>

<ref name=sugita>{{cite journal|last1=Sugita|first1=T.|last2=Shiraki|first2=Y.|last3=Hiruma|first3=M.|title=Real-time PCR TaqMan assay for detecting, a causative agent of tinea capitis, from hairbrushes|journal=Medical Mycology|volume=44|issue=6|pages=579–581|doi=10.1080/13693780600717153|pmid=16966179|year=2006|doi-access=free}}</ref>

<ref name=gupta2000>{{cite journal|last1=Gupta|first1=A.K.|last2=Summerbell|first2=R.C.|title=Tinea Capitis|journal=Medical Mycology|date=March 2000|volume=38|issue=4|pages=255–287|pmid=10975696|doi=10.1080/714030949|doi-access=free}}</ref>

<ref name=pomeranz>{{cite journal|last1=Pomeranz|first1=AJ|last2=Sabnis|first2=SS|last3=McGrath|first3=GJ|last4=Esterly|first4=NB|title=Asymptomatic dermatophyte carriers in the households of children with tinea capitis.|journal=Archives of Pediatrics & Adolescent Medicine|date=May 1999|volume=153|issue=5|pages=483–6|pmid=10323628|doi=10.1001/archpedi.153.5.483|doi-access=free}}</ref>

<ref name=sidrim>{{cite journal|last1=Sidrim|first1=JJ|last2=Rocha|first2=MF|last3=Leite|first3=JJ|last4=Maranhão|first4=FC|last5=Lima|first5=RA|last6=Castelo-Branco Dde|first6=S|last7=Bandeira Tde|first7=J|last8=Cordeiro Rde|first8=A|last9=Brilhante|first9=RS|title=Trichophyton tonsurans strains from Brazil: phenotypic heterogeneity, genetic homology, and detection of virulence genes|journal=Canadian Journal of Microbiology|date=November 2013|volume=59|issue=11|pages=754–60|pmid=24206358|doi=10.1139/cjm-2013-0670}}</ref>

<ref name=nenoff>{{cite journal|last1=Nenoff|first1=P|last2=Krüger|first2=C|last3=Ginter-Hanselmayer|first3=G|last4=Tietz|first4=HJ|title=Mycology – an update. Part 1: Dermatomycoses: causative agents, epidemiology and pathogenesis.|journal=Journal der Deutschen Dermatologischen Gesellschaft|date=March 2014|volume=12|issue=3|pages=188–209; quiz 210, 188–211; quiz 212|pmid=24533779|doi=10.1111/ddg.12245|doi-access=}}</ref>

<ref name=asawanonda>{{cite journal|last1=Asawanonda|first1=P|last2=Taylor|first2=CR|title=Wood's light in dermatology.|journal=International Journal of Dermatology|date=November 1999|volume=38|issue=11|pages=801–7|pmid=10583611|doi=10.1046/j.1365-4362.1999.00794.x}}</ref>

<ref name=graser>{{cite journal|last1=Gräser|first1=Yvonne|last2=Scott|first2=James|last3=Summerbell|first3=Richard|title=The New Species Concept in Dermatophytes—a Polyphasic Approach|journal=Mycopathologia|date=14 May 2008|volume=166|issue=5–6|pages=239–256|doi=10.1007/s11046-008-9099-y|pmid=18478366|citeseerx=10.1.1.681.6863}}</ref>
}}

{{Mycoses}}
{{Taxonbar|from=Q5928559}}

[[Category:Arthrodermataceae]]

{{Sourceattribution|Trichophyton tonsurans}}