PORTUGUESE

MYCOLOGY - CHAPTER FOUR  

SUPERFICIAL MYCOSES 

Dr Errol Reiss Ph.D.
Research Microbiologist (retired)
Centers for Disease Control and Prevention
Atlanta, Georgia, USA

Dr Errol Reiss' contribution to this Section is written in his private capacity. No official support or endorsement by the Centers for Disease Control and Prevention, Department of Health and Human Services is intended nor should be inferred.

Dr Art DiSalvo
Emeritus  Director, Nevada State Laboratory
Emeritus Director of Laboratories, South Carolina Department of Health and Environmental Control

 

Superficial mycoses. The term “superficial mycosis” applies to diseases affecting the outermost layer of the skin (stratum corneum), or growing along hair shafts. The most common superficial mycosis is pityriasis versicolor, causing patches of hypo- or hyper-pigmentation of the neck, shoulders, chest, and back, and caused by lipophilic basidiomycete yeasts of the genus Malassezia.

Other superficial mycoses:

White piedra: soft, beige nodules on the distal ends of hair shafts (Trichosporon species),
Black piedra: small firm black nodules on the hair shaft (Piedraia hortae)
Tinea nigra: brown to black stain on the palm of the hand or sole of the foot (Hortaea werneckii.)
Clinical descriptions and microscopic morphology of these agents may be found in Veasey et al., 2017

Cutaneous mycoses, the dermatophytes (def: “skin fungi”.)
The dermatophytes are confined to grow on the non-living outer layers of the skin (stratum corneum), and only exceptionally invade living tissue. Unlike superficial mycoses, dermatophyte infections can be itchy, inflammatory, and affect the smooth skin, hair, and nails. There are three genera of dermatophytes: Microsporum, Trichophyton and, less commonly, Epidermophyton. Dermatophytes produce extracellular enzymes (keratinases) capable of hydrolyzing keratin.

Athlete’s Foot. This is general term, usually applied to dermatophytosis, but also to other infections and non-infectious conditions, singly or in combination, as follows (alphabetic order, not order of prevalence):

• Bacterial infection (erythrasma, Pseudomonas, staphylococci, streptococci.)
• Fungal infection (tinea pedis)
• Injury due to over-vigorous removal of peeling skin.
• Psoriasis, eczema, or keratolysis exfoliativa (excessive sweating and friction can cause the skin to exfoliate. Exposure to detergents and solvents also can cause exfoliation)
• Soft corns-- areas of white moist skin between the toes.

Dermatomycoses. Uncommon causes of cutaneous mycoses are fungi other than dermatophytes. Mold agents of nail infections, are Neoscytalidium, Scopulariopsis, Aspergillus spp., Fusarium spp. Candida albicans primary skin conditions (e.g.: diaper rash) also are considered dermatomycoses.

Skin manifestations of systemic or disseminated mycoses include blastomycosis, cryptococcosis, sporotrichosis, talaromycosis (formerly penicilliosis.)

DERMATOPHYTES AND DERMATOPHYTOSIS

Dermatophytosis (syn: ringworm, tinea) is a communicable skin disease of the non-living outer layer of the epidermis, the stratum corneum, and may invade hair and nails, caused by a group of hyaline molds in three genera: Microsporum, Trichophyton, and, less commonly, Epidermophyton.

These fungi break down keratin in skin, hair, and nails. They do not invade living tissue or, in hair, beyond the keratogenous zone. The classic skin lesion is ringworm -- circular with an active border, inflammation, scaling, and pruritus.

“Ringworm.” This term originated in the 15th century to describe any skin rash patterned in a ring formation. It is a misnomer because the etiology is fungal, not parasitic. In 1841, David Gruby, a Paris-based physician, described a fungus that is a cause of scalp ringworm and, from the 1850’s, ringworm was considered a fungal disease. This discovery was made even before dermatology was a recognized medical specialty. Scalp ringworm in children caused by Trichophyton tonusurans is sometimes called Gruby’s disease.

“Tinea” (def.: Latin, "larva" or "worm,") This refers to dermatophyte infections on particular body sites, not to genus and species of the causative agent! (Table 1). The ancient Romans associated skin lesions on humans with holes in wool blankets caused by the larvae of moths, the Tineidae.

The dermatophytoses are characterized by anatomic site-specificity according to genera. e.g.: Epidermophyton floccosum infects only skin and nails, but does not invade hair shafts and follicles. Microsporum spp. infect hair and skin, but do not involve nails. Trichophyton spp. may infect hair, skin, and nails.
 

 

TABLE 1. SUMMARY OF CLINICAL FORMS OF DERMATOPHYTOSIS, THEIR ECOLOGY, AND CAUSATIVE AGENTS
Tinea type	Body site	Causative Agent(s)
		Anthropophilic	Zoophilic	Geophilic
Barbae	Beard		T. verrucosum, T. mentagrophytes, M. canis
Capitis	Scalp	T. tonsurans, M. audouinii, T. schoenleinii (rare)	M. canis
Corporis	Smooth skin	T. rubrum/T. violaceumb, E. floccosum	M. canis	M. gypseum, M. nanumc
Cruris	Groin	As above
Imbricata	Smooth skin	T. concentricuma
Pedis	Feet	T. rubrum, T. interdigitale	T. mentagrophytes
T., Trichophyton, M., Microsporum, E, Epidermophyton,  a geographic restriction to South Sea Islands etc. b T. rubrum species complex c name change to Nannizzia nana   Reference: de Hoog et al., 2017

Figure 1
 Trichophyton rubrum. Colony Morphology, (S) surface; (R) reverse.
Photo credit: Jim Gathany CDC

Figure 2
T. rubrum microscopic morphology. Microconidia “Birds on a wire”
Photo credit: E. Reiss, CDC

Figure 3
Microsporum canis. Colony Morphology, (S) surface; (R) reverse.
Photo credit: Jim Gathany, CDC

  Figure 4
M. canis. Microscopic morphology: spindle-shaped thick-walled, multi-celled macroconidia (microconidia uncommon), lactofuchsin stain.
Photo credit: E. Reiss, CDC

  Figure 5
Epidermophyton floccosum. Microscopic morphology: macroconidia are oval to club-shaped, most with 2-4 septa, walls smooth, often in clusters of 2 or 3, microconidia absent.
Photo credit: Geraldine Kaminski Library, #163

ETIOLOGIC AGENTS
(Kidd et al., 2017)

There are 3 genera of dermatophytes:

Trichophyton species (14 species.)
As a group, these species infect skin, hair, and nails, but single species have anatomic site restrictions. They rarely cause subcutaneous infections and those occur in immuno-compromised individuals. Trichophyton spp. take 2 to 3 wks to grow in culture. Microconidia are the characteristic structures of the genus Trichophyton. Macroconidia, when present, are smooth, with thin-walls, septate (0-10 septa), and pencil-shaped. Colonies consist of loose aerial mycelium secreting pigments in a variety of colors.
 

Trichophyton rubrum
This most common cause of tinea corporis does not infect hair. It can rarely cause subcutaneous infections in immunocompromised individuals, such as patients with chronic myelogenous leukemia.

• Colony morphology (Figure 1). Flat to slightly raised, white to cream, suede-like with a pinkish-red reverse. The downy type has a yellow-brown to wine-red reverse.
• Microscopic morphology (Figure 2). Granular type: numerous clavate to pyriform microconidia formed evenly on hyphae, resembling “birds on a wire.” Moderate numbers of smooth, thin-walled multiseptate, pencil shaped macroconidia. It is the parent strain of downy type. The downy type has fewer microconidia, macroconidia usually absent

Trichophyton tonsurans
A major causative agent of tinea capitis in the U.S.

• Colony morphology.
  Vary in texture and color. Suede-like to powdery, flat with a raised center or folded, often with radial grooves. Color varies from buff to yellow, (the so called “sulfureum” form) to dark-brown. The reverse varies from yellow-brown to red-brown to mahogany.
• Microscopic morphology.
  Numerous microconidia along hyphae or on short conidiophores. Vary in size and shape from long clavate to broad pyriform, at right angles to the hyphae (“match stick” shape) and may enlarge into balloon forms. Occasional smooth, thin-walled, irregular, clavate macroconidia in some cultures.

Trichophyton interdigitale
This anthropomorphic species is a common cause of tinea pedis.

• Colony morphology.
  Flat, white to cream color, powdery to suede-like surface. Reverse is yellowish and pinkish brown, becoming red-brown with age.
• Microscopic morphology.
  Sub-spherical to pyriform microconidia, occasional spiral hyphae and spherical chlamydoconidia. Occasional slender, clavate, smooth-walled, multiseptate macroconidia

 

Microsporum species (3 species: M.canis, M. audouinii, M. ferrugineum). The genus Microsporum is identified by its macroconidia.

Microsporum canis is a common zoophilic dermatophyte species infecting smooth skin and hair of humans, nails rarely are affected. Scalp infections with this species are identified because infected hairs fluoresce bright green when illuminated with UV-emitting Wood's light.

• Colony morphology (Figure 3). Surface is loose, cottony, white to cream color; reverse usually a bright yellow, but may be non-pigmented.
• Microscopic morphology. Macroconidia large, spindle-shaped, multicelled, thick walls, and echinulate (spiny) often with a terminal knob (Figure 4); microconidia are uncommon.

Epidermophyton floccosum

This species infects skin and nails and rarely hair.

• Colony morphology. Suede-like surface, greenish-brown or khaki, often raised and folded in the center. Reverse is yellowish-brown.
• Microscopic morphology. No microconidia. Multiple smooth, club-shaped macroconidia, 2-6 cells, often in clusters of 2 or 3 ( Figure 5)
   

Geographic distribution: Dermatophytes occur worldwide, but some species are geographically limited. Dermatophytes causing human infections may have different natural sources and modes of transmission. Knowledge of the species of dermatophyte and source of infection are important for proper treatment control of the source. Invasion by zoophilic or geophilic species may cause inflammatory disease in humans (Table 2.)

• Anthropophilic – These spp. are usually associated with humans only; transmission from human-to-human is by close contact or through contaminated objects, e.g.: sharing caps and combs, contact by high school wrestlers (tinea gladiatorum.)
• Zoophilic - Usually associated with animals; transmission to humans is by close contact with animals (cats, dogs, cattle) or with contaminated products. Sometimes transmission is from human to human in outbreaks, or from human to animal, e.g.: child with tinea capitis or corporis spreading the infection to pet kitten.
• Geophilic – Species are found in the soil and are transmitted to humans by direct exposure.
   

Table 2. Classification of dermatophytes based on ecologic source and host response
	Geophilic	Zoophilic	Anthropophilic
Infection	Acute inflammation	Moderate inflammation	Non-inflammatory
Transmission	From environment	Animal -> Human Human <- Animal	Human-> Human
Resolution	Rapid	Self-limited outbreaks	Chronic

 

EPIDEMIOLOGY

Incidence and prevalence, risk groups, and factors

A survey of cutaneous fungal infections in the USA (1995-2004) was conducted from records of ambulatory clinic visits (Panackal et al., 2009.) Overall percentages of the type of dermatophytosis reported for this period were: tinea unguium--23.2%, whereas tinea corporis/manuum, tinea pedis, tinea capitis/barbae, and tinea cruris represented 20.4%, 18.8%, 15.0%, and 8.4%, visits respectively. In addition, 7.2% of visits were to diagnosis pityriasis versicolor.

In their study, Panackal et al., 2009, found the prevalence of tinea capitis in the African-American population was 12 times that among the white population. Of all tinea capitis cases, 85.6% occurred among children below 15-years-old. The southern USA showed a significantly higher proportion of visits (39.5% for tinea capitis than did other regions.

School-based screening is important to identify children requiring treatment for tinea capitis or for the carrier state (Hay 2017.) The last 10–20 years saw the spread of dermatophytes, especially Trichophyton tonsurans, in the Americas, Europe, and Africa. Changes in the epidemiology of tinea capitis are a rise of M. canis in some parts of Europe and the spread of T. tonsurans in urban communities in the USA, the UK, and France. Other areas affected in what could be described as an epidemic are South America and West Africa. Trends in tinea capitis are influenced by movement of populations, seen in rises in Trichophyton violaceum and Microsporum audouinii in countries previously not endemic. Persistence of tinea capitis in some communities challenges treatment and community infection control, but this infection is no longer regarded as a health priority.

Tinea cruris. Clinic visits in the USA during the1995 - 004 study period approximately 75% of cases were among males compared with females, with most infections among adults between 25-44 years of age.

Tinea pedis may be the most common dermatophytosis world-wide, affecting 70% of the population at some time. Risk factors are wearing occlusive shoes for long periods of time, such as in manual laborers, walking barefoot at community pools, in gym shower rooms, and those living in closed communities. Prevalence increases with age. The frequency of tinea pedis is several-fold higher among males than females.

Onychomycosis is the most common inflammatory disease of the nails, causing 15–40% of all nail disturbances. It includes tinea unguium, Candida, and those caused by non-dermatophyte molds. An estimated one-third of nail infections are acquired from local spread from tinea pedis, and 80% of these affect the big toes. Risk factors for tinea unguium and other fungal causes of onychomycosis include increasing age, peripheral vascular disease, trauma and excessive sweating. Fungal nail disease is more prevalent in persons with immunosuppressive conditions, diabetes, HIV/AIDS.

 

TRANSMISSION

Dermatophytosis is a communicable disease with fungal elements and/or conidia persisting on fomites like towels, bedsheets, caps, combs; and on surfaces like gym shower rooms. Outbreaks of tinea capitis, once very prevalent among poor children in early decades of the 20th century (Fox 1909) are seen today in pediatric refugees (Mashiah et al., 2016.) Asymptomatic adult carriers may be a source of tinea capitis in children. Another example is transmission between pets or livestock and humans.

DETERMINANTS OF PATHOGENICITY

Dermatophytes have a number of genes encoding proteinases. These secreted proteinases act at acidic and neutral pH. Endoproteinases produce large peptides, whereas exoproteinases release amino acids and short peptides. But proline containing peptides make up roadblocks, requiring a prolyl peptidase to act so that further proteolysis can occur (Gräser et al, 2018.)

An important characteristic of dermatophytes is that they utilize compact hard keratin as a nutrient source. But dermatophyte secreted proteinases are incapable of degrading hard keratin unless accompanied by the reduction of cysteine disulfide bridges, which are key to the resistant nature of keratin. During keratin degradation, dermatophytes excrete sulfite as a reducing agent, which cleaves disulfide bonds so that reduced keratin can be attacked by secreted proteinases. Sulfitolysis is an essential step in the digestion of compact keratinized tissues, which precedes the action of all proteinases.

  Figure 6
Kerion
Photo Credit: H.J. Shadomy, Ph.D

  Figure 7
Tinea corporis. Active border, central clearing.
Source: E. Reiss

  Figure 8
Tinea barbae Ringworm of the bearded areas face and neck syn.:“barber’s itch”. The infection occurs as a follicular inflammation, or as a cutaneous granulomatous lesion.
Source: CDC Public Health Image Library #4807

Figure 9
Tinea capitis “black dot ringworm” in scalp of a child caused by T. tonsurans original no. #9_1
Photo credit: Prof. Tadahiko Matsumoto, MD.

  Figure 10
Tinea pedis, intertriginal form caused by T. rubrum Shows scaling macerated skin between the toes.
Photo Credit: Geraldine Kaminski Library #309 and Drs G. Donald and D. Hill, Adelaide, S.A.

  Figure 11
Tinea unguium, distal lateral subungual (#730_3)
Photo credit: Prof. Tadahiko Matsumoto MD.

  Figure 12
Pityriasis versicolor caused by Malassezia species.
Photo credit: H.J. Shadomy, Ph.D.

CLINICAL FORMS

Dermatologists use the term “tinea” to refer to a variety of lesions of the skin, scalp, or nails.

Other terms used in dermatophytosis:

Kerion (Gr., kerion – honeycomb.)
In tinea capitis, or scalp ringworm, a large boggy swelling on the scalp, with ulcerated areas exuding pus, and accompanied by hair loss. May become secondarily infected with bacteria (Figure 6).

Please follow a link out to a case of kerion before and after griseofulvin therapy from Images in Clinical Medicine of the New Engl J Med (http://www.nejm.org/doi/10.1056/NEJMicm1514152?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dwww.ncbi.nlm.nih.gov&)

Favus.
A form of tinea capitis characterized by crusts, or “scutula,” that form along the hair shaft. They are composed of pus, from the infected follicle, combined with hyphae, spores and cell debris. May result in permanent balding (alopecia.) Favus is rare and is associated with Trichophyton schoenleinii hair invasion. (Reiss et al. 2012)

Tinea corporis.
Small circular lesions with active red border and central scaling. Lesions may occur anywhere on the smooth skin of the body (Figure 7)

Tinea barbae
Ringworm of the bearded areas of the face and neck (Figure 8).

Tinea capitis
Scalp. Three types of this infection are, gray patch, black dot, and favus. Black dot, caused by T. tonsurans, in its classic presentation, involves scaly patches of alopecia with hairs broken at the skin line (black dot form) and crusting (Figure 9). If left untreated it may progress to kerion -- boggy tender plaques and pustules. (Figure 6). Adults are known to harbor dermatophytes in their scalps in a carrier state.

Hair invasion in tinea capitis

• Ectothrix form of infection. Intrapiliary hyphae grow down towards the bulb of the hair. The common causes are Microsporum species. Fluorescence under Wood’s light (UV 365 nm) is present in most ectothrix infections. Ectothrix infections are usually scaly and inflamed. Hair shafts break off 2–3 mm or more above scalp level.
• Endothrix. This form is caused by T. tonsurans and members of the T. rubrum/violaceum complex of African origin and are fluorescent under Wood’s light. Hairs break at scalp level leaving stubs (black dot ringworm.)
• Favus. The favic type is caused by T. schoenleinii. Affected hairs are less damaged and may continue to grow. There are air spaces in the hair shafts with fungal hyphae forming large clusters at the base of hairs where they enter the follicle.

Tinea cruris
Tinea cruris or “jock itch” is a contagious infection of the groin, perineum and/or perianal area usually occurring in male adolescents and young men. The scrotum and penis are spared. Transmission is by fomites, or by autoinoculation of dermatophytes on the feet or hands. The differential diagnosis includes Candida intertrigo which affects the scrotum, has satellite lesions, and is red but without an active border.

Tinea pedis
Infection of toe webs and soles of feet, "Athlete's foot" (although this term also includes other causes of foot infection, see above)

Intertriginal (Figure 10)
Toe webs affected by erythema, maceration, fissuring, and scaling, often accompanied by pruritus.

Inflammatory/vesicular type
Painful, pruritic vesicles or bullae, most often on the instep or anterior plantar surface. Lesions can contain either clear or purulent fluid; after they rupture, scaling with erythema persists. Cellulitis, lymphangitis, and adenopathy can complicate this type of tinea pedis. May be more severe in diabetic persons.

Moccasin foot
Chronic hyperkeratotic tinea pedis. This type of tinea pedis presents as chronic plantar erythema with slight scaling to diffuse hyperkeratosis. It can be asymptomatic or pruritic. The term “moccasin tinea pedis”, refers to its moccasin-like distribution. Both feet are usually affected. Typically, the dorsal surface of the foot is clear. Scratching feet may result in the “two feet, one hand” presentation.

Tinea unguium (def.: a form of onychomycosis caused by dermatophytes) –
Nail infections. Seen mostly in adults, toenails are most often affected. This infection is chronic resulting in discoloration, thickening, raised and deformed nails. T. rubrum is frequently the causative agent. Tinea unguium is resistant to topical antifungal agents. Onychomycosis is classified in subtypes. Hay and Baron (2011) show illustrations of each type:

• Distal and lateral subungual (Figure 11): Subungual hyperkeratosis and onycholysis, yellow-white (or other color) longitudinal streaks and onycholytic areas in the center of the nail.
• Superficial: Patchy white (may be black) areas of infection on the nail surface originating under the proximal nail fold. Molds, other than dermatophytes, can present a deeper form of this type.
• Proximal subungual: Diffuse pattern or transverse striate pattern originating in the proximal nail plate moving slowly towards the outer edge as the nail grows. Secondary to paronychia. A range of fungi involved include dermatophytes (T. rubrum), Fusarium, C. albicans and Aspergillus spp.
• Endonyx: Nail is penetrated directly through the nail plate which has a white appearance, many fungi in the nail plate, with no subungual hyperkeratosis or onycholysis.
• Mixed patterns of the above types may occur. Total dystrophic onychomycosis: The end stage of a variety of subtypes; the nail plate crumbles the nail bed is thickened ridged, opaque.

Candidal onychomycosis. Candida albicans can infect the skin around the nail = paronychia. The undersurface of the nail may be colonized, with onycholysis of the nail plate. In patients with chronic mucocutaneous candidiasis or other immunodeficits several digits may be show oncholysis and paronychia.

Molds which are non-dermatophytes can cause nail infections. These molds, (except Neoscytalidium dimidiatum) do not digest keratin. Scopulariopsis brevicaulis, is a common causative agent. Other species include Acremonium spp., Aspergillus spp., Fusarium spp. and Onychocola canadensis. Non-dermatophyte molds may account for about 20% of onychomycosis in North America. Many of these molds do not respond to antifungal agents intended for dermatophytes or for Candida nail infections. Risk factors for non-dermatophyte mold nail infections are similar to those for dermatophyte causes of onychomycosis.

Tinea versicolor
Characterized by a blotchy discoloration of skin which may itch. Up to 25% of the general population may have this lesion at any one time. Diagnosis is usually possible by direct microscopic examination of KOH-treated skin scrapings which show a typical aspect of mycelia and spores described as "spaghetti and meatballs." Tinea versicolor is caused by Malassezia furfur (Figure 12).
 

• Tinea Capitis
  Topical therapy with ketoconazole-containing shampoo (Nizoral®) is effective against Trichophyton tinea capitis. Selenium sulfide (Selsun blue®) is another shampoo choice. Oral terbinafine is preferred therapy for T. tonsurans tinea capitis because it is well-tolerated, has a high cure rate, and is inexpensive. The kerion form caused by Microsporum spp. should be treated with griseofulvin. Delay in treating kerion risks scarring and permanent hair loss. Griseofulvin binds to newly produced keratin, forming a barrier to further invasion by the fungus. After treatment begins, a child may return to school but should avoid sharing caps, combs, brushes for 2 wks. Family members may be asymptomatic carriers, and treatment with fungicidal shampoo may be advisable (selenium sulfide or ketoconazole product.)
   
• Tinea corporis
  Old fashioned remedies consisted of Whitfield’s ointment (salicylic and benzoic acid) which stimulates sloughing of epidermal cells. Modern treatment consists of topical creams, lotions, gels, and shampoos containing azole antifungal agents, e.g.: clotrimazole, ketoconazole, or miconazole. High school wrestlers with the gladiatorum form of tinea corporis should be treated with topical antifungal agents for 72 h before returning to wrestle. Therapy for related superficial and cutaneous mycoses: intertriginous candidiasis is treated with nystatin powder. Pityriasis versicolor is treated with Selsun blue® or Nizoral® shampoos, terbinafine topical solution.
   
• Tinea unguium onychomycosis
  Mycologic cure is defined as a negative KOH prep and negative culture. Complete cure is defined as less than 5% of clinical involvement of the target toenail. Oral therapy is more effective than topical treatment of tinea unguium and the drug of choice is terbinafine which provides complete cure rates ranging from 44 - 46% (reviewed by Gupta et al. 2017.) Rarely, elevated serum aminotransferase and liver injury have been reported in patients taking oral onychomycosis therapies.

• Topical therapy
  Topical therapies for toenail dermatophytosis require good compliance for 6 mo to 1 year to achieve results. Cure rates are usually below 50% because the nail plate acts as a barrier to drug. In the U.S. three topicals approved for onychomycosis are: ciclopirox 8% nail lacquer (Ciclodan®, Penlac®), tavaborole 5% solution (Kerydin®), and efinaconazole 10% solution (Jublia®,) Lacquers are typically applied transungually to the dorsal and the ventral aspect of the nail plate.
   
• Mechanism of Action
  Efinaconazole has low keratin affinity and penetrates through the nail plate. Transungual and subungual routes of delivery are achieved with spreading around and under the nail plate. Tavaborole is a boron-containing compound that inhibits fungal growth by binding to leucyl-tRNA synthetase (LeuRS), an aminoacyl-tRNA synthetase (AARS.) Tavaborole binds the editing site of LeuRS, trapping tRNA and preventing DNA translation and protein synthesis (Gupta et al., 2015.) Ciclopirox and cyclopyrox olamine are hydroxypyridone compounds (6-cyclohexyl-1-hydroxy-4-methyl-2(1H)-pyridone.) The ethanolamine moiety, when present, does not add to the antifungal effect. In nail lacquers, ciclopirox is free acid whereas in other formulations it is ethanolamine salt. The principal mode of antifungal activity of ciclopirox olamine is due to iron chelation, which restricts the availability of iron to the fungal cell and consequently inhibits growth (Niewerth et al., 2003.)
   
• Clinical trial results
  Tavaborole. Follow-up from clinical trials of tavaborole in a sub-set of patients who had complete or almost clear nail after 48 wks of once-daily tavaborole were evaluated at week 60. Of 62 patients who completed post-treatment follow-up, cure was higher in the tavaborole-treated group versus placebo (28.6% vs. 7.7%. Treatment success was 53.1% for the tavaborole group versus 23.1% in the vehicle group. Tavaborole topical solution, 5%, appears to provide durable clinical benefit for dermatophyte-associated onychomycosis of the toenail (Gupta et al, 2018.)

Efinaconazole. Gupta and Studholme (2016) reported complete cure of 29.4% (40 out of 136 patients) after 48 wks of daily application of efinaconazole in patients with onychoymycosis and tinea pedis. In a larger phase III trial consisting of 993 non-diabetic patients a complete cure rate of 18.8% was achieved. Lower cure rates were observed in diabetic patients. Mycologic cure rates were higher (56%) than complete cure rates (18.8%.) Ciclopirox. Mycologic cure rates of 29-36% and clinical cure rates of 6-9% were achieved (reviewed by Gupta et al. 2017.)

Laser therapy for onychomycosis (Liddell and Rosen 2015).

Mechanisms proposed for laser action against fungi are (1) laser energy may be preferentially absorbed by fungal pathogens resulting in photothermal and photomechanical damage; or (2) damage resulting from the formation of free radicals by incident laser energy and light absorption by fungal pigment xanthomegnin, present in high concentration in Trichophyton rubrum. Most commonly the Nd: YAG 1064 nm laser is used. The 1064 nm wavelength passes into the nail bed heating fungal cells resulting in damage and growth inhibition.
Lasers received regulatory approval for “temporary cosmetic improvement” of onychomycosis, not as a fungicidal therapy for onychomycosis.

From 22 clinical studies with sufficient data to analyze, 13 studies reported clinical and mycologic cures in at least half of treated patients (Francuzik et al. 2016.) But small sample sizes enrolled, different study designs, with few sufficiently powered randomized controlled studies, make a conclusion of efficacy in laser treatment of onychomycosis difficult. A small number of studies report outcomes 12 mo after final laser treatment. Efficacy was reduced at final follow up with a significant number of relapses or recurrences. Most studies so far lack placebo or standard of care control groups, report different criteria clearance of nail debris, have small enrollments. Clinical benefit remains to be determined compared with other topical or systemic therapies. At this time laser therapy results in a low number of adverse events and mild intensity but prolonged remission of symptoms remains to be demonstrated.
 

Photo credit: used by permission from Brian J. Harrington, Ph.D., M.P.H. Professor University of Toledo, Toledo, OH.

  Figure 14
Skin scrapings mounted in 0.1% Calcofluor White stain showing Microsporum canis. Epi-illumination UV light with supplementary 520nm barrier filter.
Photo credit: used by permission from Brian J. Harrington, Ph.D., M.P.H. Professor University of Toledo, Toledo, OH.

Specimen collection

• Nails are clipped for microscopic exam and culture. Clip a generous portion of the affected area including scrapings of subungual debris. Transfer to a black piece of paper or place in a sterile container (see medium selection below.)
• A tinea capitis sample can be taken by scraping the black dots (hairs broken off at the skin line). A Wood’s lamp is useful to collect these specimens if tinea capitis is due to Microsporum canis but hairs infected with Trichophyton tonsurans do not fluoresce. Scraping for direct examination is preferred including skin scales and hair stumps. Cut hairs are not suitable. Plastic toothbrushes may be used to brush scalps for culture when there is little obvious scaling.
• Skin scrapings are taken with a #15 scalpel blade or the edge of a glass slide directly onto a microscope slide or test tube. If specimens are to be stored, keep them at room temperature, as dermatophytes are sensitive to cold.

Direct examination by KOH prep. (Kelly 2012)

Skin scrapings and plucked hairs are examined in the microscope in a 10% KOH mount. Addition of Calcofluor (CFW, a fluorescent brightener) can increase sensitivity of detection, but requires a fluorescence microscope (Figures 13, 14.)

Place two drops of 10% KOH on the specimen, followed by a coverslip. (Optionally, add 1 or 2 drops of Calcofluor white reagent, mix, and then coverslip) If it does not clear rapidly, place slide in petri plate and allow to stand 10 min. For tissue or scrapings, place the slide on 35oC bench top heat block for 15-20 min. (For KOH-Calcofluor, examine under fluorescent microscope.)

 

More Information

 

Observe under low power, then high-dry objective. (Take care because KOH can damage microscope lenses.)
KOH dissolves squamous cells leaving fungal elements intact. Dermatophytes show septate, branching hyphae of even diameter, chains of rectangular arthrospores (arising from fragmented hyphae.) Up to 35% of dermatophyte-infected nails fail to grow in culture, so microscopy is important in making the diagnosis. False-negatives may be caused by inadequate specimen size. False-positives occur when hair shafts or clothing fibers are mistaken for hyphae. These artifacts are larger than hyphae, not segmented, nor branched.

Media for growth

Consult the Difco and BBL Manual of Microbiological Culture Media Catalog for detailed descriptions of media
(https://www.bd.com/resource.aspx?IDX=9572)

Preferred media for growth of dermatophytes are Inhibitory Mold Agar, Potato Dextrose agar. These media are superior to the commonly used Sabouraud Dextrose Agar because they stimulate sporulation. Addition of antibiotics and cycloheximide suppress bacteria and saprobic fungi, but allow growth of dermatophytes. Pairing cultures in medium without cycloheximide is optional but facilitates recovery of fungi other than dermatophytes.

Dermatophyte test medium is an option. It contains papaic digest of soybean meal, glucose, phenol red (pH indicator), cycloheximide, gentamicin, and chloramphenicol. Dermatophytes produce typical morphology and a pink to red color in the medium around the colony within 10-14 d incubation.

Implant cutaneous specimens by gently pressing the samples into the agar surface of plate or slant tubes. One agar plate, or agar slant, should contain chloramphenicol and cycloheximide and another with chloramphenicol only (see recommended media, above). Incubate for 7-14 d at 26-30°C: Plates in an inverted position (agar side up) with increased humidity and slant tubes with caps loosened to allow air to circulate.

Results

If direct microscopy was negative and there is no growth after 7 d, report as negative.

• If a dermatophyte grows it is reported, and then plates are kept at 26-30°C to identify it by colony and microscopic morphology. (If a slow grower like T. verrucosum is suspected, longer incubation is advised.)
• Negative cultures with positive microscopy can be reported after 7 d, but then reincubate an additional wk before discarding after 2 wks. Report again if a slow-growing dermatophyte is isolated.
• If there is no growth from a specimen after a fungus was seen by microscopic exam of the specimen, review the culture plate or slant for pin point colonies near the planted specimen using a dissecting microscope. Further detailed advice may be found in the reference: Public Health England 2016.
   

Patients infected with a dermatophyte may show vesicles, often on the hands, from which no fungi can be recovered or demonstrated. These lesions, which often occur on the dominant hand (i.e.: right-handed or left-handed), are secondary to immunologic sensitization to a primary (and often unnoticed) infection located somewhere else (e.g.: feet). These secondary lesions do not respond to topical treatment but will resolve after the primary infection is successfully treated.

References

Return to the Mycology Section of Microbiology and Immunology On-line

This page last changed on Friday, December 28, 2018
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