The pathogenesis of Tinea capitis due to Microsporum audouini and Microsporum canis. I. Gross observations following the inoculation of humans

Diagnosis and treatment of dermatophytosis in dogs and cats.: Clinical Consensus Guidelines of the World Association for Veterinary Dermatology

BACKGROUND

Dermatophytosis is a superficial fungal skin disease of cats and dogs. The most common pathogens of small animals belong to the genera Microsporum and Trichophyton. It is an important skin disease because it is contagious, infectious and can be transmitted to people.

OBJECTIVES

The objective of this document is to review the existing literature and provide consensus recommendations for veterinary clinicians and lay people on the diagnosis and treatment of dermatophytosis in cats and dogs.

METHODS

The authors served as a Guideline Panel (GP) and reviewed the literature available prior to September 2016. The GP prepared a detailed literature review and made recommendations on selected topics. The World Association of Veterinary Dermatology (WAVD) provided guidance and oversight for this process. A draft of the document was presented at the 8th World Congress of Veterinary Dermatology (May 2016) and was then made available via the World Wide Web to the member organizations of the WAVD for a period of three months. Comments were solicited and posted to the GP electronically. Responses were incorporated by the GP into the final document.

CONCLUSIONS

No one diagnostic test was identified as the gold standard. Successful treatment requires concurrent use of systemic oral antifungals and topical disinfection of the hair coat. Wood's lamp and direct examinations have good positive and negative predictability, systemic antifungal drugs have a wide margin of safety and physical cleaning is most important for decontamination of the exposed environments. Finally, serious complications of animal-human transmission are exceedingly rare.

Cutaneous, Subcutaneous and Systemic Mycology

The first description of dermatophytosis was recorded by Celsus, a Roman encyclopaedist who described a suppurative infection of scalp (‘porrigo’ or ‘kerion of Celsus’) in De Re Medicina (30 A.D.). Throughout the middle ages, several descriptions of dermatophytosis were produced where it is described as ‘tinea’. The keratin-destroying moths which made circular holes in the woollen garments are known as Tinea. Due to similarity in the structure of circular lesion of dermatophytosis on the smooth skin with the circular hole made by moth, Cassius Felix introduced the term ‘tinea’ to describe the lesions. In 1806, Alibert used the term ‘favus’ to describe the honey-like exudate in some scalp infections. However, the fungal aetiology of tinea was first detected by Robert Remak, a Polish physician who first observed the presence of hyphae in the crusts of favus. This detection is also a landmark in medical history because this is the first description of a microbe causing a human disease. He himself did not publish his work, but he permitted the reference of his observations in a dissertation by Xavier Hube in 1837. Remak gave all the credits of his discovery to his mentor Schoenlein who first published the fungal etiological report of favus in 1839. He observed the infectious nature of the favus by autoinoculation into his own hands and also successfully isolated the fungus later (1945) and named Achorion schoenleinii (Trichophyton schoenleinii) in honour of his mentor. In 1844, Gruby described the etiologic agent of tinea endothrix, later became known as Trichophyton tonsurans. The genus Trichophyton was created and described by Malmsten (1845) with its representative species T. tonsurans. Charles Robin identified T. mentagrophytes in 1847 and T. equinum was identified by Matruchot and Dassonville in 1898. Raymond Jacques Adrien Sabouraud (France) first compiled the description of Trichophyton in his book (Les Teignes) in 1910 which was based on his observation in artificial culture. The sexual state of dermatophyte was described by Nannizzi (1927). Emmons (1934) first reported the classification of dermatophytes based on vegetative structures and conidia. Gentles (1958) established the successful treatment of tinea capitis with griseofulvin.

Feline dermatophytosis: aspects pertinent to disease management in single and multiple cat situations

PRACTICAL RELEVANCE

Dermatophytosis (ringworm) is a superficial fungal skin disease of cats that, depending on the geographic region and practice caseload, may be encountered uncommonly through to commonly. This is a self-curing disease in an immunocompetent cat.

GLOBAL IMPORTANCE

Dermatophytosis is prevalent worldwide and is one of a number of zoonotic skin diseases that cat owners are at risk of contracting.

CLINICAL CHALLENGES

Dermatophytosis causes non-specific signs of hair loss, erythema and scaling, making it a differential diagnosis for many skin diseases of cats. The fact that this disease is infectious and contagious, and does not have any one classic clinical presentation, makes knowledge of diagnostic tools important in detection. The veterinarian's role is in early disease recognition and institution of appropriate therapy to hasten resolution of the disease.

AIM

The focus of this article is to provide an update and review of the most pertinent aspects that may be helpful in the management of dermatophytosis in any single or multiple cat situation.

EVIDENCE BASE

Where appropriate, evidence from the literature is used to supplement a summary of the author's clinical experience and research in feline dermatophytosis.

Adamson's Fringe, Horatio George Adamson, and Kligman's Experiments and Observations on Tinea Capitis

Adamson's fringe is located at the upper margin of the keratogenous zone of the hair follicle where the nucleated hair shaft cornifies completely and gets converted to hard anucleated keratin. It marks also the area of complete keratinization of the cuticle and Henle's layer of the inner root sheath and the beginning of the stem of the follicle. In Tinea capitis, dermatophytic infection of the hair shaft is restricted to this zone and the fungi do not penetrate further down the infected hair in the bulb of the follicle. The fungi in Adamson's words form “a fringe of mycelium surrounding the hair shaft and project below the lower margin of the sheath of spores around the root-stem.” Horatio George Adamson (1865--1955), a British dermatologist first described this phenomenon, in 1895, and this article describes Adamson's fringe with a short biography of Adamson and discusses Kligman's experiments and observations on Tinea capitis which validated the observations of Adamson and the concept of Adamson's Fringe and described the pathogenesis in Tinea capitis.

Medical experiments on humans and the development of guidelines governing them: the central role of dermatology

The advancement of medical science has come, at times, at the expense of patient comfort and dignity. Over the years, guidelines for human experimentation have become more defined and regulated, often after events in which researchers egregiously abused or neglected their subjects. From this specialty's very beginning, dermatologists have also been guilty of crossing these lines of professional behavior and ethics. Questionable studies sponsored and performed by some of dermatology's most esteemed names continued even into the late 20th century.

Tinea capitis: focus on African American women

Tinea capitis is a common cutaneous fungal infection in US school children, but adults may be carriers of tinea pathogens in the scalp. However, few cases of actual tinea capitis in adults have been reported in the literature. A retrospective analysis of all adult patients with positive scalp fungal cultures from June 1997 to March 2000 were reviewed. Seventy-nine cases of tinea capitis were identified. Nine (11.4%) were adults, 7 of whom were African American women, who were an average of 46 years old (range, 25 to 64 years). Three of these patients had prior exposure to a child with tinea capitis. These results suggest that tinea capitis affects adult African Americans, particularly women. Widespread scalp culture is indicated for papulosquamous disease and alopecia in this segment of the population.

Tinea capitis

Tinea capitis is dermatophytosis of the scalp hair follicles, generally producing inflammatory or noninflammatory alopecia. Infection occurs predominantly in prepubertal children older than 6 months, although infection can occur in all age groups. Tinea capitis is one of the most common infectious conditions in children, and it occurs worldwide.

International summit on cutaneous antifungal therapy, focus on tinea capitis, Boston, Massachusetts, November 11-13, 1994

This article reports the highlights of presentations made at an international symposium held on November 11-13, 1994, in Boston, Massachusetts, on the subject of cutaneous antifungal therapy. Some of the key points pertaining to the epidemiology, etiology, pathogenesis, presentation, and management of tinea capitis are discussed.

Cutaneous defenses against dermatophytes and yeasts

Predispositions to the superficial mycoses include warmth and moisture, natural or iatrogenic immunosuppression, and perhaps some degree of inherited susceptibility. Some of these infections elicit a greater inflammatory response than others, and the noninflammatory ones are generally more chronic. The immune system is involved in the defense against these infections, and cell-mediated immunity appears to be particularly important. The mechanisms involved in generating immunologic reactions in the skin are complex, with epidermal Langerhans cells, other dendritic cells, lymphocytes, microvascular endothelial cells, and the keratinocytes themselves all participating in one way or another. A variety of defects in the immunologic response to the superficial mycoses have been described. In some cases the defect may be preexistent, whereas in others the infection itself may interfere with protective cell-mediated immune responses against the organisms. A number of different mechanisms may underlie these immunologic defects and lead to the development of chronic superficial fungal infection in individual patients. Although the immunologic defects appear to be involved in the chronicity of certain types of cutaneous fungal infections, treatment of these defects remains experimental at the present time.

The dermatophytes

The etiologic agents of the dermatophytoses (ringworm) are classified in three anamorphic (asexual or imperfect) genera, Epidermophyton, Microsporum, and Trichophyton. Species capable of reproducing sexually belong in the teleomorphic genus, Arthroderma, of the Ascomycota. On the basis of primary habitat association, they may be grouped as geophilic (soil associated), zoophilic, and anthropophilic. Adaptation to growth on humans by most geophilic species resulted in diminished loss of sporulation, sexuality, and other soil-associated characteristics. The dermatophytes have the ability to invade keratinized tissue (skin, hair, and nails) but are usually restricted to the nonliving cornified layer of the epidermis because of their inability to penetrate viable tissue of an immunocompetent host. However, invasion does elicit a host response ranging from mild to severe. Acid proteinases, elastase, keratinases, and other proteinases reportedly act as virulence factors. The development of cell-mediated immunity correlated with delayed hypersensitivity and an inflammatory response is associated with clinical cure, whereas the lack of or a defective cell-mediated immunity predisposes the host to chronic or recurrent dermatophyte infection. Chronic dermatophytosis is mostly caused by Trichophyton rubrum, and there is some evidence that mannan produced by this fungus suppresses or diminishes the inflammatory response. Since dermatophytes cause a communicable disease, modes of transmission and control are discussed as well as a survey of recent trends in therapy. Collection of specimens, culture media, and tests for identification are also presented. Genetic studies have led to an understanding of incompatibility mechanisms, pleomorphism and variation, resistance to griseofulvin, and virulence. Molecular biology has contributed to our knowledge of the taxonomy and phylogenetic relationships of dermatophytes.

Tinea capitis: new perspectives on an old disease

Tinea capitis caused by Trichophyton tonsurans is a common infection in children, and has become a significant public health problem in the United States. Epidemics of tinea capitis occur both in families and in institutions such as schools and day care centers. Infection is often difficult to eradicate. Fomites and asymptomatic carriers likely contribute to the spread of the disease and to re-infection of treated patients. The morphology of tinea capitis is diverse, from seborrhea-like scaling to tender, inflammed nodules on the scalp. Because a lengthy course of systemic griseofulvin is required to treat this infection, management of tinea capitis can be challenging. As newer antifungal agents are developed, more effective and convenient therapy for tinea capitis may become available.

Tinea capitis: epidemiology, diagnosis, treatment, and control

Since the 1970s there has been a steady rise in the number of cases of tinea capitis in the United States, most of them caused by Trichophyton tonsurans. Although the infection is seen most frequently in black children, it can occur in white persons and can affect persons of all ages. Control of tinea capitis is difficult for several reasons, including subtle clinical infection, asymptomatic carriage of fungus, fomite spread, and the need for weeks to months of oral medications. Although griseofulvin remains the mainstay of therapy, preliminary studies of itraconazole and terbinafine suggest that these compounds may also be useful in the treatment of tinea capitis. Selenium sulfide shampoo, prednisone, and oral antibiotics are frequently used as adjunctive therapy. The role of fomites in the spread of tinea capitis has yet to be fully understood, as does the best means of decontamination.

Pathogenesis of hair infection and black dots in tinea capitis caused by Trichophyton violaceum: a histopathological study

The majority of tinea capitis in southern Taiwan occur in adult women and are caused by Trichophyton violaceum. We report the histopathological findings of a series of 10 cases of tinea capitis caused by T. violaceum, the largest such study to date. Our study provides new information regarding the process of hair infection, mechanism of black dot formation, and chronicity of infection caused by this fungus. The cuticle remains intact. The fungi enter the proximal cortex where the cuticle is immature. They then colonize the proximal keratinized cortex and generate septate hyphae which transform gradually into arthrospores as they are carried upwards by the growing hair. At the infundibular level, the hair cortex is almost completely replaced by spores and swells, impeding further exit of the growing hair and causing the already weakened hair to coil up inside the infundibulum, forming a black dot. In one patient who had infection for more than 20 years, there were changes suggestive of cyclic reinfection of the same follicles which might contribute to the chronicity of the infection.

Tinea capitis in adults

Scalp ringworm is unusual after puberty. Etiological, epidemiological and clinical data regarding cases of tinea capitis in the elderly observed over a period of 15 years are discussed and some explanations are given for the conditions which favoured the mycotic infection of the scalp in adults. This study underlines that tinea capitis in the elderly is usually characterized by very variable and often atypical lesions and that female preponderance in adult cases of scalp ringworm is striking and unexplained. Moreover, all the dermatophytes we isolated from scalp lesions in children can cause tinea capitis in adults.

Adherence of dermatophyte microconidia and arthroconidia to human keratinocytes in vitro

The early interaction, adherence, between dermatophyte conidia and human keratinocytes has been studied in vitro. Two spore forms were used: microconidia and arthroconidia produced in vitro. The adherence of spores from three dermatophyte species, Trichophyton rubrum, T interdigitale, and T quinckeanum, was investigated using keratinocyte suspensions from different skin sites. Time-dependent adherence was demonstrated for all fungi studied with maximum adherence occurring between 3 and 4 h. There were no significant differences in adherence rates between the organisms studied. An order of affinity was established between keratinocytes from different sites and significant differences were demonstrated in adherence of microconidia to skin cells derived from sole versus knee. No differences in adherence rates were demonstrated in atopics versus patients with chronic dermatophytosis and normals. Adherence was inhibited, but not abolished, by subinhibitory concentrations of ketoconazole, itraconazole, and griseofulvin. The interaction between microconidia, arthroconidia, and keratinocytes was verified with scanning and transmission electron microscopy.

Structural abnormalities of the hair shaft

Abnormalities of the hair shaft are varied and often confusing. They do require accurate recognition, which can be helpful in the diagnosis and management of a hair disorder, or in the detection of underlying disease. A reliable evaluation of hair shaft abnormality is dependent on familiarity with the vast structural variations in normal hair, the hair growth cycle, and the changes produced by weathering. These structural abnormalities can be congenital or acquired, and some are associated with hair fragility. The classification used here has the advantage of simplicity and is keyed to easy recognition of the abnormalities under the light microscope. The four major types of abnormality are fractures, irregularities, twisting, and extraneous matter affecting the hair shaft. The diagnostic features of the different hair shaft abnormalities are outlined.

Tinea capitis in Philadelphia

From 1962 to 1979, there was a dramatic change in tinea capitis infections in children in the Philadelphia area. This has been primarily due to the virtual disappearance of tinea capitis due to Microsporum organisms. This dramatic change in a common, highly infectious childhood disease is most likely due to a sudden change in hair styles, particularly in black boys, which prevents infectious spores from reaching the scalp.

Antifungal activity of dermatological shampoos

The effect of several "medicated" shampoos on the growth of a variety of fungi was determined. Shampoos with as low as 0.5% coal tar were inhibitory to all strains, 2.5% selenium sulfide and 1 and 2% zinc pyrithione were significantly more inhibitory. Since these shampoos have substantivity for the human scalp, they may be useful as adjunctive therapy to griseofulvin in the treatment of scalp infections and minimize the risk of spread of viable spores to others in the environment.

The areal extent of dermatophyte infection

After stripping with vinyl tape, dermatophytes may be cultured throughout the depth of the stratum corneum. In the present study skin strippings were used to investigate the horizontal spread of the dermatophyte infection. In five cases of tinea cruris and in twenty-two cases of tinea corporis, fungi could be cultured not only from the visible lesion, but in the majority of cases also from the normal-looking skin up to 6 cm from the margin of the lesion. No relationship could be found between the size and age of the lesion and the invasion of surrounding, normal-looking skin.

Experimental bovine Trichophyton verrucosum infection. Preliminary clinical, immunological and histological observations in primarily infected and reinoculated cattle

The cutaneous application of different doses of viable Trichophyton verrueosum to the unabraded skin of cattle of various ages resulted in clinically recognizable ringworm infection of varying extent and duration. Confluent lesions covering the whole inoculated area were produced by 10⁷viable units of the fungus, whereas the minimal infective dose of 10³ viable units produced limited areas of infection only. The level of nutrition within the limits imposed had no effect on the extent or severity of lesions. The fungus was found to invade the keratinized portions of skin and hair of cattle of all ages at the same rate. However, both the cutaneous inflammatory response and the resolution of lesions were most rapid in older animals. The ability to eliminate infection more rapidly was associated with a marked delayed hypersensitivity response commencing 14 days after infection. Such hypersensitivity was not detectable by this means after the resolution of lesions.

T. verrueosum could not be isolated in culture from skin lesions until 21 days after inoculation and could only be isolated for half the period that lesions were present. Cattle were resistant to cutaneous reinfection with viable T. verrueosum on previously infected or fresh skin sites at 2 months and at more than one year after the resolution of primary lesions. A mild delayed hypersensitivity response developed in every site within 48 hr. of reinoculation. The intravenous inoculation of previously-infected cattle with 10⁴viable units of T. verrueosum resulted in an immediate-type cutaneous reaction at the original site of infection.