NAME: Epidermophyton floccosum, Microsporum spp., Trichophyton spp.
CHARACTERISTICS: These keratinophilic and keratinolytic ascomycetous molds are recognizable by their typical macrospora, which are also used to identify their genera (6). Macrspora are primarily distinguished by the thickness and roughness of their wall (7). Depending on the genera, they may have microconidia (Microsporum spp. and Trichophyton spp.) or they may not (E. flocossum). In the laboratory, they grow efficiently on Sabouraud dextrose agar, at 25˚C. Microsporum spp. and Trichophyton spp. have demonstrated the ability to produce a form that can accomplish meiosis (also known as a perfect form).
PATHOGENICITY/TOXICITY: Dermatophytosis can affect all keratinized areas of the body (hair, skin and nails) (2). Depending on the region that is affected, the symptoms may vary. If hair is infected (tinea capitis, tinea barbea), there may be hair loss (ectotrix) or breakage (endotrix). On the skin, lesions may look circular or annular and elevated, producing a ringworm infection form. Zoophilic dermatophyte infections are more inflammatory (vesicle, pustules and blisters) than those caused by antropophilic dermatophytes. Infection of human nails may present as discoloration, dystrophy, hyperkeratosis and occasionally onycholysis (2) . The disease is not fatal. The main effects are aesthetic and will persist until treated with the appropriate medication.
EPIDEMIOLOGY: This pathogen occurs worldwide and infections are relatively frequent (8). The main pathogen in northern Europe and North America is Trichophyton rubrum, and Microsporum canis. Zoophilic dermatophytes are more common in southern Europe and Arabic countries. Farm worker are more susceptible to infection with tinea barbea (9). In the case of tinea cruris, men are more susceptible than women. Tinea cruris is commonly associated with tinea pedis and occurs when ambient temperature and humidity are high.
HOST RANGE: The dermatophytes can infect all mammals and reptiles. Infection of birds is rare (1) . Some species are host-specific (10). Depending on the host and the site of the infection the form of the lesion may vary.
INFECTIOUS DOSE: Unknown
MODE OF TRANSMISSION: Direct or indirect contact with skin or scalp lesions of infected people, animals or fomites (i.e. floors, shower stalls, clothing, hairbrushes, etc. (8) ) contaminated with desquamated epithelium (9). In individuals with suppressed cell-mediated immunity, infection may occur via broken skin.
INCUBATION PERIOD: The incubation period is from several days to a few weeks, depending on the species and the host (9).
COMMUNICABILITY: They present a low to moderate communicability depending on species (11). For zoophilic species (i.e M. canis, M. equinum, M. gallinae, M. persicolor, T.equinum, T. mentagrophytes, T. sarkisovii, T. simmii and, T. verrucosum (1)), transmission occurs mostly between humans and animals, with limited human-to-human transmission (12). Antropophilic species are highly contagious between humans (13).
RESERVOIR: Common reservoirs include cat, dog, macaque, rabbit, sheep, human and soil (14). The dermatophyte's reservoir is often indicated by their nomenclature: animal (zoophilic), human (antropophilic), and soil (geophilic).
ZOONOSIS: Reported human dermatophytosis is often acquired from animals, usually from mammals and reptiles (1). Zoonosis from birds is rare but has been documented.
DRUG SUSCEPTIBILITY: Depending on the agent and the site of infection, the pharmaceutical susceptibility may vary (9). For tinea capitis, griseofulvin, or an oral azole drug (ketoconazole, itraconazole and voriconazole) are used, but treatment may require several months to be effective. For tinea corporis, tinea cruris, tinea pedis, tinea manuum and tinea faciei, there are a variety of effective topical treatments, including naftifine (1%), terbinafine (1%), butenafine (1%), chlotriminazole (1%), econazole (1%), ketoconazole (1%), miconazole (2%), oxyconazole (1%), sulconazole (1%), cyclopyrox (1%) and tolnaftate (1%). For nail infections, topical therapy normally fails and systemic oral therapy for many months is often required.
DRUG RESISTANCE: Resistance against ketoconazole has been shown by Microsporum gyseum, as well as against miconazole and clotrimazole in certain strains (15). Susceptibility of Trichophyton mentagrophytes has been decreasing against fluconazole, and possibly against ketoconazole and griseofulvin (16).
SUSCEPTIBILITY TO DISINFECTANTS: Dermatophytes are susceptible to phenolic compounds, formaldehyde, glutaraldehyde, iodophors and sodium hypochloride (1%) (17).
PHYSICAL INACTIVATION: The infectious substance can be inactivated by UV C (18), gamma (19) and microwave (aerosol) (20) radiation; moist heat (121°C for at least 20 min (21)); and dry heat (165-170°C for 2 hours).
SURVIVAL OUTSIDE HOST: This agent can survive on a variety of surfaces and mediums, including, but not limited, to sand, floors, shower stalls, clothing, and hairbrushes) (8). Water can also be a source of infection (contamination reported in public bath). Depending on the species, dermatophytes can survive up to twenty months on skin scales at room temperature (22). Most dermatophytes can survive in salt water (50% NaCl) for at least 52 weeks (23).
SURVEILLANCE: Monitor for symptoms (9) . Confirm infection using potassium hydroxide denaturation followed by microscopic examination of cultured scrapings from the head or by skin or nail biopsy.
Note: All diagnostic methods are not necessarily available in all countries.
FIRST AID/TREATMENT: Treat with appropriate fungicide as directed by a physician (9). The length of the treatment and the dosage will depend on the fungicide employed.
IMMUNIZATION: There are currently no vaccines available for humans. Commercial vaccines intended to prevent zoophilic infection are available for cattle, horses, cats and dogs (10) .
PROPHYLAXIS: None currently available, but some studies suggest silver nanoparticles as a prophylactic agent (24).
LABORATORY-ACQUIRED INFECTIONS: As of 1976, there were 161 reported cases of dermatomycosis, most frequently associated with T. mentagrophytes. Most were acquired through contact with naturally or experimentally infected laboratory animals (mice, rabbits, guinea pigs) and their bedding. Infections are rare by handling cultures (one case). Processing of clinical material has not been associated with laboratory infections (17) .
SOURCES/SPECIMENS: This pathogen can be found in keratinized tissues of infected human and animal hosts and medium contaminated by the tissue (1). It can also be found in the contaminated soil and on laboratory instruments (25).
PRIMARY HAZARDS: Contact with infected animals and their bedding or environment are primary hazards, along with institutions where communal hygiene activities occur. The cultured pathogen is an obvious hazard(14) .
SPECIAL HAZARDS: None
RISK GROUP CLASSIFICATION: Risk Group 2 pathogens (26). The risk group applies to the Microsporum spp. and Trichophyton spp. genus as a whole, and may not apply to every species within the genus.
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, and cultures. These containment requirements apply to the Microsporum spp. and Trichophyton spp. genus as a whole, and may not apply to each species within the genus.
PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable. Eye protection must be used where there is a known or potential risk or exposure to splashes (27).
OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC). The use of needles, syringes, and other sharp objects should be strictly limited. Additional precautions should be considered with work involving animals or large scale activities.) (27).
SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply suitable disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up (27).
DISPOSAL: All material should be decontaminated before disposal with steam sterilization, incineration or chemical disinfection (27).
STORAGE: Samples and biological material should be store in appropriately labelled and sealed containers (27).
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: July 2010
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada.
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Public Health Agency of Canada, 2010