Microsporum gypseum is a type of fungus known as a dermatophyte, which means it thrives on keratin, the protein found in skin, hair, and nails. It is a relatively common cause of ringworm, or tinea, infections in both people and various animal species globally. This organism is classified as a geophilic fungus, indicating that its natural and primary home is the soil, where it breaks down organic material. The ability of M. gypseum to act as a pathogen for mammals makes it a significant microorganism to understand for public and veterinary health.
Identifying Microsporum gypseum
M. gypseum is distinct from other dermatophytes because of its geophilic nature, meaning it primarily lives in the earth. This differs from anthropophilic species that transmit human-to-human or zoophilic species that prefer an animal host. M. gypseum can survive in the soil for extended periods, retaining its ability to cause infection.
It tends to flourish in warm, humid environments where soil moisture is sufficient for growth. Exposure often occurs through direct contact with contaminated soil, such as during gardening, agricultural work, or outdoor play. People who work closely with the earth, like farmers or children, are more susceptible to picking up the spores. Infected animals, which are often asymptomatic carriers, can also transmit the fungus from the soil to humans.
Clinical Manifestations in Humans and Animals
In humans, infection with M. gypseum most commonly presents as Tinea corporis (ringworm of the body) or Tinea capitis (ringworm of the scalp). Tinea corporis typically appears as single or multiple round to oval lesions on the skin. These lesions are generally reddened (erythematous), with scaly patches in the center and well-defined, slightly raised borders that may contain vesicles.
A distinguishing feature of M. gypseum infection is its tendency to provoke a more intense inflammatory response compared to other dermatophytes. This heightened inflammation can sometimes lead to pustular lesions or be mistaken for other skin conditions, such as impetigo or eczema, delaying correct diagnosis. When the scalp is affected, Tinea capitis often results in inflamed, sometimes pustular patches with broken hairs, which can lead to scarring and permanent hair loss (kerion formation).
The clinical presentation in domestic animals, such as dogs and cats, involves similar signs of dermatophytosis. They may exhibit patches of hair loss, scaling, or crusting, often seen on the head, paws, or ears. M. gypseum often causes a more noticeable inflammatory reaction in animals. Infected pets can serve as a reservoir, potentially transmitting the fungus to humans, even if their own symptoms are mild.
Diagnosis and Confirmatory Testing
Diagnosis begins with a physical examination, followed by collecting a sample of the infected tissue, such as a skin scraping or plucked hair. A common initial laboratory procedure is a Potassium Hydroxide (KOH) preparation. The sample is treated to dissolve cellular debris, allowing fungal elements (hyphae and spores) to be visible under a microscope.
For definitive identification, the sample is sent for fungal culture on a specialized medium. M. gypseum is known for its rapid growth, often developing a powdery or granular colony. The colony color is typically white to buff, sometimes having a cinnamon tone, which aids in preliminary identification. Microscopically, the fungus is characterized by abundant, spindle-shaped macroconidia, which are thick-walled and divided into four to six internal cells.
Unlike some other Microsporum species, M. gypseum typically does not fluoresce under a Wood’s lamp (a common diagnostic tool using long-wave ultraviolet light). Confirming the species requires the combination of the macroconidia’s specific morphology and the culture’s macroscopic appearance. Accurate laboratory identification prevents misdiagnosis and ensures the correct treatment is prescribed.
Effective Treatment Strategies
Treatment for M. gypseum infection is determined by the location and extent of the disease. Localized skin infections, such as small patches of Tinea corporis, are managed with topical antifungal creams or ointments. These agents, including medications like terbinafine or imidazole derivatives, are applied directly to the affected area. Treatment is often continued for at least four weeks to ensure complete eradication.
More widespread skin infections, or any case involving the scalp (Tinea capitis), require systemic therapy with oral antifungal medications. Systemic treatment is necessary because the fungus invades the hair shaft, making topical medication ineffective. Common oral treatments include Griseofulvin, Terbinafine, or Itraconazole, which circulate through the bloodstream to reach the infection site.
The duration of oral medication varies but continues until two consecutive fungal cultures, taken at one to two-week intervals, are negative for growth. Preventing reinfection is important since M. gypseum originates in the soil. This involves concurrent environmental decontamination, such as washing contaminated clothing and bedding, and cleaning tools or surfaces. Treating any infected pets is also necessary to break the cycle of transmission.