Ringworm is actually a fungal infection known medically as tinea corporis or tinea circinata.1 Unfortunately, its common name may give patients the impression that it is similar to pinworm and contracted in a similar manner.
Etiology of Tinea Corporis
Various superficial infections are caused by a group of fungi known collectively as dermatophytes.2 The infections they cause are known as dermatophytoses. Dermatophytoses include tinea corporis (ringworm of the body), tinea pedis (athletes foot), tinea cruris (jock itch), tinea unguium (tinea of the fingernails), tinea manuum (tinea of the hand) and tinea capitis (ringworm of the scalp).
Many species of fungi can survive by digesting keratinous organic debris in soil. Those that decompose soil keratin in this manner are known as geophilic fungi. However, keratin is a protein also found in animal tissues. Apparently, certain fungi, known as zoophilic fungi, evolved the ability to parasitize the keratin in tissues of animals that have close contact with soil (e.g., cats, dogs, pigs, mice).
Keratin is also found in cornified human epidermis. Certain fungi can also invade human appendages that are rich in keratin, which accounts for their appearance on the skin, the nails and the hair. These anthropophilic fungi seldom penetrate more deeply than the uppermost layers of skin (the stratum corneum).3 Dermatophytic fungi infect humans and are placed into three genera, Epidermophyton, Trichophyton, and Microsporum. Some of these fungi retain the ability to digest keratin from multiple sources; thus, a person may contract a dermatophyte through contact with infected people, animals or soil.3
Transmission of Tinea Corporis Fungi
In America, several specific fungi commonly infect humans to produce tinea corporis. They include Trichophyton rubrum, Trichophyton mentagrophytes, Trichophyton tonsurans, and Microsporum canis.2 The three Trichophyton species may be transmitted through contact with an infected person (anthropophilic spread).
Microsporum canis is contracted through contact with an infected animal (e.g., cat or dog),2,4 and T. mentagrophytes can be transmitted in this manner as well. However, in one report, six neonates in an intermediate care nursery developed tinea corporis and/or capitis as a result of contact with a nurse infected with Microsporum canis.5
While several other fungi also cause tinea corporis, one deserves special mention. Microsporum gypseum infection is usually contracted through close contact with soil (e.g., gardening in freshly turned earth on ones bare knees).6
The clinical presentation provides clues to the route of transmission. Fungi that cause less severe inflammation are probably of anthropophilic origin (human contact). On the other hand, if the fungal infection is highly inflammatory, it is more likely to have been transmitted through contact with an infected animal or soil.1
Human-to-human contact occurs whenever people are in close proximity to one another. Day care centers are a common locus of infection.7 Infected fomites may also transmit the fungus.
Several papers have described an unusual method of transmission of tinea corporis. Outbreaks of tinea corporis have occurred in several athletic teams. In one example, ten members of a high school wrestling team in Alaska experienced active tinea corporis.8 Most lesions were located on the arms, trunk, head and neck, precisely matching the areas of closest contact with fellow wrestlers. Because there have been so many reports of such tinea spread among members of wrestling teams, the phenomenon is known as "tinea corporis gladiatorum."8-10
Epidemiology of Tinea Corporis
Age: Tinea corporis is more common in individuals who have not yet reached puberty.2
Family Contacts: Tinea corporis is commonly contracted from an infected family member. Often, the index case has tinea capitis, which can produce several cases of athletes foot or tinea corporis until it is properly treated.
Geographic Location: Dermatophytes thrive in warm and humid environments. For this reason, they are more common in tropical or subtropical geographic locations.1
Immunocompromised Status: Fungi that infect humans can be divided into two categories: pathogenic and opportunistic. The pathogenic fungi are capable of infecting patients who have normal immune status. Opportunistic fungi have lower virulence, are often commensal with humans, and require lowered immune competence or damaged epithelial tissues to produce clinical infection.11 Dermatophytic fungi are usually considered to be pathogenic, but some evidence of an opportunistic nature exists. For instance, a neutropenic patient exhibited patches and plaques on the buttocks and lower abdomen, attributed to Trichophyton rubrum.12 With continued lowering of the patients immune status, the lesions worsened and assumed an unusual presentation. Deep local invasion in these cases can produce granuloma or abscess formation.
Manifestations of Tinea Corporis
Tinea corporis commonly presents as a roughly oval or ring-shaped lesion. The outer margins may have vesicles, redness and scaling as the skin reacts to toxins and allergens. The affected skin responds to the infection by proliferating more rapidly, exhibiting an increased thickness.3 The center is often relatively normal in appearance, although it also may appear to be scaly. Without proper treatment, several lesions may grow together to form a large polycyclic lesion. Tinea corporis is commonly found on the face and extremities.7 Lesions may number from 1 to 18 or more.8 About one-half of patients report pruritus.
TINEA INCOGNITO AND TRICHOPHYTON CONCENTRICA
|Occasionally, the pharmacist is asked to examine
a patients skin and notices a strange lesion that does not resemble characteristic
forms of tinea. It may be tinea incognito, a result of incorrectly applying steroids
(e.g., nonprescription hydrocortisone) to a tinea infection. The ability of the steroid to
reduce inflammation allows the tinea to spread in an uncharacteristic manner.1
Should the patient have recently returned from travel to such areas as Papua New Guinea, Indonesia, Malaysia, Vietnam or the South Pacific, they may have encountered a common dermatophyte known as Trichophyton concentrica, which produces concentric scaly rings in clusters which may coalesce to involve most of the skin surface. Oral prescription medication is indicated.18
Physician Diagnosis of Tinea Corporis
If the pharmacist is unsure of etiology, the patient should be referred to a physician. The physician will confirm a fungal diagnosis by obtaining scale from a site of infection, preferably the active outer margin.3 Potassium hydroxide 10%15% is added to this material on a glass slide. Dimethyl sulfoxide may be added so that heating is not necessary. If a fungal infection is present, microscopically visible hyphae will appear on the slide. Alternatively, the fungi can be cultured with the use of Sabourads glucose agar.
Treatment of Tinea Corporis
Tinea corporis can be easily treated by the patient with various nonprescription antifungals. Proper treatment usually allows complete cure, although the organisms may infect lanugo hairs, in which case the condition can recur (known as recrudescence).13 In this case, prescription therapy may be necessary to eradicate the condition.
Allylamines: Two topical allylamines are available, naftifine (Naftin) and terbinafine (Lamisil). These broad-spectrum antifungals interfere with ergosterol biosynthesis. Because ergosterol is required for fungal cells to create new cell membranes, its unavailability disables fungal reproduction. Naftifine was demonstrated to be superior to clotrimazole in reducing redness, fissuring and pruritus.14
Ciclopirox Olamine (Loprox): This chemical is a broad-spectrum antifungal that disrupts synthesis of fungal cell membrane proteins when applied topically.14
Imidazoles: The nonprescription topical imidazoles include clotrimazole and miconazole and the related synthetic chemicals econazole (Spectazole), ketoconazole (Nizoral) and oxiconazole (Oxistat). Imidazoles also block biosynthesis of ergosterol through inhibition of cyto-chrome P-450 14-alpha-demethylase.13 They are effective when applied twice daily.15 However, ketoconazole is effective in a once-daily application.16
Tolnaftate: Tolnaftate is a nonprescription topical thiocarbamate.17 It inhibits synthesis of ergosterol in a growing dermatophyte.
Undecylenic Acid and the Undecylenate Chemicals: These nonprescription ingredients are effective when used topically in 10%25% total undecylenate concentration.2
Oral Therapy: Topical prescription therapy produces lower incidence of adverse reactions than oral medications and therefore is preferred for most cases of tinea corporis. However, the patient may have extreme inflammation caused by inoculation with a zoophilic dermatophyte such as T. verrucosum or M. canis. In these cases, the infection may also undergo more extensive spread due to multiple contacts with the animal by the patient. Oral therapy is preferred to help eradicate the fungus in these cases. Griseo-fulvin inhibits cell division of dermatophytic organisms.17 Levels in skin fall rapidly when the medication is discontinued, mandating sustained therapy for a complete cure. Ketoconazole is highly active against a broad spectrum of fungi when given orally. It often takes about four weeks of treatment with oral ketoconazole to cure tinea corporis. Such short-term oral ketoconazole therapy does not usually result in hepatotoxicity. However, therapy lasting for longer periods can result in liver damage.
A tinea infection will often appear as a round or oval-shaped lesion with an outer red margin. The inside of the lesion often appears to be healthy skin, while the outer margin is inflamed, red and scaly. The circular lesion gives the appearance that a worm is circling beneath the skin, accounting for the common name "ringworm." Actually, the outer ring is where the fungi are.
Pharmacists can often recognize tinea corporis and can suggest over-the-counter treatments. Some (Desenex Antifungal Ointment, Cruex) contain zinc undecylenate and/or undecylenic acid. Tolnaftate (Tinactin, Aftate) is also a popular ingredient. Clotrimazole is found in Mycelex OTC, Lotrimin AF Cream and Lotrimin AF Solution. Miconazole is found in Micatin products. Miconazole is also the ingredient in Lotrimin AF Spray Powder. All of these ingredients are safe and effective for tinea corporis when used as directed on their labels. Products containing salicylic acid and benzoic acid have no proof of efficacy and should be avoided.
Apply antifungal products in the morning and at nightideally after a shower or bath. Reapply the product after activities such as swimming or exercising, as it may no longer be present in amounts that would kill the fungi. If the condition fails to clear up in four weeks, stop using the product and see a physician. Topical antifungals should not be used on children younger than two years of age. Consult a physician if a young child appears to have a tinea infection.
If your tinea corporis clears after treatment but returns within a short period of time, you may not have treated it for a sufficient period of time to kill the fungus. Some people notice that their symptoms (itching, pain, cracked skin) resolve after several days. They then stop using the product. However, the fungus has just been beaten back a little and rebounds when the product is stopped. Thus, it is important to continue using the product as directed on the label. Other patients may properly treat the fungal infection of the skin, but be unaware of an infection on the nails or in the hair. Then they can reinfect healthy skin when they touch it. If you suspect that a fungal infection of the nails or hair is present, see a doctor. Nonprescription products cannot penetrate the hair follicles or nails to cure infections there.