Fungal, viral, and parasitic skin infections
Fungal infections (dermatophytoses)
Fungal, or mycotic, infections, such as tinea pedis (athlete’s foot), tinea cruris (jock itch), and tinea corporis (ringworm), are extremely common. These pathogens infect the keratinized outer layer of the skin, and can also involve hair and nails, typically causing little inflammation in the underlying skin. The fungus invades the skin where it has been damaged or is consistently moist. All of these lesions are pruritic and characterized by a distinct border with scaling areas that have a clear center. Secondary bacterial infections may occur with excoriation.
The provider typically diagnoses a fungal infection by noting how the skin looks and the patient’s complaints of pruritus. The skin may be scraped to obtain cells for examination under a microscope, and sometimes the provider may order a skin culture, in which a suspicious area is swabbed or scraped using sterile technique. The sample is sent to the laboratory for analysis. Treatment consists of topical antifungal agents, such as clotrimazole (Lotrimin), ketoconazole (Nizoral), econazole, or nystatin (Mycostatin). Antibiotics may be necessary if a secondary infection occurs. Because mycotic infections thrive in dark, moist areas, the patient should be advised to keep the site clean and dry and to wear loose clothing if possible. All types of dermatophytoses can become chronic infections if not managed carefully.
Tinea unguium, or onychomycosis, is a fungal infection of the toenails and fingernails. Unlike athlete’s foot, which occurs on the skin’s surface, nail fungus lives in the nail bed and the nail plate. The nail provides the fungus with an extremely well-protected place to live - topical antifungals can’t penetrate the nail plate to reach the infection, which is why nail fungus is especially difficult to treat and typically requires oral rather than topical medication. The primary sign of nail fungus is the appearance of the nail, which turns yellow, white, or opaque. The texture also changes, and the nail becomes thick and brittle. If the fungus has been present for a long time, the nail can become twisted or distorted. The most effective treatment for nail fungus is oral terbinafine hydrochloride (Lamisil) or itraconazole (Sporanox); both inhibit the production of fungal cells. However, the drug must be taken for 6 weeks to treat fungal infection of a fingernail and for 12 weeks for infection of a toenail; treatment carries the risk of liver complications.
Viral infections
Infections in the integumentary system can also be caused by viruses. The following sections discuss the common viral infections of the integumentary system.
Warts
Warts, or verrucae, are caused by the human papillomavirus (HPV). Infection with HPV results in hyperplasia of the epidermis and a raised, cauliflower-like appearance. Verrucae can develop anywhere, but the most common sites are the fingers and the soles (plantar warts). Most warts resolve over time, but they can be treated with topical chemicals, excised surgically, vaporized with lasers, or removed with cryosurgery.
Herpes simplex (cold sores)
Cold sores, or fever blisters, are caused by herpes simplex virus type 1 (HSV-1). The initial infection may be asymptomatic or may cause painful ulcers along the gum lines of the mouth or on the lips. After the primary infection, the virus remains dormant in the trigeminal nerve and can be reactivated by exposure to the sun or cold, by the presence of another infection such as an upper respiratory infection, or when the patient is under stress. The patient reports a feeling of burning, tingling, or numbness before the eruption of vesicles. The blisters heal in 2 to 3 weeks, but the process may be sped up by the use of topical antiviral drugs, such as acyclovir (Zovirax), docosanol (Abreva), or penciclovir cream (Denavir), or with oral antivirals, including famciclovir (Famvir), acyclovir, or valacyclovir (Valtrex). If started at the first indications of a cold sore, antiviral medications can limit the duration and severity of the outbreak.
Parasites
Parasitic infestations of the skin can occur at any age. They are spread in group settings, such as among families or childcare groups, school classes, nursing homes, prisons, and dormitories. The two most common types of skin parasites seen are scabies (itch mites) and pediculosis (lice). Both parasites infect the skin and cause itching. Both parasites can be treated, and the infection resolved.
Scabies is caused by the itch mite Sarcoptes scabiei. This little mite burrows under the skin, causing intense itching.
Pediculosis is caused by lice that populate three specific areas of the body. A person can have head lice (Pediculus capitis), body lice (Pediculus corporis), or pubic lice or crabs (Pthirus pubis). Lice crawl but cannot fly or hop.
Both itch mites and lice can move from person to person through close physical contact and sharing of inanimate objects or fomites, such as combs, brushes, clothes, and bedding.
The signs and symptoms of scabies and pediculosis are similar:
- Intense itching
- Tickling feeling as parasites move hair on the skin
- Lice: small red bumps on the skin and nits (eggs) attached to hair shafts on the scalp, body, or pubic hair
- Scabies: little burrows or tunnels can be seen under the skin; frequently in areas of the skin that fold, such as between fingers and toes, around the waist, in the armpits, and on knees and elbows
The key distinguishing sign between the two: scabies produces visible burrows in skin folds such as the finger webs, while lice leave nits cemented to individual hair shafts rather than burrowing under the skin.
Diagnosis of lice infestation is often done with a magnifying lens to see the lice and nits on hair. A Wood’s light, which produces UV light, can also be used to detect the nits. They look pale blue. For scabies, physical examination involves looking for characteristic burrows under the skin. The provider may scrape the skin and examine it under the microscope to look for eggs. Prescription shampoo, body wash, and lotion can be used to kill the parasites on the head, hair, and body. The lice and mites are generally killed quickly, but the patient must follow all instructions to make sure eggs are also killed. There may be some itching after the parasites are killed, but that does not necessarily indicate a continued infection. Women who are pregnant and the parents of infants should consult their provider before applying antiparasitic products. They are strong chemicals that may cause complications for the very young and pregnant women.
In addition to properly washing the hair and body, all clothing, bedding, personal items, and furniture should also be cleaned with hot, soapy water. If all the eggs are not removed, reinfections can occur.