This infection is usually grouped with other diseases caused by the poxviruses, but the virus is antigenically different. Atopic individuals appear to be especially prone to infection and in such persons lesions may be more numerous and difficult to eradicate.
Flesh-coloured, umbilicated papules are seen. They are usually not more than 5 mm in diameter, but the size may vary. Children are most commonly infected and flexural surfaces are the areas of skin most frequently involved. In adults, spread often occurs with sexual contact.
Irritation over the surrounding skin may induce scratching and further spread. Single lesions may occur and become quite large and inflammatory and then the diagnosis may not be easy.
The papules need only to be opened and the contents expressed; this often occurs with scratching although a sterile needle can be used. Silver nitrate or phenol may be applied or electrocautery or a Hyfrecator (which seals blood vessels using a small charge of electricity but without heat) may be used, or cryosurgery. Associated changes in the skin, such as eczema, need to be treated in order to prevent scratching and further spread of lesions.
The human papillomavirus (HPV) is a member of the papovavirus family, which includes other species-specific viruses that infect domestic animals such as dogs, rabbits, horses or cattle. It has long been recognized that tumours induced in animals by this group of viruses may undergo malignant transformation, and the oncogenic potential for humans is of increasing concern.
Types of virus
DNA hybridization techniques have demonstrated more than 50 different virus types, and immunocytochemical methods have identified virus particles in human tumours.
Previously warts have been classified according to the clinical appearance or anatomical site that they infect. It is now recognized that one or several viral types can be found in each of the clinically different lesions, e.g. plantar warts are caused by HPV-l and HPV-4. The genus is divided into types according to the homology of the
Viral DNA can be isolated from the basal cells of the epidermis, but the fully infective virion is only evident in more superficial epidermal cells. Cytology or histology shows gross disruption of the cells of the granular layer and below, which have intranuclear and cytoplasmic eosinophilic inclusions. Gross hyperkeratosis and parakeratosis are also associated with viral infection.
Common warts are individual papular lesions with a coarse or roughened surface that are seen on the palmar aspect of the fingers and on the knees; other sites are less commonly affected. Children between the ages of 11 and 16 years are principally affected. Spread is associated with trauma. Many periungal warts are seen in nail biters, who may also have warts on or around their lips.
Plantar warts (verrucae)
These lesions are often solitary and are distributed over contact areas of the foot. When they overlie a bony prominence and are associated with marked hyperkeratosis, pain and tenderness when pressure is applied may be severe. Squeezing a plantar wart or verruca may more readily induce pain than pressing on the lesion and this is a useful test in differentiating a verruca from a callosity. Paring down the skin over a verruca will demonstrate a pit in the skin at which the surface markings come to an abrupt halt; they are, however, continuous over a callus. Maceration of the skin associated with sweating may induce many superficial lesions that form a mosaic wart.
Single filiform warts
These lesions occur on the face and at the nasal vestibule or around the mouth; they may also be seen over the face or neck of older patients.
Plane warts are flat-topped and slightly rough on the surface, which is often pigmented. They are usually 2-3 mm in diameter and may require incidental lighting to discern their outline. The face, around the mouth and chin are the sites most commonly involved, and the hyperpigmentation may give children an unwashed appearance.
Young women are also affected and lesions may persist for years. The dorsa of the hands and knees are sometimes involved and trauma may demonstrate the Koebner phenomenon at these sites.
Spontaneous resolution is common and this makes it difficult to assess the value of therapy. Keratolytics containing salicylic or lactic acid may lessen the unsightly appearance of common warts, which is peculiarly loathsome to so many patients.
Drying preparations may speed resolution if maceration of the skin over the hands and feet is associated with excessive sweating. Glutaraldehyde 10% w/v may be applied twice daily with a brush to individual lesions or wiped over the surface of mosaic warts. Soaks include formaldehyde as a formalin solution at concentrations of between 2 and 5%, or potassium permanganate 0.01%. Too strong solutions or too frequent applications may induce cracking or fissuring over areas of the skin such as the toe-clefts.
Destructive methods may hasten resolution by producing local inflammatory changes and enhancing immune reactions. These include chemical cautery, electrocautery and cryo urgery.
On some occasions curettage may prompt the resolution of painful verrucae but any scarring that accompanies such procedures may give rise to chronic pain, particularly when situated over pressure points.