The incubation period for HPV ranges from 1 to 6 months; however, latency periods of up to 3 years or more are suspected. The lesions are present for several months and usually regress spontaneously within two years, although some may persist indefinitely.
HPV 1, 2, and 4 cause benign nongenital skin warts such as plantar and common warts. Although the frequency is unknown, warts are estimated to affect approximately 7 to 12% of the population. They occur most frequently in older children and young adults. Some school surveys estimate a prevalence of about 10% in older school children, with a peak at around 12 to 16 years. There is a low incidence of warts in older people, indicating that their immune systems may render them more resistant to infection. Although warts may affect any race, common warts appear approximately twice as frequently in whites as in blacks or Asians. The frequency of warts is about the same in men and women.
These benign warts can arise in any location but occur most frequently on the hands and feet. Common warts are scaly, rough, spiny papules or nodules. They occur often as single or groups of papules on the hands and fingers. It is quite common to have multiple lesions, which can appear symmetrically or unilaterally. Common warts usually are asymptomatic, but may cause cosmetic disfigurement or tenderness.
Plantar warts occur on the plantar surface of the foot and palmar warts on the palms of the hands. These warts are very thick. Mosaic warts occur when groups of plantar or palmar warts coalesce into large plaques. These warts tend to regress spontaneously, mediated by immunological response. Plantar warts usually are painful, and extensive involvement on the sole of the foot may impair ambulation.
HPV that causes nongenital warts is transmitted by direct or indirect contact. Infection with the virus occurs very easily by touching a towel or face cloth that someone with a common wart has used. Spread is facilitated by scratching. Prevention includes avoidance of using intimate products of others, walking on locker-room floors bare-footed, touching warts on other people, or scratching/picking at warts already on your own body.
Most warts regress spontaneously, but there are a range of treatments for warts. No specific antiviral drugs are available for HPV; most treatments are aimed at destroying the wart tissue without causing damage to the healthy tissue surrounding it. Treatments include topical application of caustic agents such as salicylic acid or podophyllin, cryotherapy (freezing off the wart), and surgical therapy or laser treatment. Vaccines have thus far not been successful.