Most people have warts at some time in their life, usually before the age of 20. Genital warts occur during the sexually active years. Warts result from infection with the DNA human papillomavirus (HPV), of which over 60 subtypes are now recognised. Different subtypes are responsible for several clinical variants. Transmission is by contact with in the virus, either in living skin or in fragments of shed skin and is encouraged by trauma and moisture (e.g. at swimming pools, amongst butchers, fishmongers etc.). Genital warts are frequently spread by intercourse and perianal warts may reflect homosexual activity. There appears to be a close, if not causative, relationship between human papillomaviruses especially HPV types 16 and 18, and carcinoma of the cervix. Other types of HPV may act as tumour promoters and, with ultraviolet radiation, cause skin cancer in immunosuppressed individuals.

Clinical features

Common warts appear initially as smooth, skin-coloured papules. As they enlarge, their surfaces become irregular and hyperkeratotic, producing the typical ‘warty' appearance. They usually occur on the hands but may also often be seen on the face and genitalia; multiple warts are common. Plantar warts ('verrucae') are characterised by a rough surface, protruding only slightly from the skin and surrounded by a horny collar. On paring, oozing capillary loops distinguish plantar warts from corns. Often multiple, plantar warts may be painful. Other variants of warts include mosaic warts (mosaic-like plaques of tightly packed individual warts), plane warts (smooth, flat-topped papules seen most commonly on the face and backs of hands), facial warts (often filiform and hyperkeratotic) and anogenital warts (may be papillomatous and even cauliflower-like).

Most viral warts in the healthy will eventually resolve spontaneously but this may take years. In immunocompromised patients warts persist and spread 70% of renal allograft recipients will have warts 5 vears after transplantation, and there is also an increased risk of cervical cancer.


Warts may be treated in many different ways. Common warts in children should be managed with wart paints containing salicylic acid. Stubborn lesions should be treated with liquid nitrogen cryotherapy or removed by curettage Anogenital warts are treated with either cryotherapy or podophyllin paint (applied initially for only 2 hours and avoided in pregnancy). Facial warts are most easily treated with cryotherapy or electrodesiccation. Plane warts are best left alone.


The two human polyomaviruses known as JC and BK are widely prevalent in normal people and are only associated with disease in immunosuppressed patients. JC virus is the cause of progressive multifocal leucoencephalopathy, seen most often in patients with AIDS (see section on HIV for details). BK and JC are excreted in the urine of immunosuppressed patients; an association between BK virus and Ureteric stenosis in renal transplant recipients, and haemorrhagic cystitis in marrow transplant recipients has been suggested.

Concepts of infection
Major manifestations of infection
Principles of management of infection
Diseases due to viruses
DNA viruses
Diseases due to chlamydiae
Diseases due to rickettsiae
Diseases due to bacteria
  • Streptococcal infections
  • Staphylococcal infections
  • Corynebacterial infections
  • Bacillus infections
  • Bordetella infections
  • Salmonella infections
  • Food poisoning
  • Dysentery
  • Other true bacterial infections
  • Mycobacterial infections
Diseases due to spirochaetes
  • Leptospira infections
  • Borrelia infections
  • Treponema infections
Diseases due to fungi (mycoses)
  • Cutaneous fungal infections
  • Subcutaneous fungal infections
  • Systemic fungal infections
Diseases due to protozoa
Diseases due to helminths
  • Trematode (fluke) infections
  • Cestode (tapeworm) infections
  • Nematode (roundworm) infections
  • Zoonotic helminth infections
Diseases due to arthropods
Sexually transmitted diseases
  • Sexually transmitted bacterial diseases
  • Sexually transmitted viral diseases
  • Miscellaneous conditions