Human Papillomavirus (HPV) is a group of over 200 related viruses. Most people contract HPV at some point, often without knowing it, as the infection frequently clears on its own. HPV types are categorized into high-risk strains, linked to certain cancers, and low-risk strains. Types 6 and 11 are classified as low-risk because they rarely progress to malignancy. These two strains are primarily responsible for the development of non-cancerous, visible growths.
Diseases Caused by HPV Types 6 and 11
The most common result of infection with HPV types 6 and 11 is the development of genital warts (condylomata acuminata). These two types cause about 90% of all genital warts. The warts may appear as small, flat spots or as raised, bumpy, or fleshy growths that sometimes cluster together in a cauliflower-like pattern. They can be pink, red, white, grayish, or brown and typically appear on or around the vulva, penis, scrotum, anus, cervix, and vagina.
These growths are usually asymptomatic, though their location and size can occasionally cause itching, discomfort, or minor bleeding, particularly during intercourse. A much rarer condition caused by these low-risk types is Recurrent Respiratory Papillomatosis (RRP), which involves the recurrent growth of wart-like tumors in the respiratory tract. RRP lesions most commonly grow on the vocal cords in the larynx, but they can spread into the trachea and lungs. Although the tumors are non-cancerous, their persistent recurrence can lead to voice changes, hoarseness, and airway obstruction, often requiring repeated surgical intervention.
Transmission and Diagnosis
HPV is transmitted primarily through direct skin-to-skin contact, usually during sexual activity (oral, vaginal, or anal). Transmission can occur even when the infected person has no visible warts or symptoms. The incubation period for genital warts is estimated to be between one and eight months following exposure. Juvenile-onset RRP is caused by vertical transmission of the virus from a mother with a genital HPV 6 or 11 infection to the infant during birth.
Diagnosis of genital warts is typically made by a healthcare provider through visual inspection due to their characteristic appearance. If lesions look atypical or do not respond to standard treatments, a biopsy may be performed to confirm the diagnosis and rule out other conditions. There is no routine screening test for HPV 6 and 11 in men, and the standard HPV test for women detects only high-risk types, not these low-risk strains. Diagnosing RRP, especially deep within the airway, requires specialized procedures like laryngoscopy or bronchoscopy, often followed by histopathology or PCR testing to confirm the presence of HPV 6 or 11.
Treatment Options for Low-Risk HPV
The goal of treating HPV 6 and 11 infections is to remove visible lesions, as no medication currently eradicates the underlying virus from the body. Treatment options are divided into patient-applied topical medications and provider-administered procedures.
Patient-Applied Treatments
Patient-applied treatments include topical creams such as imiquimod, an immune response modifier that stimulates the body’s immune system to attack the warts. Another option is podofilox, a cytotoxic agent designed to destroy the wart tissue.
Provider-Administered Procedures
Provider-administered treatments are used for larger, internal, or more resistant lesions and involve physical destruction methods. These procedures include cryotherapy (freezing the warts with liquid nitrogen) or the application of trichloroacetic acid (TCA), a chemical agent that burns away the tissue. For extensive or recurrent cases, surgical options are available, such as surgical excision, electrosurgery, or laser removal. Treatment for RRP is more complex, focusing on repeated surgical removal of the papillomas to maintain a clear airway, sometimes supplemented with adjuvant therapies like intralesional cidofovir injections. Warts can recur even after treatment because the virus remains latent in the surrounding tissue.
Vaccination and Prevention
The most effective method for preventing infection with HPV types 6 and 11 is vaccination. The current nonavalent HPV vaccine, Gardasil 9, protects against nine HPV types, including both HPV 6 and HPV 11. The vaccine is routinely recommended for adolescents starting at age 11 or 12, as it works best when administered before potential exposure to the virus.
A two-dose schedule is typically recommended for children who receive their first dose between ages 9 and 15, with the second dose given six to twelve months later. Individuals starting the series at age 15 or older require a three-dose schedule for full protection. Other prevention methods, such as the consistent use of condoms, can reduce the risk of transmission. However, because HPV is spread through skin-to-skin contact, condoms do not protect all exposed genital skin areas.