The human papillomavirus (HPV) is a virus that causes skin and mucous membrane (the moist lining of body cavities such as the mouth and nose that connect with the outside of the body) infections. It is usually passed from one person to another by skin-to-skin contact, including sexual contact.
There are more than 200 types of HPV that can affect different parts of the body, about 40 of which are transmitted through sexual contact. Some types of HPV can cause warts (such as genital or plantar warts) and others can lead to cancer (such as cervical or anal cancer).
HPV infection is one of the most common sexually transmitted infections (STIs) in Canada and around the world. At least 70% of sexually active men and women will have at least one HPV infection in their lifetime.
The different HPV types are classified into low and high risk based on their association with cancer. "Low risk" types rarely cause cancer. "High risk" types have a greater likelihood of causing cancer but they do not necessarily lead to cancer. These various types can cause different conditions, including:
- skin warts: These infections are also known as common, plantar, or flat warts and are caused by low-risk types. The warts can appear on your arms, face, feet, hands, and legs. They can develop at any age but are most common in children.
- genital warts: HPV types 6 and 11 cause about 90% of genital warts and are low-risk types.
- cervical dysplasia: HPV can cause lesions of abnormal cells called cervical dysplasia in a woman's cervix. These lesions are considered to be precancerous (they are not cancerous cells, but they may develop into cancer cells later). The HPV infection often resolves and clears on its own, but cervical dysplasia should be treated because it can lead to cervical cancer.
- cervical cancer: The high-risk HPV types 16 and 18 cause about 70% of all cervical cancers. Other high-risk types are 31, 33, 45, 52 and 58, which causes about 20% of cervical cancers. These high-risk types have also been linked to penile and anal cancers.
HPV can cause infections and lesions in other areas of the body, such as in the upper respiratory tract.
The majority of HPV infections are generally harmless, though they can be embarrassing. However, the HPV infections that can lead to cervical cancer and other types of cancers are a concern.
HPV enters the body, usually through a break in the skin, and then infects the cells in the layers of the skin. The virus then replicates or multiplies in the body. The time between first contracting HPV and the appearance of lesions can be weeks to months or even years. Many people don't even know they are infected with HPV.
HPV is usually transmitted by skin-to-skin contact. HPV infections that cause skin warts (e.g., plantar or common warts) can be acquired through a cut. Walking barefoot in public areas such as the gym or pool can be a risk for infection with the types of HPV that cause plantar warts.
HPV infections that cause genital warts are very contagious and are usually contracted through sexual activity with an infected person. This includes kissing or touching the skin of the infected areas (e.g., scrotum, vagina, vulva, anus) and having intercourse. Although HPV is more likely to be transmitted when lesions or warts are visible, transmission is possible even without the presence of visible warts.
Although the risk is very low, a mother with a genital HPV infection may also transmit the virus to the infant during labour.
The risk factors for HPV infection include:
- age: Children and young adults are most at risk for developing common warts and flat warts. Genital HPV infections usually occur in teenagers and young adults.
- number of sexual partners: The higher the number of sexual partners, the greater the risk of genital HPV infection.
- immune system: People who have a compromised immune system (e.g., HIV or AIDS, organ transplant recipient, or who are taking medication that suppresses the immune system) are at an increased risk of genital HPV infection.
Symptoms and Complications
Most HPV infections go unnoticed because they don't cause any symptoms. The virus may have been contracted years ago and it can remain in the body for weeks, years, or even a lifetime without showing any symptoms of an infection.
For those who experience symptoms, the type of symptoms depends on the type of HPV infection.
- Common warts are painless, firm growths with a rough surface and appear on the knees, face, fingers, and around the nails.
- Flat warts are small, smooth warts appearing in clusters on the back of the hands, face, or legs.
- Plantar warts are those appearing on the soles of the feet. They can be painful because of their weight-bearing location on the feet.
- Filiform warts form long, thin projections around the eyes, face, and neck.
- Genital warts are small, cauliflower-shaped, or flat lesions. They occur on the genital areas including the vagina, cervix, vulva, penis, scrotum, and anus. They are usually painless but they can bleed, itch, or have some discharge.
- Precancerous lesions or cervical dysplasia are abnormal cells in the cervix. These are painless and can only be detected with a Pap smear.
HPV can also cause cervical cancer, other genital cancers, and cancer of the head, neck, and throat.
Making the Diagnosis
Your doctor will make a diagnosis of skin or genital warts based on a physical exam. Sometimes, your doctor may perform a biopsy (removal of a small tissue sample) to properly diagnose genital warts and eliminate other skin conditions that may be causing the symptoms.
To diagnose and test for precancerous lesions in women, your doctor will perform a Pap smear. This test can detect abnormal lesions in the cervix, so it's important for women to get regular Pap tests, even if they have had the HPV vaccine.
HPV DNA testing is available in Canada but is limited to a small number of areas. It is not part of a regular checkup or Pap test. When it is recommended and used in certain situations, the results from HPV DNA testing and from Pap tests are used to decide a woman's cervical cancer risk.
Treatment and Prevention
There is no known cure for HPV infections. However, most infections are cleared away from the body by the immune system without treatment.
There are several treatment options for warts. Some treatments can be applied at home and others need to be done at the doctor's office. Removing warts does not always eliminate the HPV infection, as warts can reappear after treatment since the virus may still be present in the body.
Skin warts can be removed using over-the-counter treatments, such as salicylic acid to remove the layers of infected skin. The doctor can also use cryotherapy (liquid nitrogen) to freeze off the wart. Genital warts can be treated by using medications (e.g., imiquimod*, podophyllotoxin, trichloroacetic acid, sinecatechins) or by physically removing the warts (e.g., cryotherapy, electrosurgical removal, laser therapy, surgical removal). Depending on the circumstances and when a diagnosis was made, the abnormal cells in cervical dysplasia can be removed by freezing or laser surgery.
There are 2 human papillomavirus (HPV) vaccines available in Canada. One of them protects against the 2 most common types of HPV (16 and 18) that cause cervical cancer, but is used only for females and does not prevent warts. The other vaccine protect against both genital warts and cervical cancer, as well as anal cancers, and can be given to all genders. HPV vaccination require 2 to 3 shots and is part of the publicly funded immunization program in Canada for grade-school children. Most provinces and territories also fund the vaccine for individuals outside of school until a certain age or if they meet certain criteria.
While these vaccines are very effective in providing protection against the types of HPV that they cover, they cannot provide 100% protection against HPV since they do not cover all possible types. Ideally, people should be vaccinated before becoming sexually active. However, if you are already sexually active, you can still benefit from HPV vaccination.
To reduce the risk of genital warts, use a condom consistently. A condom can greatly reduce the risk of HPV infection but does not guarantee 100% protection since it does not cover all the exposed areas. Using a condom can also help protect against other STIs (e.g., chlamydia, herpes, HIV). Reducing the number of sexual partners can also help reduce the risk of HPV infection.
To reduce the risk of skin warts such as common or plantar warts, avoid walking barefoot in public areas. Always wear sandals or shoes. This will also reduce the risk of spreading the infection to other people and to other parts of your body.
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