Human papillomavirus infection

Human papillomavirus, or HPV, is a large group of more than 200 different viruses.

These viruses belong to the Papillomaviridae family and only infect humans. HPV is the most common sexually transmitted infection (STI) found globally. Most people will encounter an HPV infection during their lives. However, the virus behaves differently in every person. In about 90% of cases, the body's immune system clears the infection spontaneously within two years. Many people never even realize they have been infected because there are no symptoms.

When an infection does not go away, it is called a persistent infection. This persistence can lead to physical changes like warts or precancerous lesions. Warts occur because the virus causes cells on the outer layer of the skin to grow too rapidly. There are many different types of warts depending on where they appear. Common warts often grow on the hands, feet, elbows, or knees. Plantar warts grow inward on the soles of the feet and can cause pain. Flat warts usually appear on the face or arms.

Scientists categorize HPV types based on the diseases they cause. Some types, such as HPV 1, 2, and 63, are linked to various skin warts. HPV types 6 and 11 are very common causes of genital warts. They can also cause a rare condition called laryngeal papillomatosis. This condition involves warts forming on the larynx or respiratory tract. These warts can sometimes interfere with a person's ability to breathe.

Other types are considered high-risk because they are linked to cancer.

High-risk HPV types can cause cancer by changing how a cell works. The virus can integrate its genome, or genetic material, into the DNA of the host cell. This process can trigger the production of specific proteins called oncogenes. For example, the HPV16 protein known as E6 acts as an oncogene. E6 binds to a protein called p53. Normally, p53 is a tumor-suppressor protein that stops damaged cells from dividing. E6 causes p53 to be destroyed by the cell. Without p53, cells can grow and divide in an unregulated way, which leads to cancer.

Certain HPV types are much more dangerous than others. There are about twelve types, including HPV 16, 18, 31, and 45, that are strongly linked to cancer. HPV 16 is particularly significant because it is responsible for almost 90% of HPV-related cancers of the mouth, throat, or tonsils. It is also present in about 47% of all cervical cancers. HPV 16 and HPV 18 together account for 70% of all cervical cancer cases. Other high-risk types include 33, 35, 39, and 51.

The global impact of HPV-related cancer is very large. High-risk HPV types cause about 5% of all cancers worldwide. In the United States, HPV causes approximately 37,300 cases of cancer every year. In 2020, cervical cancer caused an estimated 604,000 new cases and 342,000 deaths globally. A very high proportion, about 90% of these cases and deaths, occurred in low and middle income countries. This is often because screening and early treatment are less available in those regions. About 1% of sexually active adults currently have genital warts.

Understanding the history of HPV helps us see how far science has come. People have noticed warts since the time of ancient Greece. However, we did not understand the viral cause until 1907. That year, Dr. Giuseppe Ciuffo proved the viral nature of warts by inoculating wart extract into the skin. Today, we use advanced tools like HPV vaccines to prevent common infections. Public health organizations also use direct testing to find the virus early. Screening allows for early treatment, which leads to much better health outcomes.