Human papillomavirus (HPV) is a small, non-enveloped, double-stranded DNA virus (8kb) from the papillomaviridae family. It’s capsid is made up of L1 and L2 proteins. HPV infection is incredibly common, with most people being exposed in their lifetime. There are over 100 different strains of HPV – some lead to warts while others are cancerous. Particular strains of HPV are the leading cause of certain throat and genital cancers, making early vaccination against this virus incredibly important.
- HPV strains 16, 18, 31, and 45 are considered the highest risk for genital cancers, with 70% of all cervical cancer cases being attributable to 16 and 18.
- HPV 16 is also known for causing oropharyngeal cancer.
- HPV strains 6 and 11 are the most common for genital warts.
- HPV strains 1, 2, 4, and 63 most often lead to plantar warts (foot).
While sexual transmission of HPV strains is most common, any skin-to-skin contact can result in viral spread. HPV infection can also spread from mother to baby during pregnancy, warts may spread on surfaces, and health-care workers are at higher risk from close contact.
The first HPV vaccine was approved for use in 2006 and in recent years data has shown that vaccination has greatly reduced HPV-related cancer prevalence (close to 90% reduction). Gardasil 9 is the only version available in the US, covers 9 strains (6, 11, 16, 18, 31, 33, 45, 52, and 58), and is recommended for children starting at the age of 11 (available as early as 9).
How does it cause cancer? Two proteins that the virus expresses – E6 and E7 – stimulate unnatural growth of cells.