What is Human papilloma virus(HPV)?
Human papilloma virus is a type of DNA virus of family Papillomaviridae. They are the most common sexually transmitted virus in US accounting the most cases of STD. They cause common warts to many cancers if left untreated. In most cases the symptoms the symptoms resolve spontaneously and doesn’t cause any complications. But in some cases, the lesions become pre-cancerous and subsequently develop cancerous lesions. The human papilloma virus are broadly of two types; the cutaneous and mucosotropic type. The mucosotropic involve the oral and anogenital mucosa. The cutaneous type involve the skin of our body.
Image credit- UCSF health
Routes of Transmission
Sexual route- It is the most common route of transmission of infections. It cause multiple lesions on the site of contacts like anus, vulva, throat, penile region or vagina.
Skin to skin contact- It is another mode of transmission of the virus when there is skin to skin contact. It may manifest as common warts of skin.
Vertical transmission- Spread of infection from mother to child can occur during labour or delivery due to contact with the genital surface.
Varieties of Human Papilloma virus strains
There are numerous strains of HPV. But few strains are of pathological significance. The common warts causing strains are 6, 11. They cause warts in skin, genital area and laryngeal papillomatosis.
Strains like HPV 16 and 18 are the infectious culprits of oropharyngeal and cervical cancers.
Risk factors for the spread of Human Papilloma virus
1. Unprotected sex- It is the predominant mode of transmission of HPV. It increases the vulnerability of mucosal damage and rapid spread of the virus.
2. Multiple sexual partners- The risk ratio is increased manifold during the lifetime of concerned partners. As we have already discussed earlier, it is the most common sexually transmitted virus worldwide including USA.
3. Immunodeficiency state- Persons with weak immunity are vulnerable for HPV related infection and complications. As the infection progresses from benign lesion to malignant cancers, there is increased propensity for cancerous cell growth in immunosuppressed states. Longstanding cases of liver disease, chronic kidney disease, AIDS, malnutrition, blood dyscrasias are particularly aggravate the immunodeficient states and infection.
4. Smoking- It also increase the risk of spread of human papilloma virus infection.
Lesions in Human Papilloma Virus
Genital warts- They are the most common among the human papilloma virus infections. They appear few months after transmission. The warts can be in seen in anal canal, vulva vagina, penis, scrotum. They are usually small pink lesions that project outwards. Most common strains involved in skin warts are 6,11. The symptoms are few and sometimes may be painful.
Oropharyngeal and laryngeal cancers
The strains involved are 16, 18, 31, 33. The initial lesions may be precancerous which may progress to malignant type during the course of time. Oropharyngeal cancers are common worldwide. Two proteins of HPV E6 nd E7 are mainly responsible for cell transformation and malignant change in cells. They are called as oncogenic proteins.
A systemic meta-analysis reviewed to determine the prevalence of HPV in head and neck cancers. In total, 5046 cases of squamous cell carcinoma, 2642 oral cancers, 969 oropharyngeal cancers and 1435 laryngeal cancers were studied. HPV prevalence was found to be 35.6% in oropharyngeal cancers , 23.5%in oral cancers and 24% in laryngeal cancers. The estimated prevalence of HPV in head and neck squamous cell carcinoma was 26%.
In a French retrospective multicenter study, HPV prevalence was 57% in tonsil cancers. Among this the strain HPV-16 was most common. It is the most important strain causing cancer of head and neck.
Cervical cancers
Human papilloma virus are also involved as etiological agents in cervical cancers. The initial lesions are cervical dysplastic lesions like cervical intraepithelial neoplasia or CIN. It can be graded into CIN I, II and III. The CIN III variety has highest propensity for malignant transformation. Cervical cancer is the fourth most common common cancer globally. Two human papilloma virus strains 16 and 18 are responsible for around 50% of high grade neoplastic lesions of cervical cancers. The immunodeficient stage patients with concomitant HIV infection are 6 times more risk of developing cervical cancers than those people without HIV.
Screening of cervical cancers
The screening of cervical cancers are done by PAP test. All women above 21 years should undergo screening for cervical cancers by PAP test in every 3 years.
Vaccination against HPV
The different vaccines used are 9 valent HPV vaccines, quadrivalent HPV and bivalent HPV vaccines. The HPV vaccines are recommended for adolescents at 11 or 12 years. But vaccination can be started as early as 9 years. ACIP also recommends vaccination through 26 years if not vaccinated earlier. Some adults between 27 to 45 years might get the vaccination after consulting the physician.
