# Human Papillomavirus

> Human papillomavirus for NEET-PG Microbiology, covering high versus low risk types, the oncogenic E6 and E7 proteins, cervical screening and HPV vaccines.

- Canonical URL: https://prepelephant.com/topics/neet-pg/microbiology/human-papillomavirus
- Exam / course: NEET-PG · Subject: Microbiology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-15
- Last updated: 2026-10-15
- Reference basis: Ananthanarayan and Paniker's Textbook of Microbiology; Jawetz, Melnick and Adelberg's Medical Microbiology; Harrison's Principles of Internal Medicine
- How to cite: "Human Papillomavirus", PrepElephant, https://prepelephant.com/topics/neet-pg/microbiology/human-papillomavirus

## Direct answer

Human papillomavirus is a small, non-enveloped, double-stranded DNA virus that infects squamous epithelium and causes almost all cervical cancers. Types 16 and 18 are the high-risk types behind about 70 per cent of those cancers, while types 6 and 11 cause most genital warts. Its oncogenic effect rests mainly on the E6 and E7 proteins, which inactivate p53 and retinoblastoma protein.

## What you must remember

- **Structure:** Icosahedral, non-enveloped capsid enclosing a circular double-stranded DNA genome of about 8 kilobases.
- **High-risk types:** Types 16 and 18 dominate, with 31, 33, 45, 52 and 58 contributing further cancers.
- **Low-risk types:** Types 6 and 11 cause anogenital warts (condylomata acuminata) and recurrent respiratory papillomatosis.
- **Oncoproteins:** E6 promotes degradation of p53, and E7 binds retinoblastoma protein to release E2F and drive cell division.
- **Koilocytes:** Enlarged, wrinkled nuclei with a perinuclear halo on cervical cytology signal productive HPV infection.
- **Culture:** HPV cannot be grown in routine culture, so diagnosis depends on DNA detection by PCR or hybrid capture.
- **Vaccines:** Prophylactic L1-based vaccines prevent infection with covered types and are most effective before sexual debut.

## From infection to invasive cancer

Cervical cancer develops over years through a sequence of viral and host events. Each step is a point where screening or vaccination can interrupt the process.

1. **Entry through micro-injury:** The virus reaches basal keratinocytes through tiny breaks in the epithelium, and the cervical transformation zone is the most vulnerable site.
2. **Episomal replication:** The viral genome persists as an episome in dividing basal cells, and productive infection is confined to the upper epithelial layers.
3. **Oncoprotein action:** E6 and E7 disable p53 and retinoblastoma protein, so cells with DNA damage keep dividing rather than undergoing apoptosis or arrest.
4. **Integration into the host genome:** In high-grade lesions the viral DNA often integrates and disrupts the E2 gene, removing its brake on E6 and E7 expression.
5. **Progression through CIN grades:** CIN1 frequently regresses, whereas CIN3 carries a meaningful risk of progressing to invasive carcinoma if untreated.
6. **Clearance or persistence:** Most infections clear within one to two years, and only persistent high-risk infection leads to cancer.

## Where the exam tries to catch you

HPV questions often test which types cause which disease, and what the vaccine can and cannot do.

- **Trap:** Naming types 16 and 18 as the cause of genital warts. **Correct:** Types 6 and 11 cause most warts, while 16 and 18 are the high-risk types that cause cancer.
- **Trap:** Confirming HPV by culture or serology in routine practice. **Correct:** HPV is detected by PCR or hybrid capture for its DNA, with cytology providing the koilocyte clue.
- **Trap:** Expecting the vaccine to treat an established infection. **Correct:** The prophylactic vaccine prevents infection with covered types and does not clear existing infection or lesions.

## Frequently asked questions

### Which HPV types cause most cervical cancers?
HPV types 16 and 18 cause about 70 per cent of cervical cancers worldwide. High-risk types 31, 33, 45, 52 and 58 account for a further share, which is why nonavalent vaccines cover them.

### Which HPV types cause genital warts?
HPV types 6 and 11 cause the large majority of anogenital warts, also called condylomata acuminata. These low-risk types rarely progress to cancer, although they can cause recurrent respiratory papillomatosis.

### Why are koilocytes important in cervical cytology?
Koilocytes are squamous cells with a perinuclear halo and an enlarged, wrinkled nucleus produced by productive HPV infection. Their presence on a Pap smear is a morphological clue to HPV infection and prompts further evaluation.

### What is visual inspection with acetic acid used for?
Visual inspection with acetic acid (VIA) is a low-cost screening test for cervical precancer. It is well suited to resource-limited settings, and India's national cancer programme recommends it as a screening tool.

### At what age is HPV vaccination most effective?
HPV vaccination is most effective before the first sexual exposure, which is why standard schedules target girls around 9 to 14 years. The vaccine prevents infection with the covered HPV types and does not treat existing lesions.