Human papillomavirus 33 (HPV33) is a high‑risk type of HPV belonging to the alpha‑9 species group. It infects mucosal epithelial cells and contributes to a fraction of cervical, vulvar, vaginal and anal cancers. HPV33 is a circular double‑stranded DNA virus in the Papillomaviridae family.
Virology and Pathogenesis
HPV33 has an approximately 8 kb circular double‑stranded DNA genome encoding early proteins (E1, E2, E4, E5, E6 and E7) and late capsid proteins (L1 and L2). Infection occurs through microtrauma exposing basal keratinocytes, where the virus establishes episomal persistence. The viral life cycle is linked to epithelial differentiation: early proteins support replication in basal layers, while late proteins are expressed in the upper layers to assemble virions. In persistent infection, viral DNA may integrate into host chromosomes, often disrupting the E2 gene and resulting in overexpression of the E6 and E7 oncoproteins. HPV33 E6 promotes degradation of the tumour suppressor p53, while E7 binds and inactivates retinoblastoma protein, driving cells into S phase and inhibiting apoptosis. These interactions lead to genomic instability and can initiate malignant transformation. Although less prevalent than HPV16 and HPV18, HPV33 is often detected in high‑grade cervical intraepithelial neoplasia. The virus downregulates interferon signalling and antigen presentation to evade immune surveillance, and persistence is more likely in smokers, immunosuppressed individuals or those with multiple sexual partners.
Clinical Impact and Prevention
HPV33, together with types 31, 45, 52 and 58, accounts for about 15 % of cervical cancers and precancerous lesions. It is associated with both squamous and glandular cervical lesions and is detected in some vulvar, vaginal, penile and anal cancers. HPV33 infection does not usually result in visible genital warts, which are caused by low‑risk types. The nonavalent HPV vaccine includes HPV33 and provides prophylactic protection by eliciting antibodies against its L1 capsid protein. Cervical screening using HPV DNA testing and cytology can identify HPV33 infections and related lesions. Treatment of high‑grade lesions involves surgical excision or ablation, and early detection prevents progression to invasive cancer. As the virus is transmitted sexually, risk reduction strategies include condom use, limiting the number of partners and abstaining from smoking, though these measures do not provide complete protection. HPV33 is a high‑risk papillomavirus that contributes to a significant minority of cervical and other anogenital cancers. Its pathogenicity is mediated through E6 and E7 oncoproteins that disrupt key tumour suppressor pathways. Vaccination, routine screening and safe sexual practices are key to reducing HPV33‑related disease. Related Terms: Oncogenic HPV, Nonavalent HPV vaccine, HPV31, Cervical cancer, HPV45