Human papilloma virus (HPV)

Papillomaviruses
Papillomaviruses are nonenveloped DNA viruses. These viruses are diverse, but all can infect the skin and mucosal tissues of a many vertebrate species, including humans. A group of genital mucosotropic human papilloma virus (HPV) types are etiologic agents responsible for virtually all cases of cervical cancer, as well as a substantial fraction of other ano-genital and head-and-neck cancers (reviewed in [1]). Cancer-associated genital HPV types, as well as another subset of HPV types associated with the development of benign genital warts (condyloma accuminata), are generally transmitted through sexual contact. Infection with genital HPV types is very common, with an estimated lifetime risk of infection of about 75% [2]. Although most genital HPV infections are subclinical and self-limiting, a subset of persistently infected individuals have lesions that progress to premalignancy or cancer.

Genome structure
The HPV genome is approximately 8,000 base pairs long and made up of 40-50% Guanine and Cytosine base pairs. Papillomaviruses have the same general genomic organization which consists of 8 open reading frames(ORF) all located on the same strand. These ORFs are designated either early (E) or late(L). The early ORFs-E1,E2,E4,E5,E6,and E7-code for nonstructural regulatory proteins. The E3 ORF does not code for a protein, and the E8 ORF has been identified only in bovine Papillomaviruses. The late ORFs-L1 and L2-code for capsid proteins. A 1-Kb non-coding region known as the upstream regulatory region (URR) ,lies between the early and late ORFs. The URR includes the origin of replication (ori), the E6/E7 gene promoter, and enhancers and silencers.

Natural Host:
HPV is capable of infecting humans only.

Epidemiology
23% of women attending sexually transmitted disease, family planning, and primary care outpatient clinics in the United States may be positive for high-risk HPV.

Prevention
I vitro studies show that carrageenan, extracted from red algae and commercially used to thicken products including sexual lubricants and infant formulas, is a potent inhibitor of HPV infection.

HPV Vaccine
The HPV vaccine can reduce the incidence of high-grade cervical intraepithelial neoplasia and HPV-associated anogenital disease.

The number needed to vaccinate to prevent the following diseases is estimated to be:
 * Condylomata acuminata (genital warts) is 8
 * Cervical cancer is 324

A cost-benefit analysis concluded that the cost is $43,600 per quality-adjusted life-year (QALY) gained.

In the United States, the Centers for Disease Control and Prevention recommends vaccination of females starting at aged 11 - 12 years.