Prevalence of human papillomavirus (HPV) infection in Basque Country women using slot-blot hybridization: a survey of women at low risk of developing cervical cancer

Epidemiology of Human Papilloma Virus (HPV) in Cervical Mucosa

In a worldwide scenario, human papillomavirus (HPV) infection is the second leading cause of cancer-related morbidity and mortality among women due to its very close association with cervical cancer. More than 100 different types of HPV genotypes have been characterized to date. Among these, approximately 24 HPV genotypes specifically infect the genital and oral mucosal system. The mucosal HPVs are most frequently sexually transmitted, and they are responsible for the most common sexually transmitted diseases throughout the world. In a majority of the cases, oncogenic/nononcogenic HPV infections spontaneously clear by themselves without any medical intervention. However, a persistent and long-term HPV infection usually leads to cervical cancer, which remains difficult to treat. In recent years, advance understanding of the structure of HPV and its pathogenesis has led to a variety of new treatments to combat HPV-related diseases, including a Food and Drug Administration-approved HPV vaccine that is very effective in young women. To effectively use this HPV vaccine worldwide, a clear understanding of HPV genotypes in different geographical populations is imperative. In this chapter, we have focused briefly on HPV genotypes and HPV prevalence in the women of different geographical populations.

Age-specific prevalence of infection with human papillomavirus in females: a global review

PURPOSE

Global data on age-specific prevalence of human papillomavirus (HPV) infection overall, and for high-risk HPV types 16 and 18, are essential for the future implementation of HPV prophylactic vaccines for cervical cancer prevention.

METHODS

A systematic review of peer-reviewed publications was conducted to summarize worldwide data on genital HPV-DNA prevalence in women. Studies with clear descriptions of polymerase chain reaction or hybrid capture detection assays were included.

RESULTS

A total of 346,160 women were included in 375 studies. Of 134 studies with age-stratified HPV prevalence data (116 low sexual risk populations, 18 high sexual risk populations), over 50% were from Europe and the Middle East (38%) and North America (19%), with smaller proportions from Asia and Australia (21%), Central and South America (11%), and Africa (10%). Across all geographical regions, data on HPV prevalence were generally limited to women over 18 years of age. Consistently across studies, HPV infection prevalence decreased with increasing age from a peak prevalence in younger women (< or =25 years of age). In middle-aged women (35-50 years), maximum HPV prevalence differed across geographical regions: Africa (approximately 20%), Asia/Australia (approximately 15%), Central and South America (approximately 20%), North America (approximately 20%), Southern Europe/Middle East (approximately 15%), and Northern Europe (approximately 15%). Inconsistent trends in HPV prevalence by age were noted in older women, with a decrease or plateau of HPV prevalence in older ages in most studies, whereas others showed an increase of HPV prevalence in older ages. Similar trends of HPV 16 and/or 18 prevalence by age were noted among 12 populations with available data.

DISCUSSION

Genital HPV infection in women is predominantly acquired in adolescence, and peak prevalence in middle-aged women appears to differ across geographical regions. Worldwide variations in HPV prevalence across age appear to largely reflect differences in sexual behavior across geographical regions. Further studies of HPV prevalence in adolescents are needed for all geographic regions.

Epidemiological study in Okinawa, Japan, of human papillomavirus infection of the uterine cervix

OBJECTIVE: To investigate the prevalence and type distribution of human papillomavirus (HPV) in women with normal cervical cytology and with cervical intraepithelial neoplasia I to III(CIN) or carcinoma of the cervix in Okinawa, Japan. METHODS: We investigated HPV DNA in 4,078 subjects with cytologically normal cervices, 279 subjects with CIN, and 383 subjects with cervical cancer in Okinawa Prefecture in Japan. The presence of HPV DNA was also compared among generations. HPV DNA was both detected and typed using polymerase chain reaction (PCR). RESULTS: The HPV positivity rate was 10.6% in the subjects who were normal on cervical cytodiagnosis. In each generation, the positivity rate was 20.4% in women aged 20-29 years and approximately 10% in the groups aged 30-89 years, with significant differences among generations. The HPV positivity rates in CIN and cervical cancer groups were 76.0% and 86.2%, respectively, with no significant difference between the groups. The positivity rate of HPV 16 decreased with age in both CIN and cervical cancer groups. CONCLUSION: Among non-cancer subjects, HPV infection rates were almost 20% in women aged 20-29 years and 10% in women aged 30-89 years. HPV16-positive CIN or carcinoma were more prevalent in the younger women, suggesting that HPV16-infected epithelial cells rapidly progress to cervical cancer.

Human papilloma virus type 16 infection and the early onset of cervical cancer

Human papilloma viruses (HPV), particularly type 16, have been associated with cervical cancer. It has been noted that the average onset of cervical cancer is occurring in younger women coupled with a higher prevalence of cervical HPV infection. However, the correlation between HPV 16 infection and the early onset of cervical cancer is still unclear. We hypothesize that HPV infection is an indicator of early onset of cervical cancer. To test this hypothesis, cervical smears from 197 women were evaluated by the polymerase chain reaction for HPV 16. These data revealed that the HPV 16-positive women were significantly younger than the HPV 16-negative women. Moreover, the average age of HPV 16-positive women with CIN 3 or invasive cancer was significantly younger compared with the other groups. These data clearly suggest that HPV 16 infection is a significant risk factor for the progression for cervical cancer in a young population of women.

Epidemiology of cervical intraepithelial neoplasia: the role of human papillomavirus

The evidence implicating specific HPV types in the aetiology of cervical cancer is now strong enough to establish a causative role. HPV infection of the cervix affects the developing immature metaplastic cells of the transformation zone. Cervical neoplasia can be viewed as the interaction of high risk papillomavirus and immature metaplastic epithelium. Once maturity is reached, there is minimal risk of subsequent development of cervical squamous neoplasia. Exposure to HPV is an extremely common event, especially in young sexually active women. Yet, despite frequent HPV exposure at that phase of life in which the cervical transformation zone is at its most vulnerable, established expressed disease is relatively uncommon. Most studies in which the natural history of CIN is not altered by cervical biopsy reveal a progression rate from low to high grade CIN of less than one third. Where viral type is taken into account, however, the progression rate from normal but high risk HPV-infected cervical epithelium to CIN 2 or 3 is higher. Despite this, most cervical abnormalities will not transform into invasive cancer, even if left untreated. The variance between the high rate of HPV infection, the intermediate rate of CIN and the relatively low rate of cervical cancer establishes a stepwise gradient of disease of increasing severity with decreasing prevalence. In an immunocompetent host, HPV infection alone does not appear to be sufficient to induce the step from high grade CIN to invasion. Epidemiological studies indicating that HPV infection with oncogenic viral types is far more common than cervical neoplasia suggest the necessity of cofactors in cervical carcinogenesis. The long time-lag between initial infection and eventual malignant conversion suggests that random events may be necessary for such conversion, and the spontaneous regression of many primary lesions suggests that most patients are not exposed to these random events. Potential cofactors include cigarette smoking, hormonal effects of oral contraceptives and pregnancy, dietary deficiencies, immunosuppression and chronic inflammation. In those women who develop cervical cancer, malignant progression is rarely rapid, more commonly taking many years or decades. Malignant progression has been documented in patients who presented initially with only low grade HPV-induced atypia. On the other hand, progression may be a misnomer, as 'apparent' progression may really represent adjacent 'de novo' development of higher grade CIN. Although most cervical cancers contain high risk HPV types, up to 15% of such cancers test negative for HPV, raising the possibility that a few, usually more aggressive, cervical cancers may arise from from a non-viral source.(ABSTRACT TRUNCATED AT 400 WORDS)

Demonstration of smoking-related DNA damage in cervical epithelium and correlation with human papillomavirus type 16, using exfoliated cervical cells

Smoking is a known aetiological risk factor for cervical cancer. Smoking-related DNA damage (DNA adducts), in cervical epithelial cells, has recently been demonstrated to suggest a causal role in the development of cervical cancer. Human papillomavirus 16 (HPV 16) is a known oncogenic virus and is also implicated as a cause of cervical cancer. It has been suggested that both smoking and HPV may act synergistically in the development of cervical cancer. We have investigated the cervical DNA adduct level and the prevalence of HPV 16 (using polymerase chain reaction) in women who had normal cervical cytology. Both the DNA adduct assay and the HPV assay were carried out on exfoliated cervical cells recovered from cervical scrapes. In 87% of the cases there was enough DNA from the exfoliative cervical cells to analyse for DNA adducts. Smokers had higher DNA adduct levels than non-smokers (P = 0.002), confirming the previous data from cervical biopsy samples. Forty-two per cent of the specimens were found to be HPV 16 positive. There was no significant difference in smoking-related DNA damage (DNA adduct levels) between HPV-positive and HPV-negative smokers. This suggests that smoking DNA damage does not augment HPV infectivity. These results do not, therefore, support the molecular synergism theory.

Antibodies to the E4, E6, and E7 proteins of human papillomavirus (HPV) type 16 in patients with HPV-associated diseases and in the normal population

In a cross-sectional study, titers of antibodies to the E4 and E7 proteins of human papillomavirus (HPV) type 16 were measured by peptide-based enzyme-linked immunosorbent assay in 1707 sera. Sera were obtained from healthy individuals (ages 1 to 95 years), from patients with HPV-associated infection (cervical intraepithelial neoplasia and cervical cancer), and from patients who were at high risk for HPV infection (attending a sexually transmitted disease clinic or referred to a colposcopist because of an abnormal Papanicolaou smear). The prevalence of anti-E7 antibodies increased with age, although the overall prevalence in the adult population was low (10.36%) compared to the frequent detection of HPV 16 DNA in the population. This suggests that only a fraction of patients infected with HPV 16 develop an anti-E7 response. The age distribution of anti-E4 antibodies showed a different pattern, i.e., the prevalence was low in the adult population (1.14%) but exceeded 20% in children and teenagers. As the specificity of the anti-E4 reaction was supported by a highly significant association with anti-E6 positivity in children's sera (p = 0.002), it was assumed that infection with HPV 16 can occur frequently early in life. As compared to healthy controls, patients at high risk for HPV infection had a significantly higher frequency (p < 0.001) of antibodies to the HPV 16 E4 protein (but not to the E6 or the E7 protein) in their sera. Therefore, we conclude that in adults E4-specific antibodies may be a marker for virus replication.