Virus peril of changing partners

HPV may help cause changes to cells in the cervix

The risk that a woman will become infected with a virus associated with cervical cancer is increased every time she has sex with a new partner.

US researchers have found the risk of infection with the human papilloma virus (HPV) is increased ten-fold for each new sexual relationship a woman has per month.

HPV is necessary but not sufficient by itself to cause these lesions

Professor Anna-Barbara Moscicki

The scientists, from the University of California, San Francisco, have been monitoring more than 800 women who attended family planning clinics in 1990.

Their findings suggest that more than half of sexually active young women in the US will become infected with HPV over a three-year period. The infection figures are thought to be similar in Europe.

However, the same study has contradicted previous research which suggests that infection with the virus is certain to trigger cellular changes that can lead to cancer.

Three in ten

The researchers found that, over a five-year period, only approximately 30% of women infected with HVP showed signs of changes to the cells of the cervix.

These changes, called LSIL, or low-grade intra-epithelial lesions, are benign in themselves, but can be the first step along the way to the development of cervical cancer.

It appears that women are more likely to develop LSIL in the first year after HPV infection. The risk tails off after four years.

Infection with other sexually transmitted diseases did not, as indicated by previous research, increase the risk of LSIL.

However, daily cigarette smoking did appear to increase the risk.

Lead researcher Professor Anna-Barbara Moscicki said: "This report shows that HPV is necessary but not sufficient by itself to cause these lesions.

"Other behavioral and biological factors must be involved, most likely persistence of the viral infection, and the woman's own immune reaction."

Long-term study

Professor Moscicki's work has overturned a number of assumptions about HPV.

Most strikingly, the researchers have shown that for most young women, HPV is not necessarily a life-long infection. Most appear to clear the virus from their bodies.

The research has also shown:

• Over 36 months, 55% of sexually active young women who did not have HPV became infected.
• Women who took oral contraceptives cut their relative risk of HPV infection in half.
• Infection with herpes simplex virus also increased the risk, as did a history of vulvar warts.
• Up to 90% of young women clear the HPV virus from their systems within 36 months. However, many become reinfected.

The Public Health Laboratory Service said the US was useful because it followed a large number of women over a long period of time.

A spokesperson said: "HPV is a common sexually transmitted infection which in some women will lead to cancerous cervical lesions.

"Prevention is the key to tackling such infections and this study reinforces the importance of safe sex and use of condoms."

A spokeswoman for the Cancer Research Campaign said the study, which matched results found in similar British research, reinforced the need for safe sex precautions to stop the spread of the virus.

What we need to find are the other factors which, when added to HPV infection, produce these changes

Cancer Research Campaign

"The majority of women who get HPV won't develop cancer, or even pre-cancerous cell changes.

"What we need to find are the other factors which, when added to HPV infection, produce these changes."

Dr Peter Sasieni, a cervical cancer expert at the Imperial Cancer Research Fund, said: "There is great optimism that a vaccine against this virus will one day eliminate cervical cancer and do away with the need for regular cervical screening."

The research is published in the Journal of the American Medical Association.