American scientists say a virus that is contracted through oral sex is the cause of some throat cancers. A Johns Hopkins University study of 300 people found that HPV (human papilloma virus) infection was found to be a much stronger risk factor than tobacco or alcohol use.

The New England Journal of Medicine study said the risk was almost nine times higher for people who reported oral sex with more than six partners.

However, experts said a larger study was needed to confirm the findings.

HPV infection is the cause of the majority of cervical cancers, and 80 per cent of sexually active women can expect to have an HPV infection at some point in their lives.

The Johns Hopkins study took blood and saliva from 100 men and women newly diagnosed with oropharyngeal cancer which affects the throat, tonsils and back of the tongue. They also asked questions about sex practices and other risk factors for the disease, such as family history.

Those who had evidence of prior oral HPV infection had a 32-fold increased risk of throat cancer.

HPV16 - one of the most common cancer-causing strains of the virus - was present in the tumours of 72 per cent of cancer patients in the study.

Oral sex was said to be the main mode of transmission of HPV but the researchers said mouth-to-mouth transmission, for example through kissing, could not be ruled out.

Most HPV infections clear with little or no symptoms but a small percentage of people who acquired high-risk strains may develop a cancer, the researchers added.

A vaccine which protects against cervical cancer caused by HPV strains 6, 11, 16 and 18, and also against genital warts is available and the researchers said the study provided a rationale for vaccinating both girls and boys.

But whether the vaccine would protect against oral HPV infection is not yet known.

Dr. Julie Sharp, science information officer at Cancer Research U.K., said: "There is conflicting evidence about the role of HPV, and this rare type of mouth cancer.

Information from: http://news.bbc.co.uk/2/hi/health/6639461.stm

HPV infection is the cause of the majority of cervical cancers, and 80 per cent of sexually active women can expect to have an HPV infection at some point in their lives.