Not so long ago, the majority of patients with oral or throat cancer were older smokers or heavy drinkers. But the face of neck cancer is changing, all because of a sexually transmitted virus.

Doctors say the number of cases of head and neck cancers in young, otherwise healthy patients in on the rise in Canada.

"Over the past 20 years, we have just seen this wave of patients that are younger people, that are healthy, that are non-smokers and non-drinkers that are developing cancers of the tonsil and the back of the tongue," head and neck surgeon Dr Anthony Nichols of the London Health Sciences Centre tells CTV News.

"This has just changed the epidemiology of these cancers as we are seeing it."

Around 2,000 cases of oral cancer are diagnosed each year in Canada. The reason for the shift, doctors say, is the spread of HPV, the human papillomavirus. It's estimated that about two-thirds of cases diagnosed today are caused by HPV.

HPV is best known as the primary cause of cervical cancer, the second most common cause of cancer death in women worldwide. But various strains of the virus can also cause oral cancer as well as anal, penile, and other head and neck cancers.

And HPV infection rates have been growing. A report released this week in The Lancet medical journal finds that half of men in the general population may be infected with HPV.

Anna Giuliano of the H Lee Moffitt Cancer Center and Research Institute in Tampa, Florida, and colleagues studied rates among more than 1,100 men aged 18 to 70 in the United States, Brazil and Mexico. They swabbed the men's genitals and found that about 40 per cent tested positive for the virus.

Many of these men are becoming infected in their 20s and developing cancers decades down the road, says Nichols.

"In terms of cancers of the tonsil and the back of the tongue we are seeing about two thirds of these cancers are caused by HPV," he says.

"And we can see that the rates are increasing by about three per cent a year. So three per cent a year in 10 years -- that is about 30 per cent each decade. In cancer terms, that is huge," he says.

The changes in oral cancer rates are in part due to changing sexual practices. HPV typically causes cancer in the place where the virus was acquired. It's thought that the growing acceptance of oral sex is partly responsible for the rising rates of oral cancers.

Dr. Marina Salvadori, a pediatric infectious diseases expert at London Health Science Centre who has been researching HPV, says that many of those infected with HPV are getting infected as teens.

She says there is a mistaken belief among this age group that oral sex is safer than traditional sex.

"They are starting encounters young, as young as 14-15 years of age," she says. "And we do know that the more oral sexual encounters you have, the more likely you are to develop HPV-related oralpharyngeal cancer."

Nichols notes that many patients with throat and oral cancers often go misdiagnosed for a time. He's seen patients treated with multiple courses of antibiotics because their family doctor assumed they had strep throat or tonsillitis.

Susan McKenzie was one of those who got missed. The 47-year-old developed odd symptoms in 2008, but for over a year, she couldn't get a diagnosis.

"I had an earache, a slight sore throat, and a bad taste in my mouth," she remembers.

"I thought it was a swollen gland. That's why I didn't go (to the doctor) right away."

Eventually, an ultrasound of her neck revealed a growing tumour on her tonsil.

The good news about HPV-related oral and throat cancers is that cure rates are high – over 80 per cent. But treating the disease can leave patients with lifelong effects.

McKenzie says the radiation she underwent damaged her saliva glands and tastebuds, so she now has a perpetually dry mouth and ahs trouble tasting food. As well, her chemotherapy damaged her hearing and she now wears a hearing aid.

"After my treatment, I was a little depressed getting used to the hearing loss and having no saliva. And I can't eat some of the foods I used to eat because it's hard to swallow them," she says.

There are two vaccines currently available in Canada that can prevent HPV infection. But they are offered as part of taxpayer-funded school vaccinations programs only to girls and young women. The vaccines are licensed for use in males, but males or their parents need to pay for it themselves.

A number of experts have called for the expansion of vaccination programs to reduce the cervical cancer rates. But some point out that the rise in oral cancer rates suggests that the vaccine could also offer men a direct benefit, too.

With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip