Medical researchers in the U.S. have found that a viral infection called Human Papillomavirus or HPV which is said to be the main reason for rising cancer cases of the back of the mouth and throat this year.

This kind of cancer is called Oropharyngeal by medical experts and grows in several locations - the back of the tongue, soft portion of the mouth's top, tonsils or side of the throat.

Too much consumption of alcoholic drinks and smoking tobacco can enhance the risk of developing this disease, according to the National Cancer Institute.

The number of patients who have been diagnosed with HPV-related oral cancer in 2004 is three times the number of victims in 1988, according to Reuters.

HPV is regarded as a common sexually-transmitted infection that can cause genital moles and cancers of the cervix and anus.

Symptoms include persistent sore throat, dull pain behind the breast bone, continuous coughing, weight loss, ear pain, and lump in the back of the mouth, throat or neck.

"The entire relationship between HPV-related head and neck cancer completely changes our ideas of who is at risk, how to treat the cancer, the prognostics of the cancer, and prevention," said Maura Gillison who headed the research at the Ohio State University which was published in the Journal of Clinical Oncology.

From the results of the study, it can be estimated that HPV-related oral cancers afflict 26 out of every million people in the United States, compared to eight out of every million people in 1988.

"The good news is that people diagnosed with the HPV-positive form of the cancer have a better diagnosis and the cancer is more responsive to treatment," Gillison stated.

There is also a potential chance for prevention using an HPV vaccine that is approved to prevent cervical and anal cancer, she said.

The vaccines are not proven to prevent oral cancer, and Gillison said it will be important to test whether they are effective for this increasingly common form.