ATLANTA - The sexually transmitted virus that causes cervical cancer in women is poised to become one of the leading causes of oral cancer in men, according to a new study.

The HPV virus now causes as many cancers of the upper throat as tobacco and alcohol, probably due both to an increase in oral sex and the decline in smoking, researchers say.

The only available vaccine against HPV, made by Merck & Co., is currently given only to girls and young women. But Merck plans this year to ask government permission to offer the shot to boys.