Nearly one-fifth of all types of cancer worldwide are caused by just a handful of viruses, bacteria and parasites, Reuters Health reports of research from the University of Oxford in the United Kingdom.

Specifically, 17.9 percent of cancer cases globally in 2002 were caused by infections ranging from HIV to the ulcer bug Helicobacter pylori.

The good news: If the infections can be prevented, then many cases of cancer could be avoided, especially in developing nations. Study leader Dr. Donald Maxwell Parkin says that a massive 1.9 million cases of cancer in 2002 are directly attributable to these preventable viral and bacterial infections.

The No. 1 culprit is H. pylori, a bacterium that causes stomach ulcers that can lead to stomach cancer, which is responsible for 5.5 percent of all cancers worldwide.

Others on the hot list are human papilloma viruses (HPV), which can cause cervical cancer, and the hepatitis B and C viruses, which cause 85.5 percent of liver cancers. The Epstein-Barr virus accounted for 1 percent of cancers in 2002, most notably Hodgkin's and non-Hodgkin's lymphoma and nasopharyngeal cancer. HIV infection can lead to variety of cancers, including lymphoma, Kaposi's sarcoma and cervical cancer.

What if these infections could be prevented? Parkin estimates it would reduce cancer by 26 percent in developing nations and 8 percent in developed countries.

The study findings were reported in the International Journal of Cancer, 2006.

--Cathryn Conroy