Infectious diseases and cancer
Viruses, bacteria and parasites emerge as the "secret agents" causing millions of cases of cancer, according to the report. WHO estimates that over 1.5 million of the total of 10 million new cancer cases a year could be avoided by preventing the infection associated with them. About 6.6 million people died from all types of cancer last year. Three main cancers are linked to infections.
Stomach cancer: About 550 000 new cases a year of stomach cancer - about 55% of the worldwide total - are attributable to a bacterium, Helicobacter pylori. The bacterium also causes duodenal and gastric ulcers and gastritis.
Cervical cancer: Sexually transmitted infection of the cervix with human papilloma viruses types 16 and 18 involves a very high risk of developing cervical cancer. Of the 529 000 reported cases a year, the viruses are held responsible for an estimated 65% of those occurring in industrialized countries, and 87% of those in developing countries - a total of 436 000 cases.
Liver cancer: About 434 000 cases a year of liver cancer, or 82% of the world total, are attributable to hepatitis B and C viruses. The viruses are transmitted in a number of ways, including through contaminated blood or blood products and through sexual intercourse. Hepatitis B causes 316 000 of the cases, and hepatitis C a further 118 000 cases. Some cases are the result of infection with both viruses.