Only one bacterium and a few viruses are implicated in causation of cancer. These viruses infect human cells. Such instances are found in cervical, liver cancer, and certain lymphomas, leukemias, and sarcomas. Susceptibility to these cancers can sometimes be spread from person to person by infectious viruses in rare cases.
Cervical Cancer: It is now known that the risk of cervical cancer is increased in women with multiple sexual partners and is especially high in women who marry a man whose previous wife had this disease. Transmission of the human papillomavirus (HPV) during sexual relations appears to be involved in such cases. Of the 100 different types of HPVs, about 30 are known to be passed from one to another person, and about 13 of them are considered to be higher risk types, since they are recognized as cancer causing HPVs.
A screening technique called the Pap test (or Pap smear) allows early detection of cancer of the cervix. Cervix is the narrow portion of the uterus that extends down into the upper part of the vagina. In this procedure, a sample of cells from the cervix and upper vagina is removed and checked under microscope for abnormalities. Since the 1930s, early detection using the Pap test has helped lower the death rate from cervical cancer more than 75 percent.
The U.S. Food and Drug Administration have approved an HPV test. This test can detect the viruses even before there are any conclusive visible changes to the cervical cells
Stomach Cancer: Viruses are not the only infectious agents that have been implicated in human cancer. The bacteriumHelicobacter pylori, which can cause stomach ulcers, has been associated with the development of cancer, so people infected with H. pylori are at increased risk for stomach cancer. Research is under way to define the genetic interactions between this infectious agent and its host tissues that may explain why cancer develops
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