A vaccination programme against cervical cancer was introduced around 2006 in the US. Now, nearly 20 years later, it is already clear cervical cancer cases are reducing. Animals were used to understand the virus that triggers most cases of cervical cancer, the papilloma virus, or wart virus, starting with rabbits in the 1930s.
Cervical cancer kills more women than any other type of cancer apart from breast cancer. It is usually triggered by a common virus called human papilloma virus (HPV). There are more than 100 different types of HPV, including 30 that are sexually transmitted. Many animals and birds can also be infected by papillomas (warts).
The first case of cancer triggered by a mammalian virus was that caused by a papilloma virus in rabbits, discovered by Dr Richard Shope and Dr Peyton Rous. Most people thought at the time that cancers could not be transmitted by viruses, but they were vindicated and Rous eventually won a Nobel Prize for his work in 1966.
In 1977, Dr Harald zur Hausen published the first research linking the papilloma virus to cervical cancer. This was still controversial, but in the early 1980s he found two previously unknown virus types, HPV-16 and HPV-18, in tumours. He was awarded the Nobel Prize for his work in 2008.
Why did it take so long to confirm HPV as a cause of cervical cancer? One important discovery was that the virus did not always cause cancer. Again, important clues came from animal research. For example, Bovine Papilloma Virus was known to cause cancer in cattle, but only in those that also ate bracken. In women, HPV also needs some kind of ‘help' to trigger cervical cancer. About half of sexually active women are estimated to be infected with HPV but only a very small proportion develop cervical cancer.
This is partly because only certain HPV types are dangerous. There are more than 100, but types 16 and 18 are responsible for 7 in 10 cervical cancers. Even so, not all women infected by types 16 and 18 develop the disease. Some shake off HPV infection altogether, perhaps because of their genes or perhaps because they have fewer risk factors, which include smoking, poor diet and a weakened immune system.
Until recently, HPV could not be grown in isolated cells or transmitted to other animals and because it can induce cancer, its effects cannot be "tested" in women. Using papilloma virus in cottontail rabbits, and the equivalent viruses found in dogs and cattle, researchers found that it was possible to protect against infection by the virus and the development of papillomas or cancer. The first of two vaccines became available in 2006.
For further information see FASEB's Breakthroughs in Bioscienceessay Viruses, cancer, warts and all: the HPV vaccine for cervical cancer
See also this briefing from the Society for General Microbiology - Viruses and cancer
