A Planet of Viruses - Carl Zimmer [9]
The discoveries of Shope and Rous led scientists to look at growths on other animals. Cows sometimes develop monstrous lumps of deformed skin as big as grapefruits. Warts grow on mammals, from dolphins to tigers to humans. And on rare occasions, warts can turn people into human jackalopes. In the 1980s, a teenage boy in Indonesia named Dede began to develop warts on his body, and soon they had completely overgrown his hands and feet. Eventually he could no longer work at a regular job and ended up as an exhibit in a freak show, earning the nickname “Tree Man.” Reports of Dede began to appear in the news, and in 2007 doctors removed thirteen pounds of warts from Dede’s body. They’ve had to continue to perform surgeries to remove new growths from his body since then. Dede’s growths, along with all the others on humans and mammals, turned out to be caused by a single virus—the same one that puts horns on rabbits. It’s known as the papillomavirus, named for the papilla (buds in Latin) that cells form when they become infected.
In the 1970s, the German researcher Harald zur Hausen speculated that papillomaviruses might be a far bigger threat to human health than the occasional wart. He wondered whether they might also cause tumors in the cervixes of women. Previous studies on cases of cervical cancer revealed patterns that were similar to sexually transmitted diseases. Nuns, for example, get cervical cancer much less often than other women. Some scientists had speculated cervical cancer was caused by a virus spread during sex. Zur Hausen wondered if cancer-causing papillomaviruses were the culprit.
Zur Hausen reasoned that if this were true, he ought to find virus DNA in cervical tumors. He gathered biopsies to study, and slowly sorted through their DNA for years. In 1983 he discovered genetic material from papillomaviruses in the samples. As he continued to study the biopsies, he found more strains of papillomaviruses. Since zur Hausen first published his discoveries, scientists have identified one hundred different strains of human papillomavirus (or HPV for short). For his efforts, zur Hausen shared the Nobel Prize for Physiology or Medicine in 2008.
Zur Hausen’s research put human papillomaviruses in medicine’s spotlight, thanks to the huge toll that cervical cancer takes on the women of the world. The tumors caused by HPV grow so large that they sometimes rip the uterus or intestines apart. The bleeding can be fatal. Cervical cancer kills over 270,000 women every year, making it the third leading cause of death in women, surpassed only by breast cancer and lung cancer.
All of those cases got their start when a woman acquired an infection of HPV. The infection begins when the virus injects its DNA into a host cell. HPV specializes in infecting epithelial cells, which make up much of the skin and the body’s mucous membranes. The virus’s genes ends up inside the nucleus of its host cell, the home of the cell’s own DNA. The cell then reads the HPV genes and makes the virus’s proteins. Those proteins begin to alter the cell.
Many other viruses, such as rhinoviruses and influenza viruses, reproduce violently. They make new viruses as fast as possible, until the host cell brims with viral offspring. Ultimately, the cell rips open and dies. HPV uses a radically different strategy. Instead of killing its host cell, it causes the cell to make more copies of itself. The more host cells there are, the more viruses there are.
Speeding up a cell’s division is no small feat, especially for a virus with just eight genes. The normal process of cell division is maddeningly complex. A cell “decides” to divide in response to signals both from the outside and the inside, mobilizing an army of molecules to reorganize its contents. Its internal skeleton of filaments reassembles itself, pulling apart the cell’s contents to two ends.