Vincent Racaniello is Higgins Professor of Microbiology & Immunology at Columbia University, where he oversees research on viruses that cause common colds and poliomyelitis. He teaches virology to undergraduate, graduate, medical, dental, and nursing students, and writes about viruses at virology.ws.
The detection of a new virus called XMRV in the blood of patients with chronic fatigue syndrome (CFS) in 2009 raised hope that a long-sought cause of the disease, whose central characteristic is extreme tiredness that lasts for at least six months, had been finally found. But that hypothesis has dramatically fallen apart in recent months. Its public demise brings to mind an instance when a virus *was* successfully determined to be behind a mysterious scourge: the case of HIV and AIDS. How are these two diseases different—how was it that stringent lab tests and epidemiology ruled one of these viruses out, and one of them in?
Are the silent viruses within us doing more than we know?
By Laura Kasman, as told to Veronique Greenwood
In the 1970s, doctors noticed that sometimes people with hepatitis B virus infection (HBV) would get suddenly much worse and go into liver failure, and they didn’t know why. But through hard work with what are now antiquated methods, they found out that there was another virus, very different genetically from HBV, but dependent on HBV to spread from person to person. It is called hepatitis D virus or delta agent, and it steals proteins made by HBV to get from cell to cell and victim to victim. The combination of HBV plus hepatitis D is always much more serious than HBV alone, and hepatitis D virus never occurs on its own.
This phenomenon, called viral interference, has been seen in the lab for a while, but it was generally thought to be an artifact with little or no importance in human disease. That’s because we didn’t have the technology to easily find and identify viruses in living people until recently.
The advent of PCR rewrote our understanding of viral interactions, as it did for many areas of biology. We learned that almost everyone has many silent viral infections cooking in them all the time, some that last for life and some that come and go. When the human genome was sequenced, it showed that 8% of the human genome is made up of dormant and disabled retroviruses (the kind of virus that causes AIDS). It’s as if scientists were looking for cockroaches in a big dark room and all we had was a little flashlight. For decades we followed one bug at a time, and it worked and we made progress, so we thought each one was alone. And then with PCR we found the light switch and yikes, they were everywhere! We didn’t notice most of them for so long because they cause no symptoms in most people. Read More