For a human, an infection often means getting sick. But for a virus, an infection means survival.
Viruses are tiny, disease-causing germs that can reproduce only inside an organism they’ve invaded. If these microbes end up outside the body, expelled through the nose by a sneeze or wiped on a sleeve, it’s hard for them to survive. When they’re unable to infect anything, viruses dry up and eventually die.
But that might be a long time, according to a team of scientists in France that recently put nasty viruses to the test. The team found that under the right conditions, a virus outside a host might survive and be able to cause infections for more than six months.
The scientists tested samples of the virus that causes H1N1 flu, better known as swine flu. In 2009, this virus swept from country to country, infecting thousands of people around the world. The scientists found that the viruses sputtered out a day after being immersed in hot temperatures and surrounded by salty water. But at cooler temperatures and in less salty water, H1N1 retained its ability to cause infections for months.
That suggests that viruses like H1N1 are tough. Jean-Claude manuguerra studies infectious diseases at the Pasteur Institute in Paris. “Did this play a role in its fabulous capacity to transmit?” he asked during an interview with Science News. “We don’t know!”
Manuguerra and his colleagues let some of the viruses dry out, which the scientists believed would kill the microbes. That wasn’t the case: The team found that the dry viruses could be brought back to life in the laboratory and remain infectious.
The French scientists aren’t the only ones studying viral survival outside the body. Researchers from the United Kingdom recently swabbed a variety of ordinary surfaces with H1N1 viruses. They tested materials likely to be touched by human hands, including fabrics, wood, plastics and metals. On wood, almost all signs of the virus were gone within a few hours.
The other surfaces told different stories. On stainless steel, for example, the viruses lived for nine hours. On other surfaces, the viruses died more quickly but left behind bits of DNA. A viral particle’s DNA holds the genetic instructions for how to infect an organism and reproduce within it.
Earlier studies have shown that viruses can make it all alone in the world, at least for a while. In 2008, scientists from Switzerland showed that flu viruses could survive on paper money for up to three days. However, the viruses lived for 17 days if mucus — like that from a sneeze or cough — also ended up on the money.
J. Owen Hendley, a physician at the University of Virginia School of Medicine in Charlottesville, told Science News that the new French study is interesting, but he remains skeptical. “I’m not sure I’m ready to accept that influenza virus lasts longer than a day,” he said. On the other hand, he noted, the investigation by Manuguerra’s team showing weeks- to months-long virus survival in the environment “is a serious piece of work. And I can’t see any holes in it. So it makes me consider the possibility that it might be right.”